SHEDDING L THE INVISIBLE LINKS WITHIN E CO-AGRI...

SHEDDING LIGHT ON THE INVISIBLE LINKS

WITHIN ‘ECO-AGRI-FOOD-SYSTEMS’ A narrative review of literature on how

agricultural management can

influence the positive and

negative impacts

of rice farming

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List of authors

Anne Bogdanski, FAO

Renee van Dis, FAO

Barbara Gemmill-Herren

Finbarr Horgan, IRRI

Pieter Rutsaert, IRRI

Buyung Hadi, IRRI

Marie-Soleil Turmel, Bioversity International

Simon Attwood, Bioversity International

Fabrice DeClerck and Rachelle DeClerck, Bioversity International

Recommend citation: Bogdanski, A., Attwood, S., DeClerck, F., DeClerck, R., Hadi, B., Horgan, F.G., Rutsaert, P.,

Turmel, M.-S., R. van Dis , and Gemmill-Herren, B. (2015). Shedding light on the invisible links within ‘eco-agri-

food-systems’. A narrative review of literature on how agricultural management can influence the positive and

negative impacts of rice farming. FAO, unpublished project report for The Economics of Ecosystems and

Biodiversity (TEEB) global initiative for Agriculture and Food.

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Contents Abbreviations .......................................................................................................................................................... 5

1. Introduction ........................................................................................................................................................ 6

1.1 Background ................................................................................................................................................... 6

1.1.1 What is the eco-agri-food complex? ...................................................................................................... 8

1.1.2 Agricultural management .................................................................................................................... 11

1.2 Problem and research questions ................................................................................................................ 12

1.3 Purpose of the review ................................................................................................................................. 12

1.4 Structure of the analysis ............................................................................................................................. 14

1.5 Applied methods ......................................................................................................................................... 14

2. Analysis ............................................................................................................................................................. 21

A. Increase in rice yields versus maintenance of water quality ........................................................................ 22

B. Increase in rice yields versus reduction of water use ................................................................................... 23

C. Increase in rice yields versus maintenance of air quality .............................................................................. 24

D. Increase in rice yields versus ghg emissions reductions ............................................................................... 26

E. Increase in rice yields versus the provision of habitat to increase food provision and dietary diversity,

ecosystem functioning and space for recreational activities ............................................................................ 27

2.1 Philippines ................................................................................................................................................... 28

2.1.1 Typology of rice farming systems ......................................................................................................... 28

2.1.2 Synergies or trade-offs? ....................................................................................................................... 32

2.1.3 References............................................................................................................................................ 50

2.2 Cambodia .................................................................................................................................................... 58

2.2.1 Typology of rice farming systems ......................................................................................................... 58

2.2.2 Synergies or trade-offs? ....................................................................................................................... 75

2.2.3 References............................................................................................................................................ 92

2.3 Senegal ...................................................................................................................................................... 101

2.3.1 Typology of rice farming systems ....................................................................................................... 101

2.3.2 Synergies or trade-offs? ..................................................................................................................... 108

2.3.3 References.......................................................................................................................................... 126

2.4 Costa Rica .................................................................................................................................................. 133


2.4.2 Synergies or trade-offs? ..................................................................................................................... 137

2.4.3 References.......................................................................................................................................... 147

2.5. California .................................................................................................................................................. 152


2.5.4 Agricultural Practices ............................................................................................................................. 157

2.5.2 Synergies or trade-offs ....................................................................................................................... 159

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2.5.3 References.......................................................................................................................................... 196

3. Conclusions ..................................................................................................................................................... 202

3.1 Synergies and Trade-offs ........................................................................................................................... 202

3.1.1 Increase in rice yields versus maintenance of water quality ............................................................. 206

3.1.2 Increase in rice yields versus reduction of water use ........................................................................ 208

3.1.3 Increase in rice yields versus maintenance of air quality ................................................................... 211

3.1.4 Increase in rice yields versus GHG emissions reductions ................................................................... 213

3.2 Study limitations ....................................................................................................................................... 215

3.2.1 Science versus reality ......................................................................................................................... 215

3.3 Next steps.................................................................................................................................................. 215

4. Acknowledgements ......................................................................................................................................... 217

5. References....................................................................................................................................................... 218

ABBREVIATIONS Alternative wetting systems AWD

Carbon Dioxide CO2

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Dry Direct Seeding DDS

Farmer Field School FFS

Global Warming Potential GWP

Government of Senegal GoS

Grande Aménagement GA

Grand Offensive for Food and Abundance GOANA

Green House Gasses GHG

Ground Cover Rice Production System GCRPS

Integrated Pest Management IPM

Integrated Production and Pest Management Programme IPPM

Iron Fe

Irrigated Rice Research Consortium IRRC

Manganese Mn

Methane CH4

Moderate Resolution Imaging Spectroradiometer MODIS

National Irrigation Administration NIA

Nitrogen N

Nitrous Oxide N2O

Panicle initiation PI

Périmètre Irrigué Privé PIP

Périmètre Irrigué Villageois PIV

Pesticide Impact Rating Index PIRI

Phosphorous P

Potassium K

Recommended Management Practices RMP

Rice Root Knot Nematode RRKN

Saturated Soil Culture SSC

Senegal River Valley SRV

Site Specific Nutrient Management SSNM

Soil Organic Carbon SOC

Soil Organic Matter SOM

Sub Saharan Africa SSA

Sulphur S

System of Rice Intensification SRI

Tropical Livestock Units TLU

Urea Deep Placement UDP

Water Use Efficiency WUE

Wet Direct Seeding WDS

Zinc Zn

1. INTRODUCTION

1.1 BACKGROUND

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Rice is central to the food security of half the world. Furthermore, rice is a source of livelihood of

around 140 million rice farming households. More than 90 percent of world rice production and

consumption is in Asia, where a recent strategy paper addressing policy makers identified a set of

significant challenges in ensuring an adequate and stable supply of rice which is affordable to poor

consumers (FAO, 2014):

The need to produce more rice to meet the rising demand driven by population growth

Deceleration in the growth of rice yields

Environmental degradation associated with intensive rice production

A decline in rice biodiversity and loss of rice heritage

The role of rice production in global climate change

Increasing competition of land, labor and water from industrial and urban sectors

Changes in dietary composition

Changes in demographic composition of labor in rural areas.

Achieving price stability for rice in the context of shocks due to increased interconnectedness

of rice with other sectors and instability in trade policies of the major exporting countries.

Many of these challenges are related to a decrease in ecosystem services, increase in negative

externalities and the degradation of natural capital1 in rice production. As an answer, the FAO has

proposed various strategic objectives to tackle these issues. The organization calls to increase the

productivity and nutritional value of rice and rice-associated biodiversity, to improve mitigation and

adaptation to climate change and reduce risk, and to minimize the environmental footprint of rice

production while enhancing the ecosystem functions of rice landscapes, including the protection and

promotion of rice heritage and cultural and landscape management.

Potential Synergies and Trade-Offs

As these objectives are not independent, but rather interlinked, reaching them is likely to require

trade-offs. The question of interest is therefore of how to reduce trade-offs between these different

goals. Where possible, one should identify synergies that allow for a maximization of benefits2, while

minimizing costs to society and the environment, (i.e. negative externalities), and the wellbeing of the

farmer him or herself through the degradation of natural capital from rice production. It is therefore

crucial to know which types of farm management practices offer the best options to reach these

synergies, and reduce trade-offs.

Typically in agriculture there should be a recognition and consideration of both the generation of goods

that is food, raw materials, water, on the one hand, and the provisioning of regulating services such

biological pest control, carbon sequestration or the moderation of extreme events, on the other. There

should also be a consideration between the generation of goods, and habitat services, e.g. food

production versus natural habitat for biodiversity, or goods and cultural services. Recently, there has

1 Natural capital is the land, air, water, living organisms and all formations of the Earth's biosphere that provide us with

ecosystem goods and services.

2 Benefits reflect the goods and services that are ultimately used and enjoyed by people and which contribute to individual

and societal well-being. In this study, they are distinguished from ecosystem services (which contribute to the generation of

benefits) and from well-being (to which benefits contribute).

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also been considerable discussion related to the delivery of several goods at the same time, e.g. the

provision of food versus the provision of water or raw materials for bioenergy (e.g. the food versus

fuel, or the food-water-energy nexus discussion) (e.g. Wratten et al, 2013; Porter et al, 2009).

Yet these diverse claims to agriculture often come with a price – apparent or less apparent trade-offs.

Making these trade-offs visible requires a thorough assessment of the situation; yet doing so is often

difficult:

1. Trade-offs among different ecosystem services are not always immediately visible. They may

be felt at different spatial or temporal scales and they might be reversible (Rodriguez et al.

2006). Accordingly, appropriate management decisions that address these trade-offs are likely

to favor the immediate and less distant ecosystem good or service, as compared to a service

or good which is only going to show an effect in the future or at a distant location.

2. Trade-offs among different ecosystem services are not easily comparable, especially when

using biophysical indicators. Compare one ton of air pollutants to one square meter of water

abstraction is non-trivial for example.

However, trade-offs are not always necessary. The new paradigm of “sustainable production

intensification” as described within the framework of FAO’s save and grow concept

(http://www.fao.org/ag/save-and-grow/) offers win-win situations among different ecosystem

services without trade-offs. The recent meta-analysis on the multiple goods and services of Asian Rice

production systems (Garbach et al. 2014), for instance, analyzed the synergies and trade-offs between

ecosystem services and yield in six agroecological systems of rice production in relation to

conventional, intensified agriculture. The study showed that both, yields and other ecosystem services

of rice production systems, can be maintained or increased simultaneously when the right farm

management system is chosen.

Yet, while these win-win situations are possible, favorable policy environments and substantial

investments in extension for rice farmers to apply these agroecological management systems are often

necessary to support their growth and adoption (Garbach et al. 2014).

The right questions to ask are therefore those that aim to inform decision makers of the benefits of

agroecological or, in general, more sustainable rice management practices and make the case for

better policy support. Showing the additional value of ecosystem services in rice production on top of

the value for the rice crop itself is a step in this direction.

This narrative review will describe a variety of trade-offs and synergies that occur in rice agro-

ecosystems between different goods or services. As the principle goal of rice agro-ecosystems is food

production, this narrative review will explore different trade-offs and synergies resulting from food

production, on the one hand, and a range of other ecosystem services, on the other. The relative

strength of each trade-off or synergy is expected to change, i.e. to increase or decrease, by applying

different farm management practices or systems.

Despite the various interdependencies between the economic and natural capital and the large

impacts of rice production systems on the environment and to wider society, many of these links and

trade-offs are still economically invisible, i.e. they do not have a price and are therefore not factored

into the economics of rice production. Consequently, the true value of rice production is not fully

http://www.fao.org/ag/save-and-grow/

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reflected in markets, price signals and policies. These often lack appropriate consideration of the value,

the damage to and incentives for the sustainable use of biodiversity and ecosystem services. Despite

the fact that there is growing recognition of the need for a better understanding and more effective

management of the ecosystem services of the rice environment, demonstrating and capturing the real

value of the eco-agro-food complex has proven to be a difficult challenge so far.

1.1.1 WHAT IS THE ECO-AGRI-FOOD COMPLEX?

Natural ecosystems, agro-ecosystems and human systems are typically evaluated in isolation from one

another, despite being points along the same gradients of land-use modification/intensification, and

their many and significant links. That is that these different systems are closely interlinked. However,

the economic invisibility of many of these links is a major reason for this ‘silo’ thinking. However,

natural ecosystems and their biodiversity as well as inputs from the human system underpin crop and

livestock production, and in turn agricultural practices influence ecosystems and human health

through externalities and the degradation of natural capital. At the same time, agro-ecosystems

generate a suite of positive externalities which both nature and human society depend on. While the

positive externality “food” (essentially a provisioning service in ecosystem service parlance) is without

question the most visible output of rice production, there are other positive externalities which are

frequently not accounted for.

Externalities and degradation of natural capital

Externalities are said to arise when (i) the actions of one economic agent in society impose costs or

benefits on other agent(s) in society, and (ii) these costs or benefits are not fully compensated for and

thus do not factor into that agent’s decision-making. Without intervention in the free market to

internalize externalities, positive externalities or benefits are chronically under-supplied and negative

externality or costs are over-supplied (TEEB, 2014). Externalizing the costs of production to third

parties (including more generally society at large) is associated with rational, self-interested behavior.

The current assumed state of large negative environmental externality costs of agriculture and food

systems implies market failure and the need for intervention in the market.

Additional to externalities, there are costs related to the degradation of natural capital. Contrary to

externalities which impact third parties, the degradation of (the privately-owned) natural capital may

harm the individual private farmer or agri-businesses themselves. This self-inflicted harm may be

irrational but is prevalent. It might arise owing to a lack of information on the nature of the

environmental dependency, the lack or inability to take a long-term perspective, the lack of necessary

inputs or technologies, attitudes to risk and uncertainty, or property rights regimes, i.e. a lack of

incentive to maintain natural capital if tenure is not assured (TEEB, 2014).

The concept: A systems approach

The eco-agro-food complex framework developed by TEEB (TEEB, 2014) is based on a systems

approach and illustrates the inter-linkages between these different ‘silos’, namely: (i) the ‘human

(economic and social) systems’ (ii) the ‘agriculture and food systems’, and (iii) ‘ecosystems and

biodiversity’. FAO has adjusted this conceptual framework to the rice farming sector. At the center of

this framework is the agriculture and food system, or more specifically the rice agro-ecosystem. It is

an agricultural ecosystem, which is managed with the intention of producing, distributing, and

consuming food, fuel, and fiber. An ecosystem is a core concept of ecology which describes interactions

between organisms and with their environment. The Convention on Biological Diversity defines

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ecosystems as a dynamic complex of plant, animal and micro-organism communities and their non-

living environment interacting as a functional unit. Agricultural ecosystems share this definition, but

are ecosystems with significant human intervention, particularly around food, fuel, or fiber production.

As a concept, an ecosystem does not have fixed spatial boundaries, defined set of organisms, or specific

ecosystem service flows. While this does not allow for direct translation into an accounting framework

as done by The System of Environmental-Economic Accounting (SEEA)

(http://unstats.un.org/unsd/envaccounting/seea.asp), for instance, it does helps to illustrate the

components, flows and outputs from to and from the system over different spatial and temporal levels.

For valuation and accounting purposes, ecosystems or ecosystem assets, are defined through the

delineation of specific and mutually exclusive spatial areas (EC 2013).

The rice agro-ecosystems described in this study differ in terms of their agro-ecological characteristics

(e.g. soil, climate, biota, landscape context), their scale, and in terms of the farm management, i.e. the

agricultural practices and technologies applied and the natural resources they depend on. The systems

might be characterized by small-scale subsistence units or large corporations. They may depend on

high inputs and be managed intensively or they may be low-input, extensive systems, presumably, with

a greater reliance on ecosystem services. Some systems are structurally more complex than others:

rice can be produced in monocultures producing one crop only, or in integrated systems which

generate multiple products together with rice including ducks and fish as in integrated rice-fish or rice-

duck systems. Rice can also be spatially intercropped with other production elements (e.g. other crops,

fruit trees, agroforestry), such as in the sorjan system in southern Bangladesh (Attwood et al, 2013).

The ecosystems and biodiversity component describes other ecosystems influenced by rice

agriculture. This could be another agro-ecosystem, or more natural ecosystem, which compared to an

agro-ecosystem is usually characterized by a higher species diversity and therefore more complex food

webs, leading to complex nutrient and energy flows.

The human system component refers to people, and encompasses society’s economic and social

interactions with the agro-ecosystem. It provides a suite of different services and inputs to agriculture

such as science and technology (including machinery, breeding, pesticides and mineral fertilizers) and

human capital (including labour and human knowledge).

Impact and dependencies3

Agro-ecosystems provide a wide variety of different benefits, but can also cause costs to the agro-

ecosystem itself, the environment and to society. Hence, rice agro-ecosystems may have positive or

negative impacts4. At the same time, rice agro-ecosystems rely or depend5 on a range of ecosystem

services from the agro-ecosystem itself, and from other land uses and landscape elements proximate

to rice (i.e. natural capital). The ecosystem services that rice agro-ecosystems depend on might be

“pure” or “polluted” through man-made or natural interventions, e.g. clean water for irrigation versus

water contaminated with heavy metals from the industry or the mining sector. Rice agro-ecosystems

3 The structure of this narrative biophysical review (and accordingly of the project) follows this terminology in order to use

the same language as used by the project valuation team/Trucost, which in turn aligns its language with existing business tools such as cost-benefit analysis with the work that they are doing with the Natural Capital Protocol. 4 The way the valuation team/Trucost is looking at impacts is that they are outputs of production. 5 The way the valuation team/Trucost is looking at dependencies is that they are inputs into production. Whether this be through clean air, good water quality (natural capital) or workers (human capital).

http://unstats.un.org/unsd/envaccounting/seea.asp

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further depend on human capital such as labor and other man-made inputs such as knowledge or

infrastructure. They further depend on the agro-ecological characteristics of the rice farming area, the

socio-cultural context and the ultimate purpose of the rice farming operations. For instance, rice might

be grown for self-sufficiency or as a commodity crop, or both.

In turn, as a result of these dependencies, rice agro-ecosystems impact, both positively and negatively,

the system itself, the surrounding ecosystems (man-made or natural) and society. This shows that the

relationship between impact and dependencies is not linear, but rather of circular nature.

(A) Dependencies

Rice agro-ecosystems are on the interface between natural and human systems. For their functioning,

they rely on natural capital as well as on human capital and other man-made inputs. Therefore,

dependencies may also be called inputs. To be more specific, agro-ecosystems depend on a range of

supporting and regulating ecosystem services generated in the system itself or from adjacent natural

ecosystems, i.e. rice systems also rely upon a range of ecosystem services from other land uses and

landscape elements proximate to rice.

They further depend on services and inputs from the human system. Rice agro-ecosystems depend on

an ecosystem service if the service is an input or if it enables, enhances or regulates the conditions

necessary for a successful outcome. In which ways and to what extent rice agro-ecosystems derivetheir

production from different sources depends, in turn, on the conditions of the agro-ecosystem, including

its soil properties, and the type of farm management practices and technologies used.

The production function of a rice agro-ecosystems may depend exclusively on chemical inputs such as

mineral fertilizers or pesticides originating from the human systems when conventional agricultural

management is chosen. Alternatively, production functions can be self generating/regulating when

derived from ecosystem services such as for pest control and soil fertility. Ecosystem Services are

amplified with additional human knowledge and labor from the human system (or management) (TEEB

2015, Figure 2.2).

(B) Impacts

Rice agro-ecosystems provide different visible or clearly perceived benefits (positive impacts) and costs

(negative impacts) to the agro-ecosystem, the environment and to society; for the purpose of this

project, they are also called outputs. Linking back to the previous section, agro-ecosystems generate

ecosystems services that are dependent on other systems, or they generate impacts which can

positively or negatively influence these inputs, natural or human capital.

Traditionally, agro-ecosystems have strictly been managed for food production, yet depending on the

type of management, they may also generate a host of other provisioning services such as raw

materials or fresh water, and supporting, regulating and cultural ecosystem services leading to a

variety of positive outputs, or positive externalities. For instance, depending on which type of farm

management is used, some rice agro-ecosystems have been shown to improve ecosystem services

such as producing nutritious foods, sequestering carbon, reducing greenhouse gas emissions,

increasing resilience, providing habitat for native flora and fauna and cultural services such as agri-

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tourism (e.g. the French wine region, the terraces rice hills of the Philippines, birding in California’s

agricultural wetlands).

At the same time, different management practices of rice production can also trigger different types

of environmental degradation that (negatively) impact not only the agro-ecosystem itself, but also the

natural ecosystem and the human system. Degradation often drives negative externalities of rice

production such as loss of habitat for flora and fauna, nutrient runoff into waterways and greenhouse

gas emissions, loss of biodiversity, water contamination and climate change are also

notable..Furthermore, degradation of agro-ecosystems can also affect the system itself and lead to the

degradation of natural capital, which in turn, might increase the cost of production. An example is the

mining of the soil resource which happens when more nutrients and organic matter are extracted than

put back into the systems. Soil structure and fertility will decrease with time leading to infertile and

eroded soils, and ultimately to decreased productivity.

Even less visible and discussed are the ways in which human management impacts on the rice agro-

ecosystem. For instance, plant hoppers are a common pest in rice that cause partial damage to, or

even the loss of the entire rice crop. In a healthy system, the number of invading and reproducing plant

hoppers is controlled by natural enemies (e.g. spiders, insectivorous bats, parasitic wasps), yet when

such predators and parasitoids are reduced or absent, invading pest populations grow exponentially,

which results in pest outbreaks and consequent crop damage. The principal causes of predator and

parasitoid decline are the overuse and misuse of insecticides originating from human systems, and the

loss of habitats within and proximate to production systems that support predator and parasitoid

populations. Hence the removal of predators through pesticide use then creates a dependency on

pesticides, rather than a dependency on natural pest control mechanisms. Also excessive fertilizer use

contributes to this phenomenon as rice which is high in certain amino acids attracts plant hoppers and

accelerates population growth.

1.1.2 AGRICULTURAL MANAGEMENT

The analysis in section 2 will discuss the various impacts and dependencies of rice agro-ecosystems

departing from a dual goal: Can two benefits derived from an ecosystem materialize at the same time?

Can we have both bioenergy and food production? Can we mitigate climate change and produce

sufficient food at the same time? Can we increase food production, while maintaining the same water

quality as before? These trade-offs are apparent in the visible parts of all the ecosystem services that

agro-ecosystems provide to society. Underlying are those ecosystem services which underpin these

visible benefits, such as regulating or supporting/habitat services.

The strength and relative importance of both impacts and dependencies is strongly influenced by the

type of agricultural management practices applied, the specific combination or set of practices chosen

which are often based on a particular methodology or certain principles, and the farming system in

which these are embedded.

It is important to note that it is seldom any single practices that make the difference, yet a combination

of practices in a specific context that are important. Nonetheless, most research projects and the

resulting papers focus on the impact of single practices or specific technologies on the agro-ecosystem,

while ignoring the specific context in which agriculture is practiced and the agro-ecosystem in which it

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is embedded. For instance, rice farmers might not have the economic means to apply the most

adequate practices, the institutional or market environment in which they operate does not permit

their adoptions, tools and technologies have not been developed for sustainable practices or they

might not be aware of them. Furthermore, the principles by which agro-ecosystems function are often

not taken into account in these studies, which makes, as one can argue, some of the research results

less exact, i.e. it is more difficult to attribute causal impacts to them.

This has been a particularly large challenge this project and its reliance on existing research and journal

papers for the review of impacts and dependencies of rice-agro-ecosystems. The project team

therefore differentiates between a) single practices such as pest control through pesticide applications

or water saving technologies such as alternate wetting; b) combinations or set of practices such as

conservation agriculture or the system of rice intensification, sometimes called management systems

and c) farming systems such as traditional farming systems, integrated farming systems or agricultural

heritage systems. The latter are often not defined in detail, which in turn make an analytical

comparison difficult (also see box 1).

1.2 PROBLEM AND RESEARCH QUESTIONS

I. What are the trade-offs and synergies between different goals of or claims on rice production

systems? What are the impacts, what are the dependencies, what are the causal agents?

II. What are the available rice management options which address these trade-offs and synergies

in each case study country?

III. What is the effect of a specific management practice or set of practises/management systems

on an ecosystem service in each case study country? Do they increase, decrease or maintain

this service?

IV. By how much does an ecosystem service increase, decrease or maintain is status quo in each

case study country through a specific management practice (i.e. what are the strengths and

relative impacts of the different farm management practises)?6

1.3 PURPOSE OF THE REVIEW

I. To identify trade-offs and synergies between different goals or claims from rice production

systems in five case study countries.

II. To identify available rice management options which address these trade-offs in the case study

countries:

6 This question will be answered through a systematic review building on a meta-analysis. This narrative review is a preparatory first step to

develop and structure the meta-analysis.

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i. By assessing the biophysical effects of different rice management practices on

ecosystem services.

ii. By evaluating which rice management practices can best address the identified

trade-offs and to suggest how synergies can be created.

III. To lay groundwork for a meta-analysis on the same topic (biophysical assessment), which will

deliver data for the monetary valuation.

Box 1. Definitions of agricultural management practices, set of practices and farming systems.

Agricultural management practices Within this project, agricultural management practices or farming practices can be broadly defined as farming activities during the pre-planting, growth and post-production of rice. This includes the application of technologies and processes used in rice agriculture. For an overview of common practices in rice agro-ecosystems, please refer to figure 1.

Figure 1. Schematic of a step-by-step production of rice by IRRI. Source: (IRRI, n.d.) Combination or set of practices In this project, we refer to a set of practices when talking about a combination of different practices which usually follow a particular methodology or certain principles. These are sometimes arbitrarily called “systems” or “management systems” which should not be confounded with “farming systems” (see definition below). For instance, conservation agriculture is based on three principles which emphasize minimum soil disturbance, crop rotation and cover crops. Another example is integrated pest management which promotes an integrated control of insect pests and the enhancement of natural enemies. Organic agriculture is yet another combination of different practices, which are usually employed under certain principles and regulations by a certification body. It is important to understand that while these sets of practices do have fixed definitions, there is often more than one definition for each. By grouping and comparing agriculture within these “tags” or “brandings”, one risks to group apples and oranges together. Farming systems Farming systems are not to be confounded with set of practices - sometimes arbitrarily called “systems” or “management systems”. Farming systems can be small subsistence units or large corporations. They are structurally complex and form various interrelationships between their numerous components (Dixon et al., 2001): different types of land, water sources and access to common property resources such as grazing lands, fish ponds and forests as well as other natural, human, social and financial capital. All these components, including the household, its resources, and the resource flows and interactions at the farm level are referred to as a farming system (Dixon et al., 2001).

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It is important to note that a farming system does not stop at the physical boundaries of the farm itself. The enabling environment is a determinant factor of the functioning of a farm system. This includes policies, institutions, markets and access to information (Dixon et al., 2001). Income from off-farm activities is also considered as part of the farming system, as it is often fundamental to maintain the farmers’ livelihood and the farm itself.

1.4 STRUCTURE OF THE ANALYSIS

I. Typology of Rice Farming in each case study country, including

i. Background information on rice agriculture in the country

ii. Rice growing environments

iii. Predominant farming systems in the country

iv. Agricultural management practices and management systems used

II. Synergies or trade-offs

i. An introduction to the issue - what are the impacts (i.e. benefits and costs) and

dependencies of rice agro-ecosystems.

ii. An analysis that describes the effect of a specific management practice or a set of

practises on the specific trade-off or synergy among two ecosystem services. Does it

or do they increase, decrease or maintain the ecosystem services?

iii. A conclusion section which details which management practice(s) or set of practices

can best address a given trade-off/lead to synergies between two or more different

ecosystem services.

III. Conclusions

i. Synergies or trade-offs

ii. Rice management options that address trade-offs and create synergies

iii. Next steps

1.5 APPLIED METHODS

The narrative literature review is a synthesis of five individual case study country/state reviews, namely

Philippines, Cambodia, Senegal, Costa Rica and California. The literature research was done by FAO

(Senegal), IRRI (Philippines) and Bioversity International (Cambodia, Costa Rica and California). The

search methods were consistent across all five case studies, with the exception being that:

the three organisations did not have access to the same data sources such as institutional

libraries, databases and subject matter experts.

apart from the main search terms (LIST), additional terms were used depending on specific

case study country needs.

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1.5.1 Philippines

Data sources

Library IRRI

Web of Science

Google Scholar

Google Search

Search strategies

Focus on the Philippines

Reliable data

Result based study

Topical Search terms ‘Philippines’+’rice’ and

biochar

biomass energy

bird

byproduct

cattle

compost

emission

energy

feed

fertilizer

greenhouse gas

herbicide

husk

insecticide

molluscicide

mulch

mushroom

pest

pesticide

raw material

rodent

snail

soil

straw

synergy

tillage

trade off

water

weed

Number of studies screened and the number of studies included

Total retrieved: 992

Number used: 103

Also ‘rice’and:

bird, rodent, rat, biodiversity


16 | P a g e

Number used: 15

1.5.2 Cambodia

Data sources

Sciencedirect

Google search

Google Scholar

Online library IRRI

Books in WorldFish library

Search terms and search strategies

1. Search for peer-reviewed literature

2. Search in references of used literature (snowballing)

3. Search for grey literature (google search

Selection criteria (inclusion/exclusion of studies) Selection criteria were that the literature had to be on rice cultivating practices in Cambodia. The paper

should consider at least one ecosystem service (e.g. food production, water quality), but preferably

two in order to examine trade-offs. We found many papers that only examined yield responses in

relation to management practices, and therefore developed section that dealt solely with that

comparison.

Number of studies screened and the number of studies included Number of studies screened (excluding grey literature): 162

Number of studies included (excluding grey literature): 20

Number of studies included (including grey literature): 34

Search terms used:

“Rice” + “Cambodia” + “…”

Water quantity

Water use

Irrigation

Water saving

Residues

Rice straw

Residue burning

Rice husk

Rice varieties

Rice breeding

Transplanting

Direct seeding

17 | P a g e

Water quality

Contamination

Eutrophication

Pesticide use

Fertilizer use

Herbicide use

Nutrient leaching

Nutrient run-off

Green manure

Pest control

Salinization

Puddling

Dry tillage

Aerobic rice

Flooding

Residues use

Rice residues left in

field

Residues fed to

livestock

Residue biomass

energy

Greenhouse gas

emission

GHG flooded

conditions

Azolla use

Climate change

mitigation

SRI

Zero tillage

Nutrient management

Green charcoal

Double cropping

Crop rotation

Bird control

Insect damage

Urea Deep Placement

IPPM

Natural enemies

Pesticides drinking

water

Organic fertilizer

Land preparation

Weed management

Alternate wetting and

drying

1.5.3 Senegal

Data sources

Library FAO

Sciencedirect

Scopus

Google search

Google Scholar

Online library AfricaRice

Online library IRRI

18 | P a g e

Search strategies

Search for peer-reviewed literature

Search in references of used literature

Search for grey literature (google search)

Search terms: “Rice” + “Senegal” + “…”

Water quantity

Water use

Irrigation

Water saving

Water quality

Contamination

Eutrophication

Pesticide use

Fertilizer use

Herbicide use

Nutrient leaching

Nutrient run-off

Green manure

Pest control

Salinization

Puddling

Dry tillage

Aerobic rice

Flooding

Residues

Rice straw

Residue burning

Rice husk

Residues use

Rice residues left in

field

Residues fed to

livestock

Residue biomass

energy

Greenhouse gas

emission

GHG flooded

conditions

Azolla use

Climate change

mitigation

SRI

Zero tillage

Rice varieties

Rice breeding

Transplanting

Direct seeding

Nutrient management

Green charcoal

Double cropping

Crop rotation

Bird control

Insect damage

Urea Deep Placement

IPPM

Natural enemies

Pesticides drinking

water

Organic fertilizer

Land preparation

Weed management


drying

19 | P a g e

Selection criteria (inclusion/exclusion of studies)

Selection criteria were that the literature had to be on rice cultivating practices in Senegal. Also

papers about rice cultivation in West-Africa were considered as it gave some examples on Senegal

sometimes. The paper should consider at least one ecosystem service (e.g. food production, water

quality).


Number of studies screened (excluding grey literature):110



1.5.4 Costa Rica

Data sources

Library CATIE

Redalyc (Red de Revistas Científicas de América Latina y el Caribe, España y Portugal (Sistema de Información Científica))

CAB-Direct

Google search

Google Scholar

Web of Science

Online library IRRI

Websites of National Research Institutes

Direct Communication with National research institutes and Governement (Ministerio de Agricultura y Ganaderia, Instituto de Investigacion Agropecuario de Costa Rica, Cooperacion Nacional Arrocero)

Search strategies

Search for peer-reviewed literature

Search in references of used literature

Search for grey literature (google search and national institute webpages)

Retrieve printed and electronic reports and documents from national institutes

The Search was conducted in both English and Spanish.

Search terms

20 | P a g e

“Rice” + “Costa Rica” + “…” and

Water quantity

Water use

Irrigation

Water use efficiency

Water quality

Eutrophication

Pesticide use

Fertilizer use

Herbicide use

Nutrient use efficiency

Nutrient run-off

Green manure

Pest control

Salinization

Puddling

Flooding

Climate change

mitigation

Zero tillage


drying

Intermittent Flooding

System of Rice

Intensification

Organic Agriculture

Weed management

Residues

Rice straw

Residue burning

Rice husk

Residues management

Residues fodder

Residue biomass

energy

Greenhouse gas

emission

Minimal tillage

Rice varieties

Direct seeding

Nutrient management

Insect damage

IPPM

Pesticides drinking

water

Organic fertilization

Bio fertilizer

Biological control

Land preparation

Ecological services

Milling

GHG flooded

conditions

Methane emissions

Nitrous oxide

emissions

Carbon sequestration


Selection criteria were that the literature had to be on rice cultivating practices in Costa Rica.

Additional references were included were information on effects of management practices was

lacking. The paper should consider at least one ecosystem service (e.g. food production, water

quality).


Number of studies screened (excluding grey literature): 62

Number of studies screened (including grey literature): 110

21 | P a g e



1.5.5 California

Data sources

Peer reviewed publications

Web of Science

Google Scholar

Grey Literature:

Google

Snowball methodology following reference cited key references

Extension materials published by University of California Cooperative Extension

Public relations information published by the California Rice Commission

Search strategies

Focus on the California

Snowball search of grey literature to identify principle drivers, trends, and management

options.

Grey literature to socialize key concepts and refine trade-off considerations

Peer reviewed information for trade-off quantification and analysis

Reliable data peer reviewed

Result based studies

Topical

Search terms

‘California’+’rice’


We did not use the more specific search terms for California, but rather read all abstracts captured by

the “California” and “rice” search and used this reading to classify papers according to the water, soil,

air, and field-based ecosystem services. Thus while fewer terms were used, the same breadth, if not

greater was captured. We focused on studies that considered how rice management practices altered

a service function as mediated by a biological process (using the definition of ecosystem services), this

included habitat provisioning services which have important economic value in the Central Valley of

California.

Of the 569 papers, 372 passed a first title review. The full abstract was read from the 372 retained, of

which 100 were read completely for inclusion in the indicator analysis. Of these, 59 had quantitative

data that was useable for the meta-analysis. 109 references were retained in the narrative report

included extension publications and California Rice Commission reports. In our ISI Web of Science

search using the terms “rice” and “California” and “ecosystem service” we found only 27 (5%) of the

papers with ecosystem service in the title or abstract. This was consistent with the same search for the

other regions (0-9%).

22 | P a g e



Number used: 109

23

2. ANALYSIS The analysis aims to identify trade-offs and synergies between different management objectives for rice

production systems in five case study countries. The report covers the following management objectives:

a. Increase rice yields

b. Maintain water quality

c. Reduce water use

d. Eliminate the burning of rice residues and thereby maintain air quality

e. Reduce greenhouse gas emissions

f. Provide habitat for aquatic species to increase food provision and dietary diversity, ecosystem

functioning and space for recreational activities

Other benefits to humankind and the environment such as pest regulation (biological control), nutrient cycling, and the provision of natural habitat are equally important for the functioning of rice production systems, however they are hardly ever management objectives as such. Therefore, they are not listed separately here, but are included in the relevant sections, as they underpin the provisioning of the above mentioned benefits.

The report focuses on five specific pairwise interactions:

A. Increase in rice yields versus maintenance of water quality

B. Increase in rice yields versus reduction of water use

C. Increase in rice yields versus maintenance of air quality

D. Increase in rice yields versus GHG reductions

E. Increase in rice yields versus the provision of habitat to increase food provision and dietary

diversity, ecosystem functioning and space for recreational activities

Reaching objectives is likely to require trade-offs. The question of interest is therefore of how to reduce

trade-offs between these different goals. Where possible, one should identify synergies that allow for a

maximization of benefits7, while minimizing costs to society and the environment. In a first step, in order

to determine the trade-offs resulting from focusing the management of the rice system, we identify the

dependencies, impacts, and causes leading to these impacts in rice agro-ecosystems.

7 Benefits reflect the goods and services that are ultimately used and enjoyed by people and which contribute to individual and societal well-

being. In this study, they are distinguished from ecosystem services (which contribute to the generation of benefits) and from well-being (to which benefits contribute).

24

In a second step, we identify available rice management options which address these trade-offs in the

case study countries. This is done by assessing the biophysical effects of different rice management

practices and systems on ecosystem services, and then by evaluating which rice management options can

best address the identified trade-offs and to suggest how synergies can be created.

A. INCREASE IN RICE YIELDS VERSUS MAINTENANCE OF WATER QUALITY

Benefits and dependencies

The principle product and benefit of rice-agro-ecosystems is rice. It is the staple food for the largest

number of people on Earth, eaten by nearly half the world’s population and the single largest food source

for the poor. Water is one of the essential inputs to rice production required for plant growth, and good

water quality is key to maintaining several ecosystem functions and processes that underpin crop

production.

Rice agro-ecosystems in the lowlands (i.e. submerged rice systems) provide freshwater habitat for aquatic

organisms, that not only supply additional food sources from the agro-ecosystems such as wildlife (fish,

birds and frogs) to supplement their diet (positive impact), and rice associated weeds for food and animal

fodder, but that are crucial for the functioning of the agro-ecosystem as such. For instance biological pest

control and nutrient cycling are two important ecosystem services that underpin the provisioning services

of rice systems - provided that the rice fields are free of chemicals. An example is how the diversity of

aquatic organisms in rice floodwaters may contribute to stability in the densities of herbivore populations

(including pests). Settle (1996) suggests that detritivores present in rice crops at early vegetative stages

(often in the soil or water) allow predator populations to establish and protect the crop against herbivores

that appear later in succession. Rice agro-ecosystems in the lowlands also provide fresh water habitat for

resident or migratory bird populations.

Trade-offs

RRice production and the maintenance of water quality in rice agro-ecosystems sometimes can – but do

not have - to be opposing goals. Depending on the management practices applied, there might be trade-

offs or synergies between both management objectives. Agricultural management (naturally geared

towards food production) can be both, a cause of declining freshwater quality (and therebyresponsible

for water pollution), or help to improve or maintain water quality.

On the one hand, certain agricultural practices geared to increase yields can be a cause of pollution

through the discharge of pollutants and sediment to surface and/or groundwater, through net loss of soil,

and through salinization and waterlogging of irrigated land (Ongley, 1996). For example, many rural

populations use freshwater reservoirs below rice paddies as source for drinking water. When rice is

treated with fertilizer or pesticides, however, the water from shallow aquifers under the agricultural land

becomes contaminated (Pingali and Roger 1995 in Bouman et al 2002).

On the other hand, agricultural management can maintain or improve water quality by using management

practices that efficiently apply nutrients and plant protection measures that do not impact on surface

and groundwater, that make sure that soils are not washed away, and that prevent salinization and

25

waterlogging through appropriate water management practices. For example, site specific nutrient

management prevents nutrient run-off and protection measures such as biological pest control,

mechanical and hand weeding as well as intercropping or crop rotations can be a sustainable alternative

to pesticide use.

B. INCREASE IN RICE YIELDS VERSUS REDUCTION OF WATER USE


Rice agriculture is mostly known to be a consumer of freshwater to ensure food production, but it is also

an important provider of water – in many instances water flows through rice systems which can serve to

either improve or reduce its quality. Rice ecosystems may serve effectively as landscape elements that

capture floodwaters during monsoon periods, and thus recharge groundwater that may be used during

drier periods. This is the concept behind the “Ganges Water Machine”

(http://wle.cgiar.org/blogs/2013/05/21/), a long debated concept to find a solution to water issues in the

Ganges River Basin, where 80% of the monsoon-driven river flow occurs during a four month period.

While rice systems do serve in this capacity already, the logistics of optimizing such functions across an

entire river basin – and around 30% of India’s cultivable land - remain challenging.

On more local levels, however, the rice terraces that characterize upland rice farming systems throughout

east, south and southeast Asia are ancient (and current) feats of landscape engineering (and important

cultural services) for watershed management and water control. Watershed management on the part of

family farmers in Asian rice production systems extends well beyond the paddy fields themselves. In

Ifugao, the Philippines, where the rice terraces have been named a UNESCO World Heritage Site, rice

terraces are supported by indigenous knowledge management of muyong, a private forest capping each

terrace cluster. The muyong is managed through a collective effort and under traditional tribal practices.

The communally managed forestry areas on top of the terraces are highly diverse, harboring indigenous

and endemic species. The terraces and forests above serve as a rainwater and filtration system and are

saturated with irrigation water all year round. These practices, in which cultural activities are harmonized

with the rhythm of climate and hydrology management, has enabled farmers to grow rice at over 1000

meters (Koohafken & Altieri 2011).

While rice agro-ecosystems provide both food and water, food production is subject to the availability of

sufficient quantities of water and can be severely affected when water resources are scarce. Rice

agriculture is a main user of freshwater, both from freshwater sources for irrigation and from rainfall.

Irrigated rice is mostly found in the lowlands, and worldwide, about 80 million hectares of irrigated

lowland rice provide 75% of the world’s rice production. This predominant type of rice system receives

about 40% of the world’s total irrigation water and 30% of the world’s developed freshwater resources

(http://ricepedia.org/rice-as-a-crop/where-is-rice-grown).

Trade-offs

The dependence on water of the rice farming sector is a huge challenge as freshwater resources are

becoming increasingly depleted due to competing water uses from the residential and industrial sector

http://wle.cgiar.org/blogs/2013/05/21/

http://ricepedia.org/rice-as-a-crop/where-is-rice-grown

26

and as rainfall is increasingly erratic due to climate change and variability. More efficient water use is

therefore a must, yet it carries a number of trade-offs.

Well-designed studies that take the full scope of this problem into account address several trade-offs at a

time are scarce, however. According to FAO water experts (Facon Thierry, personal communication) any

evidence-base on “water use efficiency” should be multi-scalar and based on sound water accounting. If

there is not a sound water accounting framework, one will miss a number of trade-offs, for instance:

More water efficient means less storage benefits and less groundwater recharge.

It also means less of a number of ecosystem services linked to biodiversity, micro-climate,

connected wetlands, part of the landscape feeding off “water losses” (such as the very productive

wooded areas/trees, etc).

Water saving regimes will increase the weed biomass as flood irrigation is practiced to suppress

weeds. Weed pressure is a major constraint for rice yield.

Many lowland rice fields exist in naturally occurring wetlands where well-managed rice agro-

ecosystem are the most analogous – and thus share characteristics and services. Increasing water

use efficiency may compromise many of these characteristics with important unintended

consequences.

One therefore needs to highlight the critical need for a sound water accounting framework (Personal

communication, Pluschke): Improved water accounting is needed to understand the impacts of different

options and to support better management outcomes. Integrated approaches based on managing not just

water withdrawals but also depletion, and on sound water accounting, have become a necessity for critical

groundwater systems, areas with significant conjunctive use of surface and groundwater, closing river

basins and systems characterized by high return flows (deltas, rice systems). Accurate accounting and

measurement of water use can help identify opportunities for water savings, increase water productivity,

and improve the rationale for water allocation among uses. Water policy and strategies for conservation,

reuse and recycling must be based on clear understanding of the hydrological cycle and sound water

accounting.

C. INCREASE IN RICE YIELDS VERSUS MAINTENANCE OF AIR QUALITY


While rice is the principle product of rice production systems, also rice straw and husks can be used and

serve as a valuable by-product of rice production. However, rice residues are still widely considered a

waste product in many areas of the world.

In Asia alone, about 550 million tons of straw are produced each year, and a large part of it is being burnt

in the field (IRRI, 2015). In general, the burning of rice straw in the field is one of the most significant

activities of global biomass burning, and contributes substantially to air pollution, leading to both a

decrease in air quality and global climate change. Burning of crop residues in the field often happens when

there are two or more annual growing seasons to save time for the next crop. In addition, some farmers

27

believe that rice straw open burning can remove weeds, control diseases, and release nutrients for the

next crop (Gaddeet al., 2009).

While straw burning indeed decreases the weed seedbank and the occurrence of pest and diseases, it in

fact leads to N loss, while the majority of P and and K remains in the ashes. It also sterilizes the soil

decreasing the number and the diversity of soil biota, thereby affecting soil organic carbon levels.

When straw is not burnt, it is often used as animal feed. Either livestock directly graze on the straw left in

the fields, or straw is removed, treated for better digestibility and sold to livestock keepers. Straw is often

used as animal bedding material, as well. Straw as energy source is under investigation, yet, logistics make

the use of straw for energy an unprofitable business (Craig Jamieson, personal communication, 2015).

Rice husks are a product of the first milling process when the husk is removed from the grain at the rice

mill. Around 20% of the paddy weight is husk (IRRI Rice Knowledge Bank, n.d.) Although there are other

potential uses, husks are still mainly considered a waste product which is either burned in the open or

dumped on wasteland.

In some cases however, rice husks are used as organic soil amendments or as complementary source for

animal feed, albeit not of best quality (nutritional value). Since untreated rice husk is low in protein and

digestible energy, it is sometimes pretreated with sodium hydroxide to reduce the silica content, a process

which improves digestibility.

Furthermore, rice husks are increasingly promoted as a relatively cheap and readily available source of

raw material for renewable energy and other uses in the growing bioeconomy. An example is the growing

number of projects which use gasification technologies to generate electricity from rice residues (e.g.

http://irri.org/rice-today/green-fuel-from-rice). One benefit from raw materials is hence the provision of

biomass for uses such as energy.

Low input systems rely on the efficient recycling of residues and other by-products to maintain soil organic

matter and nutrients availability. This is very context specific, however, and depends on many aspects

such as the crop species and variety, the agro-ecological conditions of the soil, the climate, and the

different agricultural management practices.

Trade-offs

One of the principle trade-offs between increasing rice yields and the elimination of rice straw burning,

is, as explained above, the loss of an efficient practice to eliminate pests, diseases and weeds. Eliminating

rice straw burning further requires other means to facilitate the decomposition of the residues. Hence,

when farmers stop to burn their straw, they need to revert to other pest and weed management options

and other ways to facilitate straw decomposition. Each of these options might bring about other types of

trade-offs such illustrated in the case study reports.

For example, in California, residue burning was banned, and residue incorporation and winter-flooding

was promoted instead. However, this brought about negative impacts for the climate. Residue burning

showed lower climate forcing than rice straw incorporation and flooding due to the much higher forcing

http://irri.org/rice-today/green-fuel-from-rice

28

that methane CH4 emitted from flooded wetlands and rice land emissions as compared to CO2 through

burning (see section 2.5.2.4 for references). This is not the case, however, when rice is grown aerobically,

as done in upland systems.

D. INCREASE IN RICE YIELDS VERSUS GHG EMISSIONS REDUCTIONS

Climate regulation – the reduction of GHG emissions, the sequestration of carbon and the substitution of

fossil fuel sources with renewable biomass - constitutes an important regulating ecosystem service to

humankind. Rice production is a net producer of greenhouse gas emissions, and thereby contributes to

GHG emissions from agriculture. Agriculture is one of the greatest sources of greenhouse gases (GHGs),

with agriculture accounting for 10 to 12% of total global anthropogenic GHG emissions (IPCC, 2014), and

with emissions showing a steady increase. Methane (CH4) and nitrous oxide (N2O) are the two main GHGs

from rice production. More than 90% of all rice farming systems are characterized by flooding (responsible

for CH4 emissions and N2O emissions) and to a smaller degree the application of N-fertilizers (mainly N2O

emissions) which need high amounts of energy for their production (carbon emissions). The most

common chemical fertilizer urea is produced by reaction between liquid ammonia (NH3) and carbon

dioxide (CO2), both of which emit large quantities of GHG emissions during their manufacturing process.

While rice production systems can be a major emitter of GHGs, they can be managed to increasing their

carbon sequestration capacity via increased storage of organic carbon in the top soil (Minasny et al. 2012).

A number of management practices can be used to increase the capacity of rice systems to sequester

carbon (Ghimire et al. 2012)

However, assessing overall emissions of GHG by rice production systems is complex, and the result of a

delicate calculation. The addition of organic materials such as straw and manure enhances soil organic

carbon replacing the practice of burning straw after harvest – and thus emitting GHG – still common in

many regions. However, some studies have shown that greater CH4 emissions may result from application

of organic materials, while N2O emissions may be significantly reduced (Zou et al, 2003).

CCharring - or partly burning - rice residues and adding the obtained black carbon or “biochar” to paddy

fields instead of incorporating untreated harvest residues may reduce field CH4 emissions by as much as

80%. In addition, the black carbon is highly stable - meaning the carbon can be effectively stored in the

ground for potentially hundreds or thousands of years (IRRI, n.d.)

Reduction in CH4 emissions has been found in many studies of alternate wetting and drying in rice

production (Wassman 2000). However, higher emission of N2O may then result. The extent of these

environmental effects varies depending on the farm management practices, soil properties, and agro-

ecosystem conditions. Thus, appropriate solutions are, as always, context-specific.

Due to the complexity and the high local and global importance of understanding and appropriately

managing rice production in times of climate change and variability, science on rice production and

climate change is developing at high speed. Many initiatives have set out to investigate the complex

29

interactions in rice production systems with regards to carbon sequestration and GHG emissions, and

responding management actions and good practices. This study can only be seen as an attempt to scratch

the surface of this complex undertaking.

E. INCREASE IN RICE YIELDS VERSUS THE PROVISION OF HABITAT TO INCREASE FOOD PROVISION

AND DIETARY DIVERSITY, ECOSYSTEM FUNCTIONING AND SPACE FOR RECREATIONAL ACTIVITIES

Habitat for aquatic organisms as an additional source of food for dietary diversity

Over 90 percent of the world’s rice is grown under flooded conditions, providing an environment not only

for the cropbut also for wide range of aquatic organisms (Halwart & Gupta 2004). Rice-fish farming is

practiced in many countries in the world, particularly in Asia where consumption is largely dependent on

rice as the staple crop and fish as the main source of animal protein. In these countries, food security and

prosperity long have been associated with the availability and diversity of both rice and fish. The rice and

fish production systems on which these societies depend are quite varied and greatly influenced by

seasonal rainfall and flood inundation patterns, particularly in river floodplains and deltaic lowlands. Many

traditional systems in Asia are based on concurrent cultivation of rice and fish, whereas other systems

alternate between rice cultivation in one season and fish culturing in the other. Still other systems—

especially those in more commercialized rural economies—rely on separate and permanent fish culturing

systems (Dey et al 2012). Fish in rice-fish systems does not refer only to fin-fish; it includes the wide

variety of aquatic animals living in rice fields: shrimp, crayfish, crabs, turtles, bivalves, frogs, and even

insects. Farmers may also allow aquatic weeds, which they harvest for food (Datta & Banerjee 1978).

Surveys in Cambodia, for example, have documented the harvest of over ninety different organisms from

rice paddies and used daily by rural households (Balzer et al 2002; Halwart and Gupta 2004). These wild

and gathered foods from the aquatic habitat provide important diversity, nutrition and food security, as

food resources from rice-field environments which supply essential nutrients that are otherwise not

adequately found in diets.

