The objective of this study was to relate the major chemical and mineralogical properties of soils formed on sedimentary deposits in southeastern Nigeria to the stability of their aggregates at both the macro and micro (colloidal) levels. Five profiles and twenty-five topsoil samples representing four major geological formations were studied. The soils are classified as Entisols and Ultisols. The soils are low in exchangeable cations. At both the macro and colloidal levels of aggregation, these cations and CEC were found not to have any positive influence on structural stability. A positive correlation coefficient (r=0.86) existed between Fe2O3 and Aggregated Silt+Clay (ASC) and water-unstable aggregates (WSA) <0.2 mm, (r=0.80). The major aggregating agent at the colloidal level was found to be Fe2O3. The mineralogy of the soils is dominated by kaolinite while the smectite observed in some wetland soils are assumed to be transported from drier areas. Soils containing smectites were more weakly aggregated (and hence, more structurally fragile) than soils dominated by kaolinite.
Geoderma 09/1999; 92(1-2):111-123. DOI:10.1016/S0016-7061(99)00029-4