Spatial carbon, nitrogen and phosphorus budget of a village in the West African savana : I. Element pools and structure of a mixed-farming system

The viability of mixed farming systems in West African savannas relies largely on the management of endogenous organic resources. Assessment of the organic balance at both plot and village territory scales is needed as an indicator of this viability. Distribution of carbon (C), nitrogen and phosphorus in soil and plant biomass was thus quantified for a village in southern Senegal across the different land use systems (LUS) and farm holdings. The village exhibited ring-like organisation, including a compound ring, a bush ring, and lowland paddy fields, with positive gradients of intensification and food production from the savanna to the dwellings. Marked contrasts were found between holdings, especially in livestock availability. Clear relationships were evidenced between the spatial distribution of C and nutrients and the agricultural functions of LUS and holdings, while multi-scale diversity appeared to be the main factor that ensured the functioning of the system. Intensification schemes at the village level aimed at increasing organic resources and their cycling efficiency must thus take into account their impact on this diversity. (Résumé d'auteur