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The sustainability of cassava-based bioethanolproduction in southern MaliKjeld Rasmussena, Torben Birch-Thomsena, Thilde Bech Bruunb, Ronja Egsmosea, BoElberlinga, Niels Folda, Søren Bech Pilgaard Kristensena, Ousmane Ouattarac, Laura VangRasmussena & Ibrahim Togolac

a Department of Geosciences and Natural Resource Management, University of Copenhagen,Øster Voldgade 10 DK-1350 Copenhagen K, Copenhagen DK-1350, Denmarkb Department of Plants and Environment, University of Copenhagen, Thorvaldsensvej 40,1871 Frederiksberg, Denmarkc Mali Folkecenter Nyetaa, Faladié SEMA, Rue 800, Porte 1293, BP E4211, Bamako, MaliPublished online: 23 Feb 2015.

To cite this article: Kjeld Rasmussen, Torben Birch-Thomsen, Thilde Bech Bruun, Ronja Egsmose, Bo Elberling, Niels Fold,Søren Bech Pilgaard Kristensen, Ousmane Ouattara, Laura Vang Rasmussen & Ibrahim Togola (2015): The sustainabilityof cassava-based bioethanol production in southern Mali, Geografisk Tidsskrift-Danish Journal of Geography, DOI:10.1080/00167223.2014.1002512

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The sustainability of cassava-based bioethanol production in southern Mali

Kjeld Rasmussena*, Torben Birch-Thomsena, Thilde Bech Bruunb, Ronja Egsmosea, Bo Elberlinga, Niels Folda,Søren Bech Pilgaard Kristensena, Ousmane Ouattarac, Laura Vang Rasmussena and Ibrahim Togolac

aDepartment of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10 DK-1350Copenhagen K, Copenhagen DK-1350, Denmark; bDepartment of Plants and Environment, University of Copenhagen,

Thorvaldsensvej 40, 1871 Frederiksberg, Denmark; cMali Folkecenter Nyetaa, Faladié SEMA, Rue 800, Porte 1293, BP E4211,Bamako, Mali

(Received 10 April 2014; final version received 22 December 2014)

The demand for biofuels has been rising, which has led developing countries to focus on production of feedstocks forbiodiesel and bioethanol production. This has caused concerns for the impacts on food security, food prices and environ-mental sustainability. This paper examines a hypothetical case of cassava-based bioethanol production in southern Mali,assessing its environmental, economic and social sustainability. Results demonstrate that environmental sustainability ofcassava-based bioethanol production depends on the ‘baseline’ chosen: Compared to the situation before the decline incotton production 10 years ago, the carbon stocks will increase. However, if compared to the current situation, whereconsiderable carbon stocks have accumulated in fallow fields, the loss of carbon will be substantial. Increased cassavaproduction will create greater incomes and better temporal distribution of labour input. Analysis of the significance ofcurrent cassava production for food security shows that bioethanol production should be based on the attiéké variety ofcassava, thereby avoiding interference with the important role of the bonouma in assuring food security in northern Mali.The key factor determining the economic feasibility is whether local farmers will be willing to supply cassava at arealistic price. The results indicate that this is likely to be the case.

Keywords: bioethanol; cassava; sustainability; Mali; carbon; food security

Introduction

The rapid increase in biofuel (plant oil and ethanol) pro-duction in developing countries has given rise to con-cerns with regard to the impacts on food security and theenvironment. The ‘sustainability’ of biofuel productionin general – and in poor sub-Saharan African countriesin particular – has been questioned (Amigun et al.,2011), leading to reluctance of development organiza-tions to support its further development, in spite of itspotential to reduce poverty (von Maltitz & Stafford,2011; Wicke et al., 2011). This paper assesses the sus-tainability of the proposed establishment of bioethanolproduction, using cassava as feedstock, in southern Mali.This specific case may, in certain respects, be seen as a‘best case’ of ‘1st generation’ biofuel production: cas-sava is thought to be a possible replacement for cottonas a cash crop, since cotton has been on the decline forthe last decade, and it may be argued that an expansionwill not threaten local food security. Also, in environ-mental terms, cassava is claimed to be more environmen-tally friendly than cotton. In other respects, bioethanolproduction from cassava may be problematic: cassavamay replace fallow vegetation, involving considerableloss of carbon from the vegetation and soil pools. Theproduction can also have a negative effect on the use of

cassava for food, both regionally and nationally. In eco-nomic terms, it can be questioned whether production ofbioethanol is economically sustainable without subsidiesunder the conditions encountered in southern Mali, giventhat fossil fuels for transport is presently subsidized.

In order to assess the sustainability of cassava-basedbioethanol production, we need to concern ourselveswith all three dimensions of sustainability: the environ-mental, economic and social. After having presented thecase study area, we therefore consider these three dimen-sions in order to specify what sustainability entails in thecurrent context.

