Multi-level nutrient cycle model in agro-sylvo-pastoral systems of West Africa

International audience; configured with available data on savannah agroecosystems in West Africa. It focuses on processes related to nitrogen (N), a key limiting resource for both plant and animal production. It was implemented with Gama (v1.8). Model evaluation was based on field-data from two villages of the Groundnut Basin in Senegal, where agropastoralists have contrasted farming practices. It showed that the model reproduces the differences between an “extensive” and an “intensive” system. In a context where historical quantitative data on nutrient flows are lacking, the model was used to explore past agroecosystems functioning and performances regarding N flows. Simulations highlighted bottlenecks along the N cycle like accumulation of N in manure heaps and housing areas, reducing N recycling efficiency, especially in “intensive” systems. Two major properties appeared to be outlasting the transition: i) independence towards external inputs, based on croplivestock integration; ii) spatial heterogeneity due to nutrient transfers from peripheral land units to core land units, mainly through livestock. This model can be further used to explore improved agro-sylvo-pastoral landscapes. Processes related to carbon sequestration can also be implemented.