Many rural households depend on monotonous diets that are too high in carbohydrates and too low in

animal source foods and micronutrient-rich fruits, fish and vegetables. Access to a diversified diet is often

constrained by lack of purchasing power, limited expertise and limited availability. Experience has shown

that more diversified farming systems that contain horticultural or aqua cultural components are one way

to improve households’ availability and access to such animal source foods, fruits and vegetables. While

high external input production systems, usually monocultures, may increase rice yield (compared to more

diverse, yet lower external input systems), they bear the risk to lead to monotonous diets that are high in

carbohydrates and low in animal source foods and micronutrient-rich fruits, fish and vegetables (trade-

off). More diverse, yet less external input systems may lead to higher dietary diversity and better nutrition,

with potential trade-offs in yields of rice. These hypotheses are built on many assumptions however as

the choice of diet, as said above, is not only a question of availability and access to a more diversified

choice of food produce, but also, more importantly, a question of customs and behaviour. Since

disaggregated data in this area is scarce, the question cannot be readily answered.

Habitat for aquatic organisms used for recreational activities

30

Rice agro-ecosystems also provide several cultural services, directly through the aquatic organisms living

within the systems, and indirectly through the scenery that they provide. The Rice terraces of Ifugao

province in the Philippines, for example, are a UNESCO World Heritage Site which is a magnet for tourism

in the area. However, more directly, rice systems can offer recreational activities through the habitat they

provide for aquatic organisms. This is explored in more detail in the section on California which talks about

the hunting of water fowl. Due to limited data in this field, the other case studies do not venture deeper

into this trade-off comparison.

2.1 PHILIPPINES

2.1.1 TYPOLOGY OF RICE FARMING SYSTEMS

The Republic of the Philippines is an archipelago consisting of over 7,100 islands in the western Pacific

Ocean. About 470 of those islands are larger than two square kilometers. The climate is tropical maritime

and dominated by the southwest monsoon from May to October and the northern monsoon from

November to April. At sea level, largely irrespective of latitude, this gives rise to two corresponding rice-

growing seasons. At higher elevations, for example in the central highlands (Sierra Madre) rainfall is higher

and temperatures cooler. In many mountainous regions farmers produce a single rice crop (planted in

April and harvested before August) under gravity fed irrigation or as an upland (rainfed) crop.

Because of its tropical climate, large land mass ( more than 300,000 square kilometers) and large number

of islands; the Philippines has a high faunal and floral diversity. It is included among 35 biodiversity

hotspots as designated by Conservation International and is one of the top five countries in terms of

conservation priorities (Peterson et al 2000). Conservation is a major challenge in the Philippines given its

high human population density: The Philippines population was officially reported at 100 million in July

Figure 1. Map of rice production areas in the

Philippines generated using MODIS 2013

(Moderate Resolution Imaging Spectroradiometer)

satellite images. The areas represent irrigated and

rainfed lowland rice areas. Upland areas are not

included. Source IRRI.

Figure 1. Map of rice production areas in the

Philippines generated using MODIS 2013

(Moderate Resolution Imaging Spectroradiometer)

satellite images. The areas represent irrigated and

rainfed lowland rice areas. Upland areas are not

included. Source IRRI.

31

2014. Located along the typhoon belt, the Philippines islands are subject to several extreme weather

events each year, including torrential rains, high winds and up to 19 typhoons (about half of which make

landfall) annually. For the foreseeable future, these three factors, conservation priority, high population

density and extreme weather, will influence the Philippines agricultural policy vis-à-vis sustainable rice

production.

BACKGROUND INFORMATION ON RICE AGRICULTURE IN PHILIPPINES

The Philippines is the world’s eighth largest rice producer; however, rice production occurs on only about

4.4 million hectares (2010 data, GRiSP 2014). Other major crops in the Philippines include sugarcane,

coconut, banana, pineapple, mango, maize and cassava. Rice is the staple food for most Filipinos. Per

capita rice consumption was estimated at 123.3 kilograms per year in 2009, which represented a ca. 25

percent increase from the 1995 per capita demands and a ca. 56 percent increase in national rice demand

(factoring in population increase over the same period). In 2010-11 the Philippines was the largest rice

importer and currently imports about 10 percent of its annual consumption requirements8. Attainment

of rice self-sufficiency is at the centre of the Philippines’ government agricultural policies. The country has

had considerable success in attaining higher yields, with national rice production increasing by 33 percent

between 1995 and 2010 (to about 16 million tons) (GRiSP 2014).

RICE GROWING ENVIRONMENTS IN THE PHILIPPINES

Irrigated lowland: About 70 percent of rice in the Philippines is produced in irrigated areas. Much of the

irrigated rice is produced on the central plain of Luzon - the Philippines´ largest island. Landholdings are

generally small - less than one hectare - and are managed by resident farmers. Fields are generally

delimited using earthen bunds to hold the water. Water sources include deep-well and gravity-fed

irrigation systems that are often managed through municipal authorities directed by the National

Irrigation Authority (Lampayan et al 2015). Rice production in irrigated lowland areas is characterized by

high-yielding modern varieties, generally continuous flooding, transplanting or wet direct seeding, and a

relatively low level of inputs including labour, fertilizers and pesticides compared to other south East Asian

countries. Yields can be as high as 10 tons per hectare in the dry season, but the average is much lower at

about three and a half tons per hectare.

Rainfed lowland: Rainfed rice is found mainly in the Cagayan Valley and Ilocos Norte in northern Luzon,

in Iloilo, and on the coastal plains of the Visayas. Furthermore, rainfed rice occurs under a diversity of

climatic zones, soil types and social and cultural backgrounds in Mindanao. Rainfed rice is subject to

drought during the dry months and is therefore often rotated with an upland crop such as maize or beans.

Rice yields are generally low (two to three tons per hectare) and farmers plant a higher proportion of

traditional varieties compared to irrigated farms. Only about three percent of Philippines rice production

is from traditional varieties, many of these are planted by traditional rice-growing communities in terraced

rainfed systems such as at Banaue. Labour costs are generally high, but other inputs are normally low.

Upland rice: Permanent upland rice production is mainly practiced by low-income farmers and is

characterized by farming without bunds on typically sloping terrain (greater than 18 degrees). Upland rice

8 There were a number of reasons for this increase including political miscalculations. It also needs to be noted that in the years prior to 2011, rice production increased by 33% (Roel, personal communication, 2015).

32

production is constrained by low soil fertility and a propensity to soil erosion, as well as variable water

availability. Rice is usually rotated with either vegetables or fallow. Shifting upland rice production is not

common in the Philippines, but is practiced among some native cultures. Shifting cultivation employs

traditional varieties; however, more recently, many areas with shifting rice production have been settled

by permanent farmers who often adopt modern varieties.

Coastal/Delta: It is estimated that about 76, 000 hectares of deepwater rice (with flooding > 50 cm) is

produced in the Philippines. Unlike in other regions, there are no indigenous floating rice varieties in the

Philippines, but traditional tall lowland varieties are planted instead. Deepwater and floating varieties

have been introduced to some parts of Iloilo and the Cagayan Valley (Catling 1992). Production is low (one

to two tons per hectare), but deepwater cultivation often represents an important source of food and

income in areas that are normally unsuitable for other crops. Furthermore, deepwater rice, and traditional

varieties grown in flood-prone areas have a generally low environmental footprint since farmers often do

not use any fertilizers or pesticides during production.

PREDOMINANT FARMING SYSTEMS IN THE PHILIPPINES

Several farm surveys have been conducted in recent years through IRRI in the Philippines. These surveys

indicate that rice production in the country is predominantly carried out on small family-owned farms

(smaller than one hectare), farmers are predominantly male, and the average age of active farmers is

about 55. Many rice farmers also engage in other income-generating activities including teaching,

government and barangay (local government) work, or semi-skilled labor. Farmers often produce other

crops, or manage livestock or poultry; however, on small farms, these products are mainly for home

consumption. Farming practices are generally common to communities and are characterized by generally

low inputs relative to rice farmers in other countries (Horgan, unpublished data). Some farmers produce

fish close to their rice fields and some attempts have been made to integrate rice and fish production on

lowland farms (Halwart and Gupta 2004).

AGRICULTURAL PRACTICES

Cropping calendar: Rice farmers normally plant two rice crops per year in lowland irrigated areas. At

higher elevations (rainfed irrigated) and in upland systems a single crop is planted each year – this may

be rotated with a fallow, resting period, or with a dry crop (such as vegetables). Rotations in some upland

farms can include several seasons and a range of different crops. In many lowland areas, particularly

during wet fallow periods and close to rivers and lakes, rice produces a ratoon crop9 – this can be managed

by the farmer to augment yield, or is sometimes given-over to farm laborers as an extra, in-kind income.

Land Preparation: Land is traditionally prepared in the Philippines using carabao (a native, domesticated

water buffalo); however in most areas, farm machinery is available for rent or communally owned. Land

preparation includes initial deep ploughing followed by rotation and puddling. Considerable research

9 A new crop that grows from the stubble of the crop already harvested.

33

attention at IRRI has been placed on development of conservation agriculture10, minimum tillage, and

zero tillage systems; however, these systems are not widely practiced by Filipino farmers.

Crop establishment: A variety of crop establishment methods have been developed and used in the

Philippines. Crop establishment is a key phase in rice production, the success of which can determine the

productivity and, because establishment is often expensive, the profitability of the crop. Traditionally rice

is sown either to wet bed nurseries or dry bed nurseries until the seedlings are more than 15 days old.

After this period, the seedlings are transplanted either singly or as hills of two to five plants. Transplanting

represents a major cost for the farmer and is traditionally carried out by family members or as shared

labour within the community. Several systems have been developed to reduce costs. These include dapog

nurseries, a traditional Filipino nursery system where seed is sown over banana leaves, or direct seeding

to flooded soil (water seeding) or saturated soil (wet direct seeding). Direct seeding, although

considerably cheaper, is limited by competition with weeds and vulnerability of seed to invasive apple

snails (Pomacea canaliculata)(Horgan et al 2014). Most Filipino farmers use transplanting to puddled

fields (i.e. tilled rice paddies while flooded) from wet seedbeds; however direct seeding to saturated soil

is becoming more popular.

Soil management (fertilizers): Farmers practice several different fertilizer regimes according to available

resources (including budget), season, and soil quality. Farmers will normally apply a basal application at

the time of crop establishment, with one to three further applications during crop development. Filipino

farmers apply relatively low amounts of fertilizer that are equivalent to about 100 kilograms per hectare.

Higher applications are required for hybrid rice varieties to meet the variety’s full yield potential.

Improved nutrient management is part of the Philippine government’s rice self-sufficiency strategy.

Water management: Lowland irrigated farms are normally flooded at land preparation and for puddling.

Flooding is normally continuous (continuous flooding), with two to five cm of standing water until about

two weeks prior to harvest when the field is finally drained. Because of costs associated with irrigation,

particularly pumping charges, and in some areas because of concern for water resources, farmers are

increasingly adopting intermittent flooding either as unplanned regimes that are determined by water

availability, as recommended by the System of Rice Intensification (SRI), or as planned Alternative Wetting

and Drying (AWD) schedules.

Weed management: Growing rice in flooded soil is an effective method to control weeds. Normally one

time hand weeding of continuously flooded rice is sufficient to effectively manage most weeds. Water

shortages and planned dry periods (where soil is saturated but not flooded) allow weeds to develop. Such

water management regimes are becoming more common among Filipino farmers and are likely to lead to

increased herbicide use. Most Filipino farmers will apply one herbicide treatment to flooded rice paddies;

however, many farmers still carry out hand weeding (Horgan, unpublished).

10 Please note that the term conservation agriculture (CA) is used differently by different organizations: For FAO, CA is a no-till

system by definition; in addition, CA rice is therefore characterized by no-till and residue retention. IRRI includes also systems that are minimum-till.

34

Pests and diseases: Rice is attacked by a wide range of pests and diseases. Principal among these are

apple snails at crop establishment; whorl maggot (Hydrellia philippina) and green leafhoppers

(Nephotettix spp.) at early vegetative stages; rats, planthoppers (Nilaparvata lugens, Sogatella furcifera),

blackbug (Scotinophara spp) and stemborers (Scirpophaga spp., Chilo spp.) at tillering and reproductive

stages; and rice bug (Leptocorisa oratorius) and leaf folders (Cnaphalocrocis medinalis, Marasmia patnalis)

near harvest. Yield losses attributed to each of these have been difficult to estimate and most do not

cause any appreciable losses to yield under normal circumstances (De Datta 1981; Pathak and Khan 1994).

Apple snails can cause severe loses to newly sown or transplanted rice and need to be managed or

controlled. Several cultural control methods have been devised for snails, but the large majority of farmers

now use molluscicides (Horgan et al 2014; Yanes-Figueroa et al 2014). Rats can reach high densities in

some regions, particularly in heterogeneous landscapes. Occasionally farmers use barrier systems or

rodenticides to control rats; however, most farmers apply no management actions (Singleton et al 2010).

Stemborers cause severe damage to rice in some parts of Iloilo and Mindanao. Blackbugs and

planthoppers occasionally reach outbreak proportions, the latter usually associated with high nitrogen

and pesticide inputs. Insects are mainly controlled using chemical insecticides (Horgan and Crisol 2013).

Management of most pests (rats, insects and viral diseases) requires attention to crop synchrony (with

neighbouring fields), careful selection of rice varieties and moderate fertilizer use. Most Filipino farmers

apply one or two molluscicide applications at crop establishment and between one and three insecticide

applications during crop development (De Datta 1981). Prominent rice diseases include blast, bacterial

blight and hopper transmitted viruses such as the tungro, ragged stunt and grassy stunt viruses. Resistant

rice varieties have been developed to manage bacterial diseases (De Datta 1981). Farmers are increasingly

using fungicides to control some diseases, but this is not yet widely practiced.

Harvesting: Rice is still harvested by hand in many parts of the Philippines using community cooperation

or farm laborers. Mechanization through community shared harvesters or through rental or contractual

agreements is gaining popularity and is likely to become important as the average age of farmers and

labour costs increase.

2.1.2 SYNERGIES OR TRADE-OFFS?

2.1.2.1 Increase rice yields and maintaining water quality

The focus of this section is on two management objectives: increasing food production and maintaining

water quality; and the potential trade-offs or synergies originating from aiming at both of these objectives:

I. Rice production is dependent on good quality irrigation water (dependency), and results have

shown that in some areas poor water quality can reduce yields by 50 percent (negative impact).

Poor quality irrigation water can result from several sources. This can be external to the

production system, resulting from naturally high levels of heavy metals in the soil (i.e., arsenic and

cadmium), as well as industrial, urban or mining contamination. For example, Appleton et al

(2006) describe how silt, contaminated with mercury from artisanal gold mining, was deposited

on rice fields and ploughed into the soil in the Diwawal area of Mindanao. This resulted in mercury

intoxication in ca. 38 percent of local inhabitants that was likely through consumption of

35

contaminated rice, fish and shellfish. Furthermore, fine suspended silt in the irrigation water was

implicated in reducing rice yields from six to three tons per hectare in affected areas. Because of

flood irrigation, rice is affected more by contamination of surface waters than are dry crops

(Appleton et al 2006).

II. Rice production is dependent on clean fresh water (dependency), which is affected by annual

typhoons and flooding events on the Philippine islands (causation). This can lead to increasing

salinity of rice fields in coastal areas (direct negative impact) and crop failure (secondary negative

impact) due to flooding with sea water (cause), and in lowland areas due to lodging or

submergence (cause). Flood- and salt-affected fields are associated with low productivity and

yield, decreased availability of employment opportunities for rural communities, and low farm

household income (secondary impact/consequence of direct impact). Salinity in rice fields can

also result from seepage during the dry season (cause) and lowering of the water table because

of over-exploitation (cause) (Lopez & Mendoza 2004).

III. Rice production is dependent on good water quality (dependency) to maintain a diversity of

aquatic organisms (positive impact). The diversity of aquatic organisms in rice floodwaters (cause)

provide rural human populations with wildlife (fish, birds and frogs) from rice fields to supplement

their diet (positive impact), and use rice associated weeds for food and animal fodder (positive

impact). This diversity may also contribute to stability in the densities of herbivore populations

(including pests) (direct positive impact). For example, Settle (1996) suggests that detritivores

present in rice crops at early vegetative stages (often in the soil or water) allow predator

populations to establish and protect the crop (secondary positive impact) against herbivores that

appear later in succession.

IV. The water quality on which rice production depends (dependency) is affected by the introduction

of exotic animals and plants that have been shown to shift the balance in aquatic communities

(cause) and can consequently reduce water quality (negative impact). For example, exotic apple

snails in the Philippines reduce the biomass of submerged macrophytes, and have apparently

depleted Azolla populations thereby increasing water turbidity and sedimentation (Horgan et al

2014). Furthermore, exotic rice paddy eels are thought to deplete native fauna in the floodwater

and can burrow through earthen bunds causing leakage of floodwater and accelerated draining

of the field.

V. Rice is dependent on good water quality (dependency), which is affected by fertilizer and pesticide

inputs during the production. Traditional rice cultivation, characterized by no fertilizers or

36

pesticides use, has shown to achieve high yields (positive impact). For example, Watanabe et al

(1978) indicates that 23 successive rice crops were grown in IRRI without nitrogen fertilizer and

without yield decline – yielding an average of four tons per hectare per crop. This can be explained

by biological nitrogen fixation brought about by a range of aquatic organisms including blue green

algae and bacteria, the Azolla-Anabaena complex, heterotropic bacteria in the rice rhizosphere,

and heterothropic bacteria in anaerobic soil remote from the roots (Causation) (Watanabe et al

1978).

Nitrates and potassium in water (cause) lead to eutrophication and diminishing drinking water

quality (negative impact). As with pesticides, nitrogen use has increased among rice farmers in

the Philippines. In a study of the Paganhan-Lomban watershead, Sanchez et al (2006) found that

sites with rice production contributed more suspended sediments and higher nitrogen and

potassium concentrations to water contamination when compared to sites planted with other

crops, and these levels often exceeded international maximum safe concentrations. Flooding of

fields during rice production is largely responsible for the higher surface runoff of nitrates in rice

farms (secondary cause).

Another study in three provinces of the Northern Philippines recorded high levels of nitrates,

sometimes exceeding international maximum acceptable levels in drinking wells (secondary

impact/consequences of direct impact). However, the study concluded that there were generally

low nitrate concentrations in groundwater/drinking water in rice growing areas, which caused no

risk for health. The authors argue that this was probably due to the relatively large volatilization

losses and fast chemical and microbial degradation under aerobic conditions in the tropics

(Bouman et al 2002).

VI. Agrochemicals such as pesticides used during crop production are perhaps the main contributors

to declining water quality in rural areas (Cause). Prior to the introduction of the apple snail,

molluscicides were rarely used in agriculture; however, molluscicides are now used by a large

majority of lowland rice farmers (Adalla and Magsino 2006). Furthermore, most farmers will apply

a single herbicide application and, from one to three insecticide applications, with some farmers

applying as many as six or seven insecticide applications (Fabro & Varca 2012). This suggests that

farmers make an average of ten pesticide applications in a cropcrop season. Furthermore, farmers

frequently wash their application equipment and farm machinery in local streams and rivers

(Elfman et al 2011). Because of flooding (additional cause), there is a continuous flux of

percolating water to carry the chemicals to the groundwater (negative impact) (Bouman et al

2002). For example, in a study of drinking wells in Luzon conducted between 1989 and 1990,

Bouman et al (2002) found that levels of pesticides were often above accepted maxima for drink-

water safety (secondary impact/consequences of direct impact). Pesticide use at the time of the

37

study was considerably lower than today, such that levels of contamination are likely to be

considerable higher nowadays. Other studies from the Philippines have found similarly high levels

of contamination of water (Elfman et al 2011; Bajet et al 2012) and poor management of

pesticides by farmers but that contribute to contamination of surface waters (Bandong et al 2002;

Snelder et al 2008; Elfman et al 2011).

Despite the small number of studies conducted, it is evident that issues of declining water quality are a

reality for the Philippines. Furthermore, contamination of water that results from agrochemical use during

rice farming has consequences for drinking water quality, food quality, aquatic fauna and flora, soil

fertility, biodiversity and ecosystem functioning, and tourism.

THE EFFECT OF SPECIFIC MANAGEMENT PRACTICES OR SYSTEMS

The effect of soil fertility management

The use of nitrogen in agriculture has been linked to sustaining agricultural productivity (Stewart et al

2005). Because of limits in land availability, the intensification of rice production usually occurs through

the increased use of fertilizer on existing crop land – along with the expansion of irrigation (FAO 2008).

Increasing fertilizer use does, however, bring other undesirable consequences for farmers including higher

disease incidence and a greater abundance of herbivorous insects and mites. This often leads farmers to

apply higher levels of pesticides and thereby reduce ecosystem efficiency and reduce water quality

(Horgan and Crisol 2013; Spangenberg et al 2015).

Farmers may reduce excess nutrient through proper nutrient management without reducing crop yields.

For example, Site Specific Nutrient Management (SSNM) as promoted by IRRI and the Philippines

Department of Agriculture is a needs based approach for optimally applying N, P and K to rice with the

aim of approaching yield potential for a given site and rice variety without applying excess fertilizer

(Pampolino et al 2007). In 2014, over 290,000 Filipino farmers received SSNM recommendations for

optimal fertilizer application (Johnson, pers. Comm.). In many cases, this included recommendations to

increase fertilizer inputs, which can increase rice susceptibility to pests, particularly where chemical

fertilizers are used.

Reasons for non-adoption of organic rice farming include difficult access to materials (fertilizers and

organic biocides), lower yields with little or no available premium, perceived difficulty and increased

labour costs associated with the method, and a lack of available training. In one comparative study from

the Philippines, organic rice farms produced lower yields (slightly); higher profits; used less energy; were

more energy efficient; resulted in better soil quality; had lower production costs and had lower labour

costs (mainly due to high cost for pesticide applicators and chemical costs) than conventional rice farms

(Mendoza 2004).

As a final note, inoculation of rice fields with the aquatic fern Azolla has been shown to increase nitrogen

availability to rice plants leading to increased rice yields (Watanabe et al 1977); however, since the

38

introduction of the apple snail, maintaining high densities of Azolla in rice fields, particularly lowland

fields, is unfeasible (Horgan et al 2014).

To our knowledge, concrete data on the effects of soil management using SSNM, SRI or organic rice

farming practices on water quality in the Philippines is unavailable. However, the lower amounts of

nitrogen and the form of the nitrogen in organic fertilizers may have less of an effect on aquatic

biodiversity. For example, a study by Stuart et al (2014) demonstrated that apple snail mortality is lower

following application of organic fertilizer, than where compound fertilizer, complete fertilizer or urea were

applied. SSNM will safeguard against excessive fertilizer applications (i.e., >200kg/ha) as occurs in other

countries and will therefore protect water quality.

The effect of plant protection (pests, diseases and weeds) on food production and freshwater quality

Chemical pesticides, particularly insecticides, are the most dangerous contaminants generated by rice

production in the Philippines. All pesticides are toxic to some degree, most of the commonly used

insecticides and molluscicides will negatively affect non-target aquatic invertebrates and some affect

vertebrates (Bajet et al 2012). Furthermore, several pesticides are dangerous to human health. In spite of

continued research attention toward reducing pesticide use among farmers, it is clear that increasingly

high numbers of applications are made each year and using an increasing diversity of chemical products.

Furthermore, it is still unclear whether pesticides (particularly insecticides) actually increase rice yields

(Heong et al 2015).

SRI and organic farming prohibit the use of chemical pesticides. Nevertheless, many organic farmers

attempt to replace chemical pesticides with botanical substances either purchased from a dealer or

concocted by the farmer him/herself. The effectiveness of such products is hard to evaluate; however, it

is most likely that herbivores have negligible effects on yield in general and in organic farms in particular,

and that the reported lower yields from organic farms (i.e., Mendoza 2004) are due principally to lower

fertilizer applications and low fertilizer efficiency. Organic pesticides should be treated with caution as

these may also reduce water quality and affect non-target organisms – however, there is a lack of concrete

information on the nature and effects of botanical insecticides used by Filipino farmers.

A growing awareness of the negative effects of pesticides, particularly for human health, has encouraged

some farmers to produce pesticide-free rice. This rice normally receives no premium with grain mixed

together with that from conventional farms by millers and retailers. Pesticide-free farms are likely to have

similar yields to conventional farms and avoid potential yield declines by applying standard fertilizer

regimes.

Conventional farms are encouraged to use Integrated Pest Management (IPM) to combat pests. As in

much of Asia, IPM is currently rarely practiced among Filipino farmers. Many farmers apply pesticides on

observing a pest (or an insect that looks similar to some pest) using lower action thresholds than

recommended (Bandong et al 2002). Furthermore, many agrochemical companies attempt to secure sales

by distributing prophylactic calendar schedules to chemical dealers, extension officers or farmers

(Spangenberg et al 2015). Evidence is conflicting as to whether such prophylactic schedules, or response

applications, can actually increase rice yields. Several components of pesticide-free management of apple

39

snails have been described and tested (Yanes-Figueroa et al 2014). These will dramatically improve water

quality by avoiding noxious molluscicides in rice fields.

Proper IPM demands that farmers monitor their fields for pests and take actions against pest damage

once a threshold is reached. Farmers are encouraged to apply non chemical control measures including

traps, lures or biocontrol agents, before resorting to chemical pesticides. Whether IPM can increase rice

yields depends on the potential for insects to reduce yields. Estimates of yield losses from insects vary

greatly, but at normal levels insect damage to rice in the Philippines is very low, such that management

actions may have little contribution to overall rice yield (Heong et al 2015). Integrated rodent

management, including community-based management of rodents is likely to increase yields considerably

in areas affected by rats (Singleton et al 2010); however, concrete estimates of losses to rice yield from

rodents are lacking.

IRRI is currently investigating ecological engineering as a means of promoting the natural biological

control of insect pests. Evidence from multi-site experiments indicates that planting of bunds with

vegetable crops can reduce the incidence of some pests in rice; however yields were not different

between ecological engineering plots and conventional controls (with and without pesticides).

Nevertheless, food production from the plots increased overall because of the bund crops (okra, beans

and bitter gourd)(Horgan, unpublished).

Integrated management of weeds without herbicides is possible but demands considerable labour inputs.

A range of practices are available to farmers to reduce the impact of weeds, particularly in direct-seeded

rice. These practices include increasing seedling densities, using cover crops during fallows, and using only

certified or high quality seed (Chauhan et al 2012, 2013). Such practices have the potential to improve

water quality by reducing chemical inputs.

Finally, experience with apple snails and paddy eels in the Philippines indicates the potential economic

losses that can be caused by introduced species. To avoid future introductions, proper quarantine policies

should be developed. Such policies will protect and maintain rice yields and the agricultural sector in

general.

Any plant protection practice that reduces pesticide inputs will improve water quality. Normally, water

quality is not evaluated in comparative studies of chemical versus non-chemical pest management. This

is largely because of the high costs involved in biochemical water analyses and a lack of resources

(laboratories and funding) in the country to conduct such analyses. We are unaware of any examples from

the Philippines that compare levels of contaminants in rice floodwater or groundwater associated with

different pest management options. However, several studies have shown the detrimental effects of

pesticides on aquatic fauna: In a review of over 200 published studies, Roger (1990) indicates that

pesticides have three major effects on rice field algae including knockdown of green algae and the

promotion of cyanobacteria, an increase in microalgae because of a loss of grazing invertebrates, and the

proliferation of muclaginous macrocolonies. Recent studies by IRRI have also indicated drastic changes in

the zooplankton and macrofauna of rice fields following insecticide use, including declines in the

40

abundance of ostracods and daphnia, but increases in mosquito and chironomid larvae (Horgan,

unpublished).

CONCLUSIONS

A large number of studies are available from the Philippines to compare different soil and pest

management practices on food production (principally rice yield). However, many of these studies are

now out-of-date as chemicals and farmer behaviours have changed over time. Less available are carefully

recorded data on the effects of soil and pest management on water quality.

Collectively, an image emerges of the negative effects of pesticides, particularly insecticides, on water

quality using aquatic and/or terrestrial arthropod communities as indicators. Many of these studies have

also recorded changes in rice yield associated with pesticide applications. These studies are generally

limited by issues of scale – many having been conducted on small plots and many of the insecticides that

have been examined are now unpopular among Filipino farmers. Evidence suggests that insecticides have

little effect on rice yields, but strong negative effects on water quality. In contrast, herbicides seem to

have strong positive effects on rice yield, but negative effects on water quality, albeit to a much lesser

extent than that of insecticides. Studies that examine these effects as parts of integrated systems are

largely unavailable. However, current research at IRRI on ecological engineering using vegetation patches

indicates a potential synergy between food production and water quality (based on evidence from

terrestrial stages of aquatic insects). However, other factors, including labour costs, could offset this

synergy.

The effects of nitrogenous fertilizers on rice yields are generally clear, as are the deleterious effects of

fertilizers in the floodwater environment. Evidence of how SSNM, SRI or organic agriculture might differ

from conventional farms in terms of water quality is still unavailable.

2.1.2.2 Increase in rice yields versus reduction of water use

The focus of this section is on two management objectives - increasing rice yields while reducing water

use. Associated benefits, negative impacts and dependencies are listed below:

I. Water is required for rice plant growth (although germination is typically aerobic), it promotes

nitrogen fixation and nitrogen efficiency and it effectively controls weeds (positive impacts).

II. Rice floodwater is also important as habitat for a diversity of associated plants and animals

(positive impact). For example, rice fields provide habitat for migrant and resident birds in Asia

(Borad et al 2000; Maeda 2001) and are recognized by Ramsar as an important wetland habitat

for conservation. The diversity and abundance of waders in rice landscapes is largely determined

by the availability, volume and quality of rice floodwater (Amano et al 2008) and are likely to be

affected by water saving technologies. This can also affect food provisioning services from rice

fields by decreasing supplementary foods such as fish, shellfish, mollusks, and frogs.

41

III. The Philippines climate and geographic location on the western edge of the Pacific Ocean ensure

an abundant supply of rain water that recharges aquifers and maintains rivers and lakes

(dependency).

IV. Nevertheless, some regions in the Philippines occasionally experience, or are susceptible to

physical water scarcity – particularly on the western coast of Luzon in Zambales and Ilocos Norte

(cause).

V. Furthermore, farmers in much of the country are subject to economic water scarcity (poor

irrigation infrastructure) albeit with great improvements in recent years (cause). Greater demands

for available water also represent a threat to water availability for Filipino farmers in some

regions, particularly in Central and South Luzon (cause). This arises from the increased diversion

of water to growing cities and towns, including the capital, Manila; increased pollution that makes

water quality unsuitable for irrigation; disruption and clogging of existing irrigation systems (due

to earthquakes, volcanos and development);and excessive water extraction and competition with

other users, including industry (Rejesus et al 2011; Lampayan et al 2015) .

These considerations have prompted research into alternatives to continuous flooding in rice and support

from the Philippines government for research and promotion of water saving technologies (Lampayan et

al 2015). Demands for irrigation water are greatest in lowland rice production systems and research

attention has concentrated on these areas.


The effect of water saving technologies

Given the likely trade-offs between water saving and both food production and habitat for wildlife,

decisions about water saving requirements and technologies require careful consideration. Several water-

saving technologies have been studied in the Philippines and some are currently promoted among Filipino

farmers. All water saving systems attempt to increase water productivity. The key principles for

improving water productivity apply at farm, field and basin levels, regardless of whether the crop is grown

under rainfed or irrigated conditions: (i) increase the marketable yield of the crop for each unit of water

transpired by it, (ii) reduce all outflows (e.g. drainage, seepage and percolation), including evaporative

outflows other than the crop stomatal transpiration; (iii) increase the effective use of rainfall, stored

water, and water of marginal quality. In the Philippines, this is achieved by a combination of reduced land

preparation time, adoption of intermittent flooding (or no flooding), and increased use or efficiency of

fertilizers (Hafeez et al 2007).

Reducing land preparation time: Transplanting requires that land is puddled. Puddling (churning of the

soil under saturated conditions) reduces water loss by percolation, assists weed control, and makes the

soil soft for transplanting. However puddling has associated higher tillage costs, adverse effects on soil

structure for upland crops grown in rotation with rice, and high water requirements for crop

establishment (Sudhir-Yadav et al 2014). Furthermore, irrigation for land preparation often involves water

application to cracked soils (which can reach up to 65cm deep in some soil types), and results in bypass

flow losses (water that flows through soil to the subsoil). Bypass flow can account for 41-57 percent of

42

total water applied during wetting and may continue until the soil is repuddled leading to high percolation

losses (estimated to be as high as 40% of the total water applied to the crop)(Cabangon & Tuong 2000).

Land preparation time can be reduced through direct seeding.

Wet direct seeding (WDS) and dry direct seeding (DDS) do not require puddling and reduce the time during

which the field is flooded. Wet direct seeding is practiced by farmers in the Philippines and is gaining

popularity, particularly in lowland rainfed systems. Dry direct seeding is generally not suitable for

Philippines’ conditions, but has been researched extensively at IRRI. With dry direct seeding, there are

options for reduced tillage or zero tillage) (Chauhan 2012; 2013).

Conservation agriculture is defined as an agricultural management system aiming to minimize soil

disturbance, maintain a permanent residue for soil cover, and includes a rotation of the main crops (FAO

2012). In rice systems, conservation agriculture can include several crops in rotation (but mainly corn-rice

in the Philippines) (Chauhan et al 2012). Minimum tillage is difficult to practice in rice systems because of

severe weed competition (Chauhan 2012; 2013). In reduced tillage systems, mulching with dry soil or

straw or covering the soil with plastic sheets can be used to maintain moisture in the soil and reduce weed

growth – this is equivalent to the Ground Cover Rice Production System (GCRPS) of China, but is rarely

practiced in the Philippines (Abdulai et al 2005, in Rejesus et al 2011).

Reduced flooding time: The System of Rice Intensification (SRI) includes intermittent flooding as part of

a production package. The system advises transplanting of young (eight to ten days old) single rice

seedlings, with care and spacing, and applying intermittent irrigation and drainage to maintain soil

aeration. In addition the use of a mechanical rotary hoe or weeder to aerate the soil and control weeds is

encouraged. Because it is water saving, SRI is encouraged by the National Irrigation Administration (NIA)

in the Philippines (Miyazato et al 2010). In the SRI system, ‘intermittent flooding’ - irrigation to field

capacity and managing high soil moisture without anaerobic conditions (which had also been practiced

in rice culture in India – Sandhu et al 1980) is managed through visual inspection of soil and attempts to

maintain a moist soil surface. However, such flooding regimes are prone to yield losses where water is not

carefully monitored and particularly at the vulnerable rice flowering stage.

In response to difficulties with intermittent flooding, IRRI developed Safe Alternative Wetting and Drying

(now referred to as Alternative Wetting and Drying (AWD)). AWD reduces water usage by about 30% while

maintaining yields. By this method, perched water is allowed drop to 15-20cm below the soil surface

before applying irrigation (this is monitored using a perforated water tube) which is equivalent to a soil-

water potential of >10kPa; However, the fields are flooded to 2-5cm (not 5-10cm as for traditional rice

culture) when levels drop below 15cm and are flooded continuously during flowering (Lampayan et al

2015). During the dry-field state, seepage and percolation drop to nearly zero because of the almost

complete absence of a hydraulic head (Bouman et al 2007). AWD has gained prominence in the Philippines

through cooperation between IRRI and several government institutes. Lampayan et al (2015) present an

impact pathway analysis of AWD research and extension using reports and papers developed over several

years of the Irrigated Rice Research Consortium (IRRC). It is estimated that ca. 93,000ha (82,000 farmers)

have adopted AWD, that is 2% of the total rice area of the Philippines (Lampayan et al 2015).

43

Attempts to replace flooded rice with varieties adapted for dry conditions have been largely unsuccessful

in the Philippines. Research into aerobic rice (also known as aerobic rice monoculture) has been thwarted

by depletion of soil conditions over successive cropping seasons and the lack of available high-yielding

varieties. In the aerobic rice production system, the crop is usually dry direct seeded and soils are kept

aerobic throughout the growing season. Supplementary irrigation is applied as necessary and adapted rice

cultivars that are responsive to fertilizers and with higher yield potential than upland rice varieties are

used (Kreye et al 2009). Unlike traditional upland rice cultivation in which rainfall and capillary rise are the

only sources of water, the plants in aerobic rice culture do not encounter drought, despite reductions in

water use of ca 50% (Nie et al 2009). Where aerobic rice culture has not been conducted previously (i.e.,

on new land), yields of up to 6t/ha can be achieved (Kreye et al 2009). Other rice production practices

with moderate water saving ability such as raised bed systems and Saturated Soil Culture (SSC) are rarely

practiced in the Philippines (Lampayan et al 2015).

Impact of different water saving practices on food production

In a comparative study of wet direct seeding and transplanting in the Philippines, Tabbal et al (2002)

indicated that wet seeding was better than transplanting in continuous standing water (3-17% higher

yield, 19% less water, and a 25-48% increase in water productivity); however, under saturated soil

conditions, wet seeding reduced yield by 5%. Under such conditions wet seeding did reduce water inputs

by 35% and increased water productivity by 45% compared to flooded conditions. However, Tabbal et al

(2002) caution that the results were likely influenced by low groundwater depth. Furthermore, weeds are

likely to be a problem for all forms of direct-seeded rice (Chauhan et al 2014).

Information on rice yields using SRI are difficult to assess; reports range from major increases in yield over

conventional systems to large yield declines. Furthermore, because of the range of practices included in

SRI, it is difficult to attribute any changes in yield to intermittent flooding specifically.

Estimates of the effects of safe AWD on rice yield also vary: Belder et al (2005) found no significant

differences between rice yields from continuous flooding, AWD with mid-season drainage and AWD only

during the rice vegetative phase. Similarly, Rejesus et al (2011) suggest that AWD at demonstration plots

in the Philippines caused no significant reductions in rice yield or in the time spent by farmers weeding.

Similarly, Lampayan et al (2015) indicated generally no change in rice yield at plots throughout the

Philippines; but suggested that a 9% yield increase was reported by farmers at Bohol that used gravity

irrigation, particularly those farmers located downstream. This may imply that water saved upstream, was

available to downstream farmers as a result of AWD. Lampayan et al (2015) also reported reduced water

pumping and fuel consumption (20-25% reduction in fuel and oil) that resulted in ca 32% increase in

farmer's income. The authors noted that all AWD adopters acknowledged that AWD saved time, labour

and expense.

None of the studies on intermittent flooding systems in the Philippines have evaluated herbicide use

among farmers (SRI or AWD); however, weeds are known to be problematic in drained rice systems. In

dry-seeded, conservation agriculture systems several factors interact to influence weed abundance. A

study in the Philippines showed 87% postdispersal weed seed predation was from the soil surface (see

44

Chauhan et al 2010); however, three factors (predation, germination and viability) interact to determine

the fate of weed seeds in dry production systems: Zero-tillage increases predation and germination of

seeds (i.e. positive and negative), but tillage buries seeds, reducing germination but extending viability

(positive and negative). The balance between these factors will depend on the seed bank composition and

the environment vis-a-vis predators and soil conditions (Chauhan 2012).

Reports on continuously grown upland rice in the Philippines indicate yield losses of between 30-60% as

well as yield failures (Ventura and Watanabe 1978; Ventura et al 1984). In a similar fashion, continuous

planting of aerobic rice leads to rapid yield loss (George et al 2002 in Kreye et al 2009b).

During a long-term experiment in the Philippines, aerobic rice yields were consistently lower than in

conventional, flooded rice, and yield differences increased over eight seasons of continuous cropping

(Peng et al 2006). Yield failures, or zero harvest, occur occasionally and were attributed to ‘soil sickness’:

potentially the combined effect of allelopathy, nutrient depletion, buildup of soil-borne pests and diseases

and soil structural degradation (Ventura & Watanabe 1978). Key pathogens include the Rice Root Knot

Nematode (RRKN) (Meloidogyne graminicola), which is known to cause yield declines ranging from 12 to

80% (Padgham et al 2004 and others in Kreye et al 2009). Furthermore, Pythium arrhenomanes has been

isolated from soil following aerobic rice monocropping in the Philippines and was linked to reduced

seedling growth (Van Buyten et al 2013). Rice in aerobic soils also suffer from a lower availability of Fe

and Mn due to positive redox potential (Kreye et al 2009) as well as a lower availability of Phosphorus,

which is less mobile in unsaturated soils (Kato & Katsura 2014). Despite these issues, Bouman et al (2005)

indicate that whereas aerobic rice has lower yields than flooded rice, it can attain appreciably higher water

productivity.

In terms of food production, each of the water saving technologies will have consequences through their

effects on pests and diseases. New pest complexes or disease syndromes will emerge as the systems are

adopted (Mew et al 2004).

Impact of different water saving practices on fresh water quantity

Direct seeding has a noted capacity to reduce water use in rice production and increase water

productivity. Bhagat et al (1999) reported that growing rice in saturated soil saved about 40% water

compared to flooded soils and produced similar yields when weeds were controlled by herbicides. Shallow

tillage has been recommended for cracked soils prior to flooding and is noted to reduce water loss by as

much as 31-34% (Cabangon & Tuong 2000)

Proponents of intermittent flooding generally indicate water saving of 30-40% (SRI: Miyazato et al 2010;

AWD: Lampayan et al 2015). Water saving through SRI has not been monitored in the Philippines;

however, safe AWD has been noted to reduce hours of irrigation use by about 38% without any

yield/profit loss – this included less pumping hours, the same pumping frequency (therefore without

reducing labour costs), but with less water volume (Rejesus et al 2011).

Accounting for water saving has a major caveat related to issues of scale, such that water lost in one field

through water saving technology may lead to availability or reuse downstream. This can have advantages,

as in Bohol (described above), but may also lead to little or no conservation in water resources. Bouman

45

and Tuong (2001) caution that achieving water saving without maintaining or increasing rice yields, or

food production in general, would threaten food production at large.

Impact of different water saving practices on wildlife

Reducing volumes of standing water, without increasing food production, also has unnecessary

consequences for wildlife that depend on natural and artificial wetlands. For example in Japan, an increase

in the area of dry rice fields with high drainage efficiencies has had a negative impact on wetland birds

through reduction in the abundance of prey species (Maeda & Yoshida 2009 in Amano et al 2010); the

painted snipe (Rostratula benghalensis), ruddy-breasted crakes (Porzana fusca), and common snipe

(Gallinago gallinago) have all declined in rice-paddy areas in recent years (Amado 2006; Amado &

Yamaura 2007). Although data is not yet available from the Philippines, one recent study has reported

shifts in dominance of waders at AWD sites in Luzon (Schmedly, pers. comm.).

CONCLUSIONS

Growing rice in continuously flooded fields has been taken for granted for centuries, but the “looming

water crisis” may change the way rice is produced in the future. Attention to water saving technologies in

rice production in the Philippines has grown considerably in recent years. Water saving technologies vary

in the depth and time of flooding, but each method has tried to reduce both. Some technologies tend to

consistently reduce yields by small amounts (AWD) or reduce yields substantially after continuous practice

(i.e., aerobic rice). However, most do increase water productivity.

Furthermore, because water represents an efficient control for weeds in rice cultivation, most of the

water saving technologies have concomitant problems with weeds, which is likely to lead to increased

problems of water contamination and declining water quality because of increased herbicide use.

However, most of the technologies also reduce labour and energy (fuel costs) during crop establishment

and are therefore attractive to farmers. Balancing the costs and benefits of water saving must be

conducted at larger scales than those included in most studies (i.e., need for analyses at landscape and

catchment levels) and should include other ecosystem functions (biodiversity maintenance, biomass

production) together with water productivity and food production services.

2.1.2.3 Increase in rice yields versus maintenance of air quality

Between 2006 and 2010 the average rice harvest in the Philippines was around 16 million tons from 4.4

million hectares of rice area. Average yields in irrigated and rainfed rice systems were respectively 4.1 and

2.9 tons/ha (GRiSP 2013. The total production of rice straw in 2010 was around 9 Million tons per year

(Launio et al 2013). Most farmers only cut the panicle part of the rice crop and leave large amounts of

biomass in the field due to the additional cost of removing the straw (Gadde, et al. 2009). Due to

intensification of rice production systems, rice straw has moved from a by-product of rice to waste

material that needs to be disposed in a short period of time:

I. In the absence of synthetic inputs, agro-ecosystems depend on raw material, i.e. biomass, which

is usually produced in the system itself as a by-product of food production, as input for

maintaining soil organic matter. According to Truc et al (2012) straw was used for vegetable

mulching in three villages in Central Luzon. Incorporation of the remaining straw and stubble into

46

the field returns most of the nutrients and can help to conserve the soil in the long term. Results

of Eagle et al. (2000) even conclude that the retention of straw in rice fields can result in increased

soil N supply of 12 up to 19 kg ha-1 depending on the use of N fertilizer. However, incorporating

rice straw into the wet soil also results in temporary immobilization of N and additionally, a

significant increase in methane emission (Sander et al. 2014; Wassman et al. 2000 a,b).

II. Instead of incorporating into soils or using it as mulch, rice residues can also be composted. Rapid

composting with the help of inoculants such as Trichoderma sp. can hasten the decomposition of

rice straw and reduce the accumulation of waste (Truc et al. 2012). Microbial composting can be

an effective environmentally sound alternative for the recycling of rice straw into compost (Kauser

et al. 2010).

III. Some integrated farming systems that have both crops and livestock, also rely on rice residues as

(supplementary) animal feed, but this is limited in the Philippines. According to Truc et al (2012),

19% of straw was used as cattle feed during the dry season in three villages in Central Luzon. Like

most straws, rice straw is a poor livestock feed. According to Drake et al. (2002) rice straw is a

good source of energy, but is poor in protein (2-7%) and its high silica content results in a low

digestibility. Nevertheless, rice straw can be treated in order to improve its nutritive value and

enhance feed intake and/or digestibility (Heuzé and Tran, 2013). Different types of treatments

exist such as chopping and grinding the straw (Doyle et al., 1986), chemical treatments with sodim

hydroxide, ammonia and urea (Van Soest, 2006) or heat and pressure treatments (Van Soest,

2006).

IV. Farms could potentially use rice residues as biomass for energy production such as generating

electricity through direct combustion. According to Gadde et al (2009), this could in theory

generate 4.9 TWh of energy in the Philippines and would avoid 4.31% of the estimated national

GHG emissions . Although this appears to be a promising technology, use of biomass for energy

production is not common in the Philippines.

Rice straw needs to be washed or weathered to remove alkalis that are detrimental to

combustion, then it should be dried prior to storage, compacted or baled in the field, transported

to a centralized location and chopped. The high silica content causes blades of chopping

equipment to become blunt very quickly and silica also creates problems with combustion

equipment and the lack of successful business models increases risks and costs of finance due to

low investor confidence. Hence, there are obstacles at every stage that have prevented

widespread use of rice straw for fuel. Increasingly biological routes are being explored as an

47

alternative that could help avoid some of these challenges. Anaerobic digestion – especially if co-

digested with livestock manure – has been shown to work on a farm scale, avoiding many of the

logistical challenges of larger scale plants. They can avoid the need for chopping the straw or

burning it directly, reducing the issues with silica (cite Can Tho study). Research is ongoing to try

to take the process from pilot stage to commercialization.

V. Another important by-product of rice production, besides straw, is the rice husk. 100 kilograms

of paddy rice will generate approximately 20 kg of husk. Rice husk is mainly used as an energy

source for milling or grain drying facilities in the Philippines. The husk can be used for electricity

generation, and at the same time produces the by-product biochar (carbonized organic matter).

According to Haefele et al. (2012), biochar can help to improve soils, avoid methane emissions,

and sequester carbon in soils.


Burning: The most popular way to dispose of rice straw while maintaining part of the nutrients is by

burning. According to a survey of Truc et al. (2012) in three villages of central Luzon, Filipino farmers

burned about 90% of straw in the dry season and about 60% in the wet season. A survey by Gadde et al.

(2009) produced even higher estimates. According to these authors almost 95% of the residues are burned

in the field. The most common method to burn straw in the Philippines is by burning the piles of straw at

threshing sites.

Rice straw burning causes the loss of major nutrients from the soil: almost complete N loss, P losses of

about 25%, K losses of 20%, and S losses of 5 to 60% (Dobermann and Fairhurst 2000). On the other hand,

burning effectively transforms straw to a mineral K nutrient source. Dobermann and Fairhurst (2002) also

warn that the method of burning can influence soil fertility. In the Philippines, rice straw is burned at the

threshing sites and this method can result in a centralization of certain nutrients at the places where the

residue is burned, resulting in a patchy distribution of nutrients across the field.

According to Truc et al (2012), farmers indicate that burning has been a long time practice in the

Philippines and is also conducted to reduce pest and disease incidence. If systems are in place to gain

economic benefits from rice straw, one should address a possible depletion of resources in the long term.

In their overview of raw straw management, Dobermann and Fairhurst (2002) warn of the depletion of

nutrients, and particularly K if rice straw is systematically removed from the field. Therefore taking away

rice straw from the field might impact food production in the long term.

Rice straw incorporation into soils: Wassmann et al (2000a) investigated yields and methane (CH4)

emissions from rice fields at Los Baños, Philippines, during a four years’ field experiment (1994-1997). The

experimental setting included different water regimes (continuous flooding; pre-harvestpreharvest

drainage and dual drainage), soil amendments (mineral and organic: urea, urea + ammonium sulfate, urea

+ rice straw, urea + green manure) and cultivars (IR72 IR65597, PSBRc14, Dular, Magat). Incorporation of

rice straw together with urea compared to only urea application led to a significant reduction of yields in

the dry season (3.5 t ha-1 compared to 5.4 t ha-1) but not in the wet season.

48

Composting: Corton et al (2000) compared the addition of rice straw compost with fresh rice straw as

organic fertilizer. Whereas compost increased rice CH4 emissions by approximately 23-30%, fresh straw

led to an increase of 162-250% in methane emissions compared to the absence of organic fertilizer.

Recommendations to reduce CH4 emissions are to use low C/N organic fertilizer such as chicken manure

or rice straw compost instead of fresh rice straw. The grain yield as well as total aboveground biomass

produced did not differ among the treatments.

Straw as cattle feed: Rice straw is seldom used as animal feed in the Philippines (Truc et al. 2012). No data

are available about neither the effect of rice straw as feed in the Philippines nor the use of any treatments

for rice straw to improve digestibility as discussed above.

Making biochar from rice husk: Research by Haefele et al (2011) examined the effect of biochar from rice

husk on soil characteristics in a range of different soils with acidity levels going from 4.1 to 6.6 pH. Field

experiments on different soil types showed that the application of untreated and carbonized rice husks

can increase total organic carbon, total soil N, the C/N ratio, and available P and K. Results also showed

that on a fertile soil, the high C/N ratio of the carbonized rice husk supposedly limited N availability,

thereby slightly reducing grain yields. In poor soils however, where the crop also suffers from water stress,

soil improved both chemically and physically by 16–35%.

Energy: Launio et al (2013) calculated that if a demand for rice straw is created, for example as raw

material for power or bioethanol production plants, farmers may be able to supply the straw with a direct

cost of approximately Php 5,200/ha for two seasons or Php 1.2/kg of straw considering the labor cost of

gathering and moving the straw to a storage area.

