Soil fertility research in sub-Saharan Africa: new dimensions, new challenges

This article describes spatial and temporal variation of soil nutrient stocks at different agro-ecosystem levels in East and West Africa. Whereas researchers preferably address macrovariability, African farmers tend to cherish microvariability. Next, studies at different system levels show that soils are depleted, as nutrients withdrawn by crops or lost by leaching and erosion far exceed nutrient inputs through fertilizers, deposition and biological fixation. It is shown how the absence of spatial and temporal variation in models based on soil fertility variables reduces their predictive value in land use planning and farm household decision-making