Mineralogy and geochemical properties of some upland soils from different sedimentary formations in south-eastern Nigeria

Abstract

Geochemical and mineralogical properties of soil can be used to assess their agricultural productivity potential. Ten soils from 4 geological formations in the south-eastern Nigeria were studied. Soil samples were taken from typical A and B horizons from each soil. The soil properties assessed were the free forms of Fe and Al, particle size distribution, total elements, and clay mineralogy. The soils are deep and highly weathered. Crystalline Fe and Al were more dominant than amorphous or less crystalline forms. The geochemical properties of the soils are dominated by SiO2, Al2O3, and Fe2O3, whereas MgO, TiO2, and ZrO2 occur in moderate to low quantities. Other basic elements such as Na2O, K2O, and CaO are very low in the soils, with an insignificant role in their genesis. The low contents of these elements in the soil may be the cause of their low nutrient release and storage in the soil. Ferritisation, laterisation, and kaolinitisation are the major pedogenic processes in the soil. The dominant clay mineral in all the soils was kaolinite; other minerals present though less common were illite, vermiculite, and smectites. Based on elemental contents and clay mineralogy, the soils can be grouped into 3 distinct groups: those with only kaolinite, illite, and vermiculites; and those that also contain smectite. These groupings can indicate the agricultural fertility potential.