CONCLUSIONS

The practice of straw burning is still the most popular way to dispose of raw materials. However the

convenience of this method poses a severe trade-off because of negative effects on environment through

pollution and the reuse of nutrients. Incorporating straw into the soil can provide a benefit for soil fertility,

but tradeoffs with food production through nitrogen fixation and methane emissions should be taken into

account. Several options exist to reuse rice straw outside the field i.e. for energy, mushroom production,

cattle feed, bedding for livestock, and mulching. These options only seem possible (i) at a small scale or

(ii) require large financial investments from the private sector.

2.1.2.4 Increase in rice yields versus reduction of GHG emissions

I. The fact that rice in the Philippines is mostly cultivated in water, leads to significant greenhouse

gas (GHG) emissions (negative impact). Rice production in the Philippines is predominantly

irrigated (continuous flooding) with wet tillage and transplanting as the major crop establishment

technique. Irrigated rice ecosystems provide an anaerobic environment crucial for the survival of

methanogenic bacteria. Methanogenic bacteria in irrigated rice ecosystems play an important

role in the anaerobic decomposition of organic matter, which leads to the production of methane

(CH4). Overall, water regime, soil type, temperature, organic amendments and rice cultivar affect

rate of CH4 emissions.

49

II. While CH4 is seen as the major GHG associated with paddy ecosystems, rice fields also contribute

to the emission of nitrous oxide (N2O) (negative impact). The amount of nitrous oxide produced

by rice fields is primarily driven by the N fertilizer rate, anoxic conditions and the source of C (Zou

et al. 2007) when fields are drained, allowing oxidation

III. Furthermore, the type of fertilizer (e.g. urea vs ammonium sulfate vs green manure) applied to a

rice field affects the field’s emission rate of methane gas (negative impact) (Bronson et al. 1997;

Corton et al. 2000; Wassmann et al. 2000).

IV. About 60-95% of rice straw is burned in the Philippines (Gadde et al. 2009, Truc et al. 2012),

releasing a significant amount of carbon dioxide (CO2) (negative impact) into the air and

contributing to up to 0.56% of the country’s GHG emissions.


The effect of water management practices

Water management practices that allow intermittent drying of rice fields have direct impacts on the fields’

GHG emissions. One such practice being adopted to some extent in the Philippines is alternate wetting

and drying (AWD) (Lampayan et al. 2015)).

Bouman and Tuong (2001) analyzed 31 experiments conducted across Asia and found a high degree of

variability in the yield differences between fields subjected to intermittent irrigation compared to

continuously flooded checks (ranging between 0-70% lower in fields with intermittent drying). The large

variability seemed to be driven by the timing and intensity of the drought. To mitigate the potential

problem of yield reduction, Bouman et al. 2007 defined ‘safe’ AWD as an intermittent irrigation technique

of rice fields with three key components: (1) shallow flooding for the first two weeks after transplanting

to avoid losses due to transplanting shock, (2) shallow flooding from heading to end of flowering

(component 1 and 2 are unique to ‘safe’ AWD) and (3) irrigation water applied to the field whenever the

perched water table falls to about 15 cm below the soil surface at other stages of rice growth.

Studies conducted in the Philippines showed that AWD produced comparable yield to continuous flooding

(Belder et al. 2004; Bueno et al. 2010; Lampayan et al. 2014; Tabbal et al. 2002). Bueno et al. (2010)

reported interactions between rice genotype and water management practices in determining yield

components, indicating that some varieties are more adapted to AWD than others. Comparing farm level

surveys of AWD adopters and non-adopters, Rejesus et al. (2011) estimated that the AWD technique

saved about 38% irrigation time with no statistically significant difference in yield and profit.

According to Ortiz-Monasterio et al. (2010) AWD is a water-saving technology but it does show promise

in mitigating GHG emissions from rice fields. In contrast, field drainage at mid-tillering and 14 days before

harvest (termed dual drainage) were shown to reduce methane emission to between 15 and 80% of that

in continuously flooded fields (Wassman et al. 2000). A study conducted in Central Luzon, the central rice

production area of the Philippines, showed that mid-season drainage reduced methane emission

significantly during the dry season compared to flooded controls (Corton et al. 2000). In the wet season,

50

heavy rainfalls may keep fields from drying and thus offset the potential of mid-season drainage to reduce

methane emission (Corton et al. 2000, Wassmann et al. 2000). Yan et al. (2005) analyzed previously

published studies on GHG emissions from rice fields and found that field drainage (e.g. intermittent

irrigation) reduced rice fields’ methane emissions by 52-60% compared to continuously flooded fields.

Mid-season drainage creates near saturated soil conditions that promote nitrous oxide production.

Indeed Bronson et al. (1997) reported a sharp increase in nitrous oxide emissions during mid-season

drainage. However, using the 2006 IPPC guidelines, Yan et al. (2009) estimated that the global warming

potential due to increased nitrous oxide associated with mid-season drainage is negligible compared to

the large reductions in methane emission.

The effect of soil fertility management practices

The timing and amount of fertilizer contribute greatly to rice yield. Site-specific nutrient management

(SSNM), a technology developed at IRRI and increasingly adopted in the Philippines, relies on the usage of

a leaf colour chart to guide the timing and amount of N fertilizer. Additionally SSNM uses omission plots

to guide P and K fertilizer application (Pampolino et al. 2007). Large-scale on farm experiments across Asia

to evaluate SSNM showed that on average the practice increased rice yield by 11% compared to farmers’

practice, which resulted in an average of $46/ha in profitability (Dobermann et al. 2002).

The type of N fertilizer applied to rice fields may affect both productivity and GHG emission. A study

conducted on an irrigated and intensively managed rice production system documented no differences in

yield between fields fertilized with urea and ammonium sulfate (Corton et al. 2000). When sesbania green

manure was applied in addition to urea, no differences in yield were detected compared to fields with

urea application alone (Wassmann 2000).

The amount of N fertilizer affects the amount of rice-field methane emission, thus technologies that allow

for the timely placement of fertilizer may reduce methane emission compared to technologies that focus

on fertilizer efficiency or decreasing overall fertilizer use. Pampolino et al. (2006) used a denitrification-

decomposition model to estimate nitrous oxide emission from fields with SSNM compared to those

managed under farmers’ practice. The authors reported that while SSNM did not increase N gas emission

at all locations, the practice could lower nitrous oxide emission at locations where it increased fertilizer

efficiency.

The presence of sulfate in sufficient amounts can inhibit methane formation in anaerobic systems (Aulakh

et al. 2001). In general, ammonium sulfate, both in place of (Bronson et al. 1997, Corton et al. 2000) or in

addition to urea (Wassmann et al. 2000) reduced methane emission from rice fields. However, Bronson

et al. 1997 reported that in dry seasons, fields fertilized with ammonium sulfate produced over twice the

amount of nitrous oxide compared to those fertilized with urea. Adding phosphogypsum (CaSO4), a soil

amendment used to reclaim alkaline soil, to urea also resulted in reduced methane emission compared

to fields with only urea amendment (Corton et al. 2000, Denier van der Gon and Neue 1994). Sesbania

green manure, both in addition to or in lieu of urea fertilizer has been shown to significantly increase

methane emission compared to controls treated with urea alone or with zero fertilizer (Bronson et al.

1997, Wassmann 2000).

51

The effect of crop residue management practices

Crop residue management is another practice that may contribute to GHG production from rice fields.

Between 2002 and 2006, the Philippines produced an average 10.68 Mt of rice straw per year (Gadde et

al. 2009). Expert interviews and farmer surveys conducted by Gadde et al. (2009) indicated that about

95% of all rice straw produced in the Philippines was burnt in the fields and only 5% used as input in other

agricultural activities such as animal feed or media in mushroom production. Truc et al. (2012) conducted

farmer surveys and estimated about 60-90% of rice straw is subjected to open field burning in the

Philippines. Another option available for farmers is to leave the rice residues in the field during fallow

periods and incorporate the straw into the soil during land preparation.

Bijay-Singh et al. (2008) examined a collection of previously published data from irrigated and rainfed rice

ecosystems and concluded that there is no significant trend of increasing yield associated with

incorporation of rice residue. In most studies the application of fertilizers may mask the effects of rice

residue incorporation; however, no yield increase was recorded in studies that include zero N fertilizer.

Rice straw incorporation into the soil at the land preparation stage is a viable option for farmers to

increase plant-available nutrients. Incorporation of fresh rice straw in flooded condition has been shown

to increase methane emissions (Wassmann et al 2000, Bronson et al 1997, Corton et al. 2000, Sander et

al. 2014) but not nitrous oxide (Sander et al. 2014) from rice fields. Incorporation of composted rice straw

induced less methane emission compared to fresh straw (Corton et al. 2000). Allowing for decomposition

of rice straw before rice planting by incorporating the straw early during the fallow season in anaerobic

(non-flooded) conditions may mitigate GHG emissions associated with rice straw incorporation.

Another option is to do composting of rice straw. In general, aerobic composting of organic material is

deemed to have relatively low methane emission compared to storing the organic matter before

incorporating it directly into the field. There seems to be no work published from the Philippines, but Chen

et al. (2011) reported from China that aerobically composting manure emitted 1/17th the amount of

methane compared to stored manure. When incorporated into rice fields, fields with composted manure

emitted 1/3 the amount of methane compared to fields with stored manure.

CONCLUSIONS

Continuous flooding of rice is the predominant practice in Philippines´ rice production. Water

management practices that allow for intermittent irrigation such as safe AWD has been shown to mitigate

GHG emission while maintaining yield productivity. However, the majority of farmers in the Philippines

lack the incentive to adopt water saving practices that allows for intermittent irrigation such as AWD

(Lampayan et al. 2015).

Usage of ammonium sulfate in addition to or in lieu of urea reduced methane emission from rice fields.

Furthermore, nutrient management practice that allows for high fertilizer efficiency (e.g. SSNM) allows

for a general decrease in N application into the field and, thus, reduces the potential for nitrous oxide

emission (e.g. Pampolino et al. 2006).

Crop residue management has a significant potential to alter GHG emission associated with rice fields.

Open field burning, the dominant practice of rice straw management in the Philippines, directly increases

52

CO2 emission while incorporation of fresh rice straw in flooded condition drastically increases methane

emission. Composting the straw before adding it back to the field reduces the GHG emission potential

associated with rice straw. Incorporating rice straw into the soil early during fallow season in aerobic

condition may be the best management practice for crop residue in terms of yield productivity and climate

change mitigation.

53

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2.2 CAMBODIA


BACKGROUND INFORMATION ON RICE AGRICULTURE IN CAMBODIA

Rice is by far the most important crop in Cambodia, providing approximately 70% of nutritional energy

requirements (SOER, 2004) and accounting for over 80% of all agricultural production in the country, by

area (calculated from FAOSTAT data, 2015).

Figures 2 to 5 display the changes over the last five decades of four important measures of rice production

(area harvested, yield per unit area, total production quantity and gross value of production). The dip in

all measures from the mid-1970s to the early 1980s clearly show the impact of the civil war (sensu Seng

et al. 1987), but the last decade has shown remarkable increases in production (FAOSTAT data, 2015).

Fig. 2 Area of rice (in hectares) harvested in Cambodia 1961-2013 (Source: FAOSTAT 2015). Note the drastic drop in production

in the 1970s and early 1980s due to civil war (Seng et al. 1987). Fig. 2 Area of rice (in hectares) harvested in Cambodia 1961-

2013 (Source: FAOSTAT 2015). Note the drastic drop in production in the 1970s and early 1980s due to civil war (Seng et al.

1987).

62

Fig. 3 Rice yield (in t/ha) in Cambodia 1961-2013 (Source: FAOSTAT 2015).

Fig. 4 Rice production (1000 tonnes) in Cambodia 1961-2013 (Source: FAOSTAT 2015).

Fig. 5 Rice production value (gross US$ 2004-06 equivalent) in Cambodia 1961-2012 (Source: FAOSTAT 2015).

Whilst this expansion in rice production area may lead to short term market and food security benefits

the loss of native vegetation (e.g. forests, cleared through slash and burn management) which supports

high levels of biodiversity (including a number of IUCN-listed Threatened species) and provides a range of

resources and ecosystem services upon which communities depend, can have negative environmental

and social impacts (Foley et al. 2005; Gibbs et al. 2010). Furthermore, the observed land use changes from

traditional swidden (shifting) agriculture to intensively managed and homogenized systems can also exert

impacts on the environment and livelihoods (Dressler et al. 2015). For instance, in the province of

Ratanakiri transitions from swidden farming (which includes rice) to mono-cropping of rice (and other

cash crops), driven by market pressures, hashas led to high levels of loss of forest cover (Hor et al. 2014).

63

Rice varieties produced in Cambodia exhibit enormous genetic and varietal diversity, with more than

2,000 varieties of rice and several wild rice species having been collected by the Cambodian Agricultural

Research and Development Institute, and stored at International Rice Research Institute’s (IRRI) Gene

Bank (SWC, 2006).

Areas of rice production in Cambodia oftenoften overlap with areas of high biodiversity conservation

value. For instance, the Tonle Sap lake and surrounds, have high levels of both paddy and deep water rice

production (Makara et al. 2001; Nguyen et al. 2013), but also support extremely high levels of biological

diversity, including at least 149 species of fish, 11 globally threatened and six near-threatened species of

vertebrates (Campbell et al. 2006). Whilst rice production (especially traditional, diverse rice systems) can

provide important habitat for biodiversity (Wright et al. 2012), the agri-business driven intensification of

rice production observed in the area can cause the loss of habitat for species such as the critically

endangered Bengal florican (Houbaropsis bengalensis) (Gray et al. 2007). In addition to this, several of

Cambodia’s Important Bird Areas (Hout et al. 2003) also coincide with areas of rice production (Fig. 6);

again, the dichotomy of traditional rice providing habitat for threatened and declining species (Wright et

al. 2010) and the rapid intensification of rice production is likely to apply to many of these sites.

Fig. 6 Location and size of Important Bird Areas in Cambodia (Source: Hout et al. 2003; BirdLife International 2004), with main

rice growing areas indicated by dashed polygon (Source: MAFF, 2013; data from White et al. 1997).

Cambodia is situated 10‐14˚ north of the equator and has a tropical monsoon climate, with relatively

stable average temperatures that peak around 26 to 30˚C in the early summer months before the start of

the rainy season. The wet season is from May to November, with the heaviest rainfall in the southeast

and north west. Mean monthly rainfall can exceed 500 mm during this period in some regions. There is

considerable inter-annual variability in rainfall due to the El Niño Southern Oscillation (ENSO). El Niño

64

episodes generally bring warmer and drier than average winter conditions across the region, whilst La

Niña episodes result in cooler than average summers (McSweeney et al. 2008). As most of Cambodia’s

rice is dependent upon rain and surface runoff, high variability in precipitation (as influenced by the ENSO)

can have great implications for rice production (Bell and Seng, 2003), with drier years (e.g. 2004)

experiencing greatly reduced production (Ouk et al. 2006; see also dip in production in Figs 2-5 for 2004).

In Cambodia, most rice growing areas have a mean annual rainfall of 1250–1750 mm which increases up

to 2500 mm in the south and east of the country (Bell and Seng, 2003).

Cambodia's cultivated rice land can be divided into three broad geographical areas (Library of Congress

Country Study: Cambodia, 1987). The first and generally most fertile area covers the Tonle Sap Basin and

the provinces of Batdambang, Kampong Thum, Kampong Cham, Kandal, Prey Veng, and Svay Rieng. The

second area, with typically slightly lower yields consists of Kampot and Kaoh Kong provinces, as well as

some less fertile areas of the central provinces. The third and least fertile area is situated in the highlands

and the mountainous provinces of Preah Vihear, Stoeng Treng, Rotanokiri (Ratanakiri), and Mondol kiri

(MondolKiri). In general, the most productive areas for rice production have relatively flat landforms, high

rainfall, access to freshwater bodies (e.g. river channels, floodplains) and suitable soils. A number of soil

types are considered suitable for rice production in Cambodia (White et al. 1997) and their distribution is

depicted in Fig. 7 and Table 1. In general, the soils used for growing rice in Cambodia are on low lying,

gently undulating or flat areas (although upland rice is grown), and are relatively low in nitrogen,

potassium, phosphorus and organic matter, and have low cation-exchange capacity. Consequently,

nutrient deficiencies are a major constraint to rice production in these soils (SCW, 2006).

Fig. 7 Soil types used for rice growing in Cambodia (Source: MAFF, 2013; data from White et al. 1997)

Table 1 Soil types for rice production in Cambodia, with parent materials, profile, constraints to rice production and

opportunities to improve productivity/suitability (Bell and Seng, 2003; data source??? White et al. 1997).

65

Soil type Parent material Soil profile Main constraints to production

Opportunities for improvement/management

Prey Khmer Old alluvial/colluvial from sandstone, granitic detritus

Sandy to 40–100 cm NPKS deficiency, S, Fe toxicity, Low water holding capacity, leaching, transplanting difficulties as sand settles, coarse sandy phase

Compaction at depth, fertiliser in small doses, deep rooted cultivars, direct seeding, Clay layer at depth Use high tannin green manures that break down slowly, N placement an depth

Prateah Lang Old alluvial/colluvial from sandstone and other mixed detritus

Sandy to 10–25 cm on clay subsoil

NPKS (Mg, B) deficiency, S, Fe toxicity, Low WHC, leaching, hard setting, shallow phase, ironstone, transplanting difficulties as sand settles

Upland crops on loamy phase, drainage, direct seeding, post-rice crops, supplementary irrigation, split fertiliser, deeper cultivation Use high tannin green manures that break down slowly, N placement at depth

Bakan Old alluvial/colluvial Clay-loamy topsoil over clay or Loam

Dispersive, poor structure, surface sealing, N, P, K, deficiency, S, Fe toxicity

Deeper ploughing, supplementary irrigation, land levelling, ratooning? Direct sowing, N placement at depth

Koktrap Old (and recent?) lacustrine, tidal sediments

Black clay or loam (0–20 cm) over grey clay

Very low P, shallow hardpan, Fe toxicity, NK Deficiency

Deeper ploughing Liming

Toul Samrong Mixed alluvial/colluvial sediments of mafic origin

Well structured brown or grey cracking clay or loam over clay

Shallow root depth, tillage when dry, NP(K) deficiency

Deeper tillage, level fields, supplementary irrigation

Orung Recent or old alluvium Loamy or clay over sand NPKS deficiency, leaching, tillage, dispersive, hard setting, Fe toxicity

Supplementary irrigation

Labansiek In situ weathered basalt Deep, well structured reddish clay

NP(KS) deficiency, Root depth on petroferric hardpan in places,

Upland rice

Kompong Siem Colluvial/alluvial outwash from basalt, marl, limestone or in situ basalt

Dark cracking clay (with stones and boulders in profile)

N(P) deficiency, Sticky when wet, Fe toxicity, cracks when dry, Zn deficiency

Supplementary irrigation, direct seedling. Drainage Dry season irrigation

Kein Svay Recent alluvium with annual sediment additions

Deep brown loamy to clay Texture

N(P) deficiency, submergence

Dry season irrigation

Kbal Po Recent alluvium Deep dark clay over lighter coloured clay

N(P) deficiency, potential acid sulfate in some places, sticky and low load bearing when wet, deep cracks

Supplementary dry season irrigation

Krakor Recent alluvium Deep loam—clay over lighter coloured sand, loam or clay

N(P) deficiency, potential acid sulfate in some places, sticky and low load bearing when wet

Supplementary dry season irrigation

Therefore, rice production is focused on specific areas of the country, as can be seen in the provincial area

harvested and total production of rice (Figs. 8–10). Furthermore, whilst Cambodia achieved self-

sufficiency in rice production in 2000 and some regions (e.g. Prey Veng) produced very large surpluses

(SWC, 2006), there remain Provincial rice deficits where there are large urban populations who consume,

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but do not produce, rice (e.g. deficit of almost 170,000 t in Phnom Penh; SWC, 2006), or where soils are

unsuitable (Ngo and Mund, 2006).

Fig. 8 Area of rice harvested (ha) by Province 2003-2004 (Source: Agricultural Statistics 2003-2004; Food Balance 2003-2004,

MAFF; data published in SCW 2006)

Fig. 9 Total production of rice (yield x area) (t) by Province 2003-2004 (Source: Agricultural Statistics 2003-2004; Food Balance

2003-2004, MAFF; data published in SCW 2006)

Production is largely driven by the area of land under rice, however, with yields varying greatly among

provinces (i.e. provinces with highest production not necessarily having high yields per unit area). This is

an important point (and one noted by Yu and Diao (2011) in a policy paper on rice production futures in

Cambodia), as it implies that increased production will come from increased area of land under rice as

opposed to the intensification of rice either through increased inputs, such as NPK fertilisers, or irrigation

development. Rice production in Cambodia can be highly labor intensive, and this appears to be supported

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in the high correlations between i) area of rice harvested (Fig. 11a) and ii) total rice production (Fig. 11b)

and the size of the rural population. However, no correlation is apparent between rural population size

and yield (Fig. 11c).

Fig. 10 Yield of rice harvested (t/ha) by Province 2003-2004 (Source: Agricultural Statistics 2003-2004; Food Balance 2003-2004,

MAFF; data published in SCW 2006)

Fig. 11a and 11b Linear regressions of a) area of rice harvested (ha) and rural population (R2 = 0.6485), and b) Total production

of rice (t) and rural population (R2 = 0.7415) by Province (Data source: Agricultural Statistics 2003-2004; Food Balance 2003-

2004, MAFF; NIS, 2005; Department of Geography, 2005. Data published in SCW 2006)

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Fig. 11c Linear regressions of rice yield (t/ha) and rural population (R2 = 0.0236) by Province (Data sources: Agricultural Statistics

2003-2004; Food Balance 2003-2004, MAFF; NIS, 2005; Department of Geography, 2005. Data published in SCW 2006)

Whilst rice production is the dominant form of agricultural production in Cambodia, there are many

constraints to production (or improved or expanded production) that have been identified. For instance,

farmers were asked if an issue was considered in the top three most difficult agricultural production

problems (ADB, 2014). Results from this study (Fig. 12) indicate that land access, farmer skills and

knowledge and water availability are the agricultural issues of greatest concern to farmers.

Fig. 12 Farmer perspectives on most problematic constraints to rice production (ADB, 2014).

RICE GROWING ENVIRONMENTS IN CAMBODIA

In terms of types of rice systems in Cambodia, rainfed lowland rice is by far the most dominant, with 80.3%

of Cambodia’s rice crop area being rain-fed lowland rice (2.5 million ha) (Chan 2011; Fukai et al. 2012). Of

the remainder, 14.1 percent is dry season rice (irrigated lowland rice, but commonly referred to as ‘dry

season rice’ in the literature relating to Cambodia, and hence used throughout this case study report), 3.7

percent is floating or deepwater rice and 1.9 percent is upland rice (Chan 2011; Fukai et al. 2012). The

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landscape position and hydrological gradient of rice production differs from upland rice, to

upper/medium/lower (based on landscape position) rice, to deepwater rice (Fig 13). This landscape

position also affects timing of production; as a general rule of thumb, higher areas with reduced water

availability require quickly maturing varieties and are planted early in the growing season (before mid-

October), whereas middle field areas will be planted later with intermediate-maturing varieties (mid-

October to mid-November), and lower and deepwater areas will be planted with slow maturation varieties

from mid-November onwards (Fukai et al. 2012).

Fig. 13 Classification of rice production according to landscape position and hydrological gradient (figures in parentheses are

percentages quoted for production in Cambodia). From Chan (2011) and reproduced in Fukai et al. (2012).

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Fig. 14 Locations of four major rice production types (copied from Seng, 2011 (CARDI)

http://www.jgsee.kmutt.ac.th/apnproject/Web_Postconference/pdf/5_Cambodia.pdf

Rain-fed lowland rice is typified by flat, bunded rice fields that are largely dependent on rainfall and

surface runoff for water supply (Zeigler and Puckridge, 1995; CBD, 2006; Fig. 15).

Fig. 15 Rainfed lowland rice (image © IRRI).

Yields are generally low (although higher than other forms of rice production in the region), at

approximately 2.5 tones per hectare, with low fertilizer inputs, and generally grown for subsistence

purposes (Fukai et al. 2012). Consequently, livelihoods based upon rice production tend to be rather poor

(Fukai et al. 2012), and this exacerbated by large families often producing rice for their own consumption

on less than half a hectare of land (Sareth et al, 2011). The majority of fields are ploughed using two oxen

when soil is wet or flooded. This usually occurs in May or June. The soil is ploughed to a depth of 70-100

mm and, depending on soil conditions, may require ploughing again three to six weeks after the initial

work, after which the fields are generally harrowed (Microworld, 2011). This form of rice production is

concentrated around Tonle Sap Lake and the Mekong River and uses rice varieties that are adapted to the

waterlogged soils (SCW, 2006). According to Wade et al (1999), the majority (95 percent) of rain-fed

lowland rice soils are shallow (0-25 cm) and over 60 percent of these are prone to a combination of

drought and submergence (related to wet and dry season water dynamics). Approximately 30 percent are

prone to drought, and only five percent are medium-deep soils of 25-50 cm (Wade et al. 1999). In recent

years, this traditional form of rice production has seen a decrease in available labor, due to urban

relocation of workers (Fukai and Ouk, 2012). The same authors describe the dominant research efforts of

the past two decades that have been used to try and increase the productivity of rice in these systems: i)

water environment characterization to quantify drought problems; ii) soil environment and fertiliser

management, iii) direct seeding to develop technology to cope with the labor shortage, iv) variety

improvement for rainfed lowland rice in drought-prone environment, and v) crop intensification and

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diversification that shift practices from traditional subsistence agriculture to more market-oriented

agriculture (Fukai and Ouk, 2012). In terms of crop diversification, this can often be an issue when a crop

follows rice production, due to the waterlogging and hardpan that remains after rice harvest. In some

crops such as mungbean and peanut, this can lead to crop failure owing to excess post-rice water (Mitchell

et al. 2013).

A number of constraints have been identified that impact on rainfed lowland rice production in Cambodia:

Water availability: Water supply is a key limiting factor for most areas of Cambodia because of the

monsoonal rainfall pattern and the erratic rainfall distribution during the early wet and main wet seasons.

Most of the crops grown in the early and main wet season receive less than optimal rainfall in total (Bell

et al. 2005). Hence the water storage capacity of the soil would have a large bearing on the regulation of

water availability to crops especially on sandy soils. Deep sands are generally considered unsuitable or of

low productivity for paddy rice because water is not retained in the shallow root zone of rice, and because

a plough pan does not readily form to retain water (White et al. 1997).

Frequency and (seasonal and inter-annual) distribution vary; both floods and droughts can occur in same

season, with major impacts on production; effects of sporadic rain in early wet season can include delayed

planting, build of weeds and pest outbreaks; excessive rain during maturation period can lead to reduced

grain fertility and fungal disease; drought can result in reduced yields, and drought late in season can lead

to orthopteran (grasshopper) outbreaks (Sarom, 2003).

Soil fertility: Soils are typically sandy with low fertility (low nitrogen, phosphorus, potassium and other

elements; high iron toxicity), and generally do not respond well to fertiliser application; fertiliser

application in Cambodian rice systems is very low compared to that of many other countries both

regionally and globally (Fig. 16a and 16b). Despite this, fertilizer use in Cambodian agriculture (and

therefore rice production, as this crop constitutes most of Cambodia’s arable production) has increased

in recent years (Fig 16c) (Sarom, 2003).

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Figs 16a, 16b and 16c – Fertiliser use (general for all crops, but rice is dominant crop in Cambodia, so highly applicable) in

Cambodia and other countries 2002-2012 (WorldBank data: http://data.worldbank.org/indicator/AG.CON.FERT.ZS?page=2)

Pests and diseases: There is a wide range of pests and diseases that impact upon rain-fed lowland rice in

Cambodia (for examples, see Fig. 17). These include numerous broadleaved weeds, grasses and sedges,

including Mimosa pudica, Cynodon dactylon and Panicum repens. Insect pests, particularly planthoppers

of the order Hemiptera are also a major source of rice damage and loss. For example, the planthopper

Nilaparvata lugens is known to be a major pest of rice in SE Asia (Jahn et al. 2001), causing economic

losses due to yield loss, grain quality reduction and pestpest management costs (Jahn et al. 2004).

Stemborers are another major pest, and whilst the term can apply to both Coleopteran and Lepidopteran

larvae that damage rice stems, a number of moth species are particularly problematic in rice in Cambodia,

including Sesamia inferens and Chilo polychrysus. Other notable pests include the golden apple snails

(Pomacea Pomacea canaliculata and Pomacea maculata), whichwere originally introduced to SE Asia

from South America as a potential source of human food, but rapidly establishedas major pests of rice

(Joshi, 2005). In addition to this, there are a number of diseases that affect rice in Cambodia. For instance,

a survey of rice diseases between 2005 and 2007 found widespread occurrence of diseases caused by

Acidovorax avenae subsp. avenae, Burkholderia gladioli, B. cepacia and Pantoea ananatis, representing

the first time these had been detected in Cambodia (Cother et al. 2010).

Fig. 17 Three major pests of rice in Cambodia: Brown planthopper (Nilaparvata lugens), pink stemborer (Sesamia inferens) and

the golden apple snail (all images ©IRRI).

http://data.worldbank.org/indicator/AG.CON.FERT.ZS?page=2

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Dry season rice (irrigated lowland rice, but ‘dry season rice’ is the most common nomenclature in

literature relating to Cambodia) is limited to areas that can provide irrigation sources, such as those close

to rivers and floodplains and amounts to approximately 11% of rice production (Makara et al. 2001).

A small but increasing number of rice-growing areas in Cambodia are irrigated during the dry season to

enable farmers to plant rice two or three times per year. The use of irrigation systems has been increasing

in recent years. The practice of dry season rice production also involves very high levels of seed broadcast

(e.g. 200-250 kg/ha), and may involve the SRI approach of spacing seedlings out widely (Seng, 2011). A

potential obstacle to farmers undertaking irrigated rice production is the expense of pumping water into

their farming area, if they are some distance from main water channels (Microworld, 2011). Whilst it may

appear that irrigated rice, with the opportunity for multiple crops per year, provides a distinct advantage

over rain fed rice, a number of obstacles and impediments have been identified. For instance, according

to Voe et al. (2011), under the Irrigation Scheme of Tapeing Thmor Water Reservoir, farmers complained

that they had no access to irrigation water, in addition to the increased cost of inputs and labor, forcing

farmers into debt at high interest rates.

A common practice in dry season rice production is to burn off post harvest residue, generally as a means

to dispose of stubble and also try to reduce pests. Whilst there is some evidence that some pests can be

impacted by stubble burning, this practice has a detrimental impact upon soil nutrients such as nitrogen

and also causes losses of potassium and phosphorus (Dobermann and Fairhurst, 2002).

Upland rice: This represents a minor contribution to Cambodian rice production (2-3%), and is scattered

throughout higher elevation regions of the country, mostly as a cash crop (Makara et al. 2001), but also

as part of a subsistence system (Atlin et al. 2006). It is thought to be the oldest form of rice production in

Cambodia, exceeding lowland rain-fed rice, which has been estimated at being 2,000 years old (Helmers,

1997). In general, this is the lowest yielding rice system, with drought stress being a major constraint on

production (Bernier et al. 2008), as it is an unbunded field system that is entirely dependent on rainfall

(Javier, 1997). Low yields of upland rice are driving the development and distribution of drought resistant,

high yielding varieties in order to improve upland production (Atlin et al. 2006). Upland rice is the most

diverse in terms of varieties, reflecting the wide range of environmental conditions and soil types under

which it is grown, and can be part of a shifting cultivation or permanent cultivation system (Javier, 1997).

Shifting rice cultivation often involves intercropping with other crops, such as maize, cassava, cucumber,

watermelon, eggplant and beans (Makara et al. 2001). Constraints to upland rice production are many,

including weeds, soil erosion, soil nutrient loss, fungal diseases and pests such as wild pigeons, pigs and

rats (Javier, 1997; Makara et al. 2001).

Deepwater rice: Deepwater rice is grown in low-lying areas that accumulate floodwater at a depth of 50

cm or more for at least 1 month during the growing period (Javier, 1997). Floodwaters originate from the

Tonle Sap Lake and the Mekong and Tonle-Bassac rivers, and their tributaries flood the low-lying areas

and depressions (Javier, 1997). Despite being a minority form of rice production in Cambodia (3%),

deepwater systems are highly prevalent in the Takeo and Prey Veng Provinces (Lando and Mak, 1994) that

are frequently inundated by flood waters.

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In general, land preparation for deepwater rice begins prior to the wet season, when farmers burn the

previous year’s stubble. Two ploughings and one harrowing are undertaken and dry seed is broadcast at

a rate of 120 to 150 kg/ ha. Fields are not bunded and weed growth is prolific. This may lead to weeding

of fields but few farmers apply herbicides or other pesticides. Similarly, fertilizers are rarely applied in this

system. Once the floodwaters recede, the crop is harvested (Makara et al. 2011). Whilst permanent water

inundation is highly detrimental to many crops, there are a number of rice varieties that have evolved to

tolerate such conditions, such as through the development of elongated internodes (Hattori et al. 2011).

Flooded rice systems are also a significant source of fish, other aquatic animals and edible aquatic plants

for communities, and that intensification of these systems (e.g. via pesticides) may greatly reduce these

additional ecosystem services from rice systems (Shams, 2007).

There are a number of constraints that apply to deepwater rice systems, including scarcity of high yielding

and adapted rice varieties, low soil fertility, unpredictable timing and intensity of pre-flood rainfall, onset

of flooding, rate of water rise, maximum water depth, duration of maximum water depth, timing of water

recession, and rate of water decline (Javier, 1997). Yields are generally low, but Nguyen et al. (2013) found

that fertiliser (but see environmental risks, above) and appropriate pesticide application can increase

yields.

Additional risks to flooded systems include climate change (e.g. altered precipitation rates and timing,

heat stress) for rain-fed and deepwater systems (Wassmann et al. 2009) and the construction of dams

along the Mekong river (e.g. reduction in fish stocks may require increase in agricultural area and yields

per unit area – Orr et al. (2012)).

PREDOMINANT FARMING SYSTEMS IN CAMBODIA

Agriculture is central to the GDP of Cambodia, amounting to around 20% in 2004 (SCW, 2006), with rice

being the greatest contributor in terms of area harvested (Fig. x) and income generation. Other crops

include maize, sweet potatoes, cassava, soybeans, groundnuts, sesame seed and rubber (Figs. 18a and

18b).

Fig. 18a Total production of main crops in 2013 in tonnes (Source: FAOSTAT, 2015); Fig. 18b Area harvested of main crops in

2013 in hectares (Source: FAOSTAT, 2015).

Agricultural production in Cambodia is characterized by low intensity, low input, poor soils and low

yielding production. However, for some crops (e.g. maize, cassava, sweet potatoes), yields have shown a

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considerable increase in recent years (Fig. 19). However, there have been warnings that increases in yield

should not come at the expense of land and water resources (SCW, 2006). Maize is the most important

non-rice crop, often along fertile alluvial and riverine areas, and is generally grown as a cash crop, such as

supplying overseas feed markets (SCW, 2006). Production and nutrition may also be increased through

crop diversification, increased cropping in upland areas, and increased irrigation (SCW, 2006). Cassava

tends to be an increasing crop as less fertile, marginal areas are opened up for production (SCW, 2006).

Fig. 19 Yield (t/ha) of main crops 1961-2013 (Source: FAOSTAT, 2015)


Rice varieties: A wide range of rice varieties are grown, with farmers favoring traditional varieties, but

also selecting seed based on price, taste, texture, swelling capacity, and aroma (Sar et al. 2012). Due to

many centuries of natural selection and artificial selection by farmers for different growing conditions,

soil types and climatic conditions, over 2000 traditional rice varieties are considered unique to Cambodia

(Whittaker et al. 1973; Nesbitt, 1987; Javier, 1987). In many cases, traditional rice varieties can differ

greatly in quality, due to both soil type/fertility and extent and duration of inundation (Javier, 1987). There

have been ongoing efforts since the 1950s to develop and deploy improved rice varieties (Nesbitt, 1987),

with as much as 20% of the rice crop being improved varieties of traditional rice by 1962 (Dennis, 1979).

Part of the vision of the Khmer Rouge to develop agriculture involved utilizing a very small number of rice

varieties (Pram pi taek, Ramuon sar, and Champas kok were all tested), but massive failure of irrigation

implementation meant that anticipated high yields were never realized (Nesbitt, 1987). Many varietal

develops have centered around photoperiod sensitivity, in order to cope with intermittent and

unpredictable rainfall, and maturation period, in order to adapt to different water depths. For instance,

in rainfed lowland rice, 16% of rice by area is early maturation, 33% medium maturation, and 36% late

maturation (Nesbitt, 1987). In terms of landform positioning, early maturation varieties tend to dominate

upper fields, where water depth generally does not exceed 30 cm, and late maturing varieties tend to be

grown in the lower fields, where water depth can be around 50 cm (Nesbitt, 1987). Other varietal

adaptations are related to limiting factors associated with soil, such as soil type, soil fertility and presence

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of soil toxins (Nesbitt, 1987). For many farmers, field levels, soil types and degree and duration of

inundation are likely to vary, and consequently a range of rice varieties will be grown (Javier, 1987). In

addition to yields, growth rates and vulnerability to pests and diseases, rice variety can also influence

post-harvest management processes, such as drying time (Meas et al. 2011), which in turn can have an

impact upon grain quality.

Seed quality: Seed quality is of paramount importance for farmers — this means having reliable and

affordable sources of seed that are not only high yielding, but also genetically pure, physiologically

mature, free of diseases, free of pests, etc (Javier, 1987). One of the major determinants of rice seed

quality is the institutional infrastructure and supply chains relating to rice seed — for instance, Try and

McSweeney (2012) indicated that Cambodian rice supply chains are dominated by traditional supply chain

practices, have inconsistent supply, are characterized by poor communication, numerous chain actors,

small-scale and dispersed producers, inadequate drying and storage facilities, and limited access to both

markets and market information. All of these combine to reduce Cambodia’s competitiveness in the global

rice supply chain. In addition to these many influencing factors, grain (i.e. seed for planting) quality can

also be impacted by drying time (Meas et al. 2011).

Cropping calendar: Generally one crop per year, as Cambodian rice production is dominated by lowland

rainfed rice. Planting is in the monsoon season for rainfed rice (May to July), and is harvested in December.

The dry season crop is generally planted in November and the shorter growing season (possible due to

irrigation) enables harvesting in January or February. Deepwater rice is generally planted in April and May

in the Tonle Sap area.

Land Preparation: Ploughing is generally undertaken with domesticated water buffalo, as machinery to

undertake ploughing is scarce. However, use of buffalo has been declining steadily in recent years. There

has been a good deal of experimentation in the last decade with reduced or zero tillage. However, results

have been mixed (e.g. in terms of yields, weed suppression), and conservation agriculture techniques

require greater communication, extension and policy development/implementation before large scale

adoption is likely to take place. In many cases, rice stubble is burnt, but in others, it is ploughed back into

the soil.

Planting / Crop establishment: Rice crops are manually planted by either transplanting, or broadcasting

over a wide area. Transplanting is the most common of these methods, because broadcasting generally

gives a lower output than transplanting. Transplanting is, however, extremely labor intensive, and other

approaches may have to be developed and tested as rural labor availability decreases (Microworld, 2011).

However, there has been increasing research efforts in the last decade examining broadcasting and direct

seeding, so as the approaches to these techniques are finessed, there may be a move towards these

methods in the future, should they prove to be more effective in terms of yields, survival, weed

suppression, etc.

Soil management (fertilizers): Many rice farmers use animal manure for fertilization, but farmers also use

both manure and inorganic fertilizers in both nurseries and fields, with all fertilizers applied manually.

Farmyard manure is transported by animal-drawn carts during the dry season and placed in strategic piles

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in the fields. Spreading is done by water movement and during land preparation. Inorganic fertilizers are

hand-spread and, where necessary, incorporated by harrowing (Microworld, 2011). However, fertilizer

use in Cambodia is considerably lower than other countries in the region. This, coupled with inherently

low soil fertility, is a major contributory factor in the low rise shields that typify Cambodian rice

production. However, this does present a potential opportunity for intensification of rice production, but

any such intensification must be balanced with the high potential to cause on and off-site environmental

pollution, such as reductions in water quality.

Water management / water saving technologies: An increasing number of rice-growing areas in

Cambodia are irrigated during the dry season to enable farmers to realize more than one crop per year.

However, many farmers will need to pay to pump water into the farm area, especially if they are

considerable distance from the main water channels and other water bodies (Microworld, 2011). This

presents a considerable constraint in the expansion of dry season rice, although there is potential for

microcredit to alleviate some of this cost.

Weed management: The vast majority of weed management in Cambodian rice systems is through hand

or mechanical weeding, which is extremely labour intensive. As labor availability decreases (due to urban

drift from rural populations), and the expense of hiring labor increases, this approach may become

increasingly untenable. Consequently, many farmers are now using chemical herbicides to control weeds.

This, inevitably, has implications for aspects of the environment, such as water quality.

Pests and diseases management: There is a very wide range of pests and diseases that impact upon rice

in Cambodia (see earlier section dedicated to this issue). As such, chemical pesticides are used by most

farmers in the country, but this is more prevalent in dry season rice than is in rain fed rice, and differs

greatly by region (Jahn et al. 1997). However, as pesticides are expensive, and can cause a range of

environmental issues such as mortality of beneficial fauna (e.g. spiders, predatory beetles, parasitoid

wasps), and impacts upon food quality and water quality, there are numerous reasons to limit the quantity

of pesticides applied, and seek other methods of pest control. As yet, there has been little exploration of

integrated pest management in relation to Cambodian rice. However, research and practices from other

countries related to integrated pest management (e.g. in other focal countries in this study) may be

applicable in Cambodian context. However, this will require a great deal of future research,

communication and extension. In addition to insect pests, rats are a serious problem for rice production

in Cambodia, and most farmers use rat poison (Jahn et al. 1997).

Harvesting: Crops are manually harvested and then tied into sheaves (Microworld, 2011). The sheaves

are then placed on top of standing stubble in order to dry, or transported to a threshing site where they

are dried for a period of 2-3 days. Mechanized cutting or gathering machines are generally only rarely

used, due to the considerable expenses involved.


2.2.2.1 Increase in rice yields versus maintenance of water quality

Despite the importance of maintaining water quality for rice production, the authors were unable to

locate any peer-reviewed studies that simultaneously examined rice yield and water quality in relation to

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rice production in Cambodia, and therefore this synergy/trade-off between food production and

freshwater quality, as a result of rice management actions, could not be analyzed.

Only one study from the ‘grey literature’ (Chamroeun et al. 2002) examined this trade-off, looking at the

impact of chemical fertilizer application on rice yields (as well as rice ‘quality’) and a proxy for water quality

(fish and other aquatic organism abundance). The study found that yields increased (based on farmer

estimates) (positive impact), albeit with a reported reduction in rice ‘quality’ (not quantified) (negative

impact), and with farmer estimates of fish and aquatic organism abundance falling (negative impact)

following fertilizer application (cause), and thus indicating reduced water quality (negative impact). Whilst

the findings sound reasonable and are readily explainable in terms of known contributors to both yield

and water quality (and impact on non-target taxa), the study is based upon farmer opinion, contains no

baseline measures and does not use any biophysical measures to calibrate the opinion-based findings.

The same authors also used the same method to examine the impact of pesticides on water quality

(farmer estimates of fish and other aquatic organism abundance) and found that these were also lower

under pesticide use. No measure of yield was used for this comparison. By comparison to the paucity of

studies on water quality, many studies examined yield from the perspectives of several management

actions. This is to be expected, as yield is a dominant concern of agricultural management research and

from an ecosystem service perspective, ‘provisioning’ services are far more tangible and of immediate

relevance to farmers (Estrada-Carmona et al. in prep.). Due to the very considerable number of studies

that focused on ‘yield only’ (rice ‘provisioning services’ in ecosystem services parlance) studies, we have

elected to present a section that examines yield responses to various management approaches and

interventions. Whilst this has not been conducted for other geographical case studies, the overwhelming

number of studies focused on yield was considered to have considerable utility if analysed, as it effectively

shows how yields may be influenced by management. Yield results are described in the following section

under individual management activities. Whilst data are lacking on water quality impacts of management,

inferences have been made on the ‘likely’ impact of the management action on water quality as

determined from the literature from other world regions.

THE EFFECT OF A SPECIFIC MANAGEMENT PRACTICES OR SYSTEMS

The effect of selecting different rice varieties

The use of improved rice varieties (as opposed to traditional rice varieties, upon which the majority of

farmers are reliant) is an area that has been explored by a number of researchers in terms of increasing

rice yields. Along with soil fertilisation, the development and deployment of varieties that are able to cope

with soils that are often nutrient poor and subject to both waterlogging and drying, offers an opportunity

for considerable increases in yield. Figure 21 (results) indicates that of the eight comparisons we found

examining the impact of improved varieties of on yield, all reported increases in yield where improved

varieties were compared to traditional varieties of rice. However, impacts upon other ecosystem services

(other than provisioning services as represented by yield) were either not studied, or the results were

mixed. No comparisons were made between yield and water quality, and therefore the few instances of

rice variety use on other ecosystem services are briefly described here. Rickman et al. (2001) found that

whilst yields were increased in improved varieties compared to traditional varieties, for both direct

seeded and transplanted approaches, lodging of rice was also greater in the non-traditional, improved

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varieties. Therefore, there appears to be a trade-off between rice yield and rice quality and condition.

Meanwhile, Ikeda et al. (2008) found an unsurprising positive interaction between yield of an improved

variety intended to deliver higher yields (Phka Rumduol) compared to more traditional variety (Sen Pidao)

and density of weeds, with weak density being found to be lower with the improved rice variety. Given

the high potential for improved varieties to increase yields, research priority remains to examine the

impact of movements from traditional to improve varieties on a full range of ecosystem services upon

which farmers are reliant.

Whilst no material was found in relation to the impact of rice varieties on water quality, it is feasible that

where rice varieties may require less water application, or where they are weed, pest, or disease tolerant

(and therefore requires lower rates of agrochemical application), negative water quality impacts may be

reduced.

The effect of crop calendar manipulation (double cropping)

Double cropping was found to impact on yield in a largely positive manner (although some mixed results

found from one study). For instance, Chea et al. (n.d)) found slightly increased yields when rice double

cropping was undertaken (2.6 t ha-1), compared to single cropping (2.4 t ha-1). However, in another study,

Phaloeun et al. (2004) reported increased yields under double (compared to single) cropping when all

experiments in a location were averaged (although individual experiments varied in response). No

statistical analysis available in these studies to indicate the overall effect. There were no comparisons in

these studies that compared yields with water quality or other ecosystem services for double compared

to single cropping.

The effect of land preparation

As expected for such a central component of agricultural management, several studies examined the

impact of land preparation on rice production. Land preparation prepares the rice field for planting by

helping it to control weeds, recycle plant nutrients, and to provide a soft soil mass for transplanting and a

suitable soil surface for direct seeding (IRRI, Rice KnowledgeBank, no date).

Relevant studies found in Cambodia can be classified into studies on tillage and crop residue

management. For tillage comparisons, Bunna et al. (2011) compared yield of mungbeans (as a post-rice

legume crop) under conventional and no-till methods, and in only one of four locations tested was yield

greater in the no-till treatment.

Two studies examined the impact of biochar application, with both finding increases in yield from rice

husk and bagasse (from sorghum) application (Sokchea et al. 2011), and from application of rice husk

biochar (Shackley et al. 2012). Across several studies, mixed results were found for the application of straw

residues on rice yields, although in most cases this management action resulted in increased rice yields.

A small number of studies also examined the impact of rice residue management on yield. Bunna et al., in

the same study as above, also examined the impact of rice straw amendments (at a density of 1.5 t/ha)

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on mungbean yield and found that yields were increased from 228 to 332 kg/ha, and survival was

increased from 72 to 83%. The impact of rice residue on rice yield was examined by Pheng et al. (2010),

finding that incorporating the previous seasons rice stubble into the soil decreased yields of the following

rice crop.

Finally, mechanical field levelling was found to increase rice yields (Rickman et al. 2001; CSIRO 2014).

Whilst no studies examined the link between land preparation techniques/approaches and water quality,

some potential inferences can be tentatively drawn, and provide possible areas of investigation for future

research:

Straw amendments may potentially decrease water pollutants via: i) reducing soil erosion

(reduced turbidity), ii) reducing water run-off (and hence lateral movement of chemical

pollutants), iii) reducing the need for additional chemical inputs.

Straw amendments may potentially increase water pollutants through increased nutrient status

of soil and therefore, capacity of increased water pollution.

Biochar may potentially decrease water pollutants via reduced need for other chemical inputs.

Mulch may potentially increase water quality by increasing soil water retention and therefore

reducing lateral water movement (and hence, movement of agrochemicals and other pollutants).

Field levelling may have the potential for initial negative impacts on water quality (large scale soil

erosion) followed by later positive impacts (reduced need for overall fertiliser use and associated

reduction in pollutants).

The effect of planting/crop establishment

For rice crops, the vast majority of yield comparisons found were reported in Rickman et al. (2001), a

paper that contained a series of experiments examining direct seeding compared to transplanting in

lowland rice in Cambodia over several years. Results were very mixed, with five of 11 studies reporting

greater yield with direct seeding. However, no sample sizes or measures of variance were presented with

these results (means only), so it is not possible to determine the overall magnitude of difference between

treatments. The only other studies examining the impact of crop establishment on yields were Bunna et

al. (2011), who found no consistent response (i.e. mixed results) of no-till compared to conventional till

for mung bean yields (as a break crop from rice), and Ikeda et al. (2008) who found reduced yields of rice

in direct seeding compared to transplanting. This study encapsulated the issues surrounding some

management actions when compared as stand-alone management strategies, (when in reality, they are

often conducted as a one component of a suite of management actions). The study found that interaction

components with year, varieties, water conditions, and weed management were also significant, and that

planting method alone may not account for observed yield responses.

In terms of water quality, no studies were located that addressed crop establishment methods on water

quality. However, from general findings for soil management (during crop establishment) for other crops

globally, reduced tillage practices (no-till, reduced-till, conservation agriculture) lead to increased water

infiltration, reduced run-off/erosion (Gregory et al. 2005) and (presumably, as this rarely appears to be

tested), improved water quality in the vicinity of the cropping fields. Other studies have also attested to

the benefits of a range of practices generally grouped under ‘conservation agriculture’ (no tillage, direct

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seeding approaches), such as reduced environmental impacts in rice-wheat systems (Gupta and Seth,

2007), and reduced sedimentation at the catchment scale for use of conservation agriculture technologies

(Valentin et al. 2008).


A greater number of studies examined various forms of soil fertilisation on yield (see Fig. 20), including

organic manure (increased yield or no effect in three studies), inorganic N or NPK application (increased

yield in all 20 comparisons), four comparisons of System of Rice Intensification (yield greater in SRI) and

one comparison of lime application (increased yield). On the whole, this is very consistent in terms of

response, indicating that soil fertilisation of some kind will increase yields. This is particularly relevant to

Cambodia, where fertiliser use is generally very low, and where fertiliser application has been identified

as a priority management intervention for increasing yields.

As previously mentioned in the introduction to this section, only one study examined water quality

changes from due to soil fertility management (Chamroeun et al. 2002). Whilst the findings are consistent

with studies for rice and other crops in other parts of the world, this study should be treated with caution

due to methodological issues and indirect forms of assessment (proxy, no baseline, farmer perception

rather than measurement). Given that soil fertility management with inorganic fertilisers appears to have

such a consistent positive response on yield, it is likely to be pursued by more farmers in the future.

However, the impacts on water quality in Cambodia are still not tested, and hardly appear to be

considered in many studies. Therefore, this should be a priority for future research.

In other parts of the world and for other crops, increasing soil fertility inputs is recognised as a major

source of reduced water quality (Harris et al. 2015), with inorganic fertiliser use being particularly

recognised as a source of off-site pollution (Dabrowski et al. 2009), generating calls for more efficient NPK

management in cropping systems (Andrews and Lea, 2013).

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Figure 20. Frequency results in terms of increase, no difference and decrease, from the reviewed literature, for rice yield as a

response to a range of soil fertility management interventions.

The effect of pest and weed management

Only five comparisons (in two studies) examined the impact of various forms of crop protection on rice

yield. Rickman et al (2001) found that for rice from seed broadcast, herbicidal weed control increased

grain yield from 1.85 t ha–1 (no weed control) to 2.14 t ha–1 (weed biomass also reduced). However these

data were not significantly different. The same study, however, foundyields under herbicide were slightly

lower than under no weed control for transplanted rice (again, non-significant difference). Again no

significant difference in rice yield was found when comparing manual weeding with no weeding in

transplanted rice, but yield (and reduction of weed biomass) was found to be significantly greater in

manual weeding in broadcast rice. Ikeda et al. (2008), in a multi-factorial study examining the interactions

and contributions of various management activities, found that herbicide contributed to significant weed

control, which in turn had positive effects on yield.

One study that examined the impact of pesticide management on water quality (although not yield,

precluding the opportunity for direct comparison), was Chamroeun et al. (2002), who found that pesticide,

(including herbicide) use had a detrimental impact on fish and other aquatic organisms, as an indirect

measure of water quality. However, this study used non-quantitative measures (farmer opinion) to

establish this. Therefore, whilst the trajectory of change (decline in organism abundance) may have been

determined (albeit in a non-robust manner), the magnitude of change remains unknown. According to de

Silva et al. (2013) relatively few rice farmers in Cambodia use chemical pesticides, but as rice production

intensifies, this is likely to become more prevalent with increasing negative impacts on water quality and

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fish. They indicate that where pesticides are used, they are often illegally imported from Thailand and

Vietnam, and are used with little understanding of safety requirements and responsible usage.

Consequently, the negative impacts of chemical pesticides may be a growing and insidious problem for

rice farming (both on and off site) in Cambodia. This idea is supported by presence of high amounts of

pesticide residue on vegetables in Cambodian markets (Neufeld et al. 2010).

The impact of pesticides on non-target organisms is well documented for many other production systems,

and it is likely that more targeted and robust studies may reveal similar trade-offs of production and water

quality. However, this remains a priority area of research. Related to this, is the management approach

to pesticide storage and application. In many cases, farmers do not follow instructions for pesticide

storage or application, or cannot read them, as they are rarely written in Khmer (EJF, 2002). Also, safety

equipment or clothing is rarely used by farmers, and in many cases, containers used to measure and apply

pesticides and herbicides are also used to collect drinking water (EJF, 2002). There are numerous health

issues reported amongst rice farmers in Cambodia that are frequently attributed to inadequate safety

approaches in relation to agrochemical use (EJF, 2002).

Studies from other parts of the world and other systems indicate that herbicide application can have

negative offsite impacts on water quality such as both surface and ground water pollution (Martinez et al.

2000). The impacts of herbicide application can occur both directly—chemical pollution of water—and

indirectly—reduction in native vegetation (e.g. macrophytes and fully aquatic) that have capacity to

reduce water impurities and pollutants. As such, there is likely to be a trade-off between the positive

effects of herbicides on yield (positive, via reduced competition for various resources) and water quality.

Figure 21. Frequency results in terms of increase, no difference and decrease, from the reviewed literature, for rice yield as a

response to a range of management interventions. This chart presents yield data only, which has been retained due to the

very large number of studies that present yield only data in relation to management actions.

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CONCLUSIONS

Only one study examined both yield and water quality (yield increased and water quality declined due to soil fertility

management) and one study examined water quality as a result of pesticide application (water quality declined).

By contrast, many studies examined yield in response to management actions, and all those located in the literature

review are presented in table 2, below (many are then reiterated in other tables where specific management actions

are discussed, or where other ecosystem service outcomes are examined). The overwhelming majority of

comparisons found increased yield in the management treatment compared to the ‘business-as-usual’ approach or

control treatment (increased yield = 66; no change = 8; decreased yield = 8). This indicates that there are many

approaches and strategies that can be taken in rice production that will increase yields (land preparation and soil

fertility management were extremely successful). However, relatively few studies included other ecosystem services

beyond yield (a provisioning service, in effect). In total, we found 95 treatment comparisons on rice and various

ecosystem services (including food production). Of these, 86 percent featured measures/data of food production

(expressed as yield in all cases), 14 percent for crop protection and climate change mitigation respectively, six

percent for water quantity and two percent for water quality. No comparisons examined the impact of management

actions on other raw materials (only where raw materials can be used for other ecosystem services, such as climate

change mitigation). This bias presents a very strong rationale for building ecosystem service elements into studies

focusing primarily on yield, but should sound a warning that if ecosystem service considerations are not included,

then there is little way of determining how to increase yields without the massive biodiversity loss and ecosystem

service decline that has been seen in many world regions where yield has been pursued at the expense of other

concerns and ecological limitations to production (Potts et al. 2010; Power, 2010; Tscharntke et al. 2005; 2012). In

particular, the paucity of studies examining the potential trade-offs between increased yield and water quality are

extremely concerning, given the critical importance of fresh water to both people and ecosystems, and the negative

impact that intensified agricultural management has had on water quality in other parts of the world, where this

interaction has been documented (e.g. Firbank et al. 2008).

The authors are unable to draw any conclusion regarding trade-offs or synergies between yield and water quality

due to paucity of studies examining the latter. In terms of impact upon yield, findings were somewhat varied. For

instance, soil fertility management (fertilization, using various inputs and methods) generally had a positive impact

upon yields, especially where inorganic fertilizers were used. Whilst this is a positive from a direct productivity

perspective, there are numerous potential problems that can arise from fertilizer use, such as increases in

herbivorous insects, especially sucking insects (e.g. from the order Hemiptera) (Butler et al. 2012), that are known

to impact negatively on rice. Organic manure did not appear to have significant impact upon yield (although only

one study in this category), although it is useful to note this in the context of a meta-analysis indicating that on

average, yields tend to be lower under organic than conventional systems (Seufert et al. 2012). Land preparation

(e.g. via straw residue) also tended to have a positive impact on yields, potentially due in part to the increased levels

of nutrients contained in crop residues, which are then retained in the soil, and assimilated by the following crop

(Singh and Sidhu, 2014). Weed management, either through herbicides or mechanical or manual removal displayed

rather inconsistent results, which is somewhat surprising given the extent to which weeds compete with planted

crops for resources such as water, nutrients and light. As with several other comparisons, the limited number of

results may be contributing to the inconsistent overall response. Finally, planting techniques, which were largely

obtained from a single paper (Rickman et al. 2001) displayed extremely variable results when comparing direct

seeding to transplanting. These variable results may be due in part to inherent trade-offs associated with direct

seeding in rice. For instance, advantages of direct seeding may include reduced water requirements, increased soil

organic-matter, increased carbon sequestering, and reduced greenhouse-gas emissions, but gains and

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improvements associated with these may be offset by losses associated with weed infestation, blast disease, crop

lodging and reduced kernel quality (Farooq et al. 2011).

As a final conclusion, the focus on yield is entirely understandable, given the critical need for improved production

in the region and the role that rice can play in addressing this. However, the lack of focus on other ecosystem services

and how they respond to agricultural intensification is a serious cause for concern, particularly in light of the findings

of Benayas et al. (2009), who reported that increases in provisioning services were often accompanied by

concomitant declines in biodiversity and regulating and supporting services (see Figure 1B in Benayas et al. 2009).




I. Ample water supplies are essential for growing rice (positive impact), and this has resulted in a

range of rice growing approaches and strategies in Cambodia, including rain fed, irrigated and

deepwater. At present, rain fed is by far the dominant form of rice production in Cambodia, being

reliant upon monsoonal rains (dependency). However, this limits farmers to one crop per year,

coinciding with the monsoonal season, and also leaves farmers vulnerable to inter-annual

variation in rainfall (limitation). This is a situation that may become exacerbated by climate

change, with increasingly unreliable rainfall predicted in much of the region (limitation).

An inevitable solution to this is to grow dry season rice, using irrigation (alternative to

dependency) - this allows more than one crop per year to be grown, and generally results in higher

yields. However, there are a number of constraints to many farmers investing in irrigated dry

season rice; these include expense of earthworks and irrigation equipment, cost of purchasing

pumped water, and proximity to available water sources (limitations).

There are a number of environmental constraints or potential negative impacts that also relate to

the use of irrigated rice, including, scarcity of surface water, groundwater depletion, increasing

soil salinity and development of hard pans (negative impacts) (Khan et al. 2004). Additional

environmental impacts can include waterlogging, and off site/downstream degradation of water

quality (negative impacts) (Wichelns and Oster, 2004).

II. In addition to the provision of adequate water for growing rice, there is also a major issue

surrounding adequate levels of soil moisture in order that other crops can be grown on rice fields

(positive impact). For instance, Bunna et al. (2011) found that using rice straw as mulch increased

available soil moisture for break crops (e.g. mung beans). On the whole, it is hard to draw too

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many conclusions in this area, as very little research has been done on soil moisture retention for

other crops (either break crops or intercrops) in Cambodia.

THE EFFECT OF A SPECIFIC MANAGEMENT PRACTICES OR SYSTEMS


Only a small number of studies have examined the impact of water management on yield, and few studies

looked at yield and water quantity simultaneously. Overall (see Fig 22), seven study comparisons reported

increased yield from water management, two reported no difference, and one reported decreased water

efficiency.

In terms of yield, yield increases due to irrigation were found in 15 rice varieties by Basnayake et al. (2006),

when examining the responses of varieties to water management compared to drought conditions.

Meanwhile, Ikeda et al. (2008) found that shallow flooded rice produced higher yields than deep flooded

and non-flooded rice. However, Kamoshita et al. (2014) found no effect of water management on yield.

Finally, Ly et al. (2013) found that System of Rice Intensification, which includes alternate wetting and

drying amongst its many management practices, did not significantly affect yield when compared to a

conventional production system. Vang Seng et al. (1999) examined the impact on rice yield of permanent

flooding compared to intermittent flooding onto different soil types (black clay soils, and sandy soils). In

both instances, they found that yields were increased on the permanent flooded areas, indicating that

this may be an effective management approach for increasing yield, regardless of soil porosity. However,

the increase in yields comes at the expense of greatly increased water use (and the need for infrastructure

to manage and control this water), and hence represents a considerable trade-off in yields and water use

(with water effectively representing a considerable input). Wokker et al. (2011) conducted yield

comparisons in rice that was irrigated compared to non-irrigated rice, in both dry and wet seasons. Whilst

yields increased under irrigation in both seasons, the greater increase per unit of water use occurred in

the dry season. This is unsurprising, given that in the wet season, predictability of rains permitting, water

is less likely to be a limiting factor in rice yield.

Eastick et al. (2010) examined both yields of mung bean and peanut break crops in rice systems, and water

savings. They found that irrigation, compared to traditional hand watering can techniques, resulted in

increased mung bean and peanut yields, but reduced water efficiency, indicating that there may be a

trade-off between these two elements.

In terms of other management activities and their impact upon yields and water quantity, for comparisons

of land preparation reported both increased yields and increased water use efficiency/quantity (Figure

22). For instance, the application of biochar increased yields and saw increased soil water holding capacity

(Sokchea Huy, 2012). Meanwhile, laser levelling of fields (in effect, a move towards precision agriculture)

produced three simultaneous synergies — increase yields, water use saving of 16%, and reduced weed

biomass (CSIRO, 2014).

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Figure 22. Frequency results in terms of increase, no difference and decrease, from the reviewed literature, for rice yield and

water quantity.

CONCLUSIONS

In general, and in keeping with other comparisons in this study, yield was usually increased through a

range of management actions. The authors only located six examples of water quantity being investigated,

but five were coupled with measures of yield, and therefore an estimate of general trade-off can be (very)

cautiously proposed, with management actions resulting in both increased yield and increased water use

efficiency or increased soil moisture in four of those comparisons. However, the authors reiterate that

there is an urgent need for studies to move beyond simple investigations of yield response to rice

management, and begin to quantify simultaneously, the impacts on other vital ecosystem service and

natural resource management issues such as water (quality and quantity).

In general, management activities in relation to water management, land preparation and soil

management tended to have positive or neutral outcomes for yield and water quantity available to rice.

This is unsurprising, given that water is such an integral component of the rice system. However, the small

number of studies precludes opportunities to make anything other than broad generalizations. Therefore,

more targeted research questions applicable to the rice systems in Cambodia are therefore required. Of

particular importance, are how water availability can be influenced by other components of the landscape

(e.g. native vegetation), and how various aspects of land preparation and soil management may

contribute to both yield and water quantity and retention. An area of research that may require more

investigation is that of laser levelling of fields, which was reported to have positive impacts upon yields,

water savings and weed biomass. Again, the need for ecosystem services other than provisioning (and

then, entirely consisting of yield measures) to be addressed in rice studies is an important finding, and

one that should be communicated to researchers operating in this domain.


Rice residues such as stubble and straw have been traditionally burnt after harvest in Cambodia. The

reasoning behind this management approach varies, but generally involves a perception that it will reduce

the abundance of pest species in the following crop, will reduce disease incidence, will increase soil

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fertility, and is also driven by a perception that a clean and tidy field is a healthy field. However,

alternatives to this approach are also encountered, and are to some extent becoming a focal point for

research. These include, aftermath grazing of stubble by livestock, retention of stubble, application of

straw prior to subsequent crops, and use of rice husks to generate electricity. This latter comparison will

be dealt with in the climate change mitigation section, but other elements are dealt with here. Whilst the

research question in this section relates to the trade-offs/synergies between increasing rice yield and

different uses of rice residues, no studies, that we located, examined this relationship. Therefore, we

present results and discussion of the impact of rice raw materials on yield and other ecosystem services:

I. The retention or incorporation of rice straw (cause) can have a wide range of potentially

positive responses for yields (positive impact) and other ecosystem services. For instance,

rice straw may help to reintroduce or retain nutrients in the soil, reduce soil temperature,

provide nutrients and/or substrate for soil fauna, retain moisture in soils, and increased

rates of chemical reduction in soil (both positive impacts and dependencies). A study by

Vang Seng et al. (1999) found that rice straw had a number of beneficial influences that

could result in increased yield including minimized changes in soil pH due to increased soil

reduction rates, and increased uptake of phosphorus by rice plants during periods when

soil water loss was heightened. However, results of residue application are not always

positive. For instance, Pheng et al. (2010) found that application of straw residues actually

inhibited rice growth. This may be attributable to allelopathy, except that similar results

were found for both allelopathic and non-allelopathic materials. In other cases where rice

residues have been shown to have a negative yield effect on following crops, such as

wheat, this has been attributed to phytotoxins in the rice residues (e.g. Bacon and Cooper,

1985).

II. The use of straw residues for bioenergy production (cause) is an area where raw materials

are gaining traction. Only around 17 percent of rice residues are used in Cambodia

(Mustonen et al. 2013), with enormous potential to utilize the remaining majority.

However, many of the studies were theoretical in nature (focusing on potential energy),

and not examining the Technical and economic potential, and energy supply effects from

biofuel generation of rice (positive impact). Nor did these studies explore the implications

of a move from rice as food production to rice as food AND biofuel production, a

relationship that has been explored in other parts of the world for a range of crops where

food production has been diverted to energy production (e.g. Fargione et al. 2008;

Searchinger et al. 2008; Danielsen et al. 2009; Mueller et al. 2011). Whilst in the studies

that we examined for Cambodia we found no negative impacts of rice by-products as

feedstock for alternative fuels, risks have become apparent in other countries where

using crops for biofuels have reached industrial levels, and have been heavily

institutionalized through policies and incentive approaches (Boddiger, 2007; Godfray et

al. 2010). However, this is likely to be far less of an issue as the use of a crop byproduct

as fuel should be less of a driver of land use change and food prices than using crops

entirely as fuel.

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THE EFFECT OF A SPECIFIC MANAGEMENT PRACTICE OR MANAGEMENT SYSTEMS

The effect of residue management

Table 4 and Fig. 23, below, show that management actions involving the raw materials from rice can have

a wide range of impacts upon food production and other ecosystem services. This seems to be in part due

to the different approaches to management in residue management in relation to incorporating residues

into soils or burning them. For instance, rice residues when left on the surface or incorporated into the

soil generally increased yields of rice or other crops. This generally positive effect was also evident across

different soil types such as sandy soils and black clay soils (Seng et al. 1999). For the same study, yields

were also increased through rice straw application, in both permanently flooded and intermittently

flooded treatments. This appears to indicate that application of rice straw is, in general, a very positive

management action in relation to the yields of both rice and other crops. Impacts upon other ecosystem

services were generally positive as well — for instance, rice straw and mulching were found to reduce

weed species biomass (which will almost certainly interact with crop growth, potentially leading to

increased yields), and improve retention of soil moisture (again, potentially contributing positively to yield

of rice or other crops).

Only one study examined the impact of rice stubble burning (compared to rice stubble incorporation into

the soil) and found no difference in yield, and did not examine any other ecosystem service responses.

However, there is a good deal of literature from various systems, including rice, that indicate that burning

stubble can have a variety of negative impacts on: i) human health and related costs (Kumar and Kumar,

2010); ii) air quality and greenhouse gas emissions (Mittal et al. 2009); iii) water pollution (Kumar et al.

2014); iv) soil quality/function and biota (Timsina, 2005). Whilst many farmers burn crop residues to try

and eradicate pests and increase soil fertility, there is some evidence to suggest that burning can decrease

soil fertility (e.g. phosphorus, Dormaar et al. 1979), has rather variable effects on predatory arthropods

that themselves impact upon pest species (Micinski et al. 1991), and can increase nematode pests

(Rahman et al. 2007). The relative impacts of rice residue management (especially burning versus

incorporation into soil) on a range of agronomic and ecosystem service aspects of production appear to

be a considerable research priority.

Finally, a very different approach to management, use of rice residues as raw material for biofuels was

found to have considerable potential in generating significant quantities of energy, and could be used to

mitigate climate change via replacement of fossil fuels. However, whilst this area has potential, it is by no

means a familiar approach for many countries, and requires considerable amounts of research and

development investment, and in particular policies sensitive to the risks associated with biofuels

competing with food production, forestry, biodiversity conservation, etc., for available land. Whilst there

are considerable technological advances in this area, adapting these for the specifics of local to national

challenges and contexts is likely to remain a key challenge, especially in terms of capacity building and

policy development and deployment.

Only one study examined the impacts of rice residues on both food production (yield) and GHG emissions,

Shackley et al. (2012). The authors report a significant increase in irrigated rice production of 33 percent

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following biochar application. This is primarily attributed to the nutrient increases associate with biochar

application that resulted in greater yield increases in low nutrient soils than in soils that already had

favorable nutrient status. The nutrient availability increase for the plants could manifest via: (i) direct

nutrient source and (ii) impacts on nutrient availability (nutrients are more available). Another factor in

this is that the pH of the soil (5.5) was acidic, and biochar is generally considered more effective in acidic

soils. The authors propose this potential relationship between nutrient status and the positive yield

impacts of biochar as a priority research topic for the future. The GHG emission abatement from the rice

husk biochar application was approximately 0.42 t CO2 t-1. This was primarily attributed to reduced and

aerobic respiration, as well as potential suppression of nitrous oxide or methane emissions from soil, due

to biochar application, although the authors note that the broader global literature on this topic shows

extremely high variability in greenhouse gas emission responses of biochar application, and studies that

focus on the particular characteristics and responses of soils in Cambodia need to be undertaken.


other ecosystem services, due to rice straw and biochar management.

CONCLUSIONS

As with other comparisons, yields (effectively, provisioning services) were generally increased through

residue management actions, and other ecosystem services (e.g. regulating services) varied in their

responses.

For instance, retaining soil cover or other methods of integrating rice stubble/residue into soils for the

next rice or other crop almost invariably leads to increased yields. In the very small sample of other

ecosystem services, there are generally positive responses, such as reduced weed biomass. However,

much larger scale studies across many crops, when meta-analysed, indicate that where yields increase

there is often a concomitant decrease in other ecosystem services (Benayas et al. 2009). As it is, there are

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too few studies, either comparing trade-offs within or among studies, which included both yield and other

ecosystem service responses, and therefore conclusions are difficult to draw from this comparison.

As for other areas of this study, conclusions are difficult to draw, due to general lack of paired yield and

other ecosystem service assessments within a given study. Again, this indicates that there is an urgent

need for researchers to look beyond yield in rice research, and include direct and controlled comparisons

of yield and other ecosystem services.


Greenhouse gas emissions, such as methane emissions, from rice cultivation have increased considerably

in Cambodia over the last decade (Figure 24), and are projected to increase by another 40 percent by the

year 2030 (FAOSTAT, 2015). Cambodia is not a major contributor either in total or per head per capita to

global greenhouse gas emissions, being ranked 131st in the world in terms of total greenhouse gas

emissions in 2009 (International Energy Agency, 2009). However, the percentage increase in emissions

from the period 1992 to 2009 is almost 620 percent, one of the highest increases in the world

(International Energy agency, 2009). Consequently, particularly given the capacity that Cambodia has to

expand areas under cultivation through land clearing and increase the intensification of its agriculture

through fertilizer application and tillage, greenhouse gas emissions from Cambodian agriculture are an

area for growing concern. Consequently, management opportunities for reducing greenhouse gas

emissions in this sector should be pursued as a research priority.

Figure 24. Methane emissions from Cambodian rice cultivation 1961 to 2012 (data source: FAOSTAT, 2015).

Management of rice is likely to be a source of GHG emissions (e.g. NPK application), may reduce emissions

(e.g. direct seeding compared to tillage), and elements of rice may be used as fuel that may reduce GHG

emissions (e.g. energy from rice husks and straw):

I. Fertilizer application generally leads to yield increases, but is also responsible for

emissions of greenhouse gasses such as nitrous oxide (N2O). Over the last 60 years,

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nitrous oxide levels in the atmosphere have risen sharply, and this is considered to largely

attributable to increases in nitrogen fertilizer use (Park et al. 2012). Presently, this may

not be quite the issue in Cambodia as it is in other parts of the world where fertilizer use

is high, but increased fertilizer use in Cambodia is likely to lead to similar issues in terms

of GHG emissions.

II. Alternative land preparation practices in rice production (cause) appear to have the

potential to reduce GHG emissions (positive impact). For instance, tillage (cause) tends to

release carbon into the atmosphere (negative impact), whereas reduced till practices

such as conservation agriculture are more effective in locking up soil organic carbon

(positive impact) (Kern and Johnson, 1993). In addition to sequestration of carbon in the

soil, reduced till practices (cause) save on emissions from vehicles for ploughing (positive

impact) (Hobbs, 2007).

THE EFFECT SPECIFIC MANAGEMENT PRACTICES OR SYSTEMS


In general, fertilizer application increased yield but with increased GHG emissions in all four instances

where this was examined, indicating a clear trade-off between production and climate change mitigation,

that should be a research priority in terms of seeking pathways to increase yields without increasing GHG

emissions. This was especially the case where NPK fertilizer was used (Ly et al. 2013). In another example,

Vibol and Towprayoon (2010) found that NPK application (specific fertilizer not stated) increased yields

but also increased greenhouse gas emissions. The same authors found that organic manure (effect on

yield not assessed) also increased greenhouse gas emissions by a greater amount. The soil conditions in

these studies was predominantly anaerobic.

A notable contributor to greenhouse gas emissions is inorganic fertilization — this is also consistent and

notable contributor to high yields, and therefore is a major potential contributor to addressing poverty

and food security-related issues. Therefore, there is likely to be clear trade-off between productivity on

the one hand, and greenhouse gas emissions on the other.

The effect of crop residue management practices

Another major source of greenhouse gas emissions in rice production in Cambodia, although not reported

in any of the studies we located, is that of crop residue burning. For instance, emissions from burning rice

stubble have been shown to amount to 57 to 81percent of C for CO2, fiev to nine percent for carbon

monoxide (CO), 1.16-1.50% for sulfur dioxide (SO2), and 0.43 to 0.9 percent for CH4, respectively (Miura

and Kanno, 1997).

Generating electricity and biofuels (giving a theoretical decline in GHG emissions) from rice byproducts

appeared to be an option, but this work is very theoretical and predictive in nature, and clearly more

research needs to be undertaken in this area.

93


greenhouse gas emissions.

CONCLUSIONS

From the data presented for Cambodia, and a wider reading of the literature, a number of reasonable

management recommendations can be made, but these do involve some degree of trade-off. For

instance, soil fertility management generally increases yields, especially where inorganic fertiliser is used,

or where it is combined with organic fertiliser. However, in the examples that we found, this also leads to

an increase in greenhouse gas emissions, via nitrous oxide and unutilised N from the fertiliser. Therefore,

the management recommendation would be to match fertiliser application rates to fertiliser

requirements. Therefore, a considerable research management priority is to examine mechanisms for

increasing yields through improved soil fertility management, whilst at the same time managing

greenhouse gas emissions.

Whilst only one study was available for Cambodia relating to crop residue management (Shackley et al.

2012) showing reduced GHG emissions with residue retention/application), studies from other regions

indicate that retention of rice crop residues on the surface of or in the soil may increase GHG emissions

such as CH4 and N2O (e.g. Liou et al. 2003; Lou et al. 2007; Lu et al. 2010. This may present a trade-off

between GHG emissions and yield, given that for Cambodia we found considerable data indicating that

rice yields, and the yields of other crops in the rice system, may be increased through crop residue

retention.

In terms of water management, the single study that examined System of Rice Intensification and

greenhouse gas emissions indicated that this management approach (or more accurately, a suite of

interacting management approaches) may have considerable potential to reduce greenhouse gas

94

emissions if applied more broadly. The precise mechanisms that enable System of Rice Intensification to

have such impacts, and the opportunities for effective scaling out of this approach to a scale that would

have considerable impact upon greenhouse gas emissions, remains considerable priority for further

research.

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2.3 SENEGAL


BACKGROUND INFORMATION ON RICE AGRICULTURE IN SENEGAL

About 20 percent of the total area of Senegal is arable land of which rice production occured on about

five percent in 2010 (Maclean et al., 2013). The area of rice cultivation in Senegal increased from 86,252

hectares in the year 2000 to 135,129 hectares in 2012. This increase is a direct result of the Grande

Offensive Agricole pour la Nourriture et l'Abondance (GOANA) program of the Senegalese government,

targeting self-sufficiency in rice. But not only the area of rice cultivation increased in Senegal - the amount

of rice production augmented three fold from 2000 to 2012. In 2012 the average paddy rice production

was 630,654 tons, while in 2000 this was 202,293 tons (FAOSTAT, n.d.). This means that the average yield

almost doubled from 2.34 tons per hectare in 2000 to 3.9 tons per hectare in 2013 (calculated from

FAOSTAT data, 2015). Yet, according to Maclean et al. (2013), average yields varied widely over the past

twenty years (Figure ).

The potential yield in the wet season is around nine tons per hectare, indicating a pronounced yield gap

between actual and potential yield in Senegal (Wopereis-Pura et al., 2002). In rainfed rice systems yields

are even lower. The yield gap is due to climatic challenges, like heat stress, as well as to farm management

(e.g. fertilizer application, herbicides, etc.) (Poussin et al., 2003). Also uncertain land tenure, high

development costs and insufficient access to inputs (seeds, fertilizers) are major constraints for rice

farmers (Maclean et al., 2013). Irrigated rice farmers face constraints of poor crop management, for

instance by poor timing of input application like herbicides and fertilizers, e.g. due to delays of input arrival

at the market or market limitations (Diagne et al., 2013a). Also weed infestation and bird damage are

major constraints in rice production in Senegal (Rodenburg & Johnson, 2009; Rodenburg et al., 2014). In

rain fed systems the majority of production, harvest and post-harvest tasks are conducted manually by

women (Wolfe et al., 2009). In general, the access to and use of farm inputs like fertilizer and seeds of

improved varieties is rather low and farmers face challenges of droughts, weed infestation and low soil

fertility. Hence, yields are around 1 t/ha up to 2 t/ha under more favourable conditions (like higher soil

fertility or resource inputs). Also differences between rainfed lowland and rainfed upland might exist. For

instance, rainfed lowland fields have more potential for intensification of rice production compared to

rainfed upland (Haefele et al., 2013; Maclean et al., 2013).

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Figure 1. TREND IN RICE YIELD, PRODUCTION AND AREA IN SENEGAL FROM 1990 TO 2010; Primary Y-axis: production (103tons) and area (103 hectares), Secondary Y-axis: yield (t/ha) (SOURCE: Maclean et al., 2013).

Rice is a staple food crop in Senegal and the most consumed cereal (Colen et al., 2013). In 2009, the

average consumption of rice was 71.5 kilogram per person per year, which results in a total consumption

of 984,000 tons of rice per year (Maclean et al., 2013). Senegal is one of the largest consumers of rice in

West-Africa (Maclean et al., 2013). However, in 2005 Senegal depended for 80 percent on rice imports to

comply with domestic consumption. This makes Senegal the second largest rice importer in Sub Saharan

Africa (SSA) (Brüntrup et al., 2006). FIGURE 2 shows the import and production trend from 2001 to 2013.

Over all these years import has exceeded production. According to the Grande Offensive Agricole pour la

Nourriture et l'Abondance (GOANA) program (IRIN, 2008; Matsumoto-Izadifar, n.d.), the challenge of the

Government of Senegal in 2008 is to be self-sufficient by 2015. The self-sufficiency in rice production

already rose to 40 percent in 2008, by an increase in yield (Wolfe et al., 2009). However, to further

increase rice production, farmers should have access to quality resources and should apply improved farm

management practices (such as proper timing of seeding, weed management, etc.) (Maclean et al., 2013).

In addition, currently farmers lack access to markets to sell their rice within Senegal. On top of that,

Senegalese have a strong preference for broken rice over whole grain rice for human consumption. Rice

import in Senegal mainly consists of broken rice, while on the international market broken rice is lower

rated compared to whole grain rice. Hence the price of broken rice grain is rather low. Like in Thailand,

which is the major rice import country for Senegal, where broken rice is used as food for cattle instead of

for human consumption. Import prices of broken rice (e.g. from Thailand) are even cheaper compared to

Senegalese rice (Demont et al., 2013; Wolfe et al., 2009).

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FIGURE 2. TREND IN IMPORT AND PRODUCTION OF RICE IN SENEGAL FROM 2001-2013 (SOURCES: ANSD, 2013;

WOLFE ET AL., 2009; FAOSTAT, N.D.)

RICE GROWING ENVIRONMENTS IN SENEGAL

There are three rice growing environments in Senegal: irrigated lowland, rainfed lowland and rainfed

upland rice. Figure 3 gives an overview of different rice cultivating areas across Senegal. The main areas

for rice in Senegal are the Senegal River valley (irrigated rice) and Casamance (rainfed rice).

Irrigated rice

Seventy percent of the total rice production in Senegal is irrigated and takesplace mainly in the Senegal

River Valley (Figure 23). The entire area covers around 50,000 hectares. 2800 hectares of irrigated rice are

grown in the Anambé basin in Kolda region. Average rice yields from irrigation are five to six tons per

hectare (Diagne et al., 2013). According to Wolfe et al. (2009) the yield is due to consistently applied water

levels as well as the use of several resources, like improved seed, fertilizers and herbicides and

mechanized operations. In addition, in several parts of the Senegal River Valley double cropping is possible

due to intensive cultivation. Plots under irrigated rice cultivation vary from 0.2 to two hectares. To keep

the rice fields flooded, the plots are surrounded by soil bunds (Ceuppens & Wopereis, 1999).

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

0

200

400

600

800

1000

1200

1400P

rod

uct

ion

an

d im

po

rt (

Mt)

Import

Production

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There are three types of irrigation systems in Senegal. For a great part of the irrigation infrastructure the

Government of Senegal (GoS) played a major role in the development in the Senegal River Valley. The two

main schemes managed by the government are the Large-Scale Irrigation Schemes (Grande

Aménagement, GA) and the Village Irrigation Schemes (Périmètre Irrigué Villageois, PIV). The Large-Scale

Irrigation Schemes cover areas over 1000 hectares including both canals and drainage networks. The

Village Irrigation Schemes are smaller (15-50 hectares) and only consist of canal infrastructure (no

drainage canals). The government remained mainly involved in developing irrigation infrastructure until

1994. Because of disengagement of the GoS in the nineties, private investments formed the Private

Irrigation Schemes (Périmètre Irrigué Privé, PIP). These schemes cover areas of maximum 500 hectares

and they have no drainage facilities (Wolfe et al., 2009).

Rainfed rice

Rainfed rice systems are mainly found in the Casamance region (Kolda and Ziguinchor regions), in the

south of Senegal. Although 90 percent of the inhabitants of Senegal live in this area, and the region covers

a large area of harvested rice in Senegal (over 75,000 hectares), only 30 percent of the rice of Senegal is

produced in this area. Yields are rather low, one to two tons per hectare. Plots are small (<0.1 hectares,

based on average figures) and rice production is extensive as low amounts of fertilizer are applied and no

herbicides are used. Rainfed lowland rice plots are seasonally flooded, while rainfed upland rice plots fully

depend on rainfall (Wolfe et al., 2009).

FIGURE 23. RICE CULTIVATION AREAS IN SENEGAL; AREAS HARVESTED. BLUE LINE: SENEGAL RIVER

VALLEY – GREEN LINE: CASAMANCE (SOURCE: (WOLFE ET AL., 2009))

FIGURE 23. RICE CULTIVATION AREAS IN SENEGAL; AREAS HARVESTED. BLUE LINE: SENEGAL RIVER

VALLEY – GREEN LINE: CASAMANCE (SOURCE: (WOLFE ET AL., 2009))

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PREDOMINANT FARMING SYSTEMS IN SENEGAL

As discussed before, imports exceed local production in Senegal (Demont et al., 2013). Rice farming

systems differ widely across regions in Senegal, although the majority of rice production in all regions is

small- and family-held agriculture. Mainly in the rainfed rice cultivating areas market participation is

rather low and most rice is consumed within the region. In contrast, market participation in the irrigated

rice cultivating areas is much higher as about two-thirds of the produced rice are sold (Colen et al., 2013).

This means that the Senegal River Valley in the North is more market orientated compared to rice

production in the South of Senegal. Colen et al. (2013, p. 401) argue: “These regional differences are

primarily due to the different production systems. The lack of commercial orientation in the southern

regions is both a reason for and a consequence of poor access to credit, irrigation, inputs and consumer

markets”. Also between households within a region large differences on market participation exist. Wolfe

et al. (2009) compared farm practices between different rice cultivating areas in Senegal. The results are

summarized in Table 1.

TABLE 1. RICE FARMING SYSTEMS SENEGAL ACCORDING TO REGION (SOURCE: (WOLFE ET AL., 2009))

Saint-Louis Matam Fatick Kolda Ziguinchor

Rice as staple food

Primary Primary Secondary Secondary Primary

Season Jun/Aug-Oct/Dec Jan/Feb-Apr/May

Jun/Aug-Oct/Dec Jul/Aug-Sep/Oct

Jul-Oct Jul-Oct

Varieties High-yielding (improved)

High-yielding (improved)

Local varieties (partly improved)

Local varieties

Local varieties

Farming environment

Irrigated lowland Irrigated lowland Rainfed lowland

Rainfed lowland

Rainfed lowland/upland

Parcel size Large (>1 ha) Medium (>0.25 ha)

Small (<0.1 ha)

Small (<0.1 ha)

Small (<0.1 ha)

Main cultivators Men Men & women Women Women Men & women

Land preparation Mechanized Mechanized Manual Manual Manual

Fertilizer dosage High High None to minimum

Low None to minimum

Herbicide use Common Common/None None None None

Harvesting Mechanized, manual

Manual, mechanized

Manual Manual Manual

Threshing Mechanized Manual, mechanized

Manual Manual Manual

Average yield >5 t/ha >4 t/ha 1-2 t/ha 1-2 t/ha 1-2 t/ha

Destination Consumption, sale

Consumption, sale

Consumption Consumption

Consumption

This table shows that irrigated rice cultivation has a higher input of resources, e.g. mechanization,

herbicides and fertilizer use, compared to rainfed rice farming systems. In Saint-Louis & Dagan even two

growing seasons per year are practiced and yields are much higher compared to rainfed systems.

However, according to Dingkuhn et al. (1995) double cropping gives the risk of cold stress in the wet

season and heat stress in the dry season if sowing is delayed.

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AGRICULTURAL PRACTICES Rice varieties: Stress tolerant rice varieties have been developed by breeding programs in West Africa.

AfricaRice (former WARDA) uses plant breeding to develop rice germplasm which are better able to resist

stresses due to climate change. These breeding lines are varieties from the African rice species O.

glaberrima. The breeding varieties show higher heat tolerance as well as drought tolerance, high water

use efficiency, higher salt tolerance and early maturity compared to O. sativa (Asian rice). O. sativa gives

higher yield potential compared to O. glaberrima. A variety has been developed, called NERICA (new rice

of Africa), which is the offspring of crosses between the African cultivated species O. glaberrima (stress

tolerant characteristics) and the Asian cultivated species O. sativa (high yielding) (Saito et al., 2012;

Manneh et al., 2007). Various suitable parent varieties to grown under the Sahelian conditions (e.g.

drought, extreme temperatures and salinity in the SRV) are observed, identified and released in Senegal

(in observation nurseries) (WARDA, n.d.). In addition, as nitrogen inputs are getting expensive and have

an environmental impact, plant breeders conducting research to breed rice cultivars with higher nitrogen

use efficiencies in Senegal (Gueye & Becker, 2011; Kanfany et al., 2014).

Land preparation: In several parts of Senegal rice cultivation is threatened by salinization, which mainly

occurs in the Senegal River Valley. Farmers often dry-till their soil and thereafter irrigation-drainage cycles

are applied to flush the salts out of the field. To further remove salts from the field some farmers apply

puddling. Puddling refers to tillage while the soil is flooded. Puddling is combined with irrigation-drainage

cycles as well.

Crop establishment: In Senegal, both transplanting and direct seeding (i.e. seed broadcasting) takes place

for crop establishment. Transplanted rice plants suffer less from weed competition and from limitations

in land leveling, but direct seeded rice plants can be sown with a higher plant density. Fertility and weed

management are timed according to transplanting or seeding day. Especially transplanting requires very

precise timing of management practices. The majority of farmers use direct seeding in irrigated rice

systems (Poussin et al., 2003). Transplanting is the main method in rainfed lowland rice (Nguyen & Tran,

2002).

In the Conventional Management Practices (CMP), a set of conventional practices as described by Krupnik

et al. (2010) rice seeds are planted in a wet seedbed, within a layer of 1-4 cm of water. After 21 to 23 days

the rice plants are transplanted in the wet season and after 24 to 25 days in the dry season. In the System

of Rice Intensification (SRI) rice seeds are sown in a damp seedbed, having a layer water of 0-1 cm. After

11 to 13 days in the wet seasons the rice plants are transplanted. In the dry season this is 14 to 15 days.

Given socio-economic circumstances in Senegal (e.g. limited labor availability) the actual adoption of SRI

in Senegal by farmers might be limited (Krupnik et al., 2012).

Soil fertility management: To maintain and increase soil fertility and thereby increase yield, chemical

fertilizers are applied. To keep up yields nutrient application combined with soil nutrient supply should

meet crop requirements (Haefele et al., 2004). However, nutrient use efficiencies are rather low in

Senegal. To increase fertilizer use efficiencies, timing of fertilizer application can be a useful practice.

Research in Senegal has identified that knowledge on optimal timing of N fertilizer application among

farmers is rather limited, resulting in lower rice yields. An example of improved timing of fertilizer N is the

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application of a third N split to ensure sufficient nutrient availability at critical stages of plant growth

(Haefele et al., 2002; Wopereis et al., 1999). Chemical fertilizers ending up in waterways may cause

eutrophication, hence practices to replace chemical fertilizers are recommended as well. For instance,

green manure application could reduce the need for chemical fertilizers. In addition, rice straw residues

could be incorporated to recycle Nitrogen (N) into rice fields, however, due to a high C:N ratio the N might

be immobilized at critical stages of the plant growth. In order to mitigate Greenhouse Gas (GHG) emission

from fertilizer application in Senegalese rice systems, Urea Deep Placement (UDP) is promoted. Granules

or briquettes are made of urea and applied to the soil just after transplanting of rice. The briquettes are

placed close to the roots (IFDC, n.d.). Although this sounds like a promising practice in theory, adoption

of this practice by Senegalese farmers is limited (Cox et al., 2015).

Water Management: According to de Vries et al. (2010), in irrigated lowland rice cultivation areas in

Senegal the recommended water depth is 10 to 15 centimetres permanently flooded. There is a positive

correlation between water depth and plant performance. However, irrigation is costly and water is

becoming scarcer in Senegal. Alternate wetting and drying (AWD) in which fields are not continuous

flooded has been proposed as an alternative to save water. Saving water management practices like

aerobic soil and AWD are also applied under the System of Rice Intensification (SRI) until the reproductive

stage, including a shallow water depth.

Weed management: Rice cultivation systems in Senegal have to deal with yield losses by weeds (Haefele

et al., 2000; Rodenburg & Johnson, 2009; Rodenburg et al., 2014). Growing rice under flooded conditions

reduces weed growth. However, as water is becoming scarce, alternative wetting and drying systems

could be an outcome to safe water. Under such alternative irrigation systems weed competition increases,

which could increase herbicide use (de Vries et al., 2010). To control weeds while reducing herbicide use

several practices could be applied in Senegal: Smaller row spacing (15 instead of 30 centimetres); timing

of weed management; or mechanical or hand weeding.

Pest and diseases: Rice cultivation systems in Senegal, like elsewhere, face damage by pests and diseases,

although Settle & Hama Garba (2009) argue that there are only few problems with insects. A major pest

in irrigated rice production in Senegal are birds, which are mainly controlled by scaring efforts of farmers

(de Mey et al., 2012). To control other pests, insects and diseases, pesticides are applied. To reduce

pesticide use, while limiting the damage by insects, the Integrated Production and Pest Management

(IPPM) project has been carried out in Senegal. In this program sustainable intensification is promoted by

the use of Farmer Field Schools (FFS). The project aims to provide farmers with new skills and knowledge

to increase yields by using ecological methods. The program helps farmers to modify and adapt their own

set of good farming practices. This is mainly done by showing field experiments, e.g. experiments on the

influence of natural enemies on pests11.

Harvesting: Traditionally rice is harvested and threshed manually, which is very labor intensive and

backbreaking. Private contractors or farmers' organizations invest in machinery: combine harvesters,

which combines harvest practices as well as threshing, or threshing machines. An example is the ASI

11 http://www.fao.org/agriculture/crops/thematic-sitemap/theme/pests/ipm/ippm-in-west-africa/en/

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thresher introduced in Senegal by a partnership led by AfricaRice, increasing productivity by from 1 ton of

paddy rice a day to 6 tons, while reducing labor.

Residue management: Rice residues are used for different purposes in Senegal. When residues are left in

the field after harvest rice straw is either burnt in the field, exported to be sold as food for livestock, left

in the field to feed livestock or, for a small part, incorporated in the soil (UNFCCC, n.d.; personal

communication Alassane B. Ndiaye and the head of the department of agriculture of Dagana department).

Rice straw has the potential to be used as biomass energy as well, although there is no evidence that this

is occurring in Senegal. Rice husks are used as biomass energy, in the form of briquettes (UNFCCC, n.d.).



I. As an aquatic or semi-aquatic plant, rice depends heavily on freshwater (dependency). Due to the

proximity of the Atlantic Ocean in various parts of Senegal, soils are naturally saline and sodic. The

water table is rather shallow (fluctuating from 0.5 m to 2 m) and the water is saline (Häfele et al.,

1999). Soil salinization is not only caused by capillary rise from the saline water table, but it is also

due to concentration of salt (cause), because of a lack of proper drainage systems (cause)

(Ceuppens et al., 1997). Agriculture can be challenging on saline soils as salinity is a major yield

limiting factor (negative impact) (Asch et al., 2000).

II. In the lower Senegal River Delta region, there is a rapid expansion of irrigated rice cultivation.

There is an increased input of nutrients into water systems (cause) causing environmental damage

by eutrophication (consequence of negative impact). Blooms of phytoplankton (including

cyanobacteria) are widespread (negative impact), mainly caused by phosphorous (P) inputs (in

combination with environmental factors, like changes in light and temperature) (cause). Lakes

and tributaries along the Senegal River are subject to these P inputs, while they are used by the

local populations as freshwater supplies (for example as drinking water for the capital Dakar)

(Quiblier et al., 2008).

III. A study by Johnson et al. (2004) has shown a decrease in rice of 49 percent in fields with no weed

control compared to weed free fields. Also Haefele et al. (2000) found losses in rice yield caused

by weeds (0.56 t ha-1 per 10 percent of relative weed biomass). In addition, weeds (cause) have

shown to cause yield loss of up to 30 to 100 percent ( negative impact)in aerobic rice systems in

Senegal (de Vries et al., 2010).

IV. As rice is cultivated under (partly) flooded conditions the pesticides (cause) cause harm to the

aquatic environment which provide habitat for several (non granivorous) water bird species

(negative impact), (Parsons et al., 2010). Many bird, fish and aquatic macro invertebrates’

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mortalities have been noted (consequence of negative impact/secondary impact) (Jepson et al.,

2014; Mullie et al., 1991). By pollution of the Senegal River watershed, by spraying pesticides

without protection and by eating treated rice, the pesticides may also have dangerous impacts on

human health (consequence of negative impact/secondary impact).


The effect of land preparation practices

Rice production in Senegal can be severely affected by saltwater intrusion, especially in (the delta of) the

Senegal River Valley (Häfele et al., 1999). Using irrigation-drainage cycles makes saline soils available again

for cultivation. Before the start of the growing season farmers dry-till their soils and flush the fields with

irrigation water before the rice seedlings are transplanted. This is done in order to flush the salts from the

topsoil. In addition, under flooded conditions the salts are dissolved and transported downwards from

the topsoil. In general, rice plants are able to survive under certain saline and flooded conditions, yet rice

production is threatened and limited by high levels of soil salinity (Asch et al., 2000; Ceuppens et al., 1997;

Häfele et al., 1999; Sylla et al., 1995). It is argued however that the practise of flushing or leaching is

effective at all (personal communication , Friedrich): The salts “flushed” away with freshwater in surface

drains are replaced by salts coming up in the soil as the soil water evaporates on the soil surface when the

soil dries. Once the soil is dried out, the salts cristalize again visibly on the surface; the process is very

wasteful on water and increases the salinity of the water bodies downstream, exporting salinity problems

to irrigation systems downstream.

Asch et al. (2000) found that salinity reduces growth in irrigated rice in Senegal, although carbon dioxide

(CO2) assimilation increases. Asch & Wopereis (2001) studied the influence of floodwater salinity on

germination and yield for three different rice varieties in Senegal. They concluded that floodwater salinity

decreased germination and reduced rice yields, though the rate of decrease depends on the specific

cultivar. They advise farmers early sowing and use of salt tolerant rice cultivars.

Floodwater salinity is expressed in electrical conductivity (EC) and an increase by one unit of EC (in

megaSiemens per centimeter) may lead to yield losses up to one ton per hectare (for susceptible varieties)

(Asch & Wopereis, 2001). Ceuppens et al. (1997) reported a decrease of rice yields when the average

electrical conductivity (EC) of surface water was larger than 1.3 deciSiemens (dS) per metre, and they

concluded that fields under double cropping with drainage were less saline. This was recommended as a

farm practice to control salinity. The majority of Senegalese farmers dry till their fields and to wash out

the salts from the soil, farmers flush their rice fields with fresh water. Häfele et al. (1999) did research on

the potential effect of puddling (tillage under flooded conditions) on soil desalinization. They considered

a system with five irrigation-drainage cycles to flush the salts. The baseline treatment, in which dry tillage

took place and five irrigation-drainage cycles, was compared with a treatment in which puddling took

place during the first three irrigation-drainage cycles and two irrigation-drainage cycles afterwards. The

results showed that puddling decreased the soil salinity level significantly. Though, two trade-offs need to

be taken into account. First of all, the salt content in the drainage water was in the first three drainage

cycles (after puddling) three to eight times higher for the puddling compared to the baseline treatment.

Although the authors did not address the effect of this high salt content of the drainage water, it could

112

have an effect of aquatic ecosystems in the drainage system or watershed. Additional data is needed to

understand the effect of salinity on surrounding aquatic ecosystems. Secondly, data on yield was not given

in the research, yet rice seed establishment was poor in the puddling system. The authors gave as

explanation (Häfele et al., 1999; p. 45): “presumably puddling established a lower but homogenous salt

distribution in the root zone”.


Much of the environmental impact of irrigated agriculture is linked to the management of water and salt

balances of irrigated lands. This includes both minimizing the amount of water required to remove salt

from the root-zone, and minimizing the land area required to store the salt temporarily or permanently.

Nitrogen (N) fertilizer application proves to be profitable in irrigated rice cultivation systems in Senegal to

increase yield. However, N is applied in relatively low application rates and the timing of N applications is

not optimal (Bado et al, 2011; Wopereis-Pura et al., 2002). In addition, N requirements for rice production

are hardly met by mineral fertilizer (Ndoye et al., 1996). Wopereis et al. (1999) found that farmers are

often not aware of the optimal doses of fertilizer application. Although application rates of N are low and

it is not the main cause of eutrophication in Western Africa (Quiblier et al., 2008), N use efficiencies of

rice plants are sub-optimal, resulting in losses of N (Bado et al., 2011). Bado et al. (2011) stated that

response to N by rice in Senegal can be increased by improving weed control as the presence of weeds

increases N loss. Also different varieties have different response rates to fertilizer N.

Phosphorus (P) is a substantial element for proper growth of rice crops as P is involved in energy transfer.

Like N applications in Senegal, P use efficiencies in rice cultivation in Senegal are low resulting in high

losses, which could cause environmental damage by eutrophication. This is due to the fact that in many

cases application is not adjusted to local circumstances such as climate, soil conditions and crop

management (Haefele & Wopereis, 2005).

Fertilizer application has the potential to increase rice yield. Farmers could benefit from fertilizer

application especially when there is a high fertilizer recovery rate. However, a lack of knowledge on timing,

application methods and doses, decreases the recovery rate of fertilizer application and increases run-off

and leaching of chemical fertilizers (Haefele et al., 2013). As discussed in the section 2.1, nutrients ending

up in waterways have a negative influence on water quality, affecting the (aquatic) environment and

human health. However, little data on specific influences of fertilizer use on water quality in rice

cultivation in Senegal is available.