The case study area

Location

The case study area is located in southern Mali, approx.100 km South of Sikasso, not far from the borders toIvory Coast and Burkina Faso, see Figure 1. Most of theinformation has been collected from three villages,Sieouba, Facacourou Courani and Perasso in the com-mune of Loulouni. The criteria for selecting this area asa possible location of a bioethanol production facilitywere that (1) the area is presently a center of cassavaproduction, (2) farmers are knowledgeable and

*Corresponding author. Email: kr@geo.ku.dk

© 2015 The Royal Danish Geographical Society

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well-organized, (3) land for expansion of cassava pro-duction is expected to be available due to the decline incotton production, (4) the area is well-connected, interms of infrastructure, to the rest of Mali and IvoryCoast, and (5) the rainfall, which is in the order of1200 mm/year on average, is sufficient to allow formoderately high cassava yields.

Land units, soil types and cassava production

In Figure 2, the main land units of the study area areshown. Cassava production takes place in both the wet-land areas (A), on the alluvial plains with sandy soils (B)and on the lateritic interfluves (C), yet the cassava produc-tion systems vary greatly between these three land units:

� In the wetland areas and river valleys (A), thebonouma variant of cassava is produced, oftencontinuously.

� On the alluvial plains (B), cassava is often part ofa crop rotation involving maize, sorghum and sev-eral other crops, and both the bonouma and attiekévariants are grown, with a predominance of thelatter.

� The lateritic interfluves (C) are less intensivelycultivated, yet cassava fields with the attiekévariant are found.

Generally speaking, bonouma is preferred on the siltysoils, while attieké dominates on the sandy and gravellysoils. In terms of area, the ratio of bonouma to attieké ispresently approximately 4:1.

Land use history

Cotton used to be cultivated mainly on the sandy and –to a lesser extent – gravelly soils (mostly within the Band C classes shown in Figure 2), and substantial areasof fallow land can be found where cotton used to begrown. The age of the fallow is often in the range of5–10 years, as cotton production has declined over thisperiod. Over the last decades, cultivation has expandedinto the large wetland area (part of class A in Figure 2)between Sieouba and Facacourou Courani. The cropsgrown in the wettest parts are mainly rice and – to anincreasing extent – cassava. A lowering of the watertable has been reported, allowing cultivation to expandinto previously flooded areas. The greatest part of thelateritic interfluves, escarpment and plateaus (classes Cand D in Figure 2) have mainly been used for grazingand collection of firewood, yet traces of abandoned fieldsmay be observed in the satellite images.

The agricultural system

Cultivation tends to be semi-permanent in the wettestpart of the area, and mineral fertilizers are used on bothrice and cassava fields. Farmers reported inputs in theorder of 100 kg of ammonium (N) and 50 kg of ‘supercomplexe’ (P) fertilizer per ha. While rice is grown on alevel field to allow flooding, cassava is planted in ridges/mounds, which may be up to ½ m high with a spacingof 1–1½ m. Weeds are incorporated as green manurewhen building the ridges/mounds. The ridges allow for abetter root development and serve to avoid cassava rootsrotting during periods with high water level. In the sandyplains, the traditional system has included a crop rotationinvolving maize, sorghum, sweet potatoes and cassava,as well as several other crops, followed by a fallow per-iod. Also, here, cassava is planted in ridges/mounds,which are, however, smaller than those in the wetlandfields. Mineral fertilizer and manure are used in someplaces, but not to the extent found in the wetlands. Thebonouma cassava variety has a cycle of 10–12 months,

Figure 1. The study area, with location of study villages, themain road and sample areas, for which detailed land use/covermapping has been carried out.

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and is generally planted and harvested during the rainyperiod from June-October. In this period, it is possible towork the silty wetland soils, while this is difficult in thedry season, where the soil becomes very hard, andcassava tubers are easily damaged during harvest. Theattieké variety has a cycle of 6–12 months and it isplanted and harvested year-round on the sandy soils. Thestaple food of the rural population is maize, rice and sor-ghum, supplemented by cassava. While most of themaize and sorghum (and other minor crops) cultivated inthe area is consumed locally, cassava is predominantlyconsidered a cash crop, and rice is both a crop for local

consumption and sold on the market. As mentioned,cotton used to be the dominant cash crop.

Cassava is cultivated with a combination of familylabour and hired labour. In some locations, cassava farm-ers are organized in cooperatives, which regulate market-ing and organize members in work teams for mutual-aidfieldwork (‘entraide’). Cassava is a time-consuming cropdue to the labour-intensive planting. Most cassava fieldworks, especially in the case of bonouma, coincide withthose of other crops. This may lead to competition forlabour, especially in households with limited labouravailability (Kristensen et al., 2014).

Figure 2. The land classes represented in the study area. The frames show the area covered by detailed land use/cover mapping, theresults of which are shown in Figure 3.

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The scale of bioethanol production

To assess the sustainability of cassava-based bioethanolproduction in the study area, a specific scale of the pro-duction must be assumed, in order to allow for calcula-tion of the necessary land use change, consequentchanges in carbon pools, incomes, etc. Bioethanol pro-duction facilities can have a wide range of sizes. Basedon information from Novozymes Inc. (Maard, personalcommunication, October, 2009, Interview with StefanMaard, Novozymes) we assume that in order to achieveeconomies of scale, an annual production of no less than10 mio. (or 106) liters of bioethanol is required. Facilitiesof this size are modular, implying that they may beexpanded gradually, yet with only minor reductions inmarginal production costs. This facility size is used inthe further calculations. Due to the great volume andmass of the feedstock, transport costs may be a majorfactor, and it is likely that actual production facilities willnot be much larger. Smaller scale bioethanol productionfrom cassava is feasible (Zvinavashe et al., 2011), buteconomies of scale make this option less attractive in thecontext studied here.

