West African mixed farming systems as meta-ecosystems: a source-sink modelling approach

Bisson, A.; Boudsocq, S.; Casenave, C.; Barot, S.; Manlay, R. J.; Vayssières, J.; Masse, D.; Daufresne, T.
Nutrient availability is a major limitation of the production of West African mixed farming systems. The fertility of these systems was traditionally sustained by fallowing, and nutrient transfers by livestock from savanna to croplands. However, demographic growth and socio-economic constraints require the agro-ecological intensification of these systems. To understand how agricultural practices and landscape management affect crop production, we built a meta-ecosystem model of nitrogen stocks and fluxes, and we examined different scenarios of fallow management with or without livestock. Our results suggest that crop production is highly dependent on the source-sink dynamics of nitrogen. Without livestock, maximum crop production is obtained for an intermediate duration of fallowing, highlighting a trade-off between space devoted to production (cropland) and space devoted to fertility restoration (fallow). In presence of livestock, crop production is maximum for a shorter duration of fallowing; it is markedly higher with than without livestock. This result highlights the positive roles of livestock and fallows as pumps (vectors) of nitrogen from savanna rangeland to cropland, and from fallow land to cropland, respectively. However, it also highlights the negative relationship between livestock presence and fallowing, suggesting that the optimal configuration of livestock and fallow management is highly context-dependent. Overall, we argue that the meta-ecosystem approach is particularly relevant for the study of agro-ecosystems characterized by high spatial heterogeneity. This work can be seen as a first step toward an alternative approach, integrating tools from theoretical ecology for the study of agro-ecosystems which functioning strongly depends on spatial organisation.
Type of Publication:
African mixed-farming system; Meta-ecosystem model; Crop production; Fallow; Nitrogen; Livestock
Ecological Modelling
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