The use of organic inputs, such as Green Manure (GM), could reduce the need for chemical fertilizers

while improving physical and biological soil fertility. Besides increasing chemical soil fertility, green

manures have the potential to add organic matter and organic carbon to the soil, it helps preventing

erosion, runoff and soil compaction and increases microbial activity (Frick, 2006; MacRae & Mehuys,

1985). Ndoye et al., (1996) and Rinaudo et al. (1983) both studied the effect of incorporation of Green

Manure (GM) Sesbania rostrata on irrigated lowland rice yield in Senegal (in Casamance and Dakar

respectively). It should be noted that N input from the incorporation of Sesbania rostrata is much higher

compared to mineral fertilizer N input and exact N inputs by Rostrata are unknown. Rinaudo et al. (1983)

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argued that S. rostrata as green manure (40 seedlings m-2; N2 fixed by Rostrata estimated at least 267 kg

N ha-1 per season) showed to be a suitable substitute for chemical N fertilization, as they found significant

increases yield using GM (5.71 t ha-1) compared to the N fertilizer input of 60 kg ha-1 (3.81 t ha-1) and the

control plot (2.12 t ha-1). Ndoye et al. (1996) compared the input of the GM (50 seeds m-2; average 100 kg

N ha-1 input per year) with a mineral fertilizer input of 92 kg N ha-1 on one site and 105 kg N ha-1 on another

site in Senegal. Yields under the GM system were significantly higher, with no chemical fertilizer input. In

Fangote, the average yield over seven years under GM was 3.9 t ha-1 compared to 2.0 t ha-1 with chemical

fertilizer input. In Oussouye the average over 6 years under GM was 4.1 t ha-1, compared to 2.1 t ha-1 with

fertilizer input. Although Green Manure incorporation is assumed to incur high costs of labor, costs of

fertilizer purchase and application can be higher and therefore limited accessible for African smallholder

farmers. Hence, farmers can benefit from the use of GM, yet specific numbers on costs and market

availability of GM seeds are not available (Ndoye et al., 1996).

Riara et al., (1987) studied the effect of Azolla crops on yields in irrigated rice cultivation in a research

station in Senegal. One Azola crop is equivalent to 30 kg N ha-1. The highest yield was found for a

combination of fertilizer input and Azola (60 kg N ha-1 + 2 Azola crops gives 8 t/ha), then for an application

of 120 kg N ha-1 (gives 7.2 t ha-1) and third when implementing 4 Azola crops (5.9 t ha-1). Azola could

possibly reduce fertilizer use, however, as the results show: yields will only remain high when applying at

least 60 kg N ha-1 of mineral fertilizer. This research is conducted to study the potential use of Azolla in

rice production in Senegal, however there is no evidence found on the use of Azolla by farmers. Ndoye et

al., (1996) also considered the high labor costs of Azola implementation, which could double the costs of

labor. In addition, the major limiting growing factor of Azolla is Phosphorous (P), which is a major reason

for many agronomists to not grow Azolla as the Azolla plant could be a competitor of rice for P (Rahman

& Podder, 1996; Roger, 1996). Though Rahman & Podder (1996) argue that Azolla extracts P from the

water, while rice extracts P from the soil.

The effect of plant protection practices

In order to control insects, birds, diseases and weeds, pesticides are used. For instance, de Vries et al.

(2010) found an increase in rice yield in the Wet Season (WS) of 2.8 tons per hectare (215% increase) and

an increase of 4.4 tons per hectare (147% increase) in the Dry Season (DS) under flooded conditions when

using herbicides. Literature on yield changes while using pesticides against insects and diseases has not

been found on Senegal rice cultivation.

However, pesticides can cause damage to the environment and human health. Over the past 15 years

pesticide use per hectare in the Senegal River Delta has increased four to five fold, while the area under

rice cultivation has only doubled. Pesticides are over- and misused and highly persistent toxic pesticide

substances are used (IW:LEARN, n.d.).

Among farmers in Senegal who have not participated in training programs there is little awareness on the

impact of pesticide use, on the environment as well as on human health. Moreover, farmers are not aware

of efficient use of pesticides. Currently Integrated Production and Pest Management (IPPM) programs are

carried out in Senegal, to promote sustainable intensification. The project aims to provide farmers with

new skills and knowledge to increase yields by using ecological methods (FAO, n.d.; Settle & Hama Garba,

114

2009). Settle & Hama Garba (2009) stated that there are already over 5,000 hectares of rice land in Senegal

under the IPPM program.

Pests, including weeds, can cause major problems in rice cultivation, affecting rice yields (Haefele et al.,

2000; Labrada, 2003; Nwilene et al., 2013; Rodenburg et al., 2014). Different pest management practices

have been applied and tested in Senegal:

The conventional approach to suppress pests is the use of pesticides (insecticides, fungicides, herbicides).

As discussed in section 2.3.1 pesticides ending up in (surface) water are harmful for aquatic ecosystems

as well as for human health (e.g. by drinking contaminated water). Trade-offs need to be considered

between rice production and the impact of pesticides on water quality. However, literature comparing

both ecosystem services of water quality and food production is not found for the case of Senegal. The

following information is therefore taken from different sources of information:

Regarding pests like insects (e.g. stemborers) in rice fields in Senegal, relative low amounts of

insecticides are used in general according to Settle & Hama Garba (2009). They argue that there

are relative few problems with insects. In addition, the positive effect of insecticides on rice yields

is not proven according to Settle et al. (1996).

It is also written that chemicals are used in Senegal rice systems to control granivorous birds, in

many cases insecticides, or alternative methods like the use of bird repellents, based on chemicals

or natural plant extracts (de Mey et al., 2012; Rodenburg et al., 2014). However, these practices

are not widely used by farmers. In practice most farmers send their children to the field to scare

birds during the times that birds are most problematic (personal communication, Jonne

Rodenburg).

De Vries et al., (2010) showed a significant increase in yield when using herbicides to control

weeds in rice cultivation in two sites in Senegal. They found an increase in rice yield in the wet

season (WS) of 2.8 t ha-1 (146%) and an increase of 4.4 t ha-1 (215%) in the dry season (DS) under

flooded conditions. This makes most farmers in the Senegal River Valley relying on herbicide use

(followed by hand weeding) (Rodenburg et al., 2014).

As for the effect of pesticide use on water quality in Senegal, the following information is available:

A study carried out by FAO (FAO, 2008; p. D-2) found: “76.9% of the producers use drainage water

as drinking water and health problems related to the use of this water have been identified by

60.6% of the producers,…,Residue analysis showed that detectable quantities of pesticides enter

villages in Northern Senegal through irrigation channels and drains”. Compared to European

standards of drinking water quality, neither the irrigation water nor drain water have the required

quality. Also limited protection by farmers while applying pesticides affects health is observed. In

addition, pesticides harm the environment as well. Fish mortality has been observed as well as

mortality of other aquatic organisms (FAO, 2008a).

115

Mullie et al. (1991) studied the toxicity of irrigation water after Carbofuran application (used to

control rice stem borers) on aquatic organisms. They found a significant decrease of aquatic

macro invertebrates after Carbofuran application, meaning that Carbofuran is highly toxic for non-

target species. However, data on increase in yield by using Carbofuran is not discussed in this

paper.

Although granivorous birds are seen as a major pest in rice cultivation systems in Senegal (de Mey

et al., 2012), rice fields also provide habitat for water birds (Ibáñez et al., 2010; Parsons et al.,

2010). There is limited information available on the influence of agricultural chemicals (e.g.

pesticides) on these waterbirds. Parsons et al. (2010) did research into the effect of pesticides on

birds in rice fields. They concluded that various pesticides are highly toxic for birds. Pesticides in

waterways can be widespread and besides the direct effects, several indirect effects are reported

(like reduced prey). However, their review is global and the amount of data is limited.

Specificallyin Senegal it is reported that bird mortality (e.g. of weaver and wagtails) in rice fields

was observed due to Carbofuran use.

Various alternative management practices are available. These practices have the potential to decrease

pesticide use. Three management practices to control weed in rice fields in Senegal are found, leading to

synergies as well as trade-offs:

First of all, Krupnik et al. (2010) studied the influence of weeding under the System of Rice

Intensification (SRI) system (no chemical herbicides used) and found that weed biomass was four

times higher compared to a set of Conventional Management Practices (CMP) (including chemical

herbicides) (Error! Not a valid bookmark self-reference.). In addition, the labor requirements

were much higher under SRI. Taking all practices under SRI into account, yields were similar to

CMP, despite the high level of weeds. So, the combined practices of SRI result in similar yields

with no herbicide use compared to CMP. In addition, eight different cultivars were tested under

SRI and CMP. Jaya and S202 were found to be weed-competitive cultivars. As Krupnik et al. (2010)

stated (p. 2.3.9.) “These cultivars could be advised to maximize yield on fields prone to heavy weed

infestation, in weed-prone water-saving systems, and/or where labor or tools for weeding are

limiting. However, none of these cultivars are short duration, a key characteristic for meeting the

twin goals of reduced water use and double cropping”. Although the research on SRI shows

promising outcomes, in practice it is not widely adopted by farmers in Senegal. One of the reasons

for this is a higher labor demand for, as example, hand weeding under SRI. (personal

communication, Jonne Rodenburg; Krupnik et al., 2012).

Johnson et al. (2004) found a rice yield loss in Senegal of 47 percent from a field with no weed

control, compared to a weed free field. They tested the effect of timing of weed management

(hand weeding) on rice yields and concluded that (p. 31) “critical periods for weed control,

obtaining 95% of a weed-free yield, were estimated at between 29 to 32 days after sowing in the

wet season (WS) and 4 to 83 Days After Sowing (DAS) in the dry season (DS)”. This indicates that

weed growth is season dependent and that specific recommendations are needed for different

weed species. In the DS weed control has to continue for 10 weeks, which is labor intensive. The

116

authors recommend an increased rice plant density, a rice crop with a more rapid crop canopy

closure or a more competitive rice cultivar to reduce the weed-free period in the dry season.

As reported in the study of Riara et al. (1987) on the use of Azolla in rice cultivation in Senegal,

the use of herbicides controls weed biomass better and results in a higher yield compared to hand

weeding. However, the study showed that a manual weeding treatment combined with Azolla

always increases yields, while decreasing weed biomass. No weeding only using Azolla gives a

significant increase of rice yield 1.7 tons per hectare compared to a system without Azolla and no

weeding. However, the use of Azolla in rice systems in Senegal is limited (personal

communication, Jonne Rodenburg).

These examples of weed control show the possibilities of suppressing weeds while using a decreased

amount of herbicides, possibly resulting in a lower negative impact on water quality. The use of Azolla

even shows a synergy between decreasing weed biomass and an increasing yield. So, all three practices

have a positive effect on weed biomass suppression, but trade-offs need to be considered as well. Rice

yields similar to yields under herbicide treatments cannot always be reached, production costs could

increase (e.g. Azolla plant/seed purchase, water use) and/or labor demand increases in most cases.

Unfortunately, these examples only give data on the effect on weed biomass and yield, but not on the

effect on the environment (water quality) or health.

In order to reduce pesticide inputs and manage farm inputs, FAO (FAO, 2010, n.d.) set up the Integrated

Production and Pest Management Programme (IPPM) in West-Africa. The aim is to develop and adopt

more environmentally friendly and diverse farm practices, while increasing yield and net returns as well.

In Farmer Fields Schools (FFS) farmers are made aware of good farm practices, by implementing them in

their fields. The project takes place in rice cultivation in Senegal as well, although specific outcomes on

rice cultivation are limited. After implementation of IPPM in rice cultivation in Senegal, pesticide use was

reduced by 100 percent in the pilot areas (FAO, 2008a). In addition, the yield increased by almost a quarter

under the IPPM project compared to the conventional system (pesticide use) (FAO, 2008b; Table 3). This

outcome shows a clear synergy between a reduction in pesticide use and food production. In general, in

Senegal pesticide use is reduced by over 90 percent and farmers are even starting to use biological and

botanical pesticides and organic inputs like rice straw (Settle & Hama Garba, 2009).

CONCLUSIONS

Although literature which is comparing the effect of farm management practices on food production with

the effect on water quality is lacking, the following farm management practices may positively address

the trade-off food versus water quality:

Land preparation: An often mentioned and essential practice is flushing to wash away salts. This refers to

an irrigation-drainage system, in which the rice field is flooded with freshwater, after some time the field

is drained and this needs to be repeated a few cycles. Although research on the use of Puddling with a

hydro-tiller has shown a potential reduction in the soil salinity level, the practice is not recommended as

seed establishment is rather low. Other options are to grow salinity tolerant rice cultivars or double rice

cropping. According to Ceuppens et al. (1997, p.1129) “Double cropping reduces the possibilities of upward

117

transport of salt from the saline groundwater table to the soil surface”. This is due to maintaining a flood

layer on the soil which pushes down the salinity (Rodenburg, personal communication).

Soil fertility management: To reduce high amounts of synthetic fertilizer use, synthetic fertilizers could

be (partly) replaced by green manure. Especially when the green manure roots, like Sesbania rostrata, are

inoculated; it fixes nitrogen and thereby improves the nitrogen level of the soil. However, the costs of this

method should be considered, including the increase in labor demand. Another practice is the

implementation of Azola in flooded rice fields. Azola is a source of N and substitutes the use of chemical

fertilizer N. The trade-offs of the implementation should be considered, however. High quantities of water

need to be available at very specific times (crucial for Azola growth), which might not always be feasible

in Senegal. Azola also needs a high level of P input, which could cause competition with rice plants. In

addition water has its price, as well as the increase of labor when applying Azola. Important is a proper

application of N (and other fertilizers) to increase Nutrient Use Efficiency (NUE) by rice plants in order to

reduce leaching of chemical fertilizers to surface and groundwater.

Pest, disease and weed management: Using herbicides to control weeds showed a large yield increase

compared to rice cultivation without herbicide use. However, the impact of pesticides on water quality is

negative as fish, bird and aquatic invertebrate’s mortality is observed as well as a negative impact on

human health. Implementation of IPPM can reduce pesticide application up to 100 percent in rice

cultivation in Senegal with an increase in yields, however this might only relate to insecticides and not to

herbicides. IPPM provides training and knowledge exchange to smallholder rice farmers to support them

in introduce biological pest control and the incorporation of organic material. In addition, three weed

control practices are discussed: timing of weed control, hand weeding and the application of Azola. Some

of these practices even have the potential to increase yield, while suppressing weeds. Although they seem

promising practices to suppress weeds, trade-offs considering costs (e.g. water, labor, Azola plants) need

to be considered as well as an increase in labor demand. Though, with an approved timing of weed control

in the wet season, labor input may possibly decrease.




I. Between 1950s and mid 1980s there was a severe decline in rainfall in Senegal (cause). From the

1990s onwards this decline recovered, but lately (2000-2009) the recovery is slowing down and

annual rainfall is still 15 percent lower compared to the average rainfall around 1950s (USAID,

2012). Observing the water budget of Senegal shows increasing droughts (negative impact), which

increases pressure on food production (consequence of negative impact) (Venema et al., 1996).

Seventy percent of the total rice production in Senegal is irrigated (Maclean et al., 2013), however

water in the Senegal River Valley is becoming more scarce. Two changes in water flows are seen

as major causes of water shortages: first, the water flow in the Senegal River is strongly related to

rainfall and drought causing reduction in water availability in the river. Second, seawater intrusion

into the river is reduced, because of construction of dams (additional cause) (UNEP, n.d.).

118

II. Sufficient quantities of water are required for rice plant growth (although germination is typically

aerobic) (dependency). Water further promotes nitrogen fixation and nitrogen efficiency and it

effectively controls weeds (dependencies).

III. Rice floodwater is also important as habitat for a diversity of associated plants and animals

(positive impact).

IV. Yet, rice farming competes for water with other sectors (hence potentially doing harm to other

sectors, hence a negative impact) which means that there is potentially less water available for

these on-farm benefits. For example, de Vries et al. (2010) stated that water for irrigation is

becoming increasingly scarce as water demands from Dakar are increasing (rice farming is

affected by scarcity of water, hence this is a dependency). Competition for water is also likely to

occur with the water supply company for drinking water and industrial companies like the

Senegalese Sugar Company (SSC) (UNEP, n.d.). The competition for water and the completion of

the dams cause degradation of wetlands in the Senegal River Valley, while this is the habitat for

various aquatic species (Mullie et al., 1991; Wetlands International, 2013).

V. Although the largest area of rice cultivation in Senegal is irrigated lowland rice production

(Maclean et al., 2013), irrigation is costly. It can represent up to 25 percent of the total costs of

rice production in the Senegal River Valley (dependency) (de Vries et al., 2010).



Reliance on irrigated crop production in rice is steadily increasing (Krupnik et al., 2010). At the same time,

water scarcity is becoming an issue, the competition for water with the city of Dakar is increasing and

water use becomes costly. Alternate wetting and drying systems AWD is a practise have been practised

as possible solution. AWD is a practise in which rice fields are not permanently flooded. However, weeds

are considered to be a major problem in rice cultivation in the Sahel (Haefele et al., 2000). Flooded

conditions to cultivate rice are used to suppress weeds (de Vries et al., 2010). Even a short period without

a permanent layer of water could already increase weed growth (Krupnik et al., 2010), causing yields

losses of 30 to 100 percent (de Vries et al., 2010).

An important term when considering the trade-offs between water quantity and food production is water

productivity. This describes rice yield divided by the total water input. Under water saving rice cultivation

systems, water productivity increases (de Vries et al., 2010). Research has been underway in Senegal to

quantify the effect of water saving regimes (de Vries et al., 2010; Krupnik et al., 2010). In addition, the

impact of rice-weed competition is tested as well as the interaction between weed management and

water saving regimes. This research shows that there are clear trade-offs between water quantity and

food production (Krupnik et al., 2012) (Krupnik et al., 2012).

As discussed in the water quality section, rice production in Senegal can be severely affected by saltwater

intrusion. The main area in Senegal where problems with soil and water salinity are occurring is the

119

Senegal River Delta. Flushing of the top soil is needed to remove salts. Especially on less permeable soils

in depressions extra flushing is needed. Removing of salt is needed to ensure rice cultivation on the fields,

so the fields do not have to be abandoned. However, the large amounts of irrigation water required for

this practise needs to be considered as well (Raes et al., 1995). As irrigation water needs to be pumped

from the river, additional use of water to flush the salts can be a financial challenge for rice farmers (Häfele

et al., 1999) and, in addition, water shortages are a major issue in Sub-Saharan Africa. Furthermore,

particularly in low lying areas with high water tables and saline waters flushing is no solution; the only

long term response to salinity in those conditions is permanent soil mulch cover to reduce surface

evaporation and to keep the soil moist, and to constantly grow crops – eventually even trees in the

surroundings to lower water tables (personal communication, Heodor Friedrich).

Trade-offs have to be considered between the costs and amount of irrigation water to reclaim saline soils

for rice cropping and the yields. Moreover, wet tillage practices need to be considered, like puddling,

which could even further decrease the salinity level of the soil surface, but which could have a negative

influence on seedling survival rate after transplanting (Häfele et al., 1999).

As explained before, trade-offs between water quantity and rice production need to be considered. Rice

crops in Senegal are mainly cultivated under (partly) flooded conditions and irrigation (including pumping

water from the river) which is costly for farmers. In addition, Senegal will deal more and more with water

shortages, due to high water demand of the capital Dakar. However, flooded conditions suppress weeds,

resulting in higher rice yields. De Vries et al. (2010) investigated the possibility of using alternate wetting

and drying systems (AWD) to save water, by using four different irrigation treatments. AWD systems refer

to a rice growing system without a permanent layer of water. In one of the treatments, the baseline

treatment (I4), rice was grown under flooded conditions, while the other three treatments considered

water saving regimes: I1) AWD during the whole growing season; I2) AWD during the vegetative part (until

PI) and flooded conditions after; I3) Flooded conditions during the vegetative part (until panicle initiation

(PI)) and AWD thereafter.

The research of de Vries et al. (2010) was carried out five times in 2005 and 2006 on two different sites

and both in the dry (three times) and wet (twice) season. The average water use under I1 was 878 mm,

the average water use under both I2 and I3 was 685 mm and the average water use under I4 was 1278

mm. The total AWD (I1) treatment gave the lowest yield in all five cases. In both wet seasons, the yields

of treatment I2 and I3 were higher, resulting in higher water productivity (kg grain m-3 water). However in

the three dry seasons the yield increase under flooded conditions was not significantly higher compared

to AWD and flooding. The authors concluded that major water savings can be achieved with only little

losses in yield. However, these results were dependent on a context specific weed control and nitrogen

management scheme: 150 kg N ha-1 and herbicide application 21 days after sowing. It should be taken

into account that they also tested different amounts of N application or different amount of weed

herbicides in each of the five cases. Although the yield increased significantly by applying N, there was not

significant interaction between irrigation and N application. In one of the two sites, there was no

significant effect of weed control observed in the flooded baselines treatment (I4). However, treatment

I1 and I2 performed very poorly without weed control. To conclude from this paper, yields within AWD

treatments for part of the growing seasons (I2 and I3) are not significantly lower compared to flooded

120

conditions, while major water savings are achieved. Yet the study also showed that under AWD regimes,

weed control needs more attention in order to maintain yields.

In order to study the effect of weeds on rice yields and the trade-offs between water use, weeds and yield,

Krupnik et al. (2010) analyzed the differences in yield under Conventional Management Practices (CMP)

and Adapted System of Rice Intensification (SRI) (CMP and SRI systems are explained in In order to control

insects, birds, diseases and weeds, pesticides are used. For instance, de Vries et al. (2010) found an

increase in rice yield in the Wet Season (WS) of 2.8 tons per hectare (215% increase) and an increase of

4.4 tons per hectare (147% increase) in the Dry Season (DS) under flooded conditions when using

herbicides. Literature on yield changes while using pesticides against insects and diseases has not been

found on Senegal rice cultivation.

However, pesticides can cause damage to the environment and human health. Over the past 15 years

pesticide use per hectare in the Senegal River Delta has increased four to five fold, while the area under

rice cultivation has only doubled. Pesticides are over- and misused and highly persistent toxic pesticide

substances are used (IW:LEARN, n.d.).

Among farmers in Senegal who have not participated in training programs there is little awareness on the

impact of pesticide use, on the environment as well as on human health. Moreover, farmers are not aware

of efficient use of pesticides. Currently Integrated Production and Pest Management (IPPM) programs are

carried out in Senegal, to promote sustainable intensification. The project aims to provide farmers with

new skills and knowledge to increase yields by using ecological methods (FAO, n.d.; Settle & Hama Garba,

2009). Settle & Hama Garba (2009) stated that there are already over 5,000 hectares of rice land in Senegal

under the IPPM program.

Pests, including weeds, can cause major problems in rice cultivation, affecting rice yields (Haefele et al.,

2000; Labrada, 2003; Nwilene et al., 2013; Rodenburg et al., 2014). Different pest management practices

have been applied and tested in Senegal:

The conventional approach to suppress pests is the use of pesticides (insecticides, fungicides, herbicides).

As discussed in section 2.3.1 pesticides ending up in (surface) water are harmful for aquatic ecosystems

as well as for human health (e.g. by drinking contaminated water). Trade-offs need to be considered

between rice production and the impact of pesticides on water quality. However, literature comparing

both ecosystem services of water quality and food production is not found for the case of Senegal. The

following information is therefore taken from different sources of information:

Regarding pests like insects (e.g. stemborers) in rice fields in Senegal, relative low amounts of

insecticides are used in general according to Settle & Hama Garba (2009). They argue that there

are relative few problems with insects. In addition, the positive effect of insecticides on rice yields

is not proven according to Settle et al. (1996).

It is also written that chemicals are used in Senegal rice systems to control granivorous birds, in

many cases insecticides, or alternative methods like the use of bird repellents, based on chemicals

or natural plant extracts (de Mey et al., 2012; Rodenburg et al., 2014). However, these practices

121

are not widely used by farmers. In practice most farmers send their children to the field to scare

birds during the times that birds are most problematic (personal communication, Jonne

Rodenburg).

De Vries et al., (2010) showed a significant increase in yield when using herbicides to control

weeds in rice cultivation in two sites in Senegal. They found an increase in rice yield in the wet

season (WS) of 2.8 t ha-1 (146%) and an increase of 4.4 t ha-1 (215%) in the dry season (DS) under

flooded conditions. This makes most farmers in the Senegal River Valley relying on herbicide use

(followed by hand weeding) (Rodenburg et al., 2014).

As for the effect of pesticide use on water quality in Senegal, the following information is available:

A study carried out by FAO (FAO, 2008; p. D-2) found: “76.9% of the producers use drainage water

as drinking water and health problems related to the use of this water have been identified by

60.6% of the producers,…,Residue analysis showed that detectable quantities of pesticides enter

villages in Northern Senegal through irrigation channels and drains”. Compared to European

standards of drinking water quality, neither the irrigation water nor drain water have the required

quality. Also limited protection by farmers while applying pesticides affects health is observed. In

addition, pesticides harm the environment as well. Fish mortality has been observed as well as

mortality of other aquatic organisms (FAO, 2008a).

Mullie et al. (1991) studied the toxicity of irrigation water after Carbofuran application (used to

control rice stem borers) on aquatic organisms. They found a significant decrease of aquatic

macro invertebrates after Carbofuran application, meaning that Carbofuran is highly toxic for non-

target species. However, data on increase in yield by using Carbofuran is not discussed in this

paper.

Although granivorous birds are seen as a major pest in rice cultivation systems in Senegal (de Mey

et al., 2012), rice fields also provide habitat for water birds (Ibáñez et al., 2010; Parsons et al.,

2010). There is limited information available on the influence of agricultural chemicals (e.g.

pesticides) on these waterbirds. Parsons et al. (2010) did research into the effect of pesticides on

birds in rice fields. They concluded that various pesticides are highly toxic for birds. Pesticides in

waterways can be widespread and besides the direct effects, several indirect effects are reported

(like reduced prey). However, their review is global and the amount of data is limited.

Specificallyin Senegal it is reported that bird mortality (e.g. of weaver and wagtails) in rice fields

was observed due to Carbofuran use.

Various alternative management practices are available. These practices have the potential to decrease

pesticide use. Three management practices to control weed in rice fields in Senegal are found, leading to

synergies as well as trade-offs:

First of all, Krupnik et al. (2010) studied the influence of weeding under the System of Rice

Intensification (SRI) system (no chemical herbicides used) and found that weed biomass was four

times higher compared to a set of Conventional Management Practices (CMP) (including chemical

122

herbicides) (Error! Not a valid bookmark self-reference.). In addition, the labor requirements

were much higher under SRI. Taking all practices under SRI into account, yields were similar to

CMP, despite the high level of weeds. So, the combined practices of SRI result in similar yields

with no herbicide use compared to CMP. In addition, eight different cultivars were tested under

SRI and CMP. Jaya and S202 were found to be weed-competitive cultivars. As Krupnik et al. (2010)

stated (p. 2.3.9.) “These cultivars could be advised to maximize yield on fields prone to heavy weed

infestation, in weed-prone water-saving systems, and/or where labor or tools for weeding are

limiting. However, none of these cultivars are short duration, a key characteristic for meeting the

twin goals of reduced water use and double cropping”. Although the research on SRI shows

promising outcomes, in practice it is not widely adopted by farmers in Senegal. One of the reasons

for this is a higher labor demand for, as example, hand weeding under SRI. (personal

communication, Jonne Rodenburg; Krupnik et al., 2012).

Johnson et al. (2004) found a rice yield loss in Senegal of 47 percent from a field with no weed

control, compared to a weed free field. They tested the effect of timing of weed management

(hand weeding) on rice yields and concluded that (p. 31) “critical periods for weed control,

obtaining 95% of a weed-free yield, were estimated at between 29 to 32 days after sowing in the

wet season (WS) and 4 to 83 Days After Sowing (DAS) in the dry season (DS)”. This indicates that

weed growth is season dependent and that specific recommendations are needed for different

weed species. In the DS weed control has to continue for 10 weeks, which is labor intensive. The

authors recommend an increased rice plant density, a rice crop with a more rapid crop canopy

closure or a more competitive rice cultivar to reduce the weed-free period in the dry season.

As reported in the study of Riara et al. (1987) on the use of Azolla in rice cultivation in Senegal,

the use of herbicides controls weed biomass better and results in a higher yield compared to hand

weeding. However, the study showed that a manual weeding treatment combined with Azolla

always increases yields, while decreasing weed biomass. No weeding only using Azolla gives a

significant increase of rice yield 1.7 tons per hectare compared to a system without Azolla and no

weeding. However, the use of Azolla in rice systems in Senegal is limited (personal

communication, Jonne Rodenburg).

, section 2.3). They tested these differences for seven different rice cultivars. In general the SRI system

used 15-19 percent less water compared to CMP, with similar or (slightly) higher yield levels. However,

in the beginning of the growing season (before herbicide application under CMP) average weed biomass

over all varieties was four times higher in SRI compared to CMP. During the growing season weed biomass

declined in both systems. Under SRI there are no herbicides used, only hand weeding and mechanical

weeding, and therefore the weed management was far more labor demanding (Krupnik et al., 2012).

In addition, the saline soils in the Senegal River Delta negatively influence rice yields (Asch et al., 2000;

Ceuppens & Wopereis, 1999; Ceuppens et al., 1997; Häfele et al., 1999). AWD are discussed to reduce

water use in irrigated rice systems. However, a major issue in Senegal is salinity causing decreasing crop

yields. Many farmers dry till their fields and to wash out the salts from the soil, farmers flush their rice

fields with fresh water. Therefore the authors de Vries et al. (2010) argue that, in sites in Senegal where

123

problems with salinization occur, it is recommended not to use AWD systems. The risk of stress by

salinization might be too high.

CONCLUSIONS

Under water saving systems major water savings can be achieved. However, without proper weed

management yields will suffer from weed competition. Weed control under water saving regimes is found

to be a necessity to keep yields on a certain level. To conclude, two management practices are

recommended:

1. Permanently flooded conditions require a relatively high amount of water, while no permanent layer

of water give lower yields, because of weed competition. Water saving irrigation systems are

recommended. Instead of permanently flooded rice systems, an irrigation scheme with flooded conditions

during parts of the growing season gives a synergy between water use and yield: e.g. when flooded

conditions are only applied before or after the vegetative stage water use reduces while there is little or

no yield loss. Water productivity (kg grain m−3) increases. However, a context specific weed control and

nitrogen management scheme is recommended, which might affect water quality by herbicide use. In

addition, stress by salinization could occur.

2. Water saving regimes lead to better outcomes in terms of yields when weed control management is

carefully done. The downside is that herbicides could end up in the water, affecting water quality; aquatic

organism and human health (see water quality section). Instead of herbicides, hand weeding could be

used, but this is a very labor demanding job. These trade-offs need to be considered. Various alternative

management practices to suppress weeds are discussed in the previous section.


Rice agro-ecosystems and their associated farming operations may depend on raw materials for three

different purposes, which will be discussed in this section: 1) to increase or maintain soil fertility; 2) as

source of animal feed and bedding material and 3) as source of biomass energy and 4) for other minor

uses such as craftsmanship and building materialbioenergy. As Cooper & Laing (2007; p.11) state: “The

first two are very important in maintaining balance, fertility and functionality in the rural system, and,

depending on the residue, will reduce the amount available as an energy source”. However, many African

households rely on biomass, including residues, for their energy needs as fuel for cooking. Rice husk is

already used as fuel in the form of briquettes (Ingesahel, 1998), but rice straw is normally left in the field

in African countries (either burned or buried) (Cooper & Laing, 2007):

I. First of all, related to the soil fertility aspect, rice cropping systems in Senegal are becoming more

and more intensive. Yields have not reached optimum quantities and in general in West-Africa

yields are even decreasing due to, among other things, a decrease in soil organic carbon (SOC)

(Bado et al., 2010). Recycling of crop residues in the soil are a source of carbon. Decomposition of

crop residues and roots in flooded rice systems in Senegal results in increasing SOC status (Bado

et al., 2010). Besides an increase in SOC, soil organic matter (SOM) is increased and nutrients are

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returned to the soil. Though, decomposition of plant material is slower in moist or anoxic

conditions often found in wet soils compared to aerobic conditions which characterized well-

structured soils (Bot & Benites, 2005) and rice incorporation in the soil increases GHG emissions

(Gaihre et al., 2013).

II. Second, rice crop residues could be used as feed for animals and as bedding material. In times of

drought, biomass may be very limited and nutrition is a major concern in cattle production in

Senegal. However, when residues are fed to animals they cannot directly contribute to an increase

in soil fertility. Though, livestock feed improvement based on crop residues leads to an increase

in quality and quantity of manure, which can increase soil fertility. On the other hand, an increase

in livestock productivity (beef, milk, power and quality manure) leads to an increase in food

production as well (Kayouli, 1996). Rice straw residues provide an important source of food

energy for cattle in Senegal. However, the mineral and N value of rice straw is very limited and

substitutions are recommended (Fall et al., 1989).

III. Third, many African households lack access to energy. Up to 90 percent of households in Senegal

use biofuels, such as wood or residues, as a source of fuel (UNEP RISO, 2013). Fuelwood or

charcoal used domestically may have a negative impact on forest degradation and deforestation.

Alternative sources of affordable and accessible energy are therefore explored. Under certain

circumstances, rice husks and straw could be used as an energy source (Alesbury, 2013), for

instance as green charcoal as suggested in the pilot study done by the International Biochar

Initiative (n.d.). These studies refer to pilot projects however and are not readily being employed

in the country.


Burning. In Senegal, after the harvest of the rice grains, rice straw usually remains in the field as residue.

According to UNFCCC (n.d.) in the Senegal River Valley, 80 percent of the rice straw residues are burned.

As reason for the burning of rice straw the authors mention that cattle are wandering around rice fields,

releasing their dung in the fields. As dung contains seeds, cattle are seen as a major vector for

dissemination of wild rice (which is considered a weed). Straw residues are burned, so cattle do not spent

too much time in the field grazing on these residues. The remaining 20 percent of the rice straw residues

are either fed to animals or buried in the field as fertilizer (UNFCCC, n.d.). In the Casamance region, almost

no rice straw is burned. The residues are either left in the field for grazing or the straw is buried to improve

soil fertility (UNFCCC, n.d.). However, field officers in rice cultivation in Senegal are consulted and noted

that the numbers of UNFCCC might be an over estimation. Via personal communication, the head of the

department of agriculture of Dagana department in the SRV indicated that only around 5 percent of rice

straw is burnt in the field. According to personal communication with an agricultural advisor in Senegal

(Alassane B. Ndiaye, via William settle and Makhfousse Sarr) in the Podor department only two percent of

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the rice straw is burnt. Burning rice straw in the field can emit substantial amounts of air pollutants, which

has a negative impact on the environment and human health (Sanchis et al., 2014).

Rice straw incorporation into soils. In order to raise rice production up to the potential yield, soil fertility

needs to increase. Rice straw residues left in the field after harvest could have a positive effect on

chemical, physical and biological soil fertility. Residues incorporated in the soil increase microbial activity,

they help to prevent erosion, positively affect soil structure and add carbon and organic matter to the soil

(Mandal et al., 2004). Incorporation of rice residues in the soil is only noted by an agricultural advisor in

the SRV (Alassane B. Ndiaye) via personal communication. He indicates that incorporation is likely done

for only one percent of total straw residues. Recent literature has not been found in the regard. However,

Ponnamperuma (1984) cited the work of Beye (1974) who found an increase in soil nutrient status for

total N, available P and available K after rice straw incorporation in Senegal rice growing systems. Rice

straw in Senegal consists of 0.8 percent of N, 0.17 percent of P and 1.4 percent of K. Incorporating the

straw increased total soil N by 0.01 percent compared to straw removal. Soil available P and K increased

by 9 mg kg-1 and 8 mg kg-1 respectively. An increase of 0.01 percent of total N seems to be a very low

number. However, soil N contents of soils in Senegal are found to be rather low. Krupnik et al. (2010)

found a soil N content of 0.11 percent and de Vries et al. (2010) found a soil N content of 0.08 percent.

The critical level of soil N for rice and other cereal production is considered as low when the total soil N is

0.05 percent to 0.12 percent (Tabi et al., 2012). It should be noted that the C:N ratio of rice straw is rather

high (>80). This result in higher immobilization and N might not be available at critical stages of rice crop

growth (Mohanty et al., 2010). Though, Beye (1974) found a rice yield response of one ton per hectare,

on average over six months, after the amendment of six tons of rice straw per hectare.

The research of Beye is fairly outdated though. A more recent research on rice straw and its effect on rice

production in Senegal has not been found. However, the effect of straw application on rice yields is

explored in a more recent research (2005) in Southern Mauritania, in a Sahelian irrigation scheme similar

to those found in Senegal (Van Asten et al., 2005). They found a significant increase in rice yield of, on

average, one ton per hectare after amending the soil with five tons of rice straw per hectare. The results

were independent of fertilizer application or soil type. The results of Beye (1974) are based on acid soils

in Senegal. Van Asten et al. (2005) compared the effect of straw incorporation on rice yields on pH-neutral

soils and acid soils. Nitrogen uptake and the recovery efficiency were found to be higher on acid soils.

Besides, the yield increase due to an increase in N availability from the rice straw, straw application also

increases the recovery efficiency of applied urea-N. Phosphorous is not found to be of any significant

influence. In addition, SOC and SOM levels increase by recycling rice residues (B. V. Bado et al., 2010).

Krupnik et al. (2012a) studied the effect of incorporation of rice straw and chemical fertilizer on rice yield

and nutrient balances under CMP and SRI in the SRV. They concluded that compared to no fertilizer

application, rice straw incorporation had no significant effect on yield in 9 out of 10 studied cases (5

seasons under both SRI and CMP). Straw application in addition to mineral fertilizer application showed a

significant yield increase in 2 out of 10 studied cases compared to fertilizer use only. In addition the

authors concluded: “Positive effects resulting from straw incorporation followed by fertilizer application

became apparent in the fourth season as significant additive increases in yield, straw and fertilizer N

recovery were observed under both RMP and SRI. However, continuation of these trends was only observed

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for SRI in the fifth and final season of the experiment, suggesting that integrated organic and mineral

nutrient management of soil fertility is more advantageous with SRI than RMP. Fertilizer and straw

additions also had a positive effect on partial macronutrient balances and soil quality parameter”.

Straw as cattle feed. Pressure on availability of land is increasing in Senegal, due to a decline in available

pastures and increase in cultivated areas. Crop residues, like rice straw are therefore becoming more and

more important and can represent an important source of feed energy for cattle (Fall et al., 1989; Kayouli,

1996). The head of the department of agriculture of Dagana indicated that around 70 percent of the rice

straw is exported from the field to be sold on the market as food for livestock. The remaining 25 percent

is left in the field to feed livestock (personal communication). An agricultural advisor in the SRV (Alassane

B. Ndiaye) indicated that in the SRV 97 percent of the rice straw is exported from the field and sold as

livestock food.

In 2009, 0.08 tons of rice residue per Tropical Livestock Units (TLU; The standard use for one TLU is one

cattle with a body weight of 250 kg) was supplied (FAO, 2014). However, to gain sound milk or meat

production from cattle, a diet with rice straw alone is insufficient. Rice (and other cereal) straw lacks

sufficient nutrients and minerals to meet cattle maintenance requirements. A treatment of rice straw with

urea (and molasses, which is available in Senegal rice growing areas) increases N content, intake and

digestibility (Fall et al., 1989). Kayouli (1996) stated that rice straw treated with urea improved cattle body

conditions, there is a positive effect on fattening and milk production increases significantly. It is even

reported that cattle work 1.5 to three hours per day more in the field during ploughing time when eating

urea-treated rice straw. In addition, quality (N content increases) and quantity of dung increases as well,

which can be used to fertilize the soil. So, feeding rice straw to livestock in crop-livestock systems can

potentially lead to an increase in yield. Both advantages of the increase in soil fertility by rice residue

amendments and the potentially positive impact on livestock need to be considered.

Straw and rice husk as energy source. While the previous two paragraphs, on soil fertility and feed for

cattle, have a wider focus on food production, this paragraph is about the potential of rice residues to be

used as fuel – which in turn could be used for either domestic uses, for instance cooking or boiling water,

or for electricity production used in rice processing. Rice husks could for instance be pressed into

briquettes, which can be used as green charcoal. Dasappa (2011, p. 204) stated that “energy consumption

in Africa is largely dominated by biomass amounting to more than 80 percent in some countries”.

Households in Senegal collect fuel wood, which increases deforestation. Green charcoal made out of rice

husks could be an alternative fuel source (Alesbury, 2013). According to Cooper & Laing (2007) rice husks

have an average energy potential of 918 teraJoules (TJ) in Senegal, based on an average production of

65,581 Metric tons (MT) of rice husks. The average potential for rice straw is 6,975 TJ, based on an average

production of 498,203 MT rice straw12. The emissions reduction profile report on Senegal (UNEP RISO,

2013) reported: “the potential energy from rice husks is 918 TJ, corresponding to about 15 MW of power

capacity, operating 6,500 hours/year with an electrical efficiency of 40%. The rice straws have even more

potential with a stunning 7,000 TJ, or a 120 MW power capacity, under the same circumstances”.

12 Results are divided over lower and upper rice husks and rice straw, in this report the average number is taken.

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Although the theoretic energy potential of rice husks and straw is shown, there is no literature found

regarding current uses of rice straw as source of biomass energy in Senegal.

CONCLUSIONS

This chapter discussed the trade-offs and synergies on the use of rice residues and food production. No

comparative studies between rice production and raw material use are available for Senegal. The options

to use rice residues are 1) to leave/incorporate rice residues in the field to increase soil fertility, 2) to feed

it to cattle or 3) to use it as a biomass energy source. The following points need to be considered:

1. Soil fertility (soil nutrient level as well as SOM and SOC) could be improved by leaving rice straw

residues in the field, resulting in a potential yield increase ( Haefele et al., 2004; Krupnik et al.,

2012a).

2. All rice residues fed to livestock compete with soil fertility. However, synergies are found between

soil residues fed to cows and food production as well. Livestock production seems to increase

(milk, beef) as well as productivity during ploughing time (more working hours per day). In

addition, the quality and quantity of dung improves as well which can be added to the field again

to improve soil fertility. This system is usually only viable however, when farmers have both crops

and livestock.

3. Households in Senegal highly depend on biomass energy. A trade-off needs to be considered

between the use of rice residues to improve soil fertility, animal food or to use it as a source of

biomass energy. In depth research is needed to see the amount of field residues which could

potentially be removed without affecting soil fertility. In addition, currently rice husks are used as

biomass energy source, but there is no evidence that rice straw is used as energy source in

Senegal.


The point of departure for this analysis is the trade-off between food production and climate change

mitigation. Implied impacts, dependencies and causes in Senegal are discussed as follows:

I. According to Nguyen (2002, p. 29) “the emission of methane and nitrous oxide gases from lowland

rice production” is one of the contributors to global climate change. Rainfall is a major element

(cause) in food production in Senegal (positive benefit) and rice is very sensitive to changes in

rainfall patterns. There is a strong positive correlation between precipitation and rice yield in

Senegal (WFP, n.d.).

The total GHG emissions (CO2, CH4 and N2O) per year from agriculture in Senegal were

approximately 186 Gigagram (Gg) in 1991, of which methane emissions in rice contributed 58.7

Gg. Hence, rice counted for 31.5 percent of total GHG emissions (CO2, CH4 and N2O) in agriculture

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in Senegal. Total methane emissions from agriculture in Senegal were 142.9 Gg, so rice

contributed over 40 percent of methane emission (Sokona, 1995).

II. Several farm management practices in rice fields (cause) influence GHG emissions (negative

impact). Rice in Senegal is mainly grown under flooded conditions (de Vries et al., 2010). Methane

is produced under these anaerobic conditions in waterlogged soils and consequently wetlands

(like rice fields) are the major sources of methane production (cause). Methane production and

emission in cultivated wetlands (mainly rice fields) increases by submersion and rice straw residue

incorporation (organic matter addition) (additional cause) (Le Mer & Roger, 2001). Yet, as

discussed in the previous section, rice straw burning emits GHGs as well, increasing air pollution

and global climate change (additional cause) (Gaihre et al., 2013). Addition of N by organic or

mineral fertilizer has also an impact on GHG emissions as it mainly increases N2O emissions from

the soil (Velthof et al., 2002) (additional cause).

Eshun et al. (2013, p. 120) stated: “Current estimates of greenhouse gases emissions from rice

cultivation from most countries are based on measurements performed under Asian conditions”.

The impact of GHG emissions from rice in African countries has received limited attention so far,

although the authors noted that fertilizer application was responsible for 72% of GHG emissions

(in the form of N2O) in rice cultivation in Ghana. The mineral fertilizer industry contributes (directly

and indirectly) to GHGs emissions (CH4 and N2O), but also organic matter (from organic fertilizer)

emits methane (UNEP RISO, 2013).

While all these management practices cause climate change (negative impact), they do improve

food production (positive impact).


To mitigate the impact of climate change, there is a need for agricultural practices which reduce GHG

emissions, such as improved farm management and increased nitrogen use efficiency. However, the study

in Ghana by Eshun et al. (2013) showed that the net GHG reduction practices are only adopted by farmers

with the incentive of improved profitability. This means that synergies between increased profit and

climate change mitigation need to be found. That being said, literature on practice to reduce net GHG

emissions in rice cultivation in Senegal is limited, however. In this section general practices will be

discussed with, if possible, specific attention to the case of Senegal.

As flooded conditions in rice production systems increase CH4 emissions (Le Mer & Roger, 2001).

Alternative Wetting and Drying (AWD; chapter 2) or introducing drainage periods, are seen as good

management practices to reduce CH4 emissions. However, to limit reductions in rice yield under AWD or

drainage periods, proper management should be applied: e.g. no water stress during critical stages (like

flowering), applying proper weed control to keep weed pressure low and efficient use of nutrients (de

Vries et al., 2010; Le Mer & Roger, 2001). Note that introducing drainage periods might increase water

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use (Le Mer & Roger, 2001) and drainage and soil aeration could increase the production of N2O, although

this is only for a short period of time (only during the drainage period) (Ratering & Conrad, 1998).

Fertilizer use, both organic and mineral, increase rice yields (Bado et al., 2011; Gaihre et al., 2013; S.

Haefele & Wopereis, 2005; Le Mer & Roger, 2001). However, fertilizer application also increases GHG

emissions andcause air and water pollution (Le Mer & Roger, 2001; Velthof et al., 2002) causing air

pollution, depending on the soil conditions and application methods (Le Mer & Roger, 2001; Shcherbak et

al., 2014; Snyder et al., 2009; Velthof et al., 2002). In order to reduce the impact of fertilizer use on GHG

production and emissions, different fertilizers or application methods should be applied in order to

increase nutrient use efficiencies.

As discussed in the previous section, fertilizer is one of the major contributors to GHG emissions in rice

cultivation in Africa. Controlled and slow application of fertilizer is needed (Eshun et al., 2013). For

instance in the case of urea, many farmers just spread this fertilizer into the flooded rice field, causing

high levels of nitrogen loss in the form of GHGs. To reduce CH4 and N2O emissions Urea Deep Placement

(UDP) is used in several rice cultivating countries. This method started in Bangladesh, but is recently

introduced in Senegal as well (Farming First, n.d.).(Choudhury & Kennedy, 2005; Cox et al., 2015; Farming

First, n.d.). Urea is a cheap fertilizer, adding high levels of N to the soil (Savant & Stangel, 1990). Granules

or briquettes are made of urea and are applied to the soil just after transplantation of rice. The briquettes

are placed close to the roots, so the N is absorbed by the plant more efficiently. In addition, most N stays

in the soil, which in turn increases nutrient use efficiencies (IFDC, n.d.).(IFDC, n.d.). The available studies

in West-Africa on the use of UDP are limited. The International Fertilizer Development Center (IFDC,

n.d.)IFDC, n.d.), an organization which promotes the use of UDP in West-Africa stated that “UDP allows

farmers to use less fertilizer (saving money), cuts N losses by as much as 40 percent (reducing air and

water pollution) and increases farmers’ yields by more than 20 percent”. Cox et al. (2015) documented

yield increases under UDP simulations in several areas in Senegal of 10 to 76 percent under low N

application. Increasing N application even increased yield up to 200%. Also UNEP (2013) is doing research

into the UDP practices and states that it decreases methane and nitrous oxides emissions, though exact

numbers are not given.

A second practice to reduce GHG emissions is alternative wetting and drying (AWD). Le Mer & Roger

(2001) wrote that methane is produced and emitted by wetland soils result from microbial activities. In

AWD, instead of permanent flooded conditions during the rice growing season, the field is drained and

flooded again (continuing for a few cycles) (Isbell, 2014) (Isbell, 2014). Isbell (2014, p. 1) Isbell (2014, p. 1)

quoted Dr. Merle Anders: “these cycles can substantially reduce GHGs by temporarily changing the soil

chemistry from an anaerobic to aerobic state.” Research has shown that GHG emissions can be reduced

over 45 percent. The practices is tested in several eastern Asian countries (CCAFS, n.d.).(CCAFS, n.d.). In

order to sustain yields, the soil should not be dried for too long, as over-drying could stress the plant

(Isbell, 2014).(Isbell, 2014). Research on the reduction in GHG emissions by alternate wetting and drying

in Senegal has not been found. However, in the section above on ‘water quantity versus food production’

(chapter 3) the practice of alternate wetting and drying in rice systems in Senegal has been discussed. De

Vries et al. (2010) concluded that, if proper weed management is practiced, alternate wetting and drying

is possible in Senegal with little or no yield reduction.

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To mitigate climate change it is arguedsome argue that the System of Rice Intensification (SRI) is a suitable

practice. Under SRI fields are not permanently flooded and less fertilizer is used. This results in less CH4

emission. In addition, the plants seem to have a higher resilience, which could help in climate change

adaptation (Agriwaterpedia, 2014).Under SRI fields are not permanently flooded and preferably less

chemical fertilizers are used. This results in less CH4 emission and reduced Global Warming Potential

(GWP) (Agriwaterpedia, 2014; SRI-Rice, ND; Mishra, 2009; Nguyet Minh, 2012). Krupnik et al. (2010)

showed that rice yield under the SRI system in Senegal is slightly lower compared to conventional

management practices. In contrast, as stated by Agriwaterpedia (2014) Agriwaterpedia (2014):

“Arguments against the systems include that SRI plots emit more nitrous oxide (N2O) than conventional

rice plots, which has adverse effects on climate change”. However, research on the influence of SRI

practices on climate change mitigation in Senegal is not available.

Under the SRI system organic fertilizer is used, like rice straw.Under the SRI system organic fertilizer

amendments are promoted, like rice straw or compost (e.g. Mishra, 2009; SRI-Rice, ND). In previous

chapters of this report also green manure amendments of Sesbania and Azola are discussed. Le Mer &

Roger (2001) noted that applications of organic matter increases CH4 emission, because of the high levels

of carbon: “Methane production and emission decrease when the C content and the C/N ratio of the

incorporated material decrease. A high C/N, as in rice straw, usually corresponds to an organic material

rich in labile C and thus easily usable by the microflora”. The effect of mineral fertilizer on CH4 emission

by chemical fertilizer is difficult to predict as it depends on the source of fertilizer, the amount of

application and the method of application (Le Mer & Roger, 2001).

CONCLUSIONS

Three rice management practices conducted in Senegal are discussed in the results section. However, in

depth research in Senegal on climate change is limited. The influence of rice farming practices on climate

change mitigation versus food production seems to vary; both, synergies and trade-offs, can be shown:

1. To reduce CH4 and N2O emissions under conventional nutrient application, Urea Deep Placement

(UDP) is used in several rice cultivating countries (e.g. it is currently promoted in Senegal by the

International Fertilizer Development Center). In addition, rice yields seem to increase as well under

UDP. Exact numbers of the trade-offs and synergies of this practice in Senegal are not available, but

the data available from other West-African countries are showing a synergy between climate change

mitigation and food production when using UDP.

2. Alternate wetting and drying, in which rice fields are not permanently flooded, reduces methane

emissions from rice fields. Over-drying could cause drought stress to rice plants and dry conditions

increases weed competition. However, de Vries et al. (2010) concluded that alternate wetting and

drying is possible in Senegal with little or no yield reduction. In this case, climate change mitigation

will increase while food production is sustained.

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3. Under the System of Rice Intensification (SRI) preferably fewer chemical fertilizers are used and rice

fields are not permanently flooded. This results in lower methane emission, but nitrous oxide

emissions could be higher. Yields have shown to increase under SRI practices. Green manure

amendments, like compost (promoted within) – especially with high levels of C – increase methane

production. Site-specific research is needed to see whether there is a negative impact of SRI on GHGs

emissions in Senegal. Trade-offs need to be considered between climate change mitigation, food

production and water quality (see green manure chapter 2.2 – fertilizer use).

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2.4 COSTA RICA


BACKGROUND INFORMATION ON RICE AGRICULTURE IN COSTA RICA

Costa Rica is a small country of 51,100 km2 and of a population of 4.7 million. Costa Rica has 210,000 ha

of arable land and rice is currently produced on approximately 55,709 ha (CONARROZ, 2013), a quarter of

Costa’s farm land. Rice is the main staple food of Costa Rica. The annual consumption as of 2013 was 48

kg per capita, a total of 224,369 tons nationally, half of which was imported (CONARROZ, 2013). Over the

last 50 years, national rice production has tripled. From 1961 to 2009 production area increased by a third,

while national production increased threefold. This significant increase can be attributed to the expansion

of irrigated production areas, intensification of inputs and the use of high yielding varieties (Zorrilla et

al., 2012). Elevated national import tariffs and have driven up the national market price, increasing the

profitability of intensive rice production (Arriagada et al., 2010). Figure X shows the main rice producing

areas of Costa Rica.

RICE GROWING ENVIRONMENTS IN SENEGAL

Rice is grown in irrigated lowland, rainfed lowland and rainfed upland environments (MAG, 1991). The

distribution is determined by agroclimatic factors as well as the presence of irrigation infrastructure. Costa

Rica has mountainous terrain with two ranges that run longitudinally across the central part of the country

dividing it in distinct climatic regions (Solano-Quintero, 1996). The Northern Pacific region has a dry

tropical climate with mean annual temperature of 25 a 30°C and annual rainfall of 2385mm with a

pronounced dry period from November to April. The region has a level terrain and heavy textured soils

ideal for rice production. The Central and Northern Atlantic regions have a mountainous terrain with

fertile plateaus. The climate is humid tropical with precipitation ranging from 2500 to 3500mm. The

Central and South Pacific region has a Humid tropical climate with a three month dry season. Mean annual

temperature is 28°C and annual precipitation is 3122mm.

Figure X. Main rice producing regions of

Costa Rica are circled. (Source: INTA,

Costa Rica, 2001).

Figure X. Main rice producing regions of

Costa Rica are circled. (Source: INTA,

Costa Rica, 2001).

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Upland Rice: Upland rice is produced in the Northern and Central Atlantic regions. The majority of farms

are small with average yields of two to three tons per hectare. Upland rice is also produced in small

subsistence farmer in the Central Valleys and Atlantic Coast. Rice is grown in diversified systems using

manual labor and low levels of external inputs. Variable rainfall and low soil fertility constrain yields in

upland rice systems.

Rainfed Lowland: The majority of commercial rice production areas is under rainfed lowland systems. The

main areas dominated of rainfed lowland production are the South Pacific, Central Pacific, Central North

and North Atlantic. One crop is grown per year during the rainy season. The majority of farms are small

(<50 ha), partially mechanized and have average yields are 3.25 tons per hectare.

Irrigated Lowland: Although there is a greater total area under rainfed rice production, the majority of

rice is produced in the lowland irrigated systems in the Northern Pacific Province of Guanacaste. There

are also small areas of irrigated lowland rice in the plateaus of the Central Northern and Central Pacific

Regions. In irrigated lowland systems two rice crops are grown per year: a fully irrigated crop in the dry

season and a rainfed crop in the wet season. In the Northern pacific production is highly intensified with

average yields of four tons per hectare and upwards of eight tons per hectare. The systems are highly

mechanized with intensive use of inputs.

PREDOMINANT FARMING SYSTEMS IN COSTA RICA

Approximately 66 percent of the rice producing area is under rainfed lowland and upland conditions and

the remaining 34 percent is irrigated lowland. Average yields of rainfed lowland and upland rice (3.25 tons

per hectare) tend to be lower than lowland irrigated rice (4.03 tons per hectare). A 77 percent majority

farms are small (<50 hectares), 16 percent are medium size (50- 200 hectarse) and 6 percent are large

(>200 hectares) (CONARROZ, 2013). Although the majority of farms are small, more than half of the rice

production area is managed by 54 large farm enterprises. It is estimated that 27 percent of the production

area is on soils types inappropriate for rice production (MAG, 2009)

Table X: Distribution of farm size and growing environment, hectares under rice production and average

yields.

Farms Hectares Yield (t/ha)

Large Farms 54 31,897 3.58

Medium Farms 126 12,687 3.70

Small Farms 595 11,124 3.12

Irrigated Lowland 190 19,019 4.03

Rainfed Lowland and Upland 585 36,689 3.25

Total 775 55,709 3.51

(CONARROZ, 2013)


Rice varieties

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Rice varieties have been developed by the national agriculture research institute, INTA, and private

companies, for the different agroclimatic zones of the country. The varieties have a growth cycles from

120 to 140 days (MAG, 1991). As of 2013, 26 different varieties were planted, however, the majority of

the area is shared by only five. Approximately half of the planted area was planted with the variety, Palmar

18, a commercial variety with wide disease resistance and high yield potential. Varieties have also been

developed for subsistence systems that can be planted manually in low fertility soils. Although improved

varieties are available, many farmers continue to plant older varieties with poor disease resistance

(Arriagada et al., 2010).

Seed quality

The majority of farms plant certified seed which is free of weeds and pathogens. However, due to the high

cost of certified seed, small farmers often save and replant seed that is contaminated with weeds and

pathogens resulting in greater use of herbicides and fungicides (Madriz, 2015).

Crop calendar

The crop calendar varies depending on the climatic region. In the Northern Pacific region, irrigated

lowland rice is planted twice a year, first in February-March and second in July. Lowland rainfed rice is

planted during the rainy season from mid-June to July. In the Central and South Pacific regions, the first

planting is April-May and the second from July to August. In the Atlantic Region the first plating is in May

and the second in October.

Land preparation

The standard land preparation practice in small to medium irrigated systems is to flood and till the soil

while wet (puddling). This practice breaks up the soil structure to reduce water infiltration. Pre-planting

tillage also serves to control weeds through incorporation into the soil. Some larger scale operations with

access to specialized machinery practice a form of reduced or zero-till farming. The national rice

production association (CONARROZ) is actively promoting zero-tillage rice production for soil conservation

(CONARROZ, 2014).

Planting

Rice is seeded mechanically in the dry season. In the rainy season, fields are often too wet to enter with

machinery and seed is broadcast either manually or with the use of planes. In some mechanized systems

minimal or zero-tillage is practiced and rice is directly seeded in rows. In small upland farms without access

to machinery, seed is planted into dry soil using a dibble (planting stick).

Water management

In lowland irrigated systems, fields are flooded before planting for land preparation. The water level is

then lowered for planting after which fields are flooded continuously. During the rainy season, only

supplementary irrigation is required. In the lowland rainfed and upland systems, production is dependent

on rainfall. Contour plowing is being promoted to increase water capture and retention as well as reduce

soil erosion (CONARROZ, 2012).

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Soil fertility management

In commercial systems, mineral fertilizer and agrochemical use is high. Mineral fertilizer applications

include nitrogen (N), phosphorus (P), potassium (K) and often sulfur (S) and zinc (ZN). Fertilizer rate is

determined based on the variety and yield potential following a blanket recommendation. Fertilizer

application range from 120 to150 kilograms per hectare N, 30 to 60 kilograms per hectare P, 40 to 80

kilograms per hectare K. Applications are usually divided into four split applications. Fertilizer is either

broadcast or incorporated with machinery in mechanized systems.

Weed management

Tillage is also used to control weeds in both irrigated and rainfed systems. Pre-emergent and post-

emergent herbicides are used routinely to control the remaining weeds. Herbicides commonly used

include 2,4-D propanil, pendimenthalin, butachlor and imazapic. In irrigated systems, weeds are partially

managed by flooding. More frequent herbicides applications are required in rainfed systems where water

cannot be used to control weeds. In small subsistence farms, weeds are controlled manually by machete.

Pest and diseases

Widespread problems with insects and diseases lead to frequent applications of insecticides and

fungicides (Arriagada, 2004). Pesticides are applied manually in small farms and with a tractor and sprayer

or airplane in large farms. Pesticide applications are often excessive with multiple applications to a single

crop to control different pests. Highly toxic and mobile products are often used in rice production.

Fungicide commonly used include dithiocarbamates and benzimidazoles and insecticides include

dimethoate triazofos, imidaclorpid, cipermetrina and other piretroides.

Harvesting

Rice is harvested manually in smaller farms, often using contracted labor. In medium and large fields, rice

is harvested mechanically often with rented machinery.

Milling and Quality

Milling is carried out by one of eleven rice companies are operating in Costa Rica. Rice is further dried in

ovens and then stored in silos until milling. Rice is milled mechanically to remove the husk and bran. Strict

quality standards limit the percentage of broken and discolored grains and husks allowed in different

classes of rice in Costa Rica markets.



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I. Agrochemicals. Rice needs clean irrigation water to grow (dependency). The impact of current

rice production practices on water quality is of great concern in Costa Rica. Water quality

monitoring programs have detected high concentrations of nitrates, phosphorus, and pesticides

in surface and ground waters (negative impact) surrounding rice production areas (Castillo, 2012).

The most important rice producing area of Costa Rica is the Arenal-Tempisque watershed. Water

from the agricultural zone flows into a RAMSAR wetland national park, Palo Verde, and eventually

to the coastal estuaries which account for 20 percent of the national fish production (Hazell et al.,

2001). Expansion of the irrigated area coupled with the intensification of agricultural inputs

(dependency) has converted the region into the country’s premier rice producer, contributing 45

percent of domestic production with yields up to seven tons per hectare (positive impact).

However, water contamination from current fertilization, pest control and land preparation

practices (cause) threaten biodiversity, the fishing industry and drinking water quality

(Consequence of negative impact) (Castillo, 2012).

Water contamination (negative impact) from fertilizer runoff (primary negative impact) is a major

concern in Costa Rica due to the high rates of mineral fertilizer applied (cause) to rice fields

(Daniels and Cumming, 2008). Rice is generally cultivated on land with little slope and medium to

high soil fertility. The main soil type under rice cultivation are vertisols with good inherent soil

fertility and water holding capacity if managed well (Arriagada, 2004). However, vertisols are

shrinking clays that form large cracks causing preferential flows of water, nutrients and

agrochemicals through the soil profile (additional cause) (Loaiciga and Robinson, 1995).

Water running off from the rice paddies in the irrigated production systems contain high

concentrations of P and N. Pérez-Castillo et al. (2013) monitored water quality of water running

off from rice fields using an index based on temperature, pH, oxygen saturation percentage,

electrical conductivity, biochemical oxygen demand, suspended solids, nitrate content and total

Ps content. They confirmed that quality of water leaving the rice fields was poor with levels of N

and P high enough to cause eutrophication (Consequence of primary negative impact/ secondary

negative impact) of the bordering natural wetlands.

Eutrophication from nutrient runoff alters the local wetland plant ecology, encouraging the

growth of monocultures of cattail (Typha dominguensis) (Consequence of secondary negative

impact/tertiary negative impact). Dense cattail stands in adjoining wetland have been found to

act as a buffer to absorb nutrients, especially P, thus reducing the nutrient load from entering into

connecting waterways (Positive impact resulting from tertiary negative impacts) (Varnell et al.,

2010). Conversion of non-protected wetland areas into rice fields (additional cause) would result

in the loss of this important buffer area and increase the amount of nutrients entering protected

areas and estuaries (negative impacts (Daniels and Cumming, 2008).

Intensive irrigated rice production practices which rely on external inputs (dependency) can have

a negative impact on fish populations in connecting waterbodies. A study of the environmental

externalities in the Arenal-Tempisque watershed estimated that water contamination (primary

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negative impact) from fertilizers and pesticides (cause) could reduce the value of fish catches by

10 to 50 percent (secondary negative impact) (Hazell et al., 2001). Fish populations have been

declining in Nicoya estuaries, however, there is insufficient research to determine how much of

the decreased catches can be attributed to water contamination, overfishing and climate.

Rice fields provide feed for migratory birds. Costa Rica is known as an avian biodiversity hotspot

with a cultural and economic value in terms of conservation and tourism. Rice fields can be an

important stop over area for migratory water birds (Acosta et al., 2010). However, rice farmers

tend to have a negative view of the birds visiting their fields since they feed on seedlings and

grain, causing damage to the crop (Hazell et al., 2001). Additionally, there are growing concerns

about the effect of the intensive use of pesticides and fertilizers on wetland ecology and bird

populations in the bordering protected areas.


The effect of land preparation

Tillage and puddling are commonly practiced in irrigated systems. Tillage has contrasting short term and

long-term effects on yields. Farmers use tillage as a form of weed control by uprooting and burying weeds.

In the short term weed control has a positive effect on yields, however, intensive tillage practices,

especially when combined with puddling, can increase soil erosion andlong term soil degradation

(CONARROZ, 2003; Rizo-Patrón V et al., 2013).

Minimum tillage and zero-tillage are soil-conserving management practices promoted by agricultural

extension services in Costa Rica. Field research in Costa Rica has shown that when residues and weeds are

well managed, yields can be increased or maintained while reducing production costs and soil erosion

(Alvarado, 1985; CONARROZ, 2014; Ortega and Alvarado, 2005). These management practices have been

studied in irrigated and rain-fed conditions in Costa Rica since the eighties, however, adoption rates are

constrained by access to specialized machinery and lack of extension. National agriculture extension

services plan to further extend the systems through the installation of demonstration plots throughout

the rice production regions (Madriz, 2015).

Land preparation for rice production increases sediment loads in drainage water (Daniels and Cumming,

2008; Hazell et al., 2001). Pérez-Castillo et al. (2013) reported high concentrations of suspended particles

in drainage water from rice fields. Puddling further increases the overall sediment load of outflow water.

Rizo-Patron (2003) found that peaks in total suspended particles in drainage coincided with moments of

puddling. Sedimentation causes degradation of the natural wetlands by decreasing connectivity of

lagoons and increasing phosphorus loading and disrupting wetland ecology (Hazell et al., 2001).


Application of nutrients in the form of mineral and organic fertilizers, including green manures, increases

rice productivity (Quirós and Ramírez, 2006; Molina and Rodríguez, 2012). The yield response of rice to

fertilization is a function of the variety, agroclimatic conditions and cropping system. In Costa Rica, rice

yields are increased by application N, P, K and often Zn containing fertilizers. Irrigated rice may also have

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a yield response to S fertilization. A nutrient omission study in Northern Pacific Costa Rica found that

irrigated rice with a yield potential of 3.9 tonnes per hectare has a yield response to N, P K and S of 2.3,

0.91, 0.65 and 1.1 tonnes per hectare respectively (Molina and Rodríguez, 2012). Expansion of the

irrigated area coupled with the intensification of agricultural inputs has converted the region into the

country’s premier rice producer, contributing 45 percent of domestic production with yields up to seven

tons per hectare (Arriagada, 2004).

Organic production systems rely on nutrients from organic sources such as manures, composts and green

manure crops. These forms of nutrients tend to be released more slowly into the plant soil systems thus

releasing losses due to leaching and runoff of soluble nutrients. A study comparing water quality of organic

vs. conventional rice systems in northern Costa Rica found that conventional systems increased algal

growth and the abundance of macroinvertebrate species adapted to high nutrient conditions (Rizo-Patrón

V et al., 2013). Nitrogen can also be introduced into the system through the production of green manure

crops. Green manure crops can be grown during the period between the dry and rainy season rice crop

to contribute N and organic matter to the system. In dry areas, green manures require irrigation water for

germination. A macuna green manure crop can increase yields by 20 percent while reducing mineral N

fertilizer requirements (Quirós and Ramírez, 2006).

Fertilizer use efficiency in rice production in Costa Rica is estimated at only 33 percent (MAG, 1991). Site-

specific nutrient management practices that improve the efficiency of fertilizer use and reduce losses from

the system could reduce the nutrient load of drainage water and contamination of the adjoining wetlands.

One strategy is better matching the N fertilizer requirements with crop demand. The IRRI leaf colour chart

can be used to determine site specific fertilizer requirements and currently is being promoted by the

National Rice Cooperation to manage N fertilizer applications in Costa Rica (CONARROZ, 2007). Data on

adoption of the chart does not exist, however.

Another strategy is to replace highly soluble fertilizers with less soluble, slow release sources such as

organic fertilizers, green manures and slow release mineral fertilizers. Studies in Costa Rica have also

shown that the use of slow release encapsulated urea has the potential to reduce total N application from

110kg to 66kg/ha without sacrificing production (Sanchez, 2011b).

The effect of plant protection practises

Under the conventional Costa Rican rice systems, yield losses due to lack of weed and pest control can be

as high as 75 percent. Conventional commercial rice farmers rely heavily on the herbicides, insecticides

and fungicides for rice production. On average farmers apply between 9.5 to 8.9 kilograms of active

ingredient per hectare per rice crop (Castillo, 2012). Farmers perceive the level of pesticide use as

necessary to maintain high yields and invest the same material cost in pesticides as fertilizers and seed

(Arriagada, 2004).

One of the most economically damaging pest problems in Central America is a mite-bacterial-fungal

complex. Panicle Rice Mite (Steneotarsonemus spinki) associated with the bacteria and fungi complex is

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estimated to cause a yield loss of 40 to 60 percent. Rain-fed systems can suffer greater losses of almost

75 percent, compared to almost 25 percent in irrigated systems.

Integrated pest management (IPM) methods that include planting density, semi resistant varieties and

pest monitoring are recommended by government extension programs. Biological control methods of the

Panicle Rice Mite using Hirsutella nodulosa, Bacillus thuringiensis, or predatory mites are being explored

by CONARROZ but are still not widely used by farmers (Sanchez, 2011a).

Red rice (Oryza sativa L) is one of the most economically damaging weeds in commercial white rice fields

in Latin America including Costa Rica (Castro, 1999). Red rice is difficult to control due to its physiological

similarity to the commercially cultivated white rice varieties and fields are often abandoned due to heavy

infestation. Agronomic practices used to control red rice are minimum tillage, rotation with leguminous

crops and puddling (Castro, 1999; Prendas et al., 2006).

Field results from Costa Rica comparing zero tillage to conventional tillage show that initially greater use

of herbicides may be required to control weeds without tillage (CONARROZ, 2014). However, other

reports showed that after several years of zero-tillage with residue retention on the soil surface,

populations of red rice were patchier and easier to eliminate (Ortega and Alvarado, 2005; Prendas et al.,

2006). In the long-term, weed populations and herbicide use can be reduced with a combination of zero-

tillage and residue retention.

Classically bred improved varieties with good pest resistance are available in Costa Rica. However, due to

the price of seed, many small-scale farmers continue to grow older varieties that are susceptible to

diseases and insects, thus increasing the amount of pesticide applications required to maintain yields

(Zorrilla et al., 2012). Substitution of older varieties with more resistant and efficient varieties could

reduce agrochemical use without sacrificing yields (Arriagada et al., 2010; Hazell et al., 2001).

The impact of pesticide use in rice production on fresh water quality in the Arenal-Temspique watershed

has been well documented. An early environmental assessment conducted in 1995 concluded that rice

cultivation practices had minimal impact on downstream water quality (Loaiciga and Robinson, 1995).

More recently Mena et al. (2014) studied pesticide residues and biomarkers in two native fish species in

the Palo Verde National Park. The pesticides originated from the surrounding rice and sugarcane farms.

Applications of fifteen different pesticides were documented and fish biomarker response to

organophosphate insecticides hexachloro benzene and triazole fungicides was detected. Pesticides are

often sprayed aerially using planes which increases risk for contamination of adjacent water bodies and

massive kills of fish and aquatic organisms (Castillo, 2012).

Many of the herbicides and insecticides used in rice production have high toxicity and mobility, increasing

the likelihood of contamination of connecting water bodies. Substitution of these pesticides with products

with a lower Pesticide Impact Rating Index (PIRI) would reduce the environmental impact (Pérez-Castillo

et al., 2013). Biological indicators have been used to determine the impact of rice production practices on

water quality and biodiversity. Rizo-Patrón V et al. (2013) compared the populations of aquatic

146

macroinvertebrates in the inflow and outflow water of organic and conventional rice farms. Both organic

and conventional production systems decreased water quality as indicated by the macroinvertebrate

community composition. Organic systems had a greater number of sensitive species in the outflow,

whereas conventional systems were dominated by more pollution tolerant species, indicating that organic

systems are not as damaging to aquatic biodiversity.

CONCLUSIONS

A trade-off exists between intensive rice production and water quality with implications for biodiversity

conservation and productivity of fisheries downstream. Improved tillage, fertilization and pest control

practices that reduce water contamination could reduce the extent of this tradeoff. However, apart from

comparisons of conventional versus organic systems, there is a lack of studies linking changes in

management practices with improvements in water quality. Using the available information, we identified

several practices that have the potential to reduce the extent of the trade-off between of rice production

and water quality:

For example, minimal/zero tillage can reduce both soil erosion and weed populations while

maintaining or increasing yields (CONARROZ, 2003; Ortega and Alvarado, 2005; Prendas et al.,

2006).

SSNM practices have the potential to increase fertilizer use efficiency while maintaining yields and

improving profitability. Reducing highly soluble fertilizer applications, combined with SSNM, can

decrease fertilizers lost through runoff and improve water quality while maintaining yields.

Using IPM and replacing highly toxic pesticides with biocontrol, organic pesticides or low impact

pesticides, could maintain yields while reducing the impact of water quality.

Maintaining wetland buffer areas between areas of intensive cultivation to reduce nutrient

loading of areas protected for biodiversity conservation.

147

148


I. Hydroelectric projects (cause) have driven the conversion of land to rice production in the north.

The Arenal-Tempisque Irrigation Project in the Guanacaste province has caused a rapid expansion

of agriculture into the bordering zone of the Palo Verde national park (negative impact)

(Arriagada, 2004). The project was constructed with the principle objective of energy generation

and supplies one third of the country’s electricity (positive benefit). As a benefit, the quantity of

water available for irrigation of rice field in the region has increased (positive benefit). The

introduction of irrigation increased average yields from 2.6 to 5.6 tons per hectare (positive

benefit), contributing to improving national food self-sufficiency (consequence of positive

benefit). The Guanacaste province now produces nearly half of the country’s own rice production

(CONARROZ, 2013).

Rice production uses approximately 80 percent of the water available for crop production in

Guanacaste. Fields require full irrigation in the winter season and supplementary irrigation in the

rainy season. A study done by Golcher (2013) calculated the water foot print of irrigated and

upland rice in Costa Rica. Continuously flooded irrigated rice uses 1532 cubic meters of irrigation

water and 488 cubic meters of rainwater per ton of rice produced compared to upland rice, which

uses 2704 cubic meters of rainwater per ton of rice. Irrigation represents only two percent of the

total production costs there is little incentive to improve water use efficiency (Codero, 2002). The

amount of water available for irrigation is variable, depending on rainfall and the needs for

hydroelectric power generation (Hazell et al., 2001) and there are concerns over the unequal

distribution of water resources in years with water shortages.

II. Currently 66 percent of the area of rice cultivation remains under rainfed conditions

(dependency). The main factor controlling rice productivity in the rainfed areas is increasingly

unpredictable rainfall (cause). The expansion of irrigation projects in the central and southern

regions is expected to increase the conversion of land to commercial irrigated rice production

(Madriz, 2015). Increased access to irrigation will allow rice to be cropped twice a year, reducing

vulnerability to drought (negative impact) and increasing national food production.



A diversity of practices is used in the irrigated systems: puddled or dry tilled and continuously flooded or

intermittent flooded. As discussed previously, tillage can have contrasting short and long-term effects on

productivity. Without continuous flooding weed growth tends to be greater which can reduce yields or

increase the use of herbicides. In the puddled systems, farmers use more water for land preparation;

however, the infiltration rates are reduced thus increasing water retention compared to flooded

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unpuddled fields, reducing overall water use from 15 000 to 8 000 cubic meters per hectare (Codero,

2002). Water demands can be reduced in intermittently flooded systems, especially in combination with

zero-tillage and residue retention (CONARROZ, 2003). Intermittent flooding refers to fields that have at

least one aeration period of more than 3 days during the cropping season (IPCC, 1996). Contour plowing

can also improve rainwater capture in upland systems and retention and reduce irrigation requirements

(CONARROZ, 2012).

The System of Rice Intensification (SRI) combines alternate wetting and drying, early transplanting and

organic fertilization. SRI has been tested by local research institutions but has not been widely adopted

by Costa Rican farmers (IICA, 2014). Preliminary results show that with SRI, yields were 5.5 tons per

hectare compared to 3.1 in the conventional continuously flooded system. Substantial water savings were

made using the alternate wetting and drying system. In the SRI system irrigation was applied every 15

days compared to every three days in the conventional continuously flooded system.

CONCLUSIONS

Continuously flooded systems improve yields compared to rainfed systems, yet current irrigation practices

are inefficient in the use of water. Intermittent flooding can be used to improve WUE, however, increased

weed growth can reduce yields or increase herbicide use. Zero-tillage systems with residue retention in

combination with intermittent irrigation can further improve soil moisture retention and WUE without

sacrificing yield. SRI has the potential to increase yields while reducing water consumption. The adoption

of SRI may be constrained by lack of manual labor and machinery for transplanting seedlings. Further

research should be conducted to adapt the SRI to Costa Rican condition.


I. In Costa Rican rice production systems, straw is either burned (cause), incorporated (cause) or

baled and removed for animal feed (cause).

a. Residue burning is discouraged by agricultural extension authorities.

b. Rice bran, husks and straw provide an important source of fodder for cattle, swine and poultry

(dependency and positive benefit).

c. However, straw when retained or incorporated is also an important source of nutrients and

organic matter (dependency and positive benefit).

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d. Complete removal or burning of residues (cause) could contribute to the long-term degradation

of soil fertility (negative impact), with negative impacts on crop productivity (consequence of

negative impact), however this has not been investigated in Costa Rica.

e. Rice husks can also be used to generate electricity (positive impact). A national study on the

use of agricultural residues for energy generation estimated that 38,249 tons of rice husk were

available nationally for generation of 590 TJ of energy (Coto, 2013). Husks are already being used

for energy production in large rice farms such as Tio Pelon, that uses rice husks to generate

electricity for rice milling (Augero, 2009).


There is a lack of national data on the long-term effects of residue management on soil fertility and

productivity of rice production system. Studies from other parts of the world have shown that the

retention and incorporation of residues can improve soil chemical, physical and biological properties and

have a positive effect on crop productivity (Turmel et al., 2014). In upland systems with variable rainfall,

residue retention can improve soil moisture retention and crop production. However, in continuously

flooded and cropped conditions, where rates of decomposition are slow, and annual biomass is high, soil

organic carbon can be maintained or increased, even with removal of residues (Pampolino et al. 2008)

The benefits of residue retention depend on the agroclimate,cropping system and management (Turmel

et al., 2014) however, in Costa Rica , retention of residues either on the surface or incorporated is more

favourable for long-term productivity than burning or complete removal (MADRIZ 2015).

CONCLUSIONS

Potential trade-offs exist around the use of rice residues. Residues can be used as livestock feed and

energy production, however, long-term residue removal could cause a decline in soil fertility and rice

productivity. Partially maintaining sufficient residues to maintain soil fertility while contributing to other

production activities could resolve this trade-off. However, there is a lack of national data on long-term

effects of residue management on soil fertility under Costa Rican conditions.

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2.4.2.4 Increase in rice yields versus GHG emissions reductions


mitigation. Implied impacts, dependencies and causes in Costa Rica are discussed as follows:

I. Costa Rica has the goal to become a carbon neutral country by the year 2021. The agricultural

sector accounts for 37% of the total GHG emissions, rice accounting for 5% of total emissions (CO2

equivalent) (negative impact) (World Bank et al., 2014). Although flooded rice (cause) is a

contributor to the emissions from agriculture, the main sources of emissions are livestock,

pastures and deforestation (Villalobos, 2010). Costa Rica's new GHG inventory which was part of

the Third National Communication to the UNFCCC estimate methane emissions from irrigated rice

are estimated at 4.94 kilograms per hectare with total annual emissions of 11.13 Gigagrams

(MINAE, 2014) (negative impact). Nitrous oxide emissions from grain production systems

including rice were estimated at 0,066 Gigagrams per year (negative impact) (MINAE, 2014).

II. The government plans to expand the area of irrigated rice production (additional cause) in the

coming years (Madriz, 2015) which could increase methane emissions (negative impact) unless

accompanied by a change in management practices.

III. There is a lack of national data on the influence of specific rice production practices (cause) on

climate change mitigation. The current proposal put forth in the National Climate Change Action

Strategy Plan is to promote the complete removal of residues (cause) and direct seeding (cause)

instead of incorporating residue with puddling (cause). This change in management is projected

to reduce emissions by 30% by 2021 (positive impact) (MINEAT, 2012). Several other practices

promoted in Costa Rica such as zero-tillage with residue retention, intermittent flooding and

SSNM (cause) that have the potential to mitigate climate change (positive impact) through

improved carbon sequestration, and reduction in machinery use (IPCC, 1996; Lal and Kimble,

1997). These practices have been demonstrated to also have positive or neutral effects (positive

and negative impacts) on rice yields in Costa Rica.

IV. The use of rice husks as an energy source (cause) is growing in Costa Rica (Barahona and Núñez,

2009). The largest rice farm in Costa Rica, Tio Pelon, was the first certified carbon neutral

agroindustrial company in the country (MAG, 2011). Carbon neutrality was achieved, in part,

through generation of energy from rice husks. The use of rice husks as an alternative energy

source for the cement industry was also implemented in Costa Rica as part of a Clean

Development Mechanism Project (CDM, 2006).


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Irrigation increases rice productivity compared to lowland rainfed systems (CONARROZ, 2013). In

Northern Costa Rica yields have increased by up to three tons per hectare with irrigation (Arriagada,

2004). However, continuous flooding increases anaerobic decomposition of organic matter resulting in

CH4 emissions (IPCC, 1996). Irrigated rice is estimated to produce almost five kilograms of methane per

hectare. Upland rice, which is not flooded, does not produce significant amounts of CH4. Intermittent

flooding can decrease CH4 emissions by aerating the soil to prevent highly reducing soil conditions (IPCC,

1996). However, nitrous oxide emissions are increased in intermittently flooded systems due to the

change from anaerobic and aerobic conditions (Kim et al., 2014; Zou et al., 2005). However, studies have

shown that the global warming potential of intermittently flooded rice is less than continuously flooded

rice (Kim et al., 2014; Zou et al., 2005). There is also greater yield per GWP unit considering there is no

yield reduction in intermittently flooded conditions.

The effect of residue management practices

Retention of residue can potentially increase productivity by improving soil quality in the long term.

However, residue retention combined with continuous flooding can further increase total methane

emissions (IPCC, 1996). Although there are no specific data on the interactive effects of residue

management and flooding on however the National Climate Change Action Strategy Plan estimates that

CH4 emissions could be reduced by 30% if farmers remove residue rather than incorporate them before

flooding (MINEAT, 2012)


Fertilization nitrogen increases rice productivity, however increased N inputs also results in increase

nitrous oxide omission. There is a lack of data on the effect of fertilizer management on nitrous oxide

emission and climate change mitigation in rice systems in Costa Rica (MINEAT, 2012).

CONCLUSIONS

The rice residue fertilizer and water management practices results in trade-offs and synergies between

rice production and climate change mitigation. Residue retention is more favorable than removal or

burning in terms of soil carbon sequestration. However, under continuously flooded conditions, increased

organic matter inputs can also increase CH4 emissions. Intermittent wetting and drying can reduce

methane emissions, however, application of high rates of N fertilizer combined with alternate wetting and

drying can potentially increase N2O emissions. Improved irrigation and fertilizer management can partially

reduce emissions. Practices such as zero-tillage with residue retention and intermittently irrigated aerobic

soil conditions could lead to a synergy between services by sequestering carbon, improving soil quality,

water conservation and increasing or maintaining rice production in the long-term. In continuously

irrigated systems, partial removal of residues for energy production can replacinge other non-renewable

fuel use. However, there is not much data from Costa Rica about the effect of management practices on

emission or carbon sequestration in rice systems.

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COSTA RICA Universidad Nacional, Costa Rica.

Rizo-Patrón V, F., Kumar, A., McCoy Colton, M. B., Springer, M., and Trama, F. A. (2013).

Macroinvertebrate communities as bioindicators of water quality in conventional and organic irrigated

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Sanchez, M. (2011b). Efecto de los fertilizantes con nitrogeno de liberacion controlada sobre el

rendimiento del cultivo del arroz, Region Huetar Norte de Costa Rica CONARROZ, Costa Rica.

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del Programa Nacional de Neutralidad de Carbono Programa Estado de la Nación, Costa Rica.

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2.5. CALIFORNIA


2.5.1 BACKGROUND INFORMATION ON RICE AGRICULTURE IN CALIFORNIA

California is the second largest producer of rice in the United States (California Rice Commission 2006a)

with two million tons produced annually as of 2006. The crop has a long history in the state with cultivation

in California starting during the 1840’s at the time of the California Gold Rush. Rice was introduced

primarily for the consumption of the many (about 40,000) Chinese laborers who were brought as

immigrants to the state in support of the economic boom associated with the Gold Rush, although only a

small area was cultivated to meet this requirement. The relationship between the California Gold Rush

and rice remains relevant today as one of the important concerns regarding rice cultivation and water

quality originate from soil contamination with mercury from gold mining, and the impacts of flooded rice

fields on methyl mercury production.

Commercial production began in earnest only in 1912, and was centered around Butte County located

approximately 100 km to the North of the state capital Sacramento. The broad varietal classification of

rice grown includes Long Grain Rice, Medium Grain Rice and Short Grain Rice. Today, California grows

most of the medium grain rice of the United States, and is also is a primary producer of most of the short-

grain rice favored for sushi. Production in the state is dominated by short and medium grain japonica

varieties, including cultivars developed for the local climate such as Calrose, which makes up as much as

85 percent of the state's crop (California Rice Commission 2006b). The state exports nearly half of its crop

outside of the US. It is estimated that rice cultivation employs approximately 25,000. Much of the export

rice is of premium quality specifically meeting exacting demands of Japanese and South Korean clientele

whom pay premium for a quality, GMO free product, grown with environmental considerations.

Box 1: Summary facts regarding California rice are provided by the California Rice Commission (California Rice Commission 2004):

97 percent of the state’s crop is grown in the Central Valley occupying approximately 222,000 hectares.

Production nears 2270 metric tons per year.

California supplies the entirety of American sushi rice.

Rice is one of the state’s largest crops contributing more than five billion dollars per year and supports 25,000 jobs on the production side.

California rice fields provide migratory and over-wintering habitat for nearly 230 wildlife species, including shorebird habitat, and habitat for endemic and endangered wildlife.

Rice fields are estimated to provide nearly 60% of the food needs of more than seven to 10 million wild duck and geese migrating along the Pacific flyway each winter.

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Figure 1: Hectares of cultivated rice in California. Source: USDA.

Over the past two decades, the area under rice cultivation in California has gradually grown from or from

186,155 to 227,838 hectares (figure 1). During the same time period, the yield has stabilized at 9520

kilograms per hectare (1 lb/acre = 1.12 kg/ha, Figure xx).

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Figure 2: Rice yields in California from 1910 until 2010. Rice yields have stabilized in recent history. Current mean yields of California rice are 9520 kg per hectare (8,500 pound per acre) making California the most productive rice growing region in the world. The current values range between 8000 to 10 000 kilogram per hectare. Source: California Rice Environmental Sustainability Report (Summers Consulting LLC 2012)

California is a particularly well-suited region for analyzing the relationship between crop cultivation and

the economics of ecosystems and biodiversity. This is in large part due to the location of rice cultivating

regions of California, centered in the northern half of California’s Central Valley (figure 2). This region is

known as the Pacific flyway (figure in habitat section) and provides critical overwintering and migratory

habitat for more than 230 species, and 10 million migratory waterfowl migrating between the Arctic and

Mexico.

At a smaller scale, the dependency of flooded rice cultivation on low permeability heavy clay soils maps

rice cultivation areas on former natural wetlands that are largely unsuitable for other cropping systems.

The ecosystem similarities between natural wetlands and flooded rice present specific opportunities to

manage the crop for wildlife, though specific measures to do so must be taken into account as are

discussed in this report.

The crop has a long history of engaging with conservation, even if initially this relationship was primarily

a source of conflict between the two domains. Today however, the California Rice Commission

prominently displays the tagline “Rice: the environmental crop” (http://calrice.org), and social media sites

affiliated with the crop display an equal number of photos and references to the waterfowl that grace rice

fields as they do to management practices and farmer families. The transition from a crop in full conflict

with conservation is of multiple twists and turns, with some questions regarding whether the crop has

become environmental by intention, or as a consequence of unrelated events and occurrences.

Two major developments in rice’s environmental history are particularly important. When rice was first

established in the California, the maturation of rice coincided with the arrival migratory waterfowl which

fed on the mature grain. The transition to fast growing varieties shifted the rice harvest so that it preceded

the arrival of migratory waterfowl. A second critical event in California rice’s environmental history was

driven urban expansion around the city of Sacramento. The growing urban population placed increasing

pressure to eliminate rice straw burning to improve air quality. Legislation prohibiting burning in 1991

http://calrice.org/

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forced the exploration of alternative management practices to remove rice straw. Winter flooding rapidly

became the dominant practice for residue management with the ban (figure 3, in raw material section).

Winter flooding effectively increased the availability of over-wintering habitat for migratory waterfowl,

with important conservation, and agroecological implications.

In light of the importance of these secondary drivers (short duration variety, and burning ban), critical

questions can be asked regarding the impact of the California’s enduring drought on the extent of rice

areas cultivated, and its impact on the ecosystem services provided by rice cultivation systems. While rice

farmers focus primarily on crop cultivation, conservation is deeply engrained in the crop’s branding.

Recent initiatives are being developed to provide California rice farmers with specific payments for habitat

services they provide, either through hunting rights, or through innovative leasing of farmer’s land and

water timed to coincide with the biannual migration of migratory waterfowl along the Pacific flyway

(Robbins 2014).

Figure 3: The extent and yield averages of rice production in the United States. California, Louisiana, Mississippi, and Texas the dominant rice production regions of the US. Source: USDA National Statistics Service, 2013.

While this report covers California rice in particular, the specific case of rice cultivation in the Vic Fazio

wildlife refuge, or the Yolo Basin (Figure 4below) demonstrates the potential of the crop to bring together

stakeholders from conservation, agriculture, and municipal councils together in the same room. The

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consequences of this interaction to work through trade-offs, and focus on synergies, yields important

lessons on the economics of ecosystem and biodiversity in food production landscapes. The Yolo Basin,

located between the cities of Davis and Sacramento, is jointly managed for flood protection, rice

cultivation, hunting, wildlife conservation and viewing, and environmental education. Per hectare values

provided of the services provided by the lands in this basin in terms of water quality, flood control, ground

water recharge, and avoided residual risk range between 40 to 900 US dollars (Eisenstein and Mozingo

2013). In addition, payments for habitat services, have been valued at 45 to 90 US dollars per hectare

through payments for bird friendly agricultural practices (Robbins 2014).

Figure 4: The location of the Yolo Bypass, a co-managed landscape of the Sacramento region whose primary function is providing flood protection for the City of Sacramento, but which is also managed for rice cultivation, and wildlife habitat. Source: USGS 2014.

2.5.2 RICE GROWING ENVIRONMENTS IN CALIFORNIA

California rice is dominated by a single production system: lowland rice grown in flooded conditions.

Nearly all rice is of improved japonica varieties bred to increase grain to foliar plant material ratios, and

to reduce maturation time. California rice is grown in flooded fields on heavy clay soils that have been

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precision leveled with lasers and/or GPS. Mean water levels are managed to maintain approximately 12

centimeters of water on the field. The water invariably originates either from the Sacramento River and

its tributaries, or from pumped groundwater. Much of the water is recycled and re-enters the Sacramento

River, and delta. The water level of rice fields are increasingly managed and varied during the non-

production season to support habitat services. This has impacts on several of the ecosystem services

included in this report, including water quality, greenhouse gas emissions, and particularly the quality of

habitat for different species of waterfowl and shore birds.

2.5.3 PREDOMINANT FARMING SYSTEMS IN CALIFORNIA

California rice production is predominantly large scale and uses mechanized production technologies

including laser leveling, and seeding by airplane for example. The location of rice production systems are

environmentally determined and located in regions with access to water for flood irrigation, and with

heavy, impermeable clay soils. This dependence on impermeable soils and access to water limits the

suitability of rice fields for the cultivation of other crops which has implications on weed management,

and the analysis of trade-offs. The majority of rice cultivation is located within 100 miles of the state

capitel, Sacramento.

2.5.4 AGRICULTURAL PRACTICES

Rice Varieties: Production in the state is dominated by short and medium grain japonica varieties,

including cultivars developed for the local climate such as Calrose, which makes up as much as 85 percent

of the state's crop (California Rice Commission 2006b). The state exports nearly half of its crop outside of

the US most of which is premium quality specifically meeting quality demands of Japanese and South

Korean buyers which a strong focus on quality. As a side note, the change in the early 1900’s to a rapid

growing variety of rice was an important factor in reducing the negative impact of waterfowl crop loss.

Cropping calendar: Rice farmers normally plant a single crop per year in the Central Valley with a 190-day

cultivation cycle. Field preparation begins in March and the rice is sown in April with a first fertilizer

application. A second fertilizer application is often applied in July. Harvest is in September/October and

takes approximately a month. Fields are drained prior to harvest. Post-harvest, rice straw can be rolled,

or harvested as a raw material. Fields are frequently flooded in the winter to facilitate rice straw

decomposition.

Land Preparation: Field preparation begins in March, the temperate spring. Land preparation typically

includes three to five tillage events with a chisel plow and disc, followed by several passes with a triplane

and roller to create a uniform and level seedbed. Fields are commonly laser leveled or leveled by precision

GPS which is identified as important to improving water use efficiency. Fertilizer is added at this stage as

furrows are rolled into the ground. Fields are typically ready for sowing in April as water is run into the

fields to a depth of 12 centimeters. Water depth is controlled as a means of managing weeds, and light

levels. Stale seedbed systems can be included in land preparation as a means of controlling weeds. These

are typically used in combination with reduced or no-till practices. In stale seedbed systems fields are

irrigated after land preparation in order to encourage weed germination. The weeds are then treated with

a non-selective herbicide to eliminate them prior to wet seeding with rice.

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Crop Establishment: Two seeding systems are common in California, a dry seeding system where seeds

are applied by tractor and drilled-seeded into the prepared field, or more commonly, water seeded, which

involves seeding fields aerially via airplane. For the latter, rice seeds are soaked off-site, and seeded from

the air with a pilot car at each end of the field guiding the rows as they are applied. Growth from seed to

maturity requires four to five months. For drill seeded rice, aerobic conditions are maintained prior to

permanent flooding which can help suppress the aquatic weeds that dominate rice systems.

Soil fertility management: Fertilizers are added during the land preparation phase by ground rig. A second

fertilizer application is common in July after the plants are well established. Studies found in our review

suggest nitrogen application levels on the order of 120 to 180 kilograms per hectare.

Water Management: Water is run into the fields in April, and levels are either maintained at a 12

centimeter depth until just before the harvest, or can be drained in mid-summer (June to July) as a means

of weed control followed by a second flooded phase in August. Fields are dried before the harvest to allow

machinery to operate in the field. Fields are frequently re-flooded in the winter as a primary means of

residue management. Holding water in the field is often used as a management technique to reduce the

impact of pesticide residues on water quality. Water is often re-used in California rice by transfer between

fields, or returning of irrigation water into native waterways (rivers and wetlands). Water management is

central to the majority of issues covered in this report, with very strong interaction with residue

management.

Pest and Diseases: Pest and disease management, to which we include weed management, are an

important part of cultivation practices. Weed management is particularly pervasive because rice is

continuously grown on the same fields with little opportunity for rotations due to heavy clay soils upon

which the crop is grown. This has led to the development of herbicide resistant weeds which are more

prevalent among California rice than in any other crop or region in the US (Heap 2011). Weed

management strategies are focused on achieving early weed control after seeding. Typically one to two

applications of herbicides are applied to control weeds. Insecticides are also used as needed, particularly

to control the rice water weevil (Lissorhoptrus oryzophilus) and other insect pests. Residue management

discussed below has important implications on pest and disease management options and provides

important trade-offs. Stale seedbed systems, where fields are flooded to encourage weed germination

prior to crop establishment are also used as a weed control mechanism.

Harvesting: The rice reaches a height of 0.9 meters at maturity in September (190 days after planting). At

this point fields are dried. Mechanized harvesters are used to harvest the grain from the field. The choice

of harvester head has impacts the quantity of rice grain spilled onto the field which some studies suggest

has an impact on the habitat value of rice fields.

Residue Management: Following the rice harvest, three principle management systems are possible with

important impacts on the ecosystem services of rice production. The rice straw can be burned, though

this practice has largely been banned in California except to manage pest outbreaks. Second, the rice

straw can be harvested and baled to be sold as feed, erosion control material, construction material or as

the primary material for energy production (biomass burning or biogas). Third, and most common

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practice, rice straw fields are flooded providing habitat to waterfowl which facilitate the decomposition

of rice straw. It is at this stage the ecosystem services to and from agriculture are potentially the most

antagonistic.

2.5.2 SYNERGIES OR TRADE-OFFS


Predominant issues identified with water quality and rice production systems in California center around

three principle issues: I. the impact of agrochemicals, II. the impact of mercury contamination and III. the

impact of increased sediment run-off due to residue incorporation, flooding and drainage on water

quality:

I. Because rice is grown in flooded environments, with water that is recycled into wetland, riverine,

or municipal systems, water quality is of critical importance (Crepeau and Kuivila 2000). More

than 97 percent of California rice is grown in nine contiguous counties just north of Sacramento.

The dammed headwaters of the Sacramento River form Lake Shasta, which is the source of the

majority of water to irrigate crops in the Sacramento Valley (dependency). The water is recycled

and reused several times during the irrigation season, spring to summer. Irrigation water can be

an important source of contaminants (cause) because it is typically returned the Sacramento

River, a drinking water (impact) source for downstream communities.

During the past 30 years, the rice industry states that it has successfully managed water quality

programs (cause) to mitigate concerns for the cities that use river water. Riceland farmers purport

to have successfully reduced pesticide (cause) loading in the river by more than 99 percent.

Several of these changes involved a shift to wet seeded systems (rice seedlings transplanted into

flooded fields), and the use of shorter-statured rice to survive in shallow water that is held on the

field. The California Rice Commission reports that “the use of EPA-designated ‘Reduced Risk’

formulations in California rice constitutes 25 percent of total pesticide applications today,

representing an 87 percent increase since the year 2000” (LLC 2010). This indicates a shift in the

types of pesticides used, though no reference is made on the total amount used.

A second important change in management was the California Regional Water Quality Control

Board (CRWQCB) mandating the holding of irrigation-return water in rice fields to increase the

time needed for pesticide degradation and dissipation before the water is released to the

Sacramento River (cause). These changes have had both positive and negative impacts on rice

based ecosystem services. Maintaining water in fields is one way to reduce the contamination of

adjacent systems and waterways and thereby providing increased habitat (positive impact), but

can lead to in-field concentrations of pesticides thereby provoking increased bioaccumulation

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potential for wildlife using rice fields (negative impact). New types of irrigation systems, referred

to above, that reduce or eliminate drainage by recycling rice-irrigation water within farm fields

may help solve many of these problems.

II. Less discussed in the grey literature, but common in the research literature is the issue of mercury

contamination of rice lands (cause) in the California context. Mercury is a residual problem the

gold mining era. The seasonal wetting and drying, and high biological productivity of rice based

wetlands enhances the conversion of inorganic mercury (Hg(II)) to methylmercury (MeHg), the

more toxic, organic form that biomagnifies through food webs (Windham-Myers et al. 2014). This

is particularly an issue when irrigation water from rice is returned to natural systems where the

contaminants can bioaccumulate in fish and wildlife (negative impact). Water management of rice

lands (secondary cause) can lead to sediment and aqueous methylmercury concentrations that

are up to 95 times higher than in adjacent wetlands (Windham-Myers et al. 2014).

Summer flooding (secondary cause) promotes microbial methylmercury production in surface

sediment of rice fields and wetlands, extended water residence time into the winter preferentially

enhances methylmercury degradation and storage (Windham-Myers et al. 2014). The trade-off

with summer flooding is with food production.

In contrast, the trade-off with winter flooding is improved water quality (positive impact), and

climate change mitigation (negative impact). Managing the residence time of water on the fields

before their return into natural waterways provides sufficient time for degradation but also

increase methane emissions. This is compatible with California legislation for managing water

residence time to encourage pesticide and herbicide degradation. A second trade-off is that

retaining methylmercury on fields can increase exposure to resident organisms on site (negative

impact); a concern if winter flooding is used for wildlife habitat.

Limiting carbon inputs into surface sediment in the post-harvest period reduces the creation of

methymercury (Marvin-DiPasquale et al. 2014) and also reduces the organic pollutants that are

of concern to water quality. Removing rice straw is a management option to reduce the effects of

methymercury on water quality. Trade-offs identified include increased management costs which

can be partially offset with the sale of the raw material, and decreased organic matter

incorporation into surface soils which can be offset with chemical fertilizers.

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III. Because rice fields are flooded, and drained (cause) during harvesting, the flow of water from

fields, and the sediments/contaminants it contains moving into drainage tailing have important

impacts on water quality (impact). Seasonal patterns are important here and summer

contamination levels from irrigation would require significant changes in cropping or irrigation

patterns (Oh et al. 2013). Rice field outflow can contain high concentrations of dissolved organic

carbon, an important pollutant of agricultural landscapes, along with total dissolved solids. High

concentrations of both of these impact drinking water quality (negative impact) and aquatic

ecosystem processes (negative impact) (Krupa et al. 2012). These contaminants have arisen as

important concerns related to water quality of field drains (Ruark et al. 2010). The combination

of seasonal flow patterns with soil/water management can be important drivers of these

contaminant levels.

The trade-off with residue management and food production is mediated by the retention of

residue on site (cause), or the removal of that residue off site (cause) and burning (cause). The

legislation banning rice straw burning to mitigate its impacts on air quality may have led to an

important win-win in the Sacramento region but also necessitated alternative forms of rice straw

management. Incorporating this material into soils as a source of organic carbon has become one

of the principle management options but provides two to three times the levels of dissolved

organic carbon as contrasted to burning. However as there are no established water quality

measures of dissolved organic carbon levels for California at the moment, thus no management

strategies to control these levels have been recommended (UCCE, 2012). The rolling, laying, tilling,

and flooding (or lack thereof) of rice straw thus become the treatments that are explored in the

primary research, with effects on soil nutrient loads as the primary output variables.


The effect of plant protection practices

Weeds are considered to be one of the most important pest problems in California rice. In both

conventional and organic fields, weeds are the major biotic constraint to rice production (Lundy et al.

2010) although no quantitative impact of weeds on yields are provided. California arrowhead is currently

the dominant weed of rice systems, though its impact on yield is minor at densities at, or below 200

individuals per hectare (Gibson et al. 2001). The other common weeds of California include barnyard grass,

watergrass, sprangletop, smallflower or umbrella sedge, ricefield bulrush, Gregg’s arrowhead, redstem,

ducksalad, common water plantain, and waterhyssop (UCCE, 2012). Quite often the impact of weeds as a

disservice is mentioned; however, this disservice is frequently aggravated by over application of fertilizer

in rice fields. Different species respond to different fertilizers, and fertilizer levels. Algae and

cyanobacteria can present problems during rice field establishment and can lead to yield reductions. Algae

and cyanobacteria are more responsive to P management than other weeds which respond to N

availability. The principle means of managing weeds are stale seed bed systems which have additional

management costs and require an available source of water, but which have no noted impact on yields.

Herbicide applications likewise have additional management cost implications per application, but no

noted effects on yield.

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Weeds are cited as the most important biological constraint on yield. Managing weed populations below

damage levels is an import element of rice production in the Central Valley which consists of quality seed,

soil preparation, and herbicide applications. Herbicides release rice from competition with weeds, thus

increasing yields, but can have a negative impact on water quality. In California, legislation as been the

primary tool to restrict the use of pesticides and is heavily regulated as the delta region of the state

provides water for more than 22 million inhabitants (UCCE, 2012). Of major concern with herbicide use is

the increase development of herbicide resistance which increases the negative effect of weeds on yield.

Combined management of field water and herbicide applications is used to keep weed populations at

manageable levels (no impact on yield), and reduce negative impacts on water quality. The primary

herbicide management practice utilized in rice fields for mitigating the effects on water quality are strict

water holding standards that require retention of water in fields for between five to thirty days following

herbicide application and before field water can be returned to natural systems (UCCE, 2012). This

practice has no cited impact on yield, but must be timed so that fields can be drained before harvest.

The California Rice Pesticides program, a state driven, but commodity managed water quality program,

focuses specifically on a single herbicide thiobencarb, known by the common trade names of Abolish and

Bolero. Monitoring of thiobencarb in two rice drains in California show an increase in concentrations up

to 15 micrograms per liter in 1996, dropping to less than three micrograms per liter in 2010 following

regulation regarding water holding on rice fields following chemical applications (Crepeau and Kuivila

2000). The major approach to manage herbicides and pesticides in in California has been through

legislative action regulating which chemicals can be used, and retention times on site.

Crop establishment practices can effectively reduce weed density while maintaining yields (UCCE, 2012).

In organic systems, wet-seeded establishment exhibits yields that are 1000 kilograms per hectare higher

than in alternate establishment systems while also mitigating the impact of chemical inputs on water

quality (not measured). These yields are nearly half of those of conventional system however. When

fertilizer is applied, yield differences in with conventional, stale, and no-till stale seed establishment

systems are lost suggesting that yield can be maintained with the improved weed management systems

of stale systems, and indirectly, water quality levels improved through the reduced dependence on

herbicides (Pittelkow et al. 2012).

Organic agriculture offers an alternative, but remains a challenging practice for managing weeds and pests

in rice because of reduced yields that are half of conventional systems, and two to three times higher

management costs. This is a particular challenge for rice because of its aquatic habit which makes

intercropping, and crop rotations unsuitable as a means of pest and disease management. The Lundberg

Family Farm in Richvale is one of the larger producers of organic rice in California with 2023 hectares of

farmland and 4900 hectares they contract. The authors of this case study found no published references

to specific management practices they use in the scientific or grey literature however.

Some studies have considered the community ecology of organic fields (Hesler et al. 1992, 1993). Organic

fields have greater abundances for three predatory taxa when compared to the conventional fields. No

mention of the degree to which these taxa provided pest control services is mentioned. The principle

alternatives to plant protection and water quality are directly tied to managing water quantity (time and

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amount) as will be discussed in the next section. Careful management of the timing and amounts of water

applied to fields are the principle a means of controlling pests in the absence of chemical pesticides in

organic productions systems. Organic management positively impacts water quality by eliminating

chemical pesticide inputs into cultivation systems. This reduction of such inputs improves water quality,

but often comes with significant yield reductions that can be up to half of conventional yields (Pittelkow

et al. 2012).

Hesler et al. (1993) compared eight paired plots of organic and conventional rice in the Central Valley.

Seven of the major pests considered showed no differences between the treatments with high degrees

of similarity between the pest communities of both systems (Hesler et al. 1993). However some of the

organic fields exhibited high infestation rates exceeding five percent by the insect pest Hydrellia griseola

requiring preventative action.

The effect of water management (flood timing)

Winter flooding field in the winter versus drying is an important contributor to water quality. Retaining

water on site during the winter is a principle practice for allowing increased time for pesticide and

methylmercury degradation. It can also decrease the flow of sediments into natural water systems. This

management can improve water quality, habitat for wildlife, and residue decomposition, but has

important trade-offs with methane production discussed in the climate section. There are no noted

impacts of winter flooding, or water retention on fields in food production. Whether rice straw is burned

or incorporated into the soil before winter flooding can impact total organic carbon, and dissolved organic

carbon in fields with three to four times more dissolved organic carbon in fields where rice straw has been

incorporated (Ruark et al. 2010, Linquist et al. 2014). In contrast, burning increases the phosphorus run-

off from fields. There is a trade-off with total P whose content increases in drain waters with burning

(Ruark et al. 2010, Linquist et al. 2014). Seasonal water flows driven by winter precipitation, rather than

water released from drains were identified as the primary driver of dissolved organic carbon levels in the

Sacramento and require systems that can absorb and retain water during high precipitation events.

Krupa et al. (2012) disagree with Ruark et al (2010) on the influence of rice systems on dissolved organic

carbon loads in natural systems. They argue that rice cultivation can be important sources of contaminants

particularly during the summer flooding season. Both studies agree however that managing water outflow

from fields, either by reusing in the same field (increasing residence time of water), or recycling to

adjacent fields are viable and low cost strategies for reducing the impact of rice field management on

water quality. Moving water between rice fields, can be managed so that rice fields serve as net sinks of

contaminants, rather than sources. Krupa et al. (2012) also note that release of flood waters from rice

fields during low flow events, can increase the impact of contaminants by increasing the concentration of

those contaminants as compared to high flow events. The cumulative results of these studies support

increasing retention time, and internal reuse of water to decrease negative effects of rice cultivation on

water quality. In a controlled study simulating flood pulse events, Kroger et al. (2009) show how post

harvest rice efficiently absorbs diazinon and has low pond transference. Like the previous studies, this one

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demonstrates how post harvest rice agroecosystems may provide important regulating services in

pesticide degradation of contaminated tail water.

Water running off fields can have important impacts on the fisheries of the San Joaquin Delta. Discussions

thus far have focused on maintaining water on fields to allow for pesticide and contaminant degradation.

In the early 1990’s notable impacts of pesticide were evident from agricultural drains of rice-dominated

landscapes. Finlayson et al. (1993) studied the effects of toxicity of water from the Colusa Basin Drain on

young striped bass Morone saxatilis and mysids Neomysis mercedis. The insecticides carbofuran,

malathion, and methyl parathion, which at the time were used on rice in California, were suspected to be

important causes contributing to the decline of the striped bass population in the Sacramento-San Joaquin

Estuary, either directly by mortality or indirectly by reducing food items such as mysids. Water samples

collected from the Colusa Basin Drain was significantly toxic to Neomysis mercedis, which was attributed

to lethal (up to three times the 96-h LC50 value) concentrations of methyl parathion. Drains monitored in

this study are the same cited in the California Environmental Assessment (van Diepen et al. 2004, LLC

2010) where reduced rates of pesticides have been observed since 1995, (two years following the

Finlayson et al. study). While holding water on fields is one effective method of improving water quality,

alternate pest and weed management options, and legislation regulating the use of non-degradable or

highly toxic compounds may be more important to overcome trade-offs between environmental quality,

and food production.

CONCLUSIONS

Several management options are explored, the one more practiced on-farm has included: 1) reduced use

of pesticides by managing water levels and the timing of flooding, 2) shift to US EPA recommended

herbicides and pesticides, 3) retaining agricultural waters on field to allow for degradation and

decomposition of these materials.

Studies that considered residue management are covered in this section because those practices have

been studied vis-à-vis their contribution to particulate matter, and organic matter in water flowing from

rice field. The key conclusions derived from this analysis are that incorporating rice straw into the soil and

winter flooding increase soil nitrogen and yield after a three-year lag. Waterfowl on fields facilitate

decomposition and nutrient cycling of rice straw, and eliminate the need for autumn tillage; the effects

on nutrient incorporation of rice straw is inconclusive.

The vegetation of rice fields increases the bioaccumulation of mercury compared to natural system most

likely due to increased productivity, and alternating wetting and drying cycles.

Retaining water on fields increases the degradation of agricultural pesticides and herbicides, as well as

mercury; however winter storms can overwhelm these efforts, particularly for non-degradable

substances. Managing smaller irrigation units can mitigate these impacts by reducing accumulation of

materials. No-till combined with stale rice seedbed and spring flooding reduced the need for tillage

operations, and facilitated weed management but requires additional nitrogen fertilizer to maintain

yields.

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Water quantity is the predominant trade-off in California concerning both decisions of rice farmers vis-à-

vis crop selection, and at the state level regarding prioritizing the use of water resources. Approximately

40 percent of water is the state is reserved for environmental flows, another 40 percent is consumed by

agriculture, and a final 10 percent allocated to urban uses. Historically, all rice was irrigated with surface

water from the Sacramento River and was often reused several times. Thus the distinction between water

use for environmental flows versus agricultural use is one that is confused in rice production. Pumped

groundwater, although much more costly, has been used to supplement surface supplies and is becoming

an increasingly important resource in the current drought context, however legislation to regulate ground

water use is forth-coming and may make this resource less accessible.

The minimum amount of water required to grow a crop of rice is approximately 106 cm depth per hectare

(the water lost through evapotranspiration). This is not much greater than that required for other long-

growing season field crops, however, losses due to percolation and tail water outflows can add to this

amount driving water use to 127 to 254 cm per hectare. The water that is not used is not necessarily lost

however, and is often reused to irrigate other crops, to flood natural wetlands, and/or eventually returned

to the Sacramento river system. The California Rice Commission’s Environmental Sustainability Report

(LLC 2010) reports that 57 percent of the tail waters from rice fields are used to provide water for adjacent

wetlands, which emphasizes the importance of water quality discussed in the previous chapter.

Rather than being a trade-off between actual food production and water quantity however, the water

quantity issue focuses on whether rice, compared to other crops, has the higher water use cost. This issue

has come to a particularly acute point as California enters its fourth consecutive year of severe drought in

2015 emphasizing the high dependence on the mountain (in the form of slow release snowpacks) and

floodplain ecosystems as an important source of water for irrigated agriculture. Some rice farmers

reduced their rice production area in 2014 by 30 percent, and refer to similar reductions in 2015 with

impacts on food production capacity. An NBC report (Koba 2014) indicates that nearly 25 percent of

California’s $5 billion rice crop may be lost in 2015 due to lack of water. Food security in California is not

threatened however, and the principle impacts are felt on the economy, farmer livelihoods, and

potentially on the habitat services provided by rice lands through winter flooding.

The second principal issue noted in the literature is the complex water regulations in California that enable

farmers to sell water rights. The NBC report (Koba 2014) cites that water policy in California makes the

value of the water higher than the value of the rice crop, incentivizing farmers to sell water sources

(Linquist, Personal Communication). Farmers thus commonly perform a farm-based calculus of the value

of water quantity on farm, versus its sale to the state, or to other farmers. In the current drought situation,

a growing number of farmers have favored the sale of water rights over its on-farm use. Considering such

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sales from the point of view of payments for ecosystem services merits additional consideration and is

the source of novel ideas being tested by The Nature Conservancy.

An infographic (CRC, 2014) produced by the California Rice Commission compares the quantity of water

needed to produce a serving of rice to various other uses. Interestingly, there is no reference to the dual

role that water from rice fields plays in habitat and agriculture, though this does emerge in reference to

the estimated cost of restoring natural wetlands in the habitat section of the California Rice Commission’s

Environmental Sustainability Report (LLC 2010). The California Rice Commission similarly refers to a 40

percent increase in water use efficiency associated with rice cultivation over the past 30 years. This has

been achieved though land leveling, recirculation systems, early maturation varieties, and water

conserving irrigation systems. The California Rice Commission reports that the reduction in water

consumption that are seen in the California, were accompanied with parallel increases in yield. During this

period yields have increased from 5500 kg per hectare to 8500 kg per hectare (35 percent increase) in the

same period that water use has decreased from 1.98 hectare meters to 1.24 hectare meters (LLC 2010).

Thus as compared to 30 years ago, rice farms are using 20 percent less water to grow almost 30 percent

more rice or a 40 percent increase in water use efficiency (Figure 5).

Figure 5: Decadal trend in water use

efficiency in California derived from text in

the California Rice Commission

Environmental Sustainability Report (LLC

2010)

Table: Comparison of water consumption for rice cultivation and comparable services as produced by the California

Rice Commission.

Servings of Rice Product

1 Serving of orange or broccoli

3 Washing your car

1960 1970-19801990

2000

4000 5000 6000 7000 8000 9000

0

0.5

1

1.5

2

2.5

Rice Yield (kg per ha)

Wat

er

Co

nsu

me

d

(he

ctre

me

ters

)

1960 1970-19801990

2000

4000 5000 6000 7000 8000 9000

0

0.5

1

1.5

2

2.5

Rice Yield (kg per ha)

Wat

er

Co

nsu

me

d

(he

ctre

me

ters

)

172 | P a g e

72 1 pair of blue jeans

1,000,000 Irrigating the Sacramento Capitol lawn.

Source: CRC, 2014

The focus of this section is on the two benefits of rice agro-ecosystems, food and water. Yet other positive

and negative impacts of rice-agroecosystems are implied as illustrated in the following examples. The

examples clearly show the dependencies and the positive and negative impacts of rice-agro-ecosystems.

The text also explains the causation linking these two. Predominant issues identified in in Californian rice

agro-ecosystems regarding food (quantity) and water (quantity) center around four principle issues: I.

Provision of wetland habitats (nearly 121,000 hectares) and the tail water from rice supporting natural

wetlands, are amongst the highest value contributions from water management in rice production

systems; II. Flood prevention; III. Breeding grounds of disease transmitting organisms such as mosquitos,

and IV. Weed control:

I. Where rice is grown in California is a function of heavy clay soils located adjacent to watercourses.

These areas were historically natural wetlands that were regularly inundated. These

characteristics foster benefits between rice cultivation and food production since rice is the most

suitable crop for this soil and water typology – few other crops are suitable for these sites.

Flooded rice cultivation systems are therefore relatively analogous to the natural wetlands they

replace. Managing winter floods waters on these fields (increase water quantity) (cause) provides

habitat for waterfowl (positive impact). More than 93 percent of the historic California Central

Valley wetlands have been drained and converted to agricultural and other uses. Agricultural

wetlands, such as rice and its supporting infrastructure of canals, allow some species to persist

(Shuford et al. 1998, Halstead et al. 2014). Several studies support the habitat services provided

by rice lands (Elphick 2000, 2004, 2008). Of note is the Central Valley Joint Venture, an initiative

from 1990 that aimed to reduce the use of burning for rice straw management, and promoted

the flooding of these lands for wildlife habitat. Ackerman et al. (2006) have an important data set

on radio collared white fronted geese that spans the period before and after the implementation

of the joint venture documenting important behavior changes associated with the policy. Flooding

is the primary attractant for increasing habitat quality; within flooding regimes altering water

depth attracts different avian communities (Elphick and Oring 2003) with deeper waters

attracting ducks, and shallower water management being favorable to shorebirds.

II. Historically Sacramento has suffered from severe floods prior to construction of the Yolo bypass

(cause). If and when the floodwaters from the Sacramento reach a 10 meter crest, they are

automatically diverted into the wildlife area through the Fremont weir. The city of Sacramento

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depends on the Yolo Bypass Wildlife area as its first line of defense against the flooding of the

Sacramento River. The Yolo Bypass is a jointly managed area where the US Army Corps of

Engineers, The California Department of Fish and Game, the US Fish and Wildlife Service, rice

farmers and conservation NGOs jointly manage the multiple goods and service provided by

floodable lands. In the northern portions of the Wildlife Area, rice is grown, which is then flooded

after harvest. In the case of the Yolo Bypass, the first and foremost function (highest value) is

flood protection (positive impact), with habitat and agricultural production coming second

(positive impacts). The project represents the largest public/private restoration project west of

the Florida Everglades. In addition to the flood protection role, the entire bypass forms a valuable

wetland habitat when flooded during the winter and spring rainy season.

The Yolo Bypass, first and foremost plays a critical function in protecting the city of Sacramento

from flood events. A University of California Berkeley study suggests that the value of the bypass

is on the order of $40 to $400 per hectare for flood control. This is equal to the value of these

lands for habitat. These values are non-excludable, and additive but are site specific, that is, only

fields that are located in locations where they can provide flood protection to built infrastructure

should be valued. Trade-offs that need to be managed are the potential loss of the crop when

flooding coincides with the cultivation period, and the cost of restoring field infrastructure

(leveling, canal sedimentation) following flood events. We did not find references estimating

these costs. In the Yolo Causeway, which is primarily managed for flood protection, with rice

cultivation managed as a secondary use, the restoration costs are shared between public

(California Fish and Game, US Army Corps of Engineers, City of Sacramento) and private

stakeholders (farmers).

Table. Approximate monetary values of services of connected floodplains. (Eisenstein and Mozingo 2013)

Flood risk reduction value

Conceptual Example

Annual Value per Floodplain hectare

Context Sensitivity Notes

Reduced flood stage

Yolo Bypass widening

$40-$400s Based on extent and intensity of development in affected areas

Assumes a 100-year project lifetime and a discount rate of 3%.

Avoided Residual Risk

Various sites in valley

$0-$400’s Depends heavily on local topography

Assumes sub-urban development densities.

Groundwater recharge

Gravelly Ford, Yolo Bypass

$0-$40’s Requires suitable soils and aquifers

Value and recoverability of water varies by site.

III. Many important disease vectors are dependent on wetland habitats (negative impact), and rice

fields can serve as important breeding grounds (cause) of disease transmitting mosquitoes (Wood

et al. 1991a). This risk is of increasing concern as large urban populations develop adjacent to rice

cultivation areas in the Sacramento region. Research on mosquito borne diseases saw a surge in

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studies in the 1970’s and 80’s, with little new material in the peer reviewed research past 2000

(Wood et al. 1991a, Wood et al. 1991b, Wood et al. 1992). However, it is well recognized that rice

fields can harbor and be important breeding grounds for human based vectors which have been

a concern in California rice production regions since the 50’s (Portman 1954). This is a significant

concern in the Central Valley with rises of West Nile Virus which arrived in the Central Valley in

2004 (Smallwood and Nakamoto 2009) and bird flu. West Nile Virus has had an important impact

on corvids (birds in the crow family) of the Central Valley, by some counts reducing the population

of Yellow-billed magpies, an endemic species of the valley, American crow and Loggerhead shrike

by 83%, 63%, and 63% from 1990 population levels respectively (Smallwood and Nakamoto 2009).

Mosquito populations (Anopheles freeborni and Culex tarsalis) are primarily found in riparian and

mixed use habitats within rice production systems (Wekesa et al. 1996). A. freeborni primarily

feeds on mammals, where as C. tarsalis is more of a generalist favoring birds (Wekesa et al. 1997).

Mitigating the disease tradeoff is an important research question with lessons learned from

California. Predicting where services or disservices are produced and targeting interventions

around those hotspots has been one of the primary mechanisms for ecosystem service

management. For disease control, understanding the source of the disease is the first step in this

determination.

Increasing surface water in rice fields near urban areas or in conjunction with high waterfowl

densities can also increase disease transmission risk (Wood et al. 1990, Wood et al. 1991a, Wood

et al. 1991b, Wood et al. 1992). Thus while the conservation benefits of rice straw incorporation

are notable, there are significant questions regarding increased disease risk (Lawler and Dritz

2005) where incorporating rice straw into fields, and winter flooding can nearly double mosquito

abundance in comparison to burning, or incorporating rice straw without flooding (Figure 6).

Figure 6:: Total abundances (mean and

SE) of mosquitoes collected from

Maxwell, California, rice fields subjected

to different straw management and

winter flooding treatments before the

growing season. We collected 100 350-

mL dip samples in each of four fields per

treatment on each of 10 dates in May–

August. Source: (Lawler and Dritz 2005)

For the Anopheles freeborni, two important variables determining the spatial extent of the vector

include the rate of canopy closure of wetland vegetation, and proximity of livestock pastures

which serve as blood meals for the vector (Wood et al. 1991a, Wood et al. 1991b, Wood et al.

1992). There is limited opportunity for managing these variables in the absence of incentive or

legislative systems that increase the distance (3 km) between these land use systems. Rather,

increasing mosquito density may be partially offset by targeting control methods in these disease

hotspots, most commonly targeted spraying. Targeting control mechanisms reduces their costs,

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and also reduces the environmental impact of un-targeted management practices. The use of fish

as mosquito control predates the notion of ecosystem services, with several studies in the 1970-

80s focusing on the matter, but little evidence that this is a commonly used control mechanism.

Hoy and Reed Hoy and Reed (1971) present the results of a study on the efficacy of mosquitofish

in controlling the Culex tarsalis mosquito in rice fields. Similar studies on the use of mosquitofish

(Gambusia affinis), the inland silverside (Menidia beryllina), and the fungus Bacillus thurigiensis

for mosquito control agents in rice fields (Kramer et al. 1987, 1988). The efficiency of these natural

control agents is a function of vegetation and prey species (Linden and Cech 1990). In a second

paper the efficiency of ground and aerial application of the asexual stage of Lagenindium

geganteum for mosquito control in the Central Valley is considered (Kerwin and Washino 1987).

The economics of these disease control agents are studied (Lichtenberg and Getz 1985). Chemical

control of mosquito remains a primary management methodology with studies effects on aquatic

non-target organisms (Washino et al. 1972).

Host abundance, may play a more important role in determining spatial distribution and

population size than other habitat characteristics for mosquito species. Garcia et al. (1992) found

that Anopheles spp. and C. tarsalis populations in wild rice were 6 and 2.6 times higher,

respectively, than in the white rice cover. Important ecosystem characteristics including plant

height, floral debris, water quality, and bacterial counts were important contributing components

of the system. Plant height is an important correlate with Anopheles densities (Wood et al. 1991a).

Fields that are higher risk for producing mosquitos are located in an area with a diversity of land

uses, including livestock pastures. In contrast, fields that are low mosquito producing are almost

exclusively devoted to rice cultivation (Wood et al. 1991b). High risk areas can be identified with

relatively high accuracy up to two-months before larval emergence, and control measures can

thus be targeted reducing both the cost of the measure, as well as the environmental impact of

control on water quality (Wood et al. 1992). Larval incidence coincides with the production season

(July), thus draining fields can serve as a management technique for reducing disease incidence,

but poses significant trade-offs with water quality (decrease), and water quantity through

repeated fertilization. This can be mitigated by rotating the draining and filling adjacent fields to

encourage the local reuse of water while noting the additional energetic cost of pumping water

between fields. This option is not discussed in the literature.

Somewhat counter intuitively, a reduction in flooded lands may actually increase disease risk by

amplifying or concentrating vectors in fewer sites. A recent study reported in the media (Capradio,

2014) states that the drought is concentrating waterfowl in a more limited number of locations.

The increased contact between waterfowl and mosquitos is thought to amplify West Nile Virus

with 311 cases reported for California in 2014. Thirty of these cases are reported in Glenn country,

one of the primary rice producing regions of the State. The land, and medical treatment costs

related to the disease control are not negligible, though the contribution of rice production

systems in either diluting, or amplifying the disease is poorly understood. Mitigating this effect

could include providing incentives for rice farmers not to leave their fields fallow during drought

conditions, for example by recognizing the contribution of rice fields to state level environmental

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flows. This would have a positive effect on food production equal to the area of fields returning

to production.

IV. Most arthropods studied in California rice systems relate to agricultural pests. However the

invertebrate community ecology of rice systems may reveal important relationships between

these communities and both provisioning and regulating services. A major predicted driver of

invertebrate community composition is the regular wetting and drying of rice production systems

in comparison to native wetlands (Hesler and Grigarick 1992). Several sites associated with rice

production mention pre-emergence wetting or flooding (cause) as an important means of weed

control (positive impact). The majority of these emphasize that the flooded nature of rice

production practice eliminates most of the common weeds associated with dryland agricultural

systems. This was seen as an attribute in using rice straw as an anti-erosion measure in wilderness

and protected areas (see raw materials section) – since the material is free of weed seeds

associated with dryland systems. However, noxious weeds and algae are an important component

of rice production systems, and according to some are amongst the more significant challenges

faced by rice farmers.

Figure 7: Map of the Yolo Bypass (center left) and important associated flood control structures protecting the City of Sacramento from Flood events. Source: Eisenstein and Mozingo (2013).

177 | P a g e


The effect of water management

While the authors of this case study could not identify any studies that have analyzed the effect of winter

flooding on both food production and the consumption of water, there is a large body of evidence on how

this practice has affected wetland habitats and their wildlife in California. Increasing the quantity of water

on field in the winter has a significantly positive effect on habitat quality in California rice lands. There are

trade-offs regarding disease management, and competing water uses, however the habitat quality

benefits are highest in the winter months when completing demands for water, and water stress are low.

Considering management in the 1980s, and 2008, the area that is now managed as flooded rice has

increased four to five fold as a combined effect of a 37 to 41 percent increase in the area cultivated for

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rice in the region, and a three to four fold increase in the number of fields that are now flooded in the

winter (Miller et al. 2010).

Rice lands, since the ban on burning, provide up to 121,000 hectares of overwintering habitat for

migratory waterfowl. In addition, 57 percent of the water supporting natural wetlands originates from

California rice fields. Some of the earliest studies found on California and rice focus on the habitat

attributes, including a 1947 study of fairy shrimp (Rosenberg 1946) and the tadpole shrimp (Rosenberg

1947). According to the California Rice Commission more than 230 wildlife species use California rice lands

as habitat, including more than seven million ducks and geese, and countless shorebirds whom nest in the

rice year-round. Many of these species are of special concern, threatened or endangered including the

Giant Garter Snake (Halstead et al. 2010, Wylie et al. 2010, Halstead et al. 2014). The use of rice lands as

wetlands has driven a significant increase in white fronted goose use of rice for roosting (+14%), and for

feeding (+15%) in the decade before and after the implementation of the burning ban (Ackerman et al.

2006).

The Commission’s point is that rice thus plays and important role in replacing the more than 95 percent

of California’s historical Central Valley wetlands. Some conservationists would argue that rice has played

an important role in the loss of that habitat. However, better understanding of how rice systems can be

managed to mimic or play similar conservation roles as natural wetlands has received significant attention

from the research, conservation, and production communities. The CRC suggests that “acquiring and

restoring this amount of land to create wetland for wintering waterfowl populations would initially cost

about $2 billion and about $35 million annually for upkeep”. California rice is a rare example of the explicit

management of an intensively managed annual crop for wildlife conservation benefits.

Water depth (quantity) determines which species use rice fields in the winter. Managing a diversity of

water levels increases the number of species that use these systems. Flooded fields have significantly

greater abundance and diversity of shorebirds and waterfowl with water depth being the primary driver

between these two broad groups. Shorebirds preferred lands with one time flooding and shallow depths,

whereas waterfowl preferred continuously flooded deeper fields (Strum et al. 2013). Both traditional and

alternative flooding practices will be needed to manage the tradeoffs between habitat and water scarcity.

Managing water quantity has also led to one of the most innovative public/private partnerships and

payments for ecosystem service programs. The Nature Conservancy’s “Bird Returns” program uses citizen

science, and a reverse auction system to allow farmers to bid on a water purchase by The Nature

Conservancy (TNC). TNC uses information on the arrival of migratory waterfowl as observed sightings

made by citizen birders throughout the central valley through the cell phone app eBird. This information

is then used to temporarily lease the water on a farmer’s field during the period that coincides with the

bird’s arrival and passage. Farmers are pre-selected for water applications, and bid on the lease of their

water. TNC reports that the value of this water, which goes to the lowest bidder, is both above and below

the $18 per hectare that the Federal Government provides for bird friendly rice cultivation practices

(Capradio, 2014).

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Several studies cited below and in other sections consider the impacts of overwintering waterfowl on soil

quality and residue decomposition. Notable effects on residue decomposition have been observed when

waterfowl are present, in contrast no direct link between waterfowl and mineralizable nitrogen has been

observed. Long-term studies on soil function and nutrient accumulation are missing however. The trade-

off with habitat quality is centered on winter flooding. The most significant competing use is climate

mitigation (discussed in the chapter on climate) and methane production. Impacts on plant protection are

variable depending on the disease/weed organism in question, though significant effects of waterfowl on

weed biomass reduction have been noted and are discussed below.

While the similarities between rice fields and natural wetlands benefits the conservation value of rice

lands described above, it poses several management challenges particularly related to weed and pest

management. Experiments on arthropod communities in rice under various levels of wetting and drying

found remarkably little differences in the abundances of the arthropod community in function to wetting

(Hesler and Grigarick 1992). With more than 22 taxa collected in their study the percentage similarity

between continuously flooded and intermittently flooded areas was greater than 50 percent suggesting

that the arthropod communities, including pests, are well accustomed to regular drying (Hesler and

Grigarick 1992). The situation is similar with weed communities of rice. Because rice is often the only

suitable crop in these sites, intercropping and rotations are often not possible. Thus the dominant pest

and weed management practices have centered on chemical controls with very high levels of herbicide

resistance emerging. Altering wetting and drying cycles to control weeds and other pests has been studied

as a means of managing this trade-off. The timing of the wetting and drying is often used as a management

option to provide weeds and pests such as the tadepole shrimp (Fry and Mulla 1992) or sedge and

watergrass (Pittelkow et al. 2012) a false start, or early germination prior to the rice establishment phase.

These can have significant effects on weed reductions, for example 90 to 100 percent reductions in sedge

and grass biomass (Figure 8). Several of these have been covered in the chapter on water quality where

the focus was on the effect of field water retention on the degradation of agricultural chemicals.

Figure 8: Weed biomass in weed recruitment zones of wet seeded systems at rice harvest. Means for (a) sedge

species (smallflower umbrella sedge and ricefield bulrush) and (b) redstem were averaged over 2004–2007 as

there was no year by system interaction. Means for (c) grass species (watergrass and sprangletop) were averaged

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over 2006–2007 as grasses were not present in 2004–2005. Within each panel, bars with the same letter are not

significantly different at P < 0.05. Source: (Pittelkow et al. 2012)

Another example Echinochloa oryzicola (watergrass), an exotic weed of California rice paddies, that has

evolved resistance to multiple herbicides (Boddy et al. 2013) and which requires additional management

to control its spread and impact. Boddy et al. (2013) find that the winter flooding that has been

undertaken as part of the rice straw management in the valley drives early germination of E. oryzicola and

early seedling emergence. The early timing with winter flooding enables management of the weed before

rice emergence (Boddy et al. 2013). Soil nitrogen management and varietal management can also

contribute to reducing the impact of weeds (Cavero et al. 1997). Tall cultivars (S-6) best compete with the

weed at high (>120 kg ha-1) nitrogen rates, and high weed densities. Short cultivars in contrast (M-202)

performed best at optimum nitrogen rates (120 kg ha-1) and with weed densities <50 plants m-2. Cavero

et al. (1997) suggest that above optimum N rates (>120 kg ha-1) did not increase rice yield but increased

the risk of watergrass competition suggesting, as have others, that weed regulation via water

management and food production via nutrient enrichment are compatible options.

Waterfowl can make significant contributions to weed control, in one documented case reducing grassy

weed abundance by more than half (Figure 9): 91 to 44 kg ha-1 on average, and from 204 to 89 kg ha-1 in

areas with high duck densities (van Groenigen et al. 2003). No effect on increasing yield was found in this

exclosure study however. Mean values of this weed reduction are an order of magnitude lower than those

found in the land preparation and water management methods described above, but the variance in the

results is quite high as well.

Figure 9: Effects of foraging waterfowl on

residue decomposition and weed pressure at

harvest. Pairwise comparisons with results of a

Wilcoxon pairwise signed rank test. Source: (van

Groenigen et al. 2003)

Invasive species of crayfish can pose pest problem in wet-seeded rice fields (Anastacio et al. 2005) feeding

on seedlings as they emerge, farmers have also raised concerns about the impacts of crawfish burrows in

levees on water loss. The study suggests that many seeds and seedlings are impacted, although the

consumption is low. In contrast Brady (2013) suggests that the introduction of the red swamp crawfish

has created the an opportunistic aquaculture economy, including contributing cultural services by

provided a key ingredient to Vietnamese-American restaurants. Harvesting crayfish from fields is labor

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intensive, and disruptive to rice establishment. Few other sources highlight crayfish as a problem, and no

alternate management options are discussed.

At the turn of the century, rice cultivation (food production) posed an important trade-off with wildlife

habitat as the arrival of over-wintering waterfowl coincided with the rice harvest. The shift to fast growing

varieties largely eliminated this trade-off by completing the harvest prior to the arrival of the migrants.

This shifted the ecosystem impact of waterfowl from plant predation (negative interaction), to residue

decomposition (positive interaction). Some seed eating species such as red-wing blackbirds are year-long

residents to the Central Valley, though their impact in yield is not quantified (Avery et al. 2000). Avery et

al (2000) find low efficiency of anthraquinone application on rice as a bird deterrent. During the harvest

season, some farmers deploy air cannons as a deterrent (the loud booming noise prevents birds from

settling on fields).

The primary management practices that affect these arthropods are flooding, drying and rice straw

management, including burning or incorporation into the soil. The ban on burning and the favoring of the

incorporation of straw into the soil have significantly different effects since the latter creates an important

nutrient source for invertebrates, both beneficial and noxious species (Figure XX). In one study, algae,

mosquitos and other herbivorous insect as well as predatory insects all responded positively to rice straw

incorporation and winter flooding (Lawler and Dritz 2005). While this increase is the foundation for much

of the conservation value that originates from rice production system systems, it drives and important

trade-off when mosquito populations benefit, particularly when in proximity to human populations as

described above (Wood et al. 1990, Wood et al. 1991a, Wood et al. 1991b, Wood et al. 1992). Targeted

mosquito control operations are currently used as a management tool. There is a significant trade-off

between rice/non-rice based systems and mosquito abundances – draining wetlands has long been a

primary means of controlling mosquitos. No studies on how to manage mosquito within rice production

systems were found in the literature, though repeated draining, and transfer of water between fields can

mitigate this impact.

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Figure 10: Time series of (A) seasonal dynamics

of consumer insects and (B) predatory insects

collected from quadrat samples in rice fields at

Maxwell in 1999. Error bars were omitted for

visual clarity. No impacts on yield or rice

consumption are included in this study.

Source: (Lawler and Dritz 2005).

Levee management, including reducing the density of levee systems (Espino 2012), and keeping them free

of vegetation (Palrang et al. 1994) can be alternate weevil management strategies though there are

important trade-offs with the habitat quality benefits (vegetated levee, versus bare levee), and water

management. Large field sizes reduce the positive edge effects favoring the rice water weevil

(Lissorhoptrus oryzophilus) whose densities are often greater near field edges (30 m) than further from

these edges (>60 m). This same study however found no effect of the weevil on rice yields (Espino 2012).

This may be because draining fields may alternately be used as a means of controlling the pest (Hesler et

al. 1992) with incidence being 6-32 times greater per plant in flooded conditions than in fields with early

draining though the trade-offs with water and habitat should be considered. Early season draining needed

to control the weevil can conflict with other management practices and can be costly to establish (Hesler

et al. 1992), for example the impact of maintaining water on fields to allow for agrochemical degradation,

rice straw decomposition, or habitat quality as discussed in the water quality chapter.

Stem rot (Sclerotium oryzae) is another important disease of rice which was mainly managed through

burning (Cintas and Webster 2001). Cintas and Webster (2001) considered alternate management

techniques, and while burning remains the most effectively for both controlling the disease and increasing

yield, winter flooding was found to be the best alternative for managing stem rot. There was however, no

effect of the disease on yield. The authors note that disease incidence increases with nitrogen fertilization

(Table). This has been observed in several other studies regarding water quality and weed management

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cited in the water quality chapter emphasizing the need for integrated and long term studies that consider

the impact of residue management on mineralizable nitrogen, weed and disease densities and yield.

Regarding pest and disease management, flooding is the second best alternative to burning for controlling

stem rot and other diseases. Burning remains important during disease epidemics.

Table: Effects of winter flooding and various residue management treatments on stem rot disease severity and

yield of rice at the Colusa site. Source: (Cintas and Webster 2001)

CONCLUSIONS

Managing water quantity is in all likelihood one of the most valuable elements of rice cultivation in

California. Rice production systems are characterized by their flooded nature, the ban on rice straw

burning, and legislation on water quality have both increased the duration of that flooding (field retention

for pesticide degradation, winter flooding for organic matter decomposition). This has led to additional

values of rice-based wetlands for habitat conservation associated with migratory waterfowl. Because

water is such as highly valued commodity and farmers own specific water rights, the use of water can be

purchased and sold in the same way that the rice crop is purchased and sold. Novel payments for habitat

services are emerging, complementing federal programs for bird conservation, and leasing farmers fields

during the fall and winter seasons. These leases are complementary to rice cultivation and are

asynchronous. Flood protection is a second major service provide by California rice lands. The combination

of habitat services, flood protection services, and crop production services potentially triple the value of

any single ha or cultivated rice land based on its location, and willingness to pay. The role of rice agriculture

in supporting the spread of diseases through the combined impact of migratory birds, and water-borne

vectors is of specific concern. Several confounding climate change variables including drought, and the

movement of tropical diseases into the region (West Nile virus) pose specific concerns. Alternating wetting

and drying of rice fields, particularly pre-establishment and during the summer/growing season can be an

important means of pest/weed/disease control. Reutilization of water between fields reduces the

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additional water needed, and reduces the trade-off with water quality, but requires field arrangements

and management designed for re-utilization.


The California rice straw-burning ban enacted in the 1990’s put significant pressure on farmers to find

alternative measures to remove or incorporate rice straw waste from farm fields. Air quality associated

with rice cultivation was once a major issue in California. In the 1980’s more than 95 percent of rice fields

were burned as a means of reducing the highly resistant to decomposition rice straw; currently 90 percent

of rice fields incorporate the straw and use flooding to facilitate straw decomposition (figure 11). The area

of rice straw burnt had a small but significant impact on risk of asthma hospitalization and on morbidity

as studied in Butte country California (Jacobs et al. 1997).

Residue management is the primary driver of raw materials with those raw materials either benefiting on

site functions such as soil quality, or off-site functions such as the production of construction material.

While incorporation of rice straw into soil and winter flooding are the predominant methods of dealing

with rice straw post-harvest, the California Rice Commission (2009) estimates that three to five percent

of rice area in California has straw baled for alternative uses.

Alternative management options to burning rice straw, the positive and negative impacts, and

dependencies are explained below. The impact of this rice straw management has positive or negative

impacts depending on its final use. Positive effects of baling are strong in regards to climate change

mitigation when the straw is used as a construction material, but lost when it is used as a feed. There are

neutral to positive effects of incorporation into fields regarding soil quality and mineralizable nitrogen

which have already been discussed (reducing fertilizer needs by 20 kg per hectare) (Linquist et al. 2006).

However each of these also has important negative impacts:

I. Leaving straw on the ground (cause) for soil nutrition can be an important source of carbon,

mineralizable nitrogen, phosphorus and potassium (positive impact). Studies cited in the water

quality section suggest that this addition can drive optimum nitrogen fertilization levels down by

20 kg per hectare (Linquist et al 2006) (positive impact). ANR has quantified the removal of

nitrogen, phosphorus and potassium from fields stating that baling and removal (cause) would

require additional fertilizer inputs to replace this loss (negative impact) (Table). Incorporation

requires processing rice straw by incorporation or rolling and re-flooding the fields with water as

discussed. The effects of this addition on soil fertility are poorly studied and largely overshadowed

by the large fertilizer additions made to fields.

Table: Average nutrient loss at different straw removal rates. Source: UC ANR Pub. 8425 (Nader and Robinson 2010).

Straw Harvested (kg ha-1)

Nutrient 907 1360 1814 2721

N (kg ha-1) 16.3 24.3 32.5 48.6 P (kg ha-1) 2.1 3.1 4.3 6.3 K (kg ha-1) 36.7 55.0 73.3 110.0

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Figure 11: Rice fields in California were traditionally burned until legislation was passed in 1991 banning the practice except when needed to manage pest and disease epidemics. Since then, burning has rapidly declined and is no longer a dominant practice in rice field. Incorporating rice straw into fields is now the dominant practice. Baling straw has been explored as an option, but remains low largely due to the additional management costs, and the low value of rice straw. Source CRC Rice Environmental Sustainability Report (SummersLLC 2010)

II. Rice straw cut at waterline (12 cm) yield approximately 0.6 tons of straw per hectare. Each of

these uses requires additional postharvest management interventions and specific

considerations. For example, beef feed (positive impact) requires straw that retains 13 percent

moisture, and is chopped to 10 cm bits (dairy as well), whereas mushroom producers require un-

chopped straw. Rice straw is of low nutritional quality and is typically mixed with supplemental

material in dairy operations. Farmers are therefore recommended to identify a buyer before

baling, and to understand the specific needs of the buyer in order to produce the specific product

requirements (length, and moisture content). In beef operations, a higher moisture context is

retained to improve palatability and flavor for cattle. The attractiveness of rice straw is typically

favored in drought years when access to higher quality feed is limited and more costly.

Furthermore, significant trade-offs exist as described in a 2008 article in “Biomass Magazine”.

California rice farmers pay between $10 and $20 per hectare to bale and remove rice straw

residue from their fields with few markets for these materials. Rice straw is high in silica, reaching

13 percent on a dry-matter basis, and is generally unattractive and has low palatability as a feed

material. Silica is highly abrasive, as forage it can cause excessive wear on bovine molars and is

even destructive to farm equipment, wearing out implements 40 percent faster than wheat.

III. The off-site alternative uses of rice straw are minimal according to Kadam et al. (2000), with

approximately 0.6 percent or 8,000 dry tons of the estimated 1.4 million dry tons of rice straw

generated annually, used in as an off-site raw material. With a business-as-usual approach,

alternative rice straw uses were likely still to be insignificant by the year 2000 in Kadam’s study.

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Despite the existence of a rice straw market place (http://www.ricestrawmarket.org), we

estimate this value to continue to be small in 2014 based on figure xx which shows very little

increase in rice straw baling over the past 30 years.

It must also be pointed out that off-site uses of rice straw are costly as shown by Kadam et al.

(2000) (Table). In this study, transportation distance was found to be the most significant cost

associated with rice straw management.

Table: Costs associated with rice straw harvest, baling, and transportation. Source: Kadam et al. (2000)

I. Rice straw is a preferred material for erosion control (positive impact) in construction areas, and

wildlife sites (management of post burn areas which is a major activity in California). A critical

attribute of erosion materials is that they must be certified weed free because of their use in

wildland areas. Because rice is grown in flooded environments that are non-conducive to rainfed

weed species it easily meets this standard. The high silica content of rice straw is also desirable as

it permits a slower decomposition rate than other materials. Chopped rice can be applied via

helicopter in areas being restored post fire damage – somewhat ironically servicie as temporary

erosion control until the establishment of long-term erosion control offered by reforestation.

II. Biogas or energy generation from rice straw was explored in the late 1990s early 2000s, however

cost of processing and transportation appear to largely exceed benefits (Kadam et al. 2000) –

particularly with the currently low price of fuel globally. Biogas generation can be accomplished

with anerobic digestion which offers an efficient way of converting rice straw to biogas (Zhang

and Turnbull 1999). Laboratory research calculated that 4.8 cubic feet (0.127 cubic meters) of

biogas can be produced from each pound of dried rice straw. A preliminary study of the economic

feasibility of energy production from rice straw showed that using rice straw as feedstock to

generate electric power at a cost of about $32 per ton would need to be at least 250 to 500 kW

in capacity in order to be economically viable (Zhang and Turnbull 1999). The authors emphasize

that this efficiency is achieved with on-site fuel generation (at mills or rice processing plants). The

best example of this practice, though using rice husks rather than rice straw, is Wadham Energy

power plant in Colusa county which burns 200,000 tons of rice hulls to generate 26.5 megawatts

of electricity (Jenkins et al. 2009). We found no evidence that this is a widely used practice in the

region however.

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III. Retaining rice straw in field favors invertebrate abundance (Lawler and Dritz 2005) and plant

biomass for feed; removing rice straw removes net primary productivity used by waterfowl for

food. Duck hunting is an important provisioning and cultural service of the Central Valley.

Although often viewed with skepticism by traditional conservation organizations, the hunting

community often pays more into conservation and habitat preservation than recreational bird-

watchers. These can be quantified vis-à-vis rental payments made to duck clubs, not for profit

organizations such as Ducks Unlimited, and fees paid to the California Department of Fish and

Game for hunting licenses. We cover this service in greater depth in the food diversity chapter.

THE EFFECT OF MANAGEMENT PRACTICES AND SYSTEMS

Residue management is a critical issue in California with impacts on soil, water, and habitat quality as well

as climate change mitigation effects as is seen in several chapters of this report. Air quality and disease

management were the primary drivers of decisions regarding residue burning or not. The rice straw

burning ban has eliminated this option forcing the current decision analysis to focus on rice straw as a raw

material used as a soil amendment, or as a raw material for off-site uses.

The primary trade-off between rice production and raw materials provision off-site from an ecosystem

service and rice productivity perspective is replacing the lost nutrients from rice straw removal. While

burning rice straw volatilizes most of its N and sulfur, K and P is retained in the soil. Straw removal takes

all of these nutrients, including the K out of the soil which requires additional consideration vis-à-vis

replacing those removed nutrients (Nader and Robinson 2010). When potassium is limiting, this can drive

nutrient limitations when straw is baled and removed (Eagle et al. 2000).

The trade-off between rice straw removal and soil nutrients was assessed by UC ANR (Nader and Robinson

2010) and is presented in table. These calculations assume that rice straw is baled at six percent moisture

and that 100 percent of the N and K of the straw is retained in the soil when incorporated. An additional

consideration when straw is used as beef feed, is that feed quality is correlated to soil nitrogen content.

Quality feed from straw requires attention to nitrogen management, and may require additional nitrogen

fertilization. There may be additional pesticide restrictions for straw sold as feed as well.

UC ANR (Nader and Robinson 2010) refer to concerns by some farmers that early draining of flooded fields

to allow for baling reduces the quality of rice grain (food production) and thus suggests that farmers

interested in producing rice straw select fields with well-drained soils or add traction tires to their haying

equipment to mitigate the trade-off between grain and straw quality. This is relatively non-intuitive since

California rice is specifically grown on poorly drained soils.

The trade-off vis-à-vis soil carbon and nutrients is whether to use residue as a secondary nutrient input,

or to remove this residue and replace it with synthetic fertilizers. The published studies find that rice straw

residue does not add nutrient to fields, but it reduce the rate of nutrient removal from fields and can

reduce nitrogen requirements by 20 kg per hectare. Rice straw incorporation leaves the majority of

nutrients on site though evidence suggests that it takes three years for this impact to be reflected in yield

increases. Few studies included multiyear comparisons to quantify this effect (with the exception of Eagle

et al. 2000). Most of the N and C contained in the rice straw, 25 percent of the phosphorus, and 20 percent

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of the potassium are lost under burning (Eagle et al. 2000). Baling removes all four elements with the

degree of straw removed. UC ANR provides a table of rice straw nutrient concentration (Table ), which is

informative both in assessing the value of the raw material as feed, as well as assessing nutrient removal

from rice fields. Burning drives the loss of N, C, K and P from the system.

Table: Nutrient concentration of rice straw based on measurement from 70 locations. Source: UC ANR (Nader and Robinson 2010)

Rice Straw Nutrient Concentration (%) N K Ca P Mg S Na Cl

Mean 0.77 1.74 0.30 0.10 0.20 0.08 0.15 0.52 Max. 1.12 2.70 0.50 0.17 0.30 0.15 0.50 1.20 Min. 0.53 1.10 0.19 0.05 0.12 0.04 0.01 0.10

The majority of California rice is dependent on synthetic fertilizers with application rates on the order of

120-180 kg nitrogen per hectare and 30-80 kg P per hectare. Eagle et al. (2000) provide a comprehensive

five-year study of the effect of residue management on yield. When fertilizer is applied at these rates,

there is no impact of residue management on yield. This includes no significant differences between

burning, incorporation with and without flooding, and removal. Synthetic fertilizer application subsidizes

any effect of residue management and yields are on the order of 8-10 tons per hectare. When no fertilizers

are applied, yield is reduced by half, from 8 to 10 tons ha to 4 to 6 tons per hectare. Under these

conditions, incorporated rice straw can bring yields back up to 9 tons per hectare after three to four years

of residue incorporation. In this same study however, yields dropped again to 5 tons per hectare in the

fifth and final year of study year.

Other trade-offs relate to GHG emissions versus carbon sequestration as discussed in more detail in the

next section on climate change mitigation. To summarize, Kroodsma and Field (2006) highlight the trade-

off between incorporating rice straw to fields and its removal with a focus on climate change mitigation,

discussed in the next chapter. Incorporation sequestered 1.0 Tg C between 1991 and 2000. If, however,

all the rice straw returned to the soil was instead used in power plants, assuming an energy content of

dry rice straw of 13.7 MJ/kg (Jenkins et al. 2009), Kroodsma and Field (2006) estimate that just over 0.8

Tg C would have been offset. In the long run, however, biomass gasification for energy production would

offset more carbon than the soils could sequester because soil sequestration would eventually saturate

as soils reach a new equilibrium except in the Delta region where the restoration of histosols (organic

soils) has a higher carbon storage capacity (Hatala et al. 2012). If the carbon offset involves coal and not

natural gas, burning biomass for energy would offset more carbon, as coal has higher carbon emission per

unit energy than natural gas.