In the literature (Nguyen et al., 2007; Silalertruksaet al., 2009), it is generally stated that the production of1 L of bioethanol requires 6–7 kg (fresh weight) of cas-sava. Thus, the production of 10 mio. liters of bioethanolwill require 60–70,000 tons of cassava, evenly distrib-uted over the year, since fresh cassava cannot be storedfor long under the conditions encountered in southernMali. Assuming yields in the order of 10–20 tons/ha(Fermont et al., 2008; Gibbs et al., 2008; Kristensenet al., 2014), this corresponds to a demand for land of3–7000 ha. The cultivated area per village in the studyarea is currently 500–2000 ha, and if we assume that itis possible to increase this by 50% (250–1000 ha per vil-lage), it would be realistic to cover the feedstock demandfor a bioethanol plant from expansion of cassava produc-tion in approximately 10 villages. Our analysis of presentland use (Kristensen et al., 2014) indicates that thisassumption is realistic and may even be a conservativeestimate, as we do not account for the replacement ofother crops and yield increases. If an increase to a yieldof 30 tons/ha (which is claimed to be obtained in experi-mental farms in the region) is assumed, and if a certainreplacement of other crops by cassava takes place, theadditional demand for cassava of the bioethanol plantmight be met by a handful of villages, which wouldgreatly reduce the transportation costs and thus add tothe economic sustainability of the production.

Assessing the sustainability of bioethanol production

Assessment of sustainability requires that the environ-mental, economic and social dimensions are addressed.In the current context, we have decided to focus on

certain aspects of sustainability, which we believe to becentral in the current context:

The environmental dimension:

(1) Is sufficient land available for an expansion ofcassava production?

(2) How will production of bioethanol from cassavaaffect net emissions of GHGs, directly as well asindirectly? This includes also the estimation ofdirect and indirect land use change effects: Whatvegetation/which crops will an expanded cassavaproduction replace, what will be the indirecteffects on land use (associated with land usesmoving elsewhere, replacing other vegetation andcrops), and what losses or gains in carbon stocksin vegetation and soil will this entail?

The economic dimension:

(3) Will bioethanol production from cassava be eco-nomically sustainable, with or without paymentfor the (supposedly) reduced CO2 emissions?

The social dimension:

(4) Is the social organization of farmers such that astable output of cassava can be obtained at thelevel required for operation of bioethanol plant?Is some variant of contract farming a realisticoption?

(5) Will food security be compromised by establish-ment of a cassava-based bioethanol production?

Methodology

The analysis of environmental, economic and socialdimensions of sustainability requires the use of a varietyof different methods, including both quantitative mea-surements of biophysical variables, mapping (combiningthe use of satellite images and field observation), ques-tionnaire surveys and in-depth interviews. In order toassess sustainability, we need information on change (inland use, carbon stocks, etc.), yet field work has beencarried out over a period of few months only. For thatreason, we have relied on ‘space for time substitution’.

As concerns the environmental dimension, thefollowing methods have been used:

(1) Mapping of ‘land units’ on the basis of World-view-2 high-resolution images, supported by fieldobservation. This is described in greater detail inKristensen et al. (2014)

(2) Detailed, village-scale mapping of the distribu-tion of crops, fallow fields and soil types, mostlybased on fieldwork, supported by use of satellite

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images, as also described in Kristensen et al.(2014).

(3) Counting and measurement of woody vegetation(for carbon stock assessment) in fallow fields ofdifferent ages. This is described in detail inRasmussen et al. (2012).

(4) Volume-specific soil samples were collected fromevery 10 cm of 50 cm soil pits, located at 50plots under cassava, rice or fallow. Samples wereanalysed for total carbon on a LECO TruSpecCarbon Nitrogen Determinator. Results werecompared by means of analysis of variance(ANOVA). See further details in Appendix 1.

The data for the assessment of the economic andsocial dimensions have been collected by use of thefollowing methods:

(5) Semi-structured group interviews with farmers inthe study-villages, as described in Kristensenet al. (2014) and Rasmussen et al. (2012). Sev-eral group interviews with different thematic fociwere organized in each village.

(6) Household questionnaire survey, described indetail in Kristensen et al. (2014), on householdeconomics, livelihoods, labour availability andconstraints, and agricultural strategies and landuse. 65 respondents were selected for the ques-tionnaire survey using a systematic-stratifiedsampling scheme.

(7) A survey of the key actors in the cassava valuechain aiming at understanding the function of thebonouma and attieké value chains, and in partic-ular the food security implications.

(8) Key informant interviews, described in detail inKristensen et al. (2014) and Rasmussen et al.(2012), focusing on a range of different issuesrelated to economic, institutional and socialaspects of the cassava production and valuechain.

