Clay Mineralogy of Soils in the Nigerian Tropical Savanna Regions

Abstract

AbstractThe clay mineralogy of soils from the moist southern Guinea savanna and subhumid northern Guinea savanna has been studied. All the soils occur on basement complex. Kaolinite is the dominant clay mineral in all the well‐drained soils, a property shared with the well‐drained soils of the humid tropical forests. In poorly drained soils montmorillonite forms in significant amounts in addition to kaolinite. Quartz is another mineral that occurs in the clay fraction of all the soils. Kaolinization is the dominant clay forming process under good soil drainage. The kaolinization process seems to be directed or favored by (i) the lowering of the pH of the weathering environment due to the temperature‐induced dissociation of soil water, (ii) marked leaching rainfall, and (iii) mineralogical composition of the soil or parent material. Under poor drainage montmorillonization becomes a significant clay‐forming process in addition to kaolinization due to the adequate silica, alumina, and base potentials of the soil solution.