THE BASIC FACTORS WHICH DETERMINE INHERENT SOIL FERTILITY IN UGANDA

Soil samples collected from approximately 1700 fertilizer trials carried out around 62 centres in Uganda were analysed. Mean levels of total N. organic P and cation exchange capacity at the 60 centres which had non-volcanic soils were very closely related to mean organic matter levels and largely explained the strong correlation of indices of available N, P and base status with organic matter. The indices of available P and base status were additionally related to pH and the indices of available N and P were further negatively correlated with sunshine hours. Soil organic matter itself was closely related to the content of clay, silt and free Fe. with which it is presumed it forms a stable complex, whilst soil pH decreased with rainfall in excess of evaporation. Thus soil texture, rainfall and hours of sunshine are the basic factors which largely determine inherent soil fertility in Uganda.