This paper draws upon the above-mentioned moredetailed studies of individual elements of the sustainabil-ity assessment of bioethanol production.

Results

Land availability

The mapping of land units classified the study area into(A) seasonally flooded wetlands with silty soils, (B) allu-vial plains with sandy soils, (C) interfluves with gravellyand stony, lateritic soils and (D) escarpment and highplateau with gravelly and stony lateritic soils, seeFigure 2. Borders between these land units are notalways well defined, and transition zones exist with soils

with intermediate properties. The areas of the classes aregiven in Table 1. For two selected areas, shown inFigure 2, detailed land use/cover mapping has been car-ried out by a combination of satellite image interpreta-tion and fieldwork, involving GPS-based measurementsof fields. The results are shown in Figure 3.

Parts of the seasonally flooded area have a high agri-cultural potential and bonouma is primarily cultivatedhere. Some farmers indicate that the water level in thewetlands has decreased over the last decades, allowingcultivation to progress into the wetlands. In Perasso,there appears to be land in the river valley, running justnorth of the village, available for expansion of cassavaproduction. In addition, cassava may replace other crops,not least rice, and this trend is confirmed by the ques-tionnaire survey, which finds that this crop substitutionwas the most common (Kristensen, 2014).

In the sandy plains, a number of crops are grown inrotation. Cassava, mostly attieké, is part of this rotation,and increased cassava production may be achieved byincreasing the role of cassava in the rotation or by reduc-ing the fallow periods by applying more mineral fertil-izer. Quite substantial areas in the sandy plains are lyingfallow, mostly as a consequence of the reduction in cot-ton production. These fallow areas are among the pre-ferred options for expansion of cassava production(Rasmussen et al., 2012), see Figure 4. Fallow periodsof 5–10 years are common. It should be noted that thefallow areas, available for expansion of cassava produc-tion, are often found in the higher parts of the plain withcoarser soils, and are more prone to (plant) waterscarcity in drought years.

The lateritic plains of the interfluves have less agri-cultural potential and are less intensively cultivated, andquite large areas are used only for extensive grazing andfor extraction of wood. Some of these areas have a sub-stantial woody cover and high carbon storage. If anincrease in the cultivated area was required to cover theneeds of a bioethanol plant, it is likely that cassava culti-vation would encroach on these lands, some of whichhave been cultivated earlier, as indicated by the presenceof old field boundaries visible in the satellite images.Even within the study area shown in Figure 1, there isenough presently uncultivated land in this land unit tocover the requirements for increased cassava production,provided that yields are in the same order of magnitudeas on the presently cultivated fields. It should be noted,however, that the ‘carbon debt’ associated with bringingsome of these areas into production might be consider-able because of the relatively large trees found in thedense woodlands, yet the magnitude of the debt willdepend critically on the choice of reference year/baseline.For the two areas for which detailed land cover mapshave been produced (Figure 3), 25.8 and 14.6%, respec-tively, of the land is classified as ‘fallow’ (often after

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abandonment of cotton fields) and 4.9 and 42.9% isclassified as uncultivated (and used only for grazing andharvesting of wood) (Table 1).

The escarpment and high plateau areas are mostlyused for extensive grazing and do not appear to haveany significant potential for cassava production.

All in all, there appears to be a considerable potentialfor expanding the cassava production through an increaseof the total cultivated area in both wetlands (A), alluvialplains (B) and interfluves (C). However, results of the

questionnaire survey and interviews with farmers showthat it is likely that part of an expansion of cassava culti-vation for bioethanol will take place by replacement ofother crops, e.g. maize on the sandy plains.

Carbon stocks in vegetation and soils

An expansion of cassava production will have bothdirect and indirect effects on carbon stocks in vegetationand soils. Changes in above-ground carbon stocks are

Table 1. Area of the land classes in the study area shown in Figure 2.

Land class map Square kilometers Percent of total area

Flat alluvial plain 46.0 53Lateritic plain/interfluves 22.9 26Escarpment/plateau 8.1 9Seasonally flooded area (‘bas fond’) 10.3 12Total area 87.3 100

Figure 3. Detailed land use/cover mapping of parts of the study area.

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mostly associated with the clearing of land for cultiva-tion of cassava (‘direct’ land use effects) and/or cultiva-tion of crops, which have been displaced by cassavaproduction elsewhere (‘indirect’ land use effect). In thestudy area, the major effect is likely to be the clearing offallow and woodland for conversion into cassava, asillustrated in Figure 4, showing where the farmers wouldprefer to expand cassava production, should this becomeeconomically feasible. The land use/cover categoriesused in Figure 4 are those meaningful to farmers (fieldspresently cultivated with other crops, fallows). In orderto estimate the effect of establishing cassava-basedbioethanol production, we have carried out a survey oftrees in fallow areas likely to be converted into cassava,based on the farmers’ assessment. The results are shownin Figure 5.

