The reasons for the very significant gap between potential and realized foodproduction in sub-Saharan Africa are multiple and complex. The decline infertility observed for many areas of soil has been described as the single mostimportant factor. Although this is a challengeable statement it undoubtedlyrefers to an ever-present reality for the majority of farmers in the continent -that optimizing the nutrient balance on their farms is one of the most difficultof the many agricultural management challenges they face.