FERTILITY STATUS OF SELECTED MILLET PRODUCING SOILS OF WEST AFRICA WITH EMPHASIS ON PHOSPHORUS

Major millet (Pennisetum glaucum (L. R.Br.) producing soils of West Africa ar mainly found in the Sudano-Sahelian agroecological zone. These soils are generally sandy in texture, have poor buffering capacity, and are low in native fertility. For successful management of these soils for sustainable production, fertility factors influencing nutrient availability need to be evaluated. Soils were sampled at selected locations throughout the agroecological zone. The nutrient status of these soils was determined and related to P dynamics. Soils were generally neutral to acid in reaction, but few had any measurable amounts of exchangeable Al. Total P, Bray 1 extractable P, and P adsorption maxima were low which reflected their low levels of clay and organic matter. Phosphorus sorption characteristics were controlled by the poorly crystalline Al and Fe phases and the soil clay fraction. The poorly crystalline Al and Fe phases were highly correlated with the clay fraction (r = 0.99***). The P external requirement ranged from 11 to 40 mg P kg-1 soil. Given the low levels of total and labile P in these soils, P amendments will be necessary for sustained productivity. However, moderate amounts of P amendments would be necessary as a result of the relatively low fixation capacity of these soils.