Colloidal Stability and Potential Structural Deformation Index of Four Nigerian Soils

Abstract

This study was undertaken to evaluate the effect of continuous cultivation on the colloidal stability and potential structural deformation index (PSDI) of four Nigerian soils. The four soils used for the study were; Entisol from Nsukka Hill, Ultisol from Nsukka poultry site, Inceptisol from Eha-Amufu and Inceptisol from Ikem, in Nsukka area of south eastern, Nigeria. The land use types considered were fallow and cultivated. The soils collected from 0-25cm depth were separated into five aggregate fractions, 5-2 mm, 2-1 mm, 1-0.5 mm, 0.5-0.25 mm and 0.25 mm, and changes in their colloidal stability and PSDI properties due to cultivation were determined for both dry and wet sieved fractions. The result of the study showed that the aggregates in the cultivated soils were less stable than those in the fallow soils. The colloidal stability result show less structural stability of the aggregates by the high DR values obtained. The correlation result between silt+clay and dispersion ratio (DR) for all the land use types showed that the contribution of silt+clay to the stability of these soils was low. No significant correlation was observed between Organic Carbon (OC) concentration and PSDI values and between silt + clay and total N, available P and OC in all the soils. The potential of the aggregates to disintegrate upon contact with water was more in Inceptisiol at Eha-Amufu cultivated,  IEh (C) 84.4% > Ultisol at Nsukka cultivated, UNsk (C) 74.4% > Ultisol at Nsukka fallow, UNsk (F) 72.0% > Inceptisol at Eha-Amufu fallow, IEