Effects on soil, climate and farmers’ livelihoods
2nd ECHO Asia Agricultural ConferenceSeptember 21-25, 2009Chiang Mai, Thailand
Winfried ScheeweDED-Cambodia/CEDACPhnom Penh, Cambodia
- an entry point to sustainable rice production
Does rice straw have any value? Burning of rice straw is a
common sight during the harvest period in many parts of South and Southeast Asia.
Farmers are unaware: Straw from one hectare contains 25 to 40 kg N.
= Farmers are burning money.
Yet, the energy (carbon) contained in the straw may be even more important.
Biomass open burning – Global overview
Burning of rice straw and other biomass is practiced in most Asian countries
OverviewWe will look here at some details of the recycling of rice straw by scattering it equally in the field or mulching. Effects on soil Effects on the
atmosphere Effects on farmers’
livelihoods
will be discussed
Why do farmers burn the straw? Straw was traditionally
used as fodder Mechanization
less animals needed Additional cropping cycles
straw disturbs land preparation waste
Availability of fertilizers To supposedly prevent
further spread of diseases Concept: clean field,
(variation of slash & burn)
Why farmers should NOT burn it?
1 ton of straw contains: 5 to 8 kg nitrogen 1.2 kg phosphorous 20 kg potassium 40 kg silica 400 kg carbon
Per hectare, about 5 tons of straw are left
What happens if the straw is burnt? 400 kilogram of carbon
go back to the atmosphere
93 % of the nitrogen goes back to the atmosphere, = 30 to 40 kg N/ha
25 % of the phosphorous and 21 % of the potassium disappear
Silica is left, but the heat makes it insoluble.
Straw burns with temperatures up to 700◦ C
What can farmers do instead?
Just leave the heap- do nothing (straw will slowly decay in one spot, much of the carbon will be lost)
Set up a compost pile (controlled composting)
Distribute the straw equally in the field
Mulching – some considerations (1) Scatter the straw equally
soon (immediately) after threshing in the field
The straw is left for about 4 weeks on the surface to decompose before plowing
This allows bacteria involved in the decomposition to fix nitrogen from the atmosphere
Mulching – some considerations (2)
Ideally combined with a green manure crop
If possible, the straw should be only shallowly incorporated to decom-pose more for several days under aerobe condition before further land preparation for the next planting
What are the effects on the soil?
Nitrogen and other nutrients recycled
Additional N-fixed Part of the carbon is
incorporated into the humus (SOM) content of the soil
Nutrient deficiencies minimized
Iron (and other) toxicities reduced
A closer look at Nitrogen
One tonne of rice grains absorbs about 12.5 kilogram N.
If the yield is 4.5 tons, the grain contains approx. 56 kg N.
The straw contains about 30 kg N.
Grains 56 kg NStraw 30 kg N-------------------------------------Requirement 86 kg N
- From the straw (per ha) 30 kg - N-fixation associated with the decomposition 25 kg- N-fixation by soil-borne micro-organisms 27 kg- Rain 4 kg Total 86 kg N/ha
Several farmers obtained yields of over 4 t/ha over many years without additional inputs.
Question: If no synthetic fertilizer was applied, where did the nitrogen come from?
Several kind of orga-nisms are involved in natural processes which provide nitrogen to the crop.
All need energy which the carbon of the straw supplies.
Humus contentOver time, humus
content increases pH level ↑ Nutrient supply more
balanced Plant health improved Insect problems less
likely Soil structure improved Water retention increases Nutrient deficiencies
corrected
Nutrient deficiencies corrected Farm of Isidro Prado
After 15 years of conventional cultivation Zinc deficiency became a problem
Yield declined by 60 to 70%
Straw application within two years, yield back to normal levelsof over 4.5 t/ha(40 sacks from 0.38 ha)
Iron toxicity corrected In some places iron
toxicity is a problem due to strongly reducing
conditions in the soil and/or low pH
low and unbalanced crop nutrient status
Causes stunted growth, extremely limited tillering.
These conditions can be corrected just by returning the straw
Straw management and climate (1) Burning releases carbon
Philippines: 3.26 million tons C per year (= 12 million tons CO2)
Total emissions 2006: 8.4 Giga-tons carbon
Burning causes pollution (including polycyclic aro-matic hydrocarbons, some are toxic)
Incorporation may add to releases of methane
Straw management and climate (2) The main sources of greenhouse
gases emissions in agriculture
Million tons CO2 -eq
Agriculture contributes between 17 and 32% of all global human-induced green house gases.
Of this, 12% is caused by biomass (incl. rice straw) burning
Cool Farming: Climate impacts of agriculture and mitigation potential, www.greenpeace.org (2008)
Straw management and climate (3) Decomposition under
anaerobe condition: Methane emissions ↑
If synthetic N is applied Nitrous Oxide emissions ↑
Synthetic N requires energy (~1.4% of the world's annual energy supply)
causes CO2 emission
Generally:Recycling of straw minimizes releases of CO2 + other green house gases from rice fields
Carbon (humus) in soil ↑
Straw management and climate (4) Soils can serve as carbon
sinks
Generally, soils have lost carbon due to clearing and cultivation
Claim by IRRI scientists: Irrigated soils still high in humus (or SOM)
Rainfed rice fields provide different conditions than irrigated fields
Effect on farmers’ livelihoods (1)Comparaison MASIPAG (Organic) vs. Conventional (2003)
In the year 2003, the Philippine NGO TCSAI compared yield and income 10 pairs of farmers with adjacent organic and conventional fields irrigated fields and 12 pairs with rainfed fields.
The organic farmer, who recycled the straw had a almost 10 percent higher net income than their conventional neighbors. They had less costs for inputs, but therefore higher labor costs.
However, the cost-benefit analysis did not include cost for the capital necessary to purchase inputs. Commonly, loans for rice production are obtained from informal lenders. Thus, most conventional farmer have significant deductions from their income due to higher capital costs.
Effect on farmers’ livelihoods (2)Mr. Isidro Prado:
Before recycling rice straw he needed to borrow 4,000.00 Pesos and paid up to 3,500 Pesos for each PHP 1,000.00 (=14,000.00)
Later he needed to borrow only PHP 2,000.00 for which he paid a much lower interest rates (= 3,750.00)
STOP burning rice straw Need to raise
awareness Many NGOs promote
sustainable practices Many provinces and
municipalities have issued ordinances prohibiting the burning of rice straw
STOP burning rice straw (2)
Group of Advocates for Sustainable Agriculture, Inc.
Tandag, Surigao del Sur
Ang Paggamit sa Uhot
sa malungtarong agricultura
(The use of rice straw for
sustainable agriculture)
STOP burning rice straw (3)
CITY ORDINANCE NO. 229, S-2006 (TAGUM City)
d. Agricultural Areas:
1. Agricultural wastes, e.g. rice straws, corncobs, must not be burned but be stockpiled in a proper location and composted.
Tribute The idea to recycle rice straw
in the field was among others propagated by the late Lorenzo P. Jose, a pioneering organic farmer in Central Luzon, Philippines.
Mr. Jose had learnt about this from the late Masanobu Fukuoka, a Japanese farmer and philosopher. He first published his ideas about natural farming in his book The One-Straw Revolution.
Mr. Masanobu Fukuoka. He died in 2008 in the age of 95 years.
Thank you !
The recycling of rice straw by scattering it in the field follows nature’s way.
It is a simple way to recover and maintain soil fertility.
Some progress has been made to address this “burning” issue.
Obviously more efforts are needed to inform farmers about the benefits!
Conclusion