Two factors have a great impact on the result: firstly,farmers do not necessarily clear all trees, but prefer, inmost cases, to preserve the majority of the large treesbecause they may have economic value (e.g. neem andmango), or because they provide shade. Preserving thelarger trees implies a halving of the above-ground carbonloss. Secondly, by clearing only fallow fields of an agebetween 5 and 10 years, rather than any fallow/woodlandarea, the carbon loss is also minimized, as also evidentfrom Figure 5. This appears to be the preferred behav-iour of the farmers, so the lower estimates of above-ground carbon loss are likely to be correct.

Should farmers expand cassava production intowoodland areas, carbon losses may be expected tobecome much greater. The densest woodland/forest areasencountered in the region have above-ground carbonstocks substantially higher than those reported here.

As concerns changes in the below-ground carbonstocks, they include both losses in root biomass and insoil carbon. Very little information is available on rootbiomass, and often it is assumed to be of the same order

of magnitude as the above-ground biomass. If this bio-mass was entirely lost when clearing trees, this wouldtherefore double the payback time. The change in soilcarbon stock depends on both soil type and the exactland use change. According to our data on changes insoil carbon stocks, a change from fallow or rice to cas-sava is not associated with carbon losses from the inves-tigated soil types, see Figure 6. Interestingly, a changefrom fallow to cassava on silty soils in wetlands (lebogo) seems to result in a counter-intuitive increase insoil carbon stocks. This may be because the current prac-tice of incorporating weeds into the mounds actuallyresults in a carbon sequestration in the cultivated soilscompared to the soils under fallow. Another explanationis that farmers have chosen to use the best soils (whichis often synonymous with the soils containing the mostcarbon) for cultivation, while keeping the low-qualitysoils under fallow – a pattern that has been reported byprevious studies (Bruun et al., 2009).

Thus, it may be concluded that C losses, associatedwith clearing the trees with little use to farmers (for sha-dow, fruit production and medical purposes) in youngfallows are in the order of 6.4–7.1 Mg/ha, and that thepayback time of the carbon debt does not exceed 12–14 years (assuming a substitution ratio between gasolineand ethanol of .65:1 (Henke et al., 2005)). If the cassavayields increase further, the payback time will obviouslybecome shorter.

In the case where cassava production is expandinginto wetlands, replacing rice, it is worth noting that theresult is likely to be a decrease in CH4 emissions, sincethe practice of growing cassava in ridges implies thatfields are not flooded as are rice paddies. Thus, eventhough the carbon content in the soil may be lower aftercassava production than after rice cultivation, it is proba-bly an advantage seen from a GHG reduction point ofview.

In the lateritic plains with gravelly soils, the carboncontent is generally lower than in the sandy soils (seeFigure 6), and the losses are therefore likely to be small.

Impacts on household economy and local livelihoods

Information on the impacts of the hypothetical increasein cassava production for bioethanol was obtained fromhousehold questionnaires, semi-structured group inter-views and in-depth interviews with informants, asdescribed in Kristensen et al. (2014). A key questionasked in all three contexts concerned the farmers’ inter-est in expanding cassava production, provided that theywere guaranteed a market. In addition, the farmers wereasked what price would be required to motivate anexpansion. While the great majority answered that theywould respond to a guaranteed market by increasing pro-duction, there were large discrepancies as concerns the

Figure 4. Farmers’ preferences for expansion of cassavaproduction.

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required price level, where responses ranged from 30 to100 CFA/kg. This wide range reflects the actual range ofprices obtained by farmers at different times of the year.In the high season for the bonouma variant (July–September), prices are in the 50–100 CFA/kg interval,while attieké is often sold at prices of 30–50 CFA duringthe dry season (Kristensen et al., 2014). The main prob-lem for farming households appears to be the low cashincomes during the dry season, where the demand forcassava is small and unstable, implying that some cas-sava fields are not harvested at all. Cotton used to be themain source of cash income, but since the collapse ofthe cotton value chain, farmers have had problems find-ing a replacement, which assures a stable income. There-fore, a stable market for cassava and a price guaranteewould be very much welcomed. The question remains,however, whether the price offered for cassava forbioethanol will be high enough to stimulate production.

Based on current oil prices in Mali, a profitable, unsubsi-dized bioethanol production will hardly be feasibleunless cassava is available at a price not exceeding 30–35 CFA/kg. Interviews with farmers show that a guaran-teed price of 30 CFA/kg for a contracted amount of cas-sava per household would generate the required increasein attieké production. No other crop (except for bon-ouma) in the study area is likely to produce a guaranteedgross value of 300–600,000 CFA/ha. Farming under con-tract, as outlined here, has the additional effect that useof labour and capital inputs, including fertilizers,becomes less risky, since the farmer is guaranteed anincome to cover costs of these inputs. This is very likelyto lead to increased yields.

Interviews with farmers (Kristensen et al., 2014)show that an increase in the area cultivated and/or inlabour intensity will require that labour resources areavailable at the appropriate time. According to the results

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Figure 5. Carbon debt and repayment time for three scenarios on converting fallows to cassava cultivation. The maximum estima-tion represents calculations made using a polynomial allometric model, whilst the minimum estimation represents calculations madeusing a FAO model for the removed biomass (with dbh < 40 com) and a quadratic model for the preserved biomass (dbh rangingfrom 9 to 91 cm). (A) Carbon debt allocated to changes in above-ground biomass and application of fertilizers. (B) Number of yearsof cassava cultivation required to repay the carbon debt when displacing gasoline with bioethanol. From Rasmussen et al. (2012).

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of the survey and the interviews, the majority of farmhouseholds claim to have abundant labour resources. Inview of the concentration of agricultural tasks in therainy season and the widespread use of hired labour inthis season, it may, however, be doubted whether thissurplus of labour exists in the months July–September,where most of the effort in the harvest, field preparation(including ridge-building) and planting of bonouma isconcentrated. On the other hand, it appears very likelyfrom the responses that abundant labour resources areavailable outside the rainy season.

Both the cost and the labour constraints suggest thatthe production of cassava for bioethanol should primarilytake place in the sandy plains and interfluves, and thatthe attieké variant, which can be harvested and plantedall year, will be the best suited.

Cassava value chain analysis

The following results as concerns the cassava valuechain(s) were derived from direct observation, interviewsand questionnaires:

Sieouba

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Figure 6. Effects on soil carbon stocks in the upper ½ m (upper part) and the A-horizon (lower part) of converting fallow or rice tocassava on the short and longer term. In the case of fallow to cassava, two soil types (sandy (‘tientien’) and silty (‘lè bogo’),respectively) are considered.

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(1) It was observed that the cassava value chain mayeffectively be divided into two relatively distinctstrands: one concerning (almost) exclusively thebonouma cassava variety and the other concern-ing (almost) exclusively the attieké variety.

(2) The bonouma strand (ca. 80% of the cassava pro-duction) is characterized by harvesting mainly tak-ing place in the rainy season (July–September),with minor amounts being harvested in April–Juneand October–November. The bonouma is mainlytransported as whole tubers to markets in theNorth, in particular to Segou and Mopti, where itis used for human consumption in the rainy seasonwhen other crops are in short supply. The pricesoffered to farmers by traders vary (30–100CFA/kg), but are generally relatively high (>45CFA/kg).

(3) The attieké strand (ca. 20% of the production) ischaracterized by year-round harvest (probablyreduced amounts in the rainy season, where labouris invested in bonouma harvesting and planting).Attieké is mainly used for household consumptionor bought by women’s groups processing it to theproduct ‘attieké’, which is either sold for immedi-ate consumption in ‘wet’ form or dried. It is con-sumed locally. Smaller amounts are sold inBamako. The prices offered to farmers vary lessthan in the case of bonouma, and are generally inthe 30–50 CFA/kg interval.

(4) Since bioethanol production requires a steady flowof feedstock over the year, it cannot be based onbonouma, unless the agricultural practices arechanged significantly. Expansion of bonouma pro-duction for bioethanol may be possible, yet itwould compete with its present use for food in theSegou–Mopti area, and the prices obtained in thecurrent bonouma trade are so high that use of bon-ouma for bioethanol production seems economi-cally unfeasible.

(5) Attieké production matches better with therequirements of bioethanol production. The pricelevel is closer to being compatible with the levelwhich is realistic in relation to bioethanol produc-tion, and harvest is possible year-round.

Thus, the value chain study supports the conclusionthat it would be preferable to concentrate on attiekéwhen planning feedstock production for a bioethanolproduction facility. The principle is outlined in Figure 7.

The current cassava production in the villages is soldto traders. In the case of bonouma, traders come fromSikasso, Segou and Mopti during the high season (July–September), while the year-round trading of attieké is han-dled by traders and transporters from Sikasso and mostly

sold on the market in Sikasso. Traders are associated with‘hosts’ in each village. These hosts receive demands fromtraders and organize that the requested amount of cassavais delivered at the right time and place. They also negotiatea price. The hosts thus play a key role in organizing thetrade. A bioethanol production unit may use this system orit may alternatively be based on contacts to cooperatives.Cooperatives are well known in the study area, althoughcooperatives focusing specifically on cassava productionand trade are still in their infancy.

Discussion

The results reported above describe a situation character-ized by substantially reduced incomes, reductions in thearea cultivated and underutilization of labour resourcesin the dry season, all associated with the decline in cot-ton production. Farmers in the study area are stronglymotivated to take up alternative productions, whichcould generate a cash income. Cassava is presently partlytaking this role, yet the demand is very seasonal (in thecase of bonouma for filling the hunger gap in the north),prices vary greatly over the year and, in certain periods,fields are not even harvested because there is no demand.Thus, a guaranteed year-round market for cassava, evenwith prices in the low end of what farmers are presentlyobtaining, is likely to motivate farmers to expand theproduction substantially. Such an expansion may happenby increasing the cassava area, either by replacing othercrops, such as maize and rice, by expanding cassava cul-tivation into former cotton fields presently in fallow orby increasing cassava yields. All three options are realis-tic: according to the farmers, there is land available forexpansion, and this is supported by analysis of satelliteimages. Large variations in cassava yield may beobserved and factors, such as fertilizer input, soil type,water availability and labour input are likely to influenceyields. If a market is guaranteed and extension servicesestablished, there are reasons to believe that averageyields can at least be doubled. Thus, we find it realisticthat an increase in cassava production of 50–70,000 tonsper year can be achieved within an area of less than athousand square kilometers in the study region, whichwould imply low transport costs.

Household questionnaires and interviews show thatfarmers express strong interest in expanding the cassavaproduction, and that they intend to achieve this by clear-ing fallow fields (mostly 5–10 years old, after cotton pro-duction) and/or replacing other crops, such as rice inlowland fields or maize in dryland fields by cassava. Theeffects on carbon stocks in vegetation and soils have beenthoroughly studied, and it is documented (Rasmussenet al., 2012) that clearing fallow would result in a loss ofcarbon in above-ground vegetation in the order of

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6.4–7.1 Mg C/ha, provided that farmers retain usefultrees, while changes in soil carbon pools are relativelysmall and uncertain. With present cassava yields, itwould take 12–14 years of continuous cassava produc-tion for bioethanol before the ‘carbon debt’ associatedwith clearing of fallow, would be ‘repaid’. If other cropswere replaced by cassava, no reduction in carbon storagewould take place. If cassava yields were to double, therepayment time would be almost halved. If the land useof 10 years ago was taken as the baseline, no reductionin carbon storage would have taken place, rather it islikely that carbon stocks would have increased. Thus,the more or less arbitrary choice of baseline againstwhich the effects of the cassava expansion may be com-pared has significant consequences for the assessment ofthe environmental sustainability.

The economic feasibility of cassava-based bioethanolproduction is very difficult to assess, both because theenergy market in Mali (and elsewhere) is heavily politi-cally influenced, and because future world market pricesof fossil fuels and competing renewable energy sourcesare very uncertain. The crude assessment made in thisreport is based on the assumption that a cassava price of30–35 CFA per kg would allow a profitable productionof bioethanol. This assumption may certainly be chal-lenged for a number of reasons, not least due to the pres-ent absence of a market for bioethanol in Mali. Anyestablishment of a bioethanol production must go handin hand with efforts to develop a market. Several inter-esting options exist, including use of bioethanol toreplace gasoline (fully or partly) for use in vehicles, forvillage-scale electrification and to replace fuel wood orcharcoal in households. The latter is particularly interest-ing because of its possible positive effects on vegetationcarbon stocks, biodiversity and, not the least, humanhealth. A promising market-based example is currently

developing in Mozambique (CleanStar, 2012). If theassumption of a raw material price of 30–35 CFA/kg isrealistic, our survey shows that offering this price tofarmers in the study area would trigger a substantialincrease in production, provided that the farmers weregiven a guaranteed demand and price. This price level issubstantially lower than that associated with the stronglyseasonal production of bonouma, mostly on the wetterlowland soils. Thus, on economic grounds, it is evidentthat the increase of the cassava production will mainlytake place on the drier soils, which can be cultivatedyear-round with the attieké variety, and in particular, inperiods, where there are underutilized labour resources.

As concerns the social impacts of increased cassavaproduction for bioethanol, we argue that the most criticalimpact is on food security. We have examined the foodsecurity impacts locally, regionally and nationally. Onthe local level, it appears that negative impacts on foodsecurity are unlikely. In a crisis situation, e.g. in the caseof drought, cassava may serve as food reserve, implyingimproved food security. At the regional scale, it wasnoted that cassava-based cous-cous, attieké, played a cer-tain role in urban Sikasso, and that this was either pro-duced locally by women’s groups on the basis ofcassava cultivated in the study area or imported fromCote d’Ivoire. The amounts involved were, however,quite limited, and this value chain is most likely main-tained if a bioethanol production is established. Thegreatest significance, in terms of food security, of cas-sava production is certainly associated with the large sea-sonal export of bonouma from the study area to theSegou and Mopti regions during the rainy season (July–September mainly) to fill the ‘hunger gap’. The pricesobtained by farmers producing bonouma in this seasonare, however, much higher than the price level assumedto be realistic for bioethanol production. This implies

Figure 7. The annual variation in production volumes and price levels of attieké and bonouma cassava varieties in the study area.

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that farmers will give priority to producing bonouma forexport to Segou and Mopti, and no negative effects ofbioethanol production on this value chain are expected.This further supports the conclusion from the economicanalysis that bioethanol production should rely mainlyon attieké. The only problem is that there may be adecline in supply of attieké to a bioethanol productionfacility in the rainy season when farmers invest theirlabour in harvesting and planting bonouma for export toSegou and Mopti. Thus, the bioethanol producer hasto have storage facilities for cassava, allowing them tostock the raw material for several months. Apart fromthe importance of cassava for food security in the Segouand Mopti regions, cassava does not play a major role inthe food supply of Mali, and establishment of bioethanolproduction is not likely to have major impacts on foodsecurity at national level, nor will it contribute signifi-cantly to increasing food prices.

In addition to the food security issue, other socialeffects may result from establishment of a bioethanolproduction. These include impacts on the actors in thecurrent cassava value chains, and in particular on theorganization of cassava production and marketing. Pres-ently, producers mainly interact with buyers though localintermediaries, so-called ‘hosts’. In some cases, localproducers also act as buyers themselves, and use special-ized transporters. A bioethanol production facility mayeither use this system or replace it by an alternative sys-tem. One alternative, which is already emerging in somevillages, is the establishment of cassava production andmarketing cooperatives, which may interact directly withthe bioethanol production facility. These two systems arealready competing and the competition can affect thereaction of farmers to the advent of a new, large actor.Farmers have a tradition for being organized in coopera-tives in relation to the production of cotton, and it is notunlikely that a similar form of organization will emergein the case of cassava.

Conclusions

In relation to the sustainability issues prioritized in ouranalysis, our results can be summarized as follows:

Ad question (1) Is sufficient land available for anexpansion of cassava production? Evidence from satelliteimage analysis, field mapping and interviews with farm-ers converges to show that by cultivating the land laidfallow since the abandonment of cotton cultivation andby increasing the importance of cassava in crop rota-tions, it would be possible to produce enough cassava tofeed a bioethanol plant within a radius of15 km.

Ad question (2) How will production of bioethanolfrom cassava affect net emissions of GHGs, directly aswell as indirectly? The answer to this question dependscritically on the choice of ‘baseline’. If the land use from

before the abandonment of cotton production is taken asthe baseline, no net carbon loss may result from expan-sion of cassava production, while taking current land useas the baseline may result in substantial losses, and anestimated ‘pay-back time’ of 12–14 years.

Ad question (3) Will bioethanol production from cas-sava be economically sustainable, with or without pay-ment for the (supposedly) reduced CO2 emissions? Ouranalysis shows that the profitability of cassava-basedbioethanol production depends on a number of factors,including world market prices of energy and subsidiesfor fossil as well as renewable energy. With current pricelevels, and disregarding national subsidies for fossilfuels, cassava-based bioethanol production may well beeconomically feasible, if the price of cassava does notexceed 30–35 CFA/kg (fresh weight), which correspondsto the price level of attieké at the time of field work.

Ad question (4) Is the social organization of farmerssuch that a stable output of cassava can be obtained atthe level required for the operation of a bioethanol plant?Is some variant of contract farming a realistic option?The results show that due to earlier experience with cot-ton production in the study area, the social organizationshould be adequate. Whether an organization based onthe existing system of ‘hosts’ at village level or estab-lishment of cooperatives is the most suitable solution,remains an open question.

Ad question (5) Will food security be compromisedby establishment of a cassava-based bioethanol produc-tion? The study examines food security issues at local–to-national level. It is shown that impacts locally arelikely to be negligible. At regional–to-national level, it iscritical that the role of bonouma in filling the ‘hungergap’ in the Mopti-Segou area is not affected. Relianceon attieké only for bioethanol production will eliminatethis risk.

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Appendix 1. Methodology for soil carbon analysisSoil sampling

Volume-specific samples were collected from pits in 50fields at 10 cm increments down to 50 cm. In cassava fields, anadditional sample was collected from the mound. As part ofsampling, cassava mounds were measured (height, wide anddistance between mounds) to allow for volume calculation onspecific fields.

Chemical analysesValues of pH were measured on samples from all sites, but

only in three depths: 0–10, 20–30 and 40–50 cm according tothe ISRIC procedure (van Reeuwijk, 2002), with few deviationsfrom the method. Soil and ion-exchanged water in relationship1:2.5 were shaken at 125 rpm for 50 min, after which the solu-tion was left 10 min for precipitation. The pH of the suspen-sion was then measured with a Metrohm 691 pH meter.

Soil samples were then crushed using a ball mill and ana-lysed for total carbon and total nitrogen on a LECO TruSpecCarbon Nitrogen Determinator. The presence of inorganic car-bon was investigated by HCl addition, which reveals that totalC represents organic C only.

Exchangeable potassium was extracted with ammoniumacetate, 1.0 M NH4OOCCH3. A suspension of 5 g soil and20 mL 1.0 M ammonium acetate was shaken for two hours at125 rpm. The suspension was pressure filtered through a What-mann no. 3 filter paper, which was rinsed several times withapproximately 100 mL 1.0 M ammonium acetate. A solutionconsisting of 9.9 mL extract and .10 mL caesium chloride solu-tion (100 g/L) was used to measure the potassium content byatom absorption spectrophotometry on a Perkin Elmer 400AAnalyst.

Statistical analysesCarbon and nitrogen stocks (t/ha) were determined to a

depth of 50 cm. On cassava fields, the contribution of themounds was included by calculating a hypothetical thickness ofa Ap1 horizon (spread evenly over the field). This was done bydividing the total soil in mounds with the size of the field, andthen multiplying to a field area of 1 ha. The stocks were calcu-lated by multiplying the concentration of carbon or nitrogen bythe density in the specific sample and the thickness of theinterval (i.e. the mound/Ap1 horizon or the subsequent 10 cmintervals). Stocks were calculated to a certain depth andmass-equivalent basis.

Analysis of variance (ANOVA) was carried out in the sta-tistical program R. In the case of significance in ANOVAs,parameter estimates were compared by least significant differ-ence (LSD). Data was tested for variance homogeneity throughresidual plots and for normality through quantile plots, andtransformed if needed.

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