RESEARCH ON SOIL FERTILITY DECLINE IN TROPICAL ENVIRONMENTS - INTEGRATION OF SPATIAL SCALES

Soil nutrient depletion is increasingly regarded as a major constraint to sustainable food production in tropical environments. Research in the recent past focused on different scales, but few attempts were mad e to link them. In this paper, two cases are elaborated in Central Ame rica (CA) and Sub-Saharan Africa (SSA), in which the integration of di fferent scales has been studied. Soil nutrient depletion has been calc ulated for fields, and has then been aggregated to farms, regions, and subcontinents. Key problems on aggregation of field nutrient balances to farms include nutrient flows between fields. Aggregation of farms to regions requires a generalization of individual farms into a farm t ypology. Aggregation of regions into subcontinents implies that the fa rm typology concept can mostly not be maintained, resulting in a gener alized calculation based on national soil, climate and land use data b ases. The field-farm step proved complicated for SSA due to the occurr ence of a wide variety of nutrient flows between fields, whereas in CA these flows were much less pronounced; the farm-region step turned ou t to be manageable for both CA and SSA as farm typology adequately cov ered observed variation; the region-subcontinent step proved difficult for CA due to the considerable variation in management and input leve ls in farming systems, whereas this was less the case in SSA. The stud y shows that integration of spatial scales is constrained by both data availability (the tropical parameter crisis) and by scale-specific va riability.