Abstract:
Five representative soil profiles were excavated along a
toposequence selected in the Itagunmodi area of South-Western Nigeria. The soils
were subjected to physical, chemical, and mineralogical analyses. The results
indicated soils with high fine sand and clay contents, but low silt content. The
soils were found to vary from slightly acid to strongly acid (pHH2O = 4.0 to 6.2).
Organic C, available P, and Kjeldahl N contents decreased with increasing depth.
Cation exchange capacity (CEC) ranged from 3.11 to 28.75 cmol(+)/kg soil. Base
saturation was low (<51%). From a total elemental analysis, Si was found to be
the dominant element, followed by Al, and then Fe. Extractable P, and exchangeable K, Mg, and Ca were quite low. The dominant minerals in the fine sand
fraction were quartz, feldspar, zircon, hornblende, tourmaline, and opaque ores.
The variation in the zircon/tourmaline (two resistant minerals) ratios with depth
suggests a stratification of the parent material. The change in the quartz/feldspar
ratios was an indication that the degree of weathering in the soil profile is not
uniform