California’s agriculture also offsets fossil fuel consumption through contributions to biomass energy. In

California, burning biomass for electricity usually offsets burning of natural gas. Producing electricity from

natural gas emits about 44 g C/MJ (1⁄4 160 g C/ kWh). In the 1990s, roughly two percent of California’s

electricity was produced by burning biomass, of which 20 percent was agricultural biomass (Morris, 2002

cited in Kroodsma and Field 2006). The majority of this was derived from perennial crop biomass rather

than annual crops however.

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While not discussed in detail in the current literature, current debates in California literature on reducing

the greenhouse gas emission of rice are focusing on reducing the flood interval of rice cultivation to reduce

the methane produced. We do not focus on this here, but flag that the passing of this legislation and

concomitant incentives may make the bailing options more attractive to rice farmers in the near future.

CONCLUSIONS

There are alternative uses of rice straw, including feed, erosion control, energy production and

construction material. These offsite uses comprise a small proportion of California rice farms largely

because markets for rice straw have not been developed in many areas, and baling, transporting, and

storing straw adds to the cost of growing rice which often exceeds the value of the raw material and which

is lower than conservation payments available.

The principle trade-off identified with food production was the need to dry fields earlier than would be

normally practiced for food production, with some farmers indicating concerns about impacts on rice

quality and maturation (Nader and Robinson 2010). While important questions regarding rice straw

management were debated as the California ban on burning fields was mandated, most of the literature

points to incorporating straw, and winter flooding as the preferred means of managing rice straw. Should

the value of GHG mitigation, in particular methane emissions, be valued more than habitat and soil quality

impacts of rice straw, we speculate that the value of rice straw as a raw material could potentially become

more important.

The raw material produced is little appreciated as fodder because of its low nutrient and high silica content

except in drought years when other forages are limited. Additional nitrogen fertilizer may be needed if

the straw is to be used for beef feed. The addition of the recommended 150 kg nitrogen per hectare for

beef feed poses an eventual tradeoff with increased weed abundance and water contamination.

These same traits make it valuable as an erosion control material (chopped and spread aerially). There is

an alternative market for the construction of straw bale houses, but demand remains low.

While it has been researched as a source of energy, this appears to be little developed at this stage for

the same reasons mentioned above.

We did not identify any significant trade-offs with rice grain (food) production. The harvesting of rice straw

has no notable impacts on yield unless the nutrients removed with rice straw are not replaced with organic

or inorganic fertilizers.

Nader and Robinson (2009) flag two points in their “Rice producer’s guide to marketing rice straw”

extension: (1) many farmers were not keen to harvest for rice grain and straw preferring to focus on one

or the other, (2) harvesting straw can imply early draining of the field, and early harvest of rice which can

impact its quality. Management alternatives appeared abundant for managing the latter issue. Rice straw

harvesting for feed requires collected straw within 10 days of rice grain harvest, other uses were less

stringent, though the straw harvest needed to be completed before the next wetting cycle.

2.5.2.4 Increase in rice yields versus GHG emissions reductions

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Farming generates each of the three main greenhouse gases: methane (CH4), nitrous oxide, (N2O), and

carbon dioxide (CO2). Major documented agricultural sources of greenhouse gas emissions in California

include enteric fermentation and manure management in livestock operations, agricultural soil

management and fertilizer use, rice cultivation, burning of agricultural residues, and on-farm energy use.

In this a section, we review the existing understanding of the impact of rice production systems on global

warming potential. The practices that are reviewed in the literature are crop establishment, soil fertility

management, water management and residue management. Water management and residue

management are closely linked in California, which uses a flood based cultivation system.

Biological processes and input use on farms generate mostly CH4 and N2O, which are more potent

greenhouse gases per ton than CO2; CH4 is 25 times and N2O is 298 times more potent in carbon equivalent

unit (IPCC 2007). In California rice management decisions on burning, rice straw incorporation, and

flooding interact to determine the proportion of each of these gases emitted.

Table: 2009 GHG emissions from California Agricultural practices (Source: CARB 2011, cited in Cullman et al. 2014).

Source 2009 Emissions (Tg CO2e)

Percentage of Total

Manure Management 10.34 32 Enteric Fermentation 9.28 29 Soil Management 9.02 28 Energy Use 2.63 8 Rice cultivation 0.58 2 Histosol Cultivation 0.16 0.5 Residue Burning 0.06 0.2


mitigation. Implied impacts, dependencies and causes in California are discussed as follows:

I. There is extensive literature on climate change impact of California rice based systems. Air quality

and impacts on climate change have driven several of these trade-offs. Pre-1990, the primary

trade-off was focused on burning (cause) and the impacts on air quality (negative impact), climate

change (net positive impact), and disease management (positive impact). The ban on burning to

improve air quality has shifted the climate change trade-off to the impact of water management,

for residue management. We maintain burning as a potential trade-off in the discussion here,

although it is highly unlikely that burning will re-emerge as a management option in California.

For this reason, we focus our discussion on trade-offs related to residue management which is

driven by water management options. The impacts on water/residue management on food

production are well studied by Eagle et al. (2000) and are covered in the raw materials section.

The impact of water/residue management on food production is non-significant in systems where

synthetic fertilizers are used.

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Burning of agricultural products can have significant effects on air quality. The CO2 emitted has

less impact on climate change than the CH4 emissions from rice cultivation (McCarty 2011) since

CH4 has 21 to 34 times the Global Warming Potential (GWP) of CO2. Rice systems are considered

to be globally significant sinks of CO2 but are net emitters of CH4 (McMillan et al. 2007). McMillan

et al. (2007) studied the balance in climate forcing of the two gases and suggests that CH4

emissions represent 4.8% to 5.6% of net CO2 uptake over an entire year. Assuming harvested rice

is remineralized, radiative forcing of the emitted CH4 is potentially offset by 26 to 31 percent

(McMillan et al. 2007). Field based management practices may be important in determining the

forcing ratio of the two gases. All in all however, California rice remains a relatively minor source

of greenhouse gases, accounting for less than two percent of emissions from California

agriculture. Emissions from urban land in contrast contribute 70 times more than the estimate for

agricultural lands in California (Haden et al. 2013).

The primary issues with California rice production systems are between the relative climate

forcing of rice residue management based on three primary options: (1) burning, (2) incorporation

and winter flooding, and (3) removal. The results as cited below indicated that burning has lower

climate forcing than rice straw incorporation and flooding due to the much higher forcing that

methane CH4 emitted from flooded wetlands and rice land emissions as compared to CO2 through

burning. 89 percent of rice global warming potential is attributed to CH4, and thus to flooding

practices. The impact of rice straw removal is less clear and requires a life cycle analysis of the

multiple uses of rice straw and climate forcing. The comparison between burning and flooding is

somewhat complex in that California legislation, though the 1991 Rice Straw Burning Act prohibits

burning of rice straw because of its impact on air quality (considered as an ecosystem disserve).

Burning is allowed under specific conditions, including for the periodic control of rice diseases.

We recommend the Cullman et al. (2014) review of California cropland emissions and mitigation

potential and the Lee and Sumner (2014) review of economics of these opportunities as important

reference sources.

II. Crop establishment (cause) has only a small effect on greenhouse gas emissions. Wet-seeded

systems, relative to dry seeded, can increase methane production (negative impact). The primary

management effect considered is the quantity of residue retained on the site from the previous

year, and the duration of flooding throughout a full year of the crop cycle.

III. Soil nitrogen additions (cause) can increase both the food production potential (positive impact)

and the climate change impact (negative impact) of rice cultivation systems. In addition to the

global warming potential of synthesizing nitrogen fertilizers, increased net primary productivity

of crop and weed biomass impacts the amount of carbon stored in dry cultivation systems, and

the amount of methane produced in flooded systems.

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IV. The primary effect of water management is mediated via flooded and unflooded systems, and the

duration of time that fields remain flooded. Increase water use via flooding (cause) increases the

methane produced (negative impact), whereas dry cultivation systems (cause) increase carbon

stored (positive impact), and nitrous oxide produced (negative impact). Flooding increases the

global warming potential of rice production systems but presents important trade-offs with other

services discussed in the report. It is also deeply associated with residue management of rice

production systems as discussed under bullet I.

From a historical perspective, the draining and conversion of California’s Central Valley to

agriculture drove significant soil subsidence from peat oxidation with proportionately large

degrees of carbon dioxide emitted to the atmosphere. Water management and residue

management are inextricably linked and the principle drivers of climate change mitigation in

California rice. The primary trade-off is whether to retain water in the field to facilitate rice straw

decomposition as source of nutrients (positive effect), create biodiversity habitat (positive effect),

with increased methane production (negative effect). This has become an important trade-off in

California rice management with efforts to make rice one of the first agricultural commodities in

California to receive payments for climate change mitigation by reducing the flooding duration

and methane production. This pits several environmental benefits of rice management against

each other, including established incentive systems for habitat services, and emerging incentives

for climate change mitigation because increasing/decreasing the time under which rice fields are

flooded is the primary driver of the habitat/climate change benefits. Water quality, as discussed

in the previous section also is impacted since retaining water on rice fields to allow for

pesticide/herbicide degradation is a principle means of reducing negative impacts of rice

cultivation on water quality.

The primary driver of changes and trade-offs in climate change mitigation in California rice focus

on the use or absence of winter flooding for residue management. Flooding sequesters carbon

dioxide, but emits methane. Draining in contrast increase nitrous oxide and carbon dioxide

emissions, and reduces methane emissions. These trade-offs are covered in detail in the section

below.


In addition to having one of the largest spatial extents of California crops, rice is the highest producer of

net primary productivity in California (1174 g C m-2 year-1) according to Kroodsma and Field (2006). Corn

silage comes in at a close second (1120 g C m-2 year-1). Other extensive crops such as hay, cotton wheat

and barley average 720 g C m-2 year-1 (Kroodsma and Field 2006). The primary trade-offs on climate change

mitigation are driven by three sequential management options (figure xx): (1) burn versus do not burn,

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and (2) if no burn, remove or incorporate, and (3) if incorporated flood, do not flood. The primary impacts

of these options are as follows:

(1) Burn vs. no burn

Burning volatilizes the carbon from rice. The trade-off is that this material is lost as a soil raw material,

and air quality in the Sacramento region, a large urban center, decreases. Legislation has sided with air

quality as the more important consideration in this case. In field rice, straw decomposition increases CO2

equivalent emissions by four times the levels of burning largely through methane production (Wong

2003). The halt in rice field burning supported the sequestration of 1.0 Tg C translating to 55 g C m-2 year

-1 between 1991 and 2000, a notable increase from the pre-burning ban (Kroodsma and Field 2006). Based

on a $65 per metric ton C carbon value, Kroodsma and Field (2006) suggest that the value of the rice

burning ban would be worth the equivalent of $35.75 per hectare per year. The costs of managing a rice

field is approximately $1500 per hectare per year. The trade-off is with methane production however,

with a similar study indicating that at regional scales, the change in burning legislation has led to 2.6 times

more methane produced through winter flooding and rice straw incorporation (Fitzgerald et al. 2000).

The trade-off between burn and no burn is determined by the ratio of carbon dioxide stored versus

methane emitted in no-burn situations. Peischl et al. (2012) derived daytime emission fluxes of CH4

between 0.6 and 2.0% of the CO2 taken up by photosynthesis. Their study suggested that the California

Air Resources Board (CARB) greenhouse gas inventory emission rate of 2.7 x 10(10) g CH4 yr-1 is

approximately three times lower than the range of probable CH4 emissions (7.8-9.3 x 10(10) g CH4 yr-1) in

unburnt and flooded conditions because of the decreased burning of the residual rice crop since 1991,

which leads to an increase in CH4 emissions from rice paddies in succeeding years. This value change is

not taken into account in the CARB inventory.

Figure 13: Carbon sequestration from 1990 to 2000 under five scenarios. The ‘‘baseline’’ scenario included historical trends in areas planted, yields, and harvest index on a 1950–1980 spin up, with constant harvest index from 1980 to 2000. The ‘‘no increase in perennial’’ scenario is the same as the baseline without changes in the area of perennial agriculture after 1980. The ‘‘all rice burned’’ scenario assumes that rice field burning did not phase out during the 1990s as it did in our baseline. ‘‘Prunings to soil’’ returns all almond and walnut prunings to the soils starting in 1980 instead of removing them as in the baseline. ‘‘No till’’ assumes that all tillage ceased in 1980, whereas the baseline assumes constant tillage.

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Source: Kroodsma and Field (2006)

(2) Remove or incorporate

Removing the rice straw does not present a clear trade-off as the final use of the straw determines the

direction of the impact. Using rice straw as a primary raw material for construction, or paper has a positive

impact on climate mitigation. The use of rice straw as a feed for beef or dairy cattle has an impact similar

to rice straw incorporation in terms of methane production (enteric fermentation or anaerobic

decomposition) though there are no published values comparing these effects. The table below indicates

that the impact of enteric fermentation is 16 times greater than rice cultivation; the contribution of rice

straw removal to enteric fermentation would depend on the proportion used in feed sources. Some

estimate that large scale use of rice straw for co-manufacture of paper and energy can mitigate the

greenhouse gas contribution of in field rice straw decomposition, which in the presence of an active

trading market for CO2 credits could range as much as $0.85 million to $1.7 million annually (Wong 2003).

Studies looking at burned and unburned plots, and incorporated/unincorported rice straw in California

fields indicated a fivefold increase in total methane emissions in treatments where the rice straw has been

incorporated in the fall (Bossio et al. 1999) with values ranging from 1.63 to 2.25 g C m-2 in burned plots;

and 2.25 g C m-2 to 9.0 g C m-2 in plots where rice straw is incorporated (Bossio et al. 1999).

(3) Flooded vs. unflooded

Flooding is the dominant means of residue management in California rice facilitating the decomposition

and incorporation of rice straw into the soil facilitated by waterfowl activity (see the chapter on raw

materials). Flooding drives the sequestration of carbon dioxide, but significant methane emissions which

surpass the CO2 equivalent sequestered. Reduced flooding will reduce methane production, but will

increase N2O production. An older study by Bossio et al. (1999) study considered the additional impact of

winter flooding (in addition to flooding during the growth period) and found that winter flooding had a

small reduction in methane production from 9.52 g C m-2 no winter flooding, to 8.87 g C m-2

in winter

flooded. These studies indicate that the effect of incorporation versus removal is much stronger than the

effect of winter flooding (Table xx).

Table: Estimated CH4 mitigation potential of California rice straw and water management regimes (Source: Cullman et al. 2014).

Source

CH4 Mitigation Potential (t CO2 e ha-1

yr-1)

Straw incorporated with winter flood -> Straw removed or burned with no winter flood

(Bossio et al. 1999) 1.39 (Fitzgerald et al. 2000) 2.52

Straw incorporated with winter flood -> Straw removed or burned with winter flood

Bossio et al. 1999 1.52 Fitzgerald et al. 2000 2.32

Straw incorporated with winter flood -> Straw removed or burned with winter flood

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Bossio et al. 1999 -0.13 Fitzgerald et al. 2000 1.29

This contrasts with more recent studies that indicate that managing flooding is likely to be the single

greatest opportunity to reduce the climate impact of rice productions systems. Mid-season drainage or

flooding period reduction can reduce methane emissions from rice but promote N2O emissions that offset

some of the total emission reductions (Hou et al. 2000). N2O has 198 times the global warming potential

of CO2 (IPPC 2007). Most studies that consider both CH4 and N2O have found that some form of mid-season

drainage still yields a net reduction in greenhouse gas emissions (Linquist et al. 2012b). The impact of

reducing flooding duration needs to be weighed against the relative flux rates of the two gases, as well as

the contribution of flooding to habitat, weed control, and associated services.

The impact of flooding on greenhouse gas emission can be reversed (made positive) on historically peat

dominated soils as those found in the Sacramento Delta. Hatala et al. (2012) studied the potential of rice

based systems to serve as net carbon sinks using two years of eddy covariance studies in the Sacramento

Delta. They found no difference in yield measured as total photosynthesis between study sites and

highlight several important nuances in considering the short versus long-term effects of flooding regimes

and location. Many portions of the Sacramento Delta lie below sea level and were characterized by peat

soils resulting from the continuously flooded condition of the natural state of the Delta. Draining these

soils has led to significant soil subsidence via the oxidation of peat soils. Restoring the Delta to its native

flooded condition, including using flooded rice cultivation systems, present an opportunity to reverse

subsidence and return the Delta to a net carbon sink (Hatala et al. 2012). Taking measurements at a

conventional, drained, and grazed degraded peatlands and a newly converted rice paddy in the Delta,

Hatala et al. (2012) found that the grazed degraded peatlands emitted 175 to 299 g C m-2 yr-1 as CO2 and

3.3 g C m-2 yr-1 as CH4, while the rice paddy sequestered 84 to 283 g C m-2 yr-1 of CO2 from the atmosphere

and released 2.5 to 6.6 g C m-2 yr-1 as CH4. Rice paddy flooding in this context (historically peat soils)

inhibited respiration, making rice a net CO2 sink (Hatala et al. 2012) and in contrast to the flood pulse

systems north of Sacramento present a greater opportunity for long-term carbon storage.

The effect of crop establishment

Three rice crop establishment systems could be improved to reduce methane emissions: water-seeded

conventional, wet seeded stale seedbed, and drill-seeded stale seedbed. The drill seeded system reduced

methane emissions by 47 percent compared with the conventional wet seeded system, at the same time,

the water-seeded system’s economically optimized nitrogen application rate increase by approximately

30 kg N ha-1 indicating a potentially important trade-off between N and CH4 emission management

(Pittelkow et al. 2014). Yield was not impacted by the seeding system, nor was it impacts by split

applications of nitrogen compared to single applications – rather application rate remains the principle

driver of yield. The study demonstrates that applying the appropriate dose of N as a single dose before

flooding can meet both agronomic and environmental goals.

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Figure 13: (a) CH4 and (b) N2O emissions with corresponding floodwater depth, and (c) soil temperature (5 cm depth) and precipitation over two annual rice cropping cycles. Note the break in the y-axis of panel (a). Dates of rice seeding, tillering, panicle initiation, flowering, and harvest for each growing season are indicated by S, T, PI, F, and H, respectively. Error bars represent the standard error of three replicates. For clarity only the low (N0 ), middle (N140 ), and high (N260 ) N rates are displayed. Source: (Pittelkow et al. 2012)


Alternate management practices on agricultural lands can have differential impacts on global warming

potential of specific systems. Of particular concern are methane and nitrous oxide. Adviento-Borbe et al.

(2013) provided a comprehensive analysis of the impact of nitrogen fertilization in drill seeded systems

and concluded that while N fertilizer rate applications are correlated with methane production in flooded

systems, fertilizer N rate had no significant effect on global warming potential when application rates

were on the order of 160-200 kg per hectare. At these rates, the yield scaled global warming potential of

CH4 and N2O emissions vary by site between 200 and 800 kilograms of CO2e, but show no change with

increased fertilizer application. The same study showed a sharp yield increase (4 t per hectare to 8 t per

hectare) as N was added from 0 kg to 140 kg per hectare. There were no changes in yield above 140 kg

nitrogen. However the global warming potential increased above the 200 kg nitrogen per hectare

application rate. The authors conclude that achieving the highest productivity is not at the cost of higher

global warming potential because of the disassociation between yield and increased fertilizer application

above the 140 kg per hectare level.

The most comprehensive study of trade-offs between soil fertility, food production and climate change

potential comes from (Pittelkow et al. 2013) whom weigh nitrogen inputs against yield and global warming

potential. In their study, yields ranged from 4.3 to 13.1 Mg ha−1. When considering the trade-off between

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yield and the contribution of fertilizers to global warming potential (yield scaled global warming potential),

the authors conclude that fertilizer applications rates above 140 kg per hectare have an insignificant

impact on yield (12-13 Mg per hectare), but a disproportionate impact on global warming (>108 kg CH4-

C and 620 kg N2O-N per hectare). The results of this study suggest that optimal N rates can produce

maximum yields while reducing annual yield- scaled GWP by 46 to 52 percent.

Figure 14: Two-year mean annual global warming potential (GWP) of CH4 and N2O emissions and annual yield-scaled GWP in response to N rate in a water seeded rice cultivation system of California. Maximum yields were obtained between 140 and 200 kg N ha−1. Source: (Pittelkow et al. 2013)

One trade-off that is rarely considered however is that reducing N rates below what is required to support

optimal crop growth can also “mine” the soil of nutrients and mineralize organic matter, leading to a loss

of soil carbon and increased carbon dioxide emissions. Reducing nitrogen fertilization rates could

therefore compromise both the short- and long-term productivity of agroecosystems (Cullman et al.

2014).

Conservation tillage is another means of managing soil fertility with positive effects on food production

and climate mitigation. The net changes in net soil GHG flux and N2O flux of rice cultivation were greatest

in organic rice production system with the use of cover crops in this model study (-6.38 and -7.55 Mg GHG

per hectare per year). These differences were not found in conventional rice cultivation systems with, or

without conservation tillage. The study uses a modeling approach that does not provide yield data for

rice. Cover crops are not widely used in rice cultivation in the Central Valley.

Similar results were found in a study compared the use of green manures to chemical fertilizers (Lauren

et al. 1994) and found a significant increase in methane production with no increases in yield. In this study,

100 kg N fertilizer were applied in either organic or mineral form and yields were consistent with state

averages of eight to 10 Mg per hectare independent of the form of fertilizer (organic or mineral). The

additional methane production originated from the additional organic matter additions: green manure

additionally increased methane emission by 1.5 to 1.8 times relative to straw only additions (Lauren et al.

1994).

CONCLUSIONS

The patterns in trade-offs that emerge from these studies, while complex to quantify, highlight the impact

of burning, incorporation and flooding on climate change mitigation. In general, the current practice of

incorporating rice straw and flooding gives rice a negative carbon balance. Burning primarily emits carbon

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dioxide and degrades air quality with important health risks for urban populations; incorporation stores

that carbon dioxide but under flooded conditions emits methane, reducing the flooding period reduces

methane, but increases nitrous oxide production. The two greatest means of significantly increasing the

climate mitigation potential of rice are through straw removal and use as a raw material (construction,

erosion control), and expanding rice cultivation with conservation agriculture in the Delta region of

California which was historically under organically rich peat soils.

Rice cultivation has a relatively low impact on statewide greenhouse gas emissions suggesting that

economics of ecosystems and biodiversity would struggle to find suitable incentive mechanisms to offset

this potential. Overall, the relative mitigation potential of rice is ranked as “low to medium” with a

biophysical mitigation potential ranging between -0.13 to 2.52 tons of CO2 equivalent per hectare and

year (Cullman et al. 2014).

The principle levers for achieving this potential occur through reduced flooding, careful fertilizer

management, and through drill seeded stale seedbed systems (Assa and Horwath, 2009). The question of

floodwater management poses potential trade-offs with habitat and water quality services that were

previously discussed when they target winter rather than summer flooding. Recent publications that

consider both the biophysical and the economic aspects of California rice and greenhouse gas emissions

all generally conclude that rice has complex interaction with CH4, and N2O compared to other crops. Gains

in reducing CH4 typically yield higher N2O emissions, though CH4,forcing is generally thought to be greater

- though consensus seems to move towards slightly greater impact of reducing flooding and drill seeding

on CH4, emission reductions. These marginal benefits may have greater trade-offs in relation to other

services provided by rice, including yield, habitat, and water quality.13

2.5.2.5 Increase in rice yields versus the provision of cultural services

Hunting, fishing and gathering from California rice lands may not be as critical as in many developing

countries where there is a direct relationship between these resources and food security. Duck hunting

however, is an important economic and cultural activity in the region and can be classified as a

provisioning and cultural ecosystem service with important economic value. The growth in increased

extent of cultivated rice lands in California and in particular the use of winter flooding to manage rice

straw and stubble has significantly increased waterfowl populations and hunting opportunities.

Several uncertainties have been flagged as being of relevance to this service. Some of the issues that

revolve around this service are directly focused on the extent and timing of water that is maintained in

rice field, managing the diversity of water depths on fields (shorebird versus waterfowl). These are

covered in the water quality and quantity sections. Although water management is the dominant control

13 We flag the following reference for the economic valuation: Garnache, C., J.T. Rosen-Molina, and D.A. Sumner. 2010. “Economics of Carbon

Credits from Voluntary Practices on Rice Farms in the Sacramento Valley.” In Creating and Quantifying Carbon Credits from Voluntary Practices on Rice Farms in the Sacramento Valley: Accounting for Multiple Benefits for Producers and the Environment, 11–17. Environmental Defense Fund Inc.

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issue, the cultivation methods, and baling of straw for off-site raw material development pose secondary

considerations:

I. As discussed in the water quality chapter, flooded rice cultivation systems analogous to the

natural wetlands that once dominated the central valley. More than 93 percent of the historic

California Central Valley wetlands have been lost and converted to agricultural and urban uses

(Strum et al. 2013). Adding winter floodwater (cause) to fields provides significant habitat benefits

(positive impact), and as mentioned, several conservation programs provide incentive to farmers

providing overwintering habitat. Flooding is the primary attractant for increasing habitat quality;

within flooding regimes altering water depth attracts different avian communities (Elphick and

Oring 2003) with deeper waters attracting ducks, and shallower water management being

favorable to shorebirds. Fallow fields are also important for overwintering birds and provide

night-time roost for massive colonies of cranes, geese and ducks. Not quantified, but evident in

the public relations and outreach material, and personal communication with farmers, is the value

they individually place in habitat stewardship.

II. One important trade-off with food production is the harvesting method (cause), which roughly

determines how much grain is left on the field. White-fronted geese migrate along the Pacific

flyway and make use of agricultural lands in the Klamath Basin and Sacramento Valley. Rice

provides a significant proportion of the food intake of this species (positive impact) (Ely and

Raveling 2011). Rice provides important habitat to pintail duck (Anas acuta) which has better

survivorship in rice agriculture compared to cotton (21.3 percent lower survivorship); hunting was

one of the greatest causes of mortality, accounting for upwards of 83 percent of the mortality

observed (Fleskes et al. 2002). It should be noted that this is not a population mortality level, but

rather a driver of the observed mortality associated with a “provisioning service” of central valley

rice fields and wetlands.

The effect of specific management practices

The effect of rice varieties

California’s central valley is a critical stop over point of the Pacific flyway (Figure 15). The history of rice

and habitat services has not always been an easy one. Waterfowl attracted to rice fields can serve as pests

and were treated as such in the early 1900’s. This is relatively easily addressed however since waterfowl

are a migratory group whose dependence on California wetlands is seasonal, and currently centered on

the postharvest season when their presence does not conflict with rice cultivation. Similarly, from the

conservation side, most waterfowl have moved north during their particularly sensitive nesting season,

and are absent from California rice fields during the spring and summer when cultivation activities are

most intense. Hill (1999) attributes this to some changes in rice production systems, including new

varieties that mature more quickly, and thus which were harvested before the arrival of the majority of

the migratory waterfowl. The recent history of waterfowl and rice has shifted from one of conflict to a

global example, possibly only second to coffee and cacao agroforests, of cooperation between agriculture

and conservation. It is estimated that the Central Valley is home of 20 percent of the national waterfowl

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population midwinter. The trade-off is no longer an issue in California rice production, however we flag it

here since varietal selection and habitat quality are rarely associated as mutually beneficial practices.

The effect of water management

The United States Fish and Wildlife Services (USFWS) information page on the North American Waterfowl

Management Plan states that waterfowl are the most economically important group of migratory birds in

the North American Continent. In 1985, approximately 3.2 million people were spending on average $1

billion annually to hunt waterfowl, a larger number, 18.6 million people engage in watching waterfowl

and spend an estimated $2 billion to do so (http://www.fws.gov/birdhabitat/NAWMP/index.shtm). The

plan has allocated $7.5 billion nationally, in joint ventures to protect restore and enhance 8.9 million

hectares of waterfowl habitat. Waterfowl densities are higher in surface flooded fields than in those that

are intermittently flooded by rainwaters (Eadie et al. 2008).

Figure 16: Biological flyways of the United States. Map developed by Michael A Johnson, North Dakota Game and Fish (www.flyways.us)

Table: Estimates of the economic value of migratory bird hunting in California. The estimate was produce by taking National level hunting data from the IAFWA report on “The Economic Importance of Hunting” developed by the U.S. Fish and Wildlife Service under Cooperative Grant Agreement No. 14-48-98210-97-G047. The California estimate is derived using a 20% of national based on the proportion of migratory waterfowl using California wetlands as cited in Eadie et al. (2008). These figures suggested that California migratory waterfowl hunters (cited as 250K individuals in 1996) account for approximately $9000 each per year on hunting. Source: www.dfg.ca.gov/wildlife/hunting/econ-hunting.html.

http://www.fws.gov/birdhabitat/NAWMP/index.shtm

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US Migratory Birds California (20%)

Jobs 95,748 19,150

Retail Sales 2,996,257,139 $599,251,400 Multiplier Effect $8,154,525,482 $1,630,905,100 Salaries and Wages $2,116,17,982 $423,235,600 State Sales and Tax Revenues $178,480,197 $35,696,000 State Income Tax Revenues $37,995,873 $7,599,200 Federal Income Tax Revenues $216,155,138 $43,231,000

Total $13,699,591,811 $2,316,702,000

The effect of harvesting

Estimates of the caloric and habitat needs of the northern pintail highlight the dependence of this species,

amongst others, on rice cultivation areas including the retention of sufficient foraging material on site

post-harvest (Miller et al. 1989, Miller and Wylie 1996, Miller and Newton 1999). Several management

practices in addition to winter flooding (water quantity) can have an important impact on the quality of

foraging habitat for wintering waterfowl. Harvesting practices can impact conservation value with best

practices using conventional harvesting techniques (cutter bars) and shallow flooding of fields (Day and

Colwell 1998). These harvesting techniques can have important consequences on the “waste seed”

remaining postharvest, and available for consumption by waterfowl. Conventional harvesting can leave

upwards of 388 kg ha-1 whereas strip harvesters reduce this amount to 245 kg ha-1 (Fleskes et al. 2012).

These values are three to four percent of mean yield in California rice fields, or a one percent difference

between harvest tools. Increased use of stripper heads have an unknown potential to reduce habitat

quality, though this remains untested, and little is known regarding the alternate food sources provided

by rice lands.

CONCLUSIONS

Of the non-production services produced by California rice lands, recreating hunting of water fowl is likely

to be the most valued at this stage of the crops history in California. While carbon markets are emerging,

the complexities of managing GHG emissions in rice fields suggests a narrow margin of change available.

Rice farming is currently in the position where conservation groups refer to the loss of rice lands with the

same degree of concern that they refer to loss of native habitat. Private hunting clubs, and conservation

organizations such as The Nature Conservation are increasingly paying farmers for this ecosystem service,

and paying well.

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3. CONCLUSIONS

3.1 SYNERGIES AND TRADE-OFFS

For each case study country we identified the trade-offs and potential synergies that originate from aiming

to obtain more than one benefit from rice agro-ecosystems; i.e. more than increasing rice production

alone. These aims, set by small-scale farmers or commercial producers, the society or policy makers, are

as diverse as rice agro-ecosystems themselves. They might aim at increasing food production, stable or

resilient food production, or clean and healthy food production (i.e. food safety). Another goal might be

rice production only, or it might be a production of diverse food products, which includes rice as the main

crop but is supplemented by protein-rich animal products and vitamin containing vegetables and aquatic

plants.

But the claim or demand posed on rice agro-ecosystem goes way beyond food production alone. By-

products of rice are promising sources of raw material for feed, and fibre. International and national

politics require rice agro-ecosystems to be climate-smart, and therefore call for rice agro-ecosystems that

not only produce food, but also reduce their GHG emissions and increase their carbon storage potential

in addition to be being resilient to climate change and climate variability. Rice agro-ecosystems can be

threatening freshwater sources for drinking water and biodiversity, when agricultural management is not

adequate, and the large amount of water used for rice production poses a threat to water scarce regions

or areas where there is a high demand for water from urban, industrial or other agricultural sectors. Last,

but not least, rice agro-ecosystems constitute an important type of wetland and therefore harbour many

different animal and plants species. Hence they are vital for the conservation of biodiversity, which does

not only have an intrinsic value, but also serves as an additional source of food and feed. The different

aquatic species also provide many regulating ecosystem services considered in this study such as biological

nitrogen fixation and biological pest control, thereby lowering the need for external inputs.

While this is all true when describing the potential of rice agro-ecosystems in the world, national, regional

or even local realities need to be taken into account when painting a global picture of rice agro-

ecosystems. Trade-offs and synergies originating from different demands on rice farming are highly

context specific. This narrative review therefore set out to describe the particular context and to identify

those context specific factors that make each agro-ecosystem unique. However, research studies and grey

literature do only reflect part of the global picture – usually they document or analyse those realities that

are funding priorities, the mandate of specific research centres, or communities which collaborate with

research organisations, NGOs or development organisations. Less is known however about the reality

beyond these documented cases. It is more than likely that many rural populations do not have access to

practises, technologies, systems and concepts that have been tested or promoted by these institutions.

Little is known about the actual adoption rates of many of the practises and systems covered in this

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review. The results have therefore to be taken with caution, and should be complemented with field

studies.

To identify the myriad of trade-offs and potential synergies originating from pursuing different goals in

rice agro-ecosystems, we described the dependencies of rice agro-ecosystems, their impacts and the

causes between the two. Or put differently, we analysed the inputs and the outputs of rice production

systems, and explained how and why they are interlinked. These different interactions sometimes lead to

synergies and sometimes to trade-offs. The results of the case study analyses are summarized in the tables

below (3.1.1 to 3.1.5).

What becomes apparent from these analyses is that one rice agricultural system can meet two or more

claims posed to rice-agro-ecosystems at the same time, yet it is a question of how to manage these claims.

To illustrate this point, consider the following:

I. Rice agro-ecosystems may have positive or negative impacts on a farm and its natural capital (on-

site) or the environment and the human society (off-site). Yet the first question to ask is – who or

what is the causal agent? Is it the rice farming system and its management itself, or is it the

farming system affected by an external originator or polluter? Evidence shows that the benefits

and costs resulting from the rice agro-ecosystems are originating from both, off-site, that is from

external sources such as the industry, natural disasters or invasive species, and from on-site

triggers through different types of agricultural management.

While off-site causes that result into positive and negative impacts of rice agro-ecosystems might

be mitigated through appropriate agricultural management, the control of and the full

responsibility for these impacts, usually negative, cannot be bourne by agriculture alone.

On the other hand, those benefits and costs caused on-site, through different types of agricultural

management, fall under the full control of the rice farm itself. This is where appropriate decisions

of which management practises to apply need to be taken. Policy makers can support this

decision making process by providing the right incentives or by passing laws and regulations

which control agricultural management, directly or through institutions. For instance, policy

makers can provide the means to build capacity among rice farmers, to support rural

communities with extension services and the private sector with incentives to pursue goals or

ways that go beyond increasing profit. It is therefore of interest to policy makers to know the

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myriad of dependencies, impacts and causal agents impacting and impacted by management

decisions in a specific context.

II. Identifying dependencies, causal agents and impacts is not as straight forward as one might think.

There is a myriad of different aspects that need to be taken into account, some of which are

independent of each other, and some of which are intrinsically interlinked.

For example, the issue of rice over-fertilization in Costa Rica has been studied in depth. Taking

over-fertilization as the principle trigger, there is a long chain of impacts which trickle down from

this first causal agent. Throughout the chain, other causal agents might add to the already

provoked impacts. Please see table X (example 1 and 2) below to illustrate this fairly complex

chain of dependencies, causal agents and positive and negative impacts.

Table X. Causal chain of causal agents and impacts in rice agro-ecosystem. The tables should be read level by level

from left to right. Red circles in the dependency column indicate primary dependencies of interested to the causal

chain, while non-circled dependencies describe the overall underlying inputs to the system.

Example 1: Over-fertilization of rice fields.

Level Dependencies Cause Positive Impact Negative Impact

1 Fresh water (quality) Fresh water (quantity/reliability) Soil (biological, chemical and physical dimensions) Plant propagules (seeds, seedlings, etc.) Landscape elements (e.g. wetlands) Pesticides, synthetic or natural

Fertilizers, synthetic or organic Labor (human, animals, machinery) Knowledge Infrastructure, including machinery Policies (e.g. those that promote subsidies for agricultural inputs)

Over-fertilization Increased rice production

Water contamination and run-off

2 Water contamination and run-off

N/A Eutrophication, when the nutrient in the run-off water surpass certain reference limits

3 Eutrophication Cattail plants grow Aquatic communities are negatively affected, e.g. fish die

4a Cattail plants Plants serve as buffer, absorbing nutrient run-off from rice fields

N/A

4b Fish die N/A Less food for people and wildlife

5 Plants serve as buffer, absorbing nutrient run-off from rice fields

Protected wetland areas are not contaminated

N/A

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Institutions (e.g those that deliver capacity building on rice)

Example 2: Conversion of wetlands adjacent to rice-fields into new rice fields additional to over-fertilization.

Level Dependencies Cause Positive Impact

Negative Impact

1 Fresh water (quality) Fresh water (quantity/reliability) Soil (biological, chemical and physical dimensions) Plant propagules (seeds, seedlings, etc.) Landscape elements (e.g wetlands) Pesticides, synthetic or natural Fertilizers, synthetic or organic Labor (human, animals, machinery) Knowledge (e.g understanding the role of cattails and buffer zones) Infrastructure, including machinery Policies (e.g. those that promote subsidies for agricultural inputs or protected area policies,) Institutions (e.g those that deliver capacity building on rice, or those that those enforcing protected area policies)

Conversion of wetlands adjacent to rice-fields into new rice fields

Increased rice production

Loss of buffer zone around rice fields

2 Loss of buffer zone around rice fields

N/A No habitat for cattail plants

3 No habitat for cattail plants

N/A No buffer function of plants, hence fertilizer run-off into protected areas

4a Fertilizer run-off into protected areas

N/A Eutrophication

4b Eutrophication N/A Loss of biodiversity in protected areas, incl. aquatic species

5 Loss of biodiversity in protected areas, incl. aquatic species

N/A Less food for people and wildlife

III. As mentioned above, rice agriculture can address some of the issues identified in this report by

changing current rice management practises or by improving current farming operations, some

of which are discussed and analysed in the report (see next section 3.2). However, this narrative

report does not claim to be a manual of how to do this nor does it aim to give a comprehensive

list of management practises that reduce costs of rice farming to the environment and the society.

It does show however, that rice farm management practises are as diverse as global rice agro-

ecosystems. It does illustrate that many solutions need to be context specific, and that there is no

one size fits all solution to addressing the issues encountered with rice farming.

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3.1.1 INCREASE IN RICE YIELDS VERSUS MAINTENANCE OF WATER QUALITY

Table X. Trade-offs and win-win situations resulting from pursuing two goals: Production of food (Increasing rice production) versus the maintenance of

freshwater quality

Goals Action/Causal factors Location of causal factors (On-site or off-site)

Benefits (Positive impacts)

Location of benefits (On-site or off-site)

Costs (Negative impacts)

Location where costs are incurred (On-site or off-site)

Dependencies

Increasing rice production & Maintenance of fresh water quality

Extreme events such as flooding or typhoons that increase water salinity

Off-site None N/A Crop loss; Polluted freshwater

On-site and off-site

Fresh water (quality) Fresh water (quantity/reliability) Soil (biological, chemical and physical dimensions) Plant propagules (seeds, seedlings, etc.) Pesticides, synthetic or natural Fertilizers, synthetic or organic Labor (human, animals, machinery) Knowledge Infrastructure, including machinery Policies (e.g. those that promote subsidies for agricultural inputs)

Increasing rice production & Maintenance of fresh water quality

Silt deposition on rice fields, contaminated with mercury from artisanal gold mining

Off-site None N/A Crop loss; polluted freshwater


Increasing rice production & Maintenance of freshwater quality

Introduction of exotic animals and plants that increase water turbitity

Off-site Rice production maintained; Possibly new food sources


Polluted freshwater On-site


Appropriate soil fertility practises such as biological nitrogen fixation or proper nutrient management such as Site Specific Nutrient Management (SSNM)

On-site Increased rice production Habitat for aquatic organisms (additional sources food and feed, agents for biological pest control, soil fertility, etc.) Freshwater reservoirs below rice paddies as source for drinking water

On-site Possibly higher labour costs with SSNM

N/A

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Avoided/Less costs of synthetic inputs

Institutions (e.g those that deliver capacity building on rice) Increasing rice

production & Maintenance of freshwater quality

Inappropriate soil fertility practises leading to over fertilization

On-site Increased rice production

On-site Polluted freshwater with consequences for habitat and drinking water quality



Appropriate pest management practises (e.g natural pest control measures)

On-site Maintained rice production; Safe, uncontaminated rice; Maintained freshwater quality Less costs of inputs

On-site None


Inappropriate pest management practises (e.g using levels of pesticides above accepted maxima for drink-water safety)

On-site Maintained rice production

Contaminated rice (toxic residues); reduced food diversity; polluted fresh water with consequences for habitat and drinking water quality Cost of inputs

Off-site

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3.1.2 INCREASE IN RICE YIELDS VERSUS REDUCTION OF WATER USE

Table X. Trade-offs and win-win situations resulting from pursuing two goals: Production of food (increasing rice production) versus the use of freshwater

(quantity)






Dependencies

Increasing rice production & Use of freshwater quantity

Full immersion of rice plants from rainfall or irrigation water

On-site Rice production, incl. Rice plant growth; Nitrogen fixation; Weed control; Habitat for a diversity of associated plants and animals

On-site GHG emissions from constantly flooded rice paddies

Off-site Fresh water (quality) Fresh water (quantity/reliability) Soil (biological, chemical and physical dimensions) Plant propagules (seeds, seedlings, etc.) Pesticides, synthetic or natural Fertilizers, synthetic or organic Labor (human, animals, machinery) Knowledge Infrastructure, including machinery Policies (e.g. those that promote subsidies for agricultural inputs)


Physical water scarcity (reduced rainfall)

Off-site Depend on the degree of water scarcity

Depend on the degree of water scarcity


Economic water scarcity (poor irrigation infrastructure)

On-site Depend on the degree of water scarcity

On-site Depend on the degree of water scarcity

Off-site


Greater demands for available water from other sectors

Off-site Depend on the degree of competition

On-site Depend on the degree of competition

Off-site


Water-saving technologies (a combination of reduced land preparation time, adoption of intermittent flooding

On-site Rice production, incl. Rice plant growth Reduced GHG emissions


Reduced weed control; thereby an increased need for pesticide use Reduced nitrogen fixation; thereby an

On-site

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(or no flooding), and increased use or efficiency of fertilizers

increased need for fertilizer use Reduced or destroyed habitat for a diversity of associated plants and animals

Institutions (e.g those that deliver capacity building on rice)


Hydroelectric projects Off-site Energy production; Increased availability of irrigation water Increased rice production


As a result of increased availability of irrigation water, a rapid expansion of agriculture. An example from Costa Rica showed that agriculture expanded beyond the borders of a neighboring national park.

N/A


Construction of the Yolo bypass wetland area in California, which includes rice fields

N/A Flood protection Rice production Provision of wetland habitat


N/A N/A


Wetlands, including rice, provide breeding grounds for disease vectors such as mosquitos

On-site N/A N/A Spreading of disease

Off-site


Irrigation On-site Rice production On-site Depending on the landscape context, scarcity of surface water and groundwater depletion Increasing soil salinity


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Development of hard pans Waterlogging Offsite/downstream degradation of water quality

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3.1.3 INCREASE IN RICE YIELDS VERSUS MAINTENANCE OF AIR QUALITY

Table X. Trade-offs and win-win situations resulting from pursuing two goals: Production of food (Increasing rice production) versus the production of raw

materials

Action/Causal factors Location of causal factors (On-site or off-site)





Dependencies

Burning of rice residues

On-site Rice production; Weed control; Time savings when preparing land for next crop establishment; Control of diseases; Release of nutrients (claimed by some farmers)

On-site Harmful air pollutants which impact on health GHG emissions Economic loss of raw materials (which if there is a market, can be sold as raw material for energy production; or used on the same farm)


Fresh water (quality) Fresh water (quantity/reliability) Soil (biological, chemical and physical dimensions) Plant propagules (seeds, seedlings, etc.) Pesticides, synthetic or natural Fertilizers, synthetic or organic Labor (human, animals, machinery) Knowledge Infrastructure, including machinery Policies (e.g. those that promote subsidies for agricultural inputs) Institutions (e.g those that deliver capacity building on rice)

Use of raw material as soil amendment (source of organic matter and to a lesser degree of nutrients)

On-site Rice production, incl. improved soil structure and fertility;

On-site Economic loss of raw materials (which if there is a market, can be sold as raw material for energy production; or used on the same farm) Conflict with use as animal fodder if animals are held on farm

On-site

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Use of raw material as animal feed (usually used on-site as emergency feed or feed complement)

On-site Rice production; incl. Improved soil structure and fertility when (residues in) animal manure are brought back to the field; Animal feed, albeit of low nutritional quality

On-site Economic loss of raw materials (which if there is a market, can be sold as raw material for energy production; or used on the same farm)

On-site

Use of raw material as source for energy for electricity production (either on-site for milling, or sold as a commodity off-site)

On-site or off-site

Rice production; incl. Costs saved for electricity during milling operations; Or gain through sale of raw material as energy commodity

On-site Rice production might be reduced when organic material is repeatedly removed from the system and not substituted adequately

On-site

Use of raw material as source for energy for cooking

On-site Rice production, incl. Costs (and time) saved for energy for cooking and heating


On-site

Great demands for raw materials from other sectors

Off-site Rice production; Gains from sale of raw material to other sectors


On-site

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3.1.4 INCREASE IN RICE YIELDS VERSUS GHG EMISSIONS REDUCTIONS

Table X. Trade-offs and win-win situations resulting from pursuing two goals: Production of food (Increasing rice production) versus climate change mitigation






Dependencies

Increasing rice production & mitigation of climate change

Production of rice in water

On-site Rice production; Habitat for associated animal and plant species;

On-site Methane emissions On-site or off-site

Fresh water (quality) Fresh water (quantity/reliability) Soil (biological, chemical and physical dimensions) Plant propagules (seeds, seedlings, etc.) Pesticides, synthetic or natural Fertilizers, synthetic or organic Labor (human, animals, machinery) Knowledge Infrastructure, including machinery


Water management practises that allow intermittent drying of rice fields

On-site Maintained rice production

Overall reduced emissions; Reduced habitat for associated animal and plant species


Soil fertility management (type, rate, and mode of fertilizer application)

On -site Depends on kind (synthetic, organic), rate and mode of fertilizer application

On-site Depends on kind (synthetic, organic), rate and mode of fertilizer application

On-site or off-site


Fertilizer (urea) production

Off-site N/A N/A CO2 emission from combustion of natural gas and other fossil fuels; Ammonia and particulate matter emissions; Formaldehyde and methanol, hazardous air

On-site or off-site

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pollutants, may be emitted if additives are used.

Policies (e.g. those that promote subsidies for agricultural inputs) Institutions (e.g those that deliver capacity building on rice)


Burning of rice straw On-site Rice production maintained or reduced; Weed control; Time savings when preparing land for next crop establishment; Control of diseases; Release of nutrients (claimed by some farmers)

On-site Harmful air pollutants which impact on health GHG emissions (carbon dioxide) Economic loss of raw materials (which if there is a market, can be sold as raw material for energy production; or used on the same farm)


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3.2 STUDY LIMITATIONS

3.2.1 SCIENCE VERSUS REALITY

This literature review is based on peer reviewed journal papers. The farm management practices and

systems described in this publication do therefore reflect those practices and technologies which have

been applied and analyzed for the sake of scientific research, be it on farmers’ fields or in experimental

research stations. Data on actual rice farm practices in Senegal is limited. Hence, it should be noted that

many rice management practices discussed in this report might not align with daily reality of rice practices

conduction by rice farmers. Science is also often funded by ephemeral priorities. Considering the

California studies, major trends in water quality, air quality, and climate change emerge in a temporal

sequence that appears related to “hot topic” issues in the region at the time.

3.3 NEXT STEPS

The case studies have clearly shown that there is the potential to address current trade-offs and problems

originating from or present in some rice agro-ecosystems when the appropriate management practices

or management systems are chosen.

Some of the trade-offs and problems originate off-site, others originate from the system itself. Those that

originate from management practises applied on farm have shown to have different effects on different

aspects of rice agro-ecosystems – positive, negative or neutral. The next step is hence to quantify these

effects, and thereby deliver a detailed biophysical assessment of rice agro-ecosystems. The biophysical

data will then build the basis for the monetary valuation conducted by Trucost.

A comprehensive screening of the available literature has shown that comparative studies which are

needed for the meta-analysis are relative scarce however:

For the Philippines, 992 papers have been screened, 103 papers have been included in the

narrative report, 29 of which are suitable for a comparative meta-analysis. For a detailed list of

screened studies, please refer to Horgan et al, 2015.

For Cambodia, 162 studies have been screened, and 34 studies have been included in the review,

14 of which belong to grey literature. .

For Senegal, 119 papers have been screened (excluding grey literature), and 70 have been

included in the narrative review. Yet only 10 papers could be identified as suitable for the

comparative analysis. For a detailed list of screened studies, please refer to Van Dis, 2015.

For Costa Rica, 110 papers including grey literature and 62 papers excluding grey literature have

been screened. 38 papers have been included in the narrative review, 17 of which have been

considered suitable for the meta-analysis.

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The narrative literature review has facilitated the structuring of the biophysical data framework, which

will constitute the basis of the meta-analysis. The biophysical data framework contains about 60 different

indicators describing impacts and dependencies which relate to the questions that the study aims to

answer. The indicators have been collected from all papers that were reviewed during this narrative

review. Due to its size, the spreadsheet has been submitted separately to this report.

The preliminary results presented in this review from five case study countries should only be seen as the

tip of the iceberg. As mentioned before, trade-offs and problems are very context specific. Some

preliminary conclusions can be drawn from five case study countries, yet to have an idea of the global

picture, of the overall nature of rice farming, one would need to conduct a global meta-analysis.

Furthermore, round table meetings with different stakeholders to present and discuss their different

“claims” of what rice-agro-ecosystems can and should deliver in a specific country situation would be

needed. Also, primary research in each country of interest, including field surveys and an analysis of

current policies, among other things, would help the cause. This is particularly important when one strives

to give concrete policy advice as opposed to making broad generalizations. This study can be seen as a

first preparatory step in this direction – no more, no less.

222 | P a g e

4. ACKNOWLEDGEMENTS Project supervision

Barbara Herren, FAO

We would like to thank the following persons for their partial or complete review of this draft:

Dylan Warren Raffa

Harpinder Sandhu

Tu Anh Vu Thanh

Roel Revilla Ravanera

Theo Friedrich

Ana Kojakowic

Craig Jamieson

Lucie Pluschke

Jonne Rodenburg

Armine Avagyan

Support staff

Elizabeth Pain, FAO

Financing institution and conceptual oversight

Salman Hussain and Dustin Miller, The TEEB secretariat of UNEP

Alexander Mueller, IASS Potsdam

The Government of Norway

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