# How far can soil fertility in agro-pastoral villages of West Africa be sustained by biomass flows?

David Berre, Nadine Andrieu, Christophe Le Page, Tidiane Diarisso, Marc Corbeels

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David Berre, Nadine Andrieu, Christophe Le Page, Tidiane Diarisso, Marc Corbeels. How far can soil fertility in agro-pastoral villages of West Africa be sustained by biomass flows?. International Symposium Farming System Design (FSD6), Farming Systems Design Community; Universidad de la República Uruguay, Aug 2019, Montevideo, Uruguay. 6 p. hal-05174814

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Submitted on 21 Jul 2025

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# How far can soil fertility in agro-pastoral villages of West Africa be sustained by biomass flows?

D. Berre<fnref n="1" />,<fnref n="2" />*, N. Andrieu<fnref n="3" />, C. Le Page<fnref n="4" />, T. Diarisso<fnref n="5" /> M. Corbeels<fnref n="6" />

## 1. Introduction

In the agro-pastoral areas of West Africa, traditional by-laws regulating the communal use of natural resources prescribe the grazing of crop residues by free-roaming resident or transhumant livestock during the dry season. New crop management practices based on recycling of crop residues as compost or their use as mulch in conservation agriculture (CA) are promoted by research and development programs in order to improve soil fertility (Corbeels et al., 2014;

Tittonell et al., 2012). These practices can potentially improve crop yields for individual farmers but may lead to conflicts between private interests (i.e., soil fertility maintenance of farmers' personal fields) and communal agreements (i.e., feeding the village herd during the dry season) (Andrieu et al., 2015). Some authors have analyzed the specific trade-offs that can occur between livestock and crop production at farm level after the introduction of CA (Naudin et al., 2011). However, such trade-offs must also be analyzed at the village scale. Agent-based models were shown to be effective tools to capture interactions on

resource use between farmers and their effects on the agricultural systems (Schreinemachers and Berger, 2011). We developed and used with farmers and

pastoralists an Agent-based Model of Biomass flows in Agro-pastoral areas of West Africa (AMBAWA). The objective of this paper is to assess the effects of introducing the practice of CA on farm productivity in a village of central Burkina Faso using an agent-based model that simulates the flows of biomass and nutrients between crop and livestock systems at the field,

<figure><img src="image_2.png" /><figcaption>**Figure 1:** Livestock (triangles) during the rainy season on the grazing (gray) and fallow (7 pale blue) areas, cultivated land being in light blue, watercourses in dark blue, protected areas in green, road in brown, and buildings in yellow (Peul encampments) and pale brown (homes of sedentary villagers).</figcaption></figure>

<footnote n="1">¹CIRAD, UPR AIDA, Bobo-Dioulasso, Burkina Faso.
AIDA, Univ Montpellier, CIRAD, Montpellier, France.</footnote>

<footnote n="2">²CIRDES, USPAE, Bobo-Dioulasso, Burkina Faso.</footnote>

<footnote n="3">³CIRAD, UMR Innovation, International Center for Tropical Agriculture, Decision and Policy Analysis
Research Area, Km 17 Recta Cali-Palmira, Apartado Aéreo 6713, Cali, Colombia
Innovation, Univ Montpellier, CIRAD, Montpellier, France.</footnote>

<footnote n="4">⁴CIRAD, UPR GREEN, F-34398 Montpellier, France.
GREEN, Univ Montpellier, CIRAD, Montpellier, France.</footnote>

<footnote n="5">⁵CERAD, Univeristé de Ségou, Mali</footnote>

<footnote n="6">⁶CIRAD, UPR AIDA, Nairobi, Kenya.</footnote>

<footnote>AIDA, Univ Montpellier, CIRAD, Montpellier, France.</footnote>

<footnote>*Speaker and corresponding author</footnote>
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farm, and village scales.

