Characterization of selected sandstone-derived soils in the ecological zones of Nigeria

Abstract

Sandstone-derived soils constitute about 18% of the land surface of Nigeria. These soils occur in all the major ecological zones and consequently are found under a wide range of rainfall and vegetation. The morphology and composition of a group of profiles selected to represent soils of the several zones have therefore been studied. The characteristics of the profiles can in part be related to the ecological zones and in part to the parent rock. Some characteristics are not clearly related to either. Both pH and base saturation decrease with increasing rainfall. The highest values are in the low rainfall zone and the lowest in the high rainfall zone. Soils of the medium rainfall zone are marked at depth by greater accumulations of silicate clays, iron oxides, and aluminium oxides than soils of both low and high rainfall regions. Kaolinite is the dominant clay mineral in all of the soils. Minor proportions of other minerals are present, and they seem to increase slightly with decreasing rainfall. Textures of all profiles strongly reflect the nature of the parent materials. The sand fractions are important in all parts of all profiles and are dominant throughout some of them.