CHARACTERISTICS AND COMPOSITION OF SOME SAVANNA SOILS IN NIGERIA

Characteristics of 12 savanna soils in Nigeria were determined. The five Alfisols, one Ultisol, three Vertisols, two Oxisols, and one Entisol included samples of a wide range of texture, acidity and constituent composition. Except for the Quartzipsamment, all samples included an appreciable amount of silt (10-69%). Kaolinite was the dominant mineral in the clay fraction of all the well-drained soils, whereas smectite was dominant in the Vertisols. Quartz was the dominant mineral in the sand fraction of most of the soils, followed by K-feldspar, but the Oxisols contained also an appreciable amount of ilmenite, magnetite and other iron oxide minerals in that fraction. Extractable P was generally highest in the surface horizons but values were below 10 mg kg-1 except in one sample. The organic C exceeded 1% in only five of the surface horizons. The cation exchange capacity values at soil pH were below 10 meq per 100 g except in the Vertisols. Harmattan dust deposits may have affected the content of silt and other characteristics of these soils.