**2. Materials and methods**

The study was carried out in Koumbia, a village situated in the cotton-growing region of Burkina Faso. During the rainy season (800–1200 mm of rain between May and October) crops are grown and cattle are assigned to the savannah rangelands. Draught oxen are kept on the respective farms and fed on the fallow fields. During the dry season, farmers harvest a certain amount of maize residues from the fields of their farm for use as fodder (based on observed practices). Cattle leave the rangeland areas and together with the draught oxen are during the day assigned to the cropped land for feeding on the remaining maize residues left in the fields (unharvested fraction), while at night they are corralled (manure production). When the residues are exhausted on the cropped land, the animals are fed on the fodder stocks of their own farm. Once these fodder stocks are consumed, the animals exit the simulation until the end of the dry season (transhumance). Based on empirical data on nutrient balances, a farm typology based on 53 household surveys (subsistence-oriented crop farmers (SO), agro-pastoralists (AP), market-oriented crop farmers (MO) and pastoralists (PA)), and simple equations of maize yields and fertility management, we translated these practices of biomass use in space and time into an agent-based model within the CORMAS (COmmon-pool Resources and Multi-Agent Simulations) platform (Bousquet et al., 1998) to simulate the impacts of residue collection for mulching (protected from livestock) at farm and village scale (Figure 1).

**3 – Results & Discussion**

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First, a sensitivity analysis (Figure 2) reveals relatively low model sensitivity of manure production per hectare to basic (without nitrogen input) maize yield (default value, 400 kg per ha) and maize harvest index (default, 0.42). On the other hand, the effect of the partitioning of cattle faeces production between day and night (default, 30% at night and 70% during the day) on total manure production per hectare is high, specifically for PA farmers who owns the majority of cattle. Introduction of CA impacts the quantity of residue available for grazing during dry season, as areas with mulch are protected from livestock. Consequently, manure deposited on cropping land is reduced (Figure 3).

For SO farmers who do not send cattle to grazing parks and for MO farmers who entrust their animals to PA farmers, this reduction affects significantly the total amount of manure available to fertilize their fields at the beginning of the next cropping season. This leads to a crop yield reduction, which to a certain extent is compensated by the yield

increase due to mulching (10% in the model). Nonetheless, figure 3 underlines the yield decrease with higher amount of land under CA. Therefore, positive effect of mulch on soil fertility does not compensate the lack of manure deposition during free grazing nor the deficit in residue for feed due to cropland protection from cattle.

<figure><img src="image_6.png" /><figcaption>**Figure 2:** Sensi
faeces productic
yield, i.e without
farming systems</figcaption></figure>

4 – Conclusions

We showed that the introduction of CA practices has contrasting effects on available manure for
crop yield enhancement depending on the type of farms and linked to the size of their herd.
With CA, the amount of available maize residues for cattle feeding during the dry season
decreases over time, so does the amount of animal manure available for soil amendment,
affecting in a distinctive way productivity of the four farming system types considered.

References

- Bousquet F., Bakam I., Proton H., & Le Page C. 1998. Cormas: Common-Pool Resources and Multi-agent Systems. Computer Science, 1416, 826 – 837.

- Corbeels M., De Graaff J., Ndah H.T., Penot E.,

<figure><img src="image_7.png" /><figcaption>**Figure 3:** Source and quantity of manure used by four farm types to fertilize maize field, and corresponding maize yield, with 10, 30 and 60% of land cultivated under CA</figcaption></figure>

CONGRESO
ELIS

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Gestión de
INSCRIPCIÓNES

local
2014. Understanding the impact and adoption of conservation agriculture in Africa: A multi-scale analysis. *Agriculture, Ecosystems and Environment*, 187: p. 155-170.

- Naudin, K., Scopel, E., Andriamandroso, A.L.H., Rakotosolofo, M., Ratsimbazafy, N.R.S.A., Rakotozandriny, J.N., Salgado, P., Giller, K.E., 2011. Trade-offs between biomass use and soil cover. The case of rice-based cropping systems in the lake alaotra region of Madagascar. *Expl Agric*, 1-16.

- Schreinemachers P., Berger T. 2011. An agent-based simulation model of human environment interactions in agricultural systems. *Environmental Modelling & Software*, 26, 845-859.

- Tittonell P., Scopel E., Andrieu N., Posthumus H., Mapfumo P., Corbeels M., Halsema G.E.v., Lahmar R., Lugandu S., Rakotoarisoa J., Mtambanengwe F., Pound B., Chikowo R., Naudin K., Triomphe B., & Mkomwa S., 2012. Agroecology-based aggradation-conservation agriculture (ABACO): targeting innovations to combat soil degradation and food insecurity in semi-arid Africa. *Field Crop Research*, 132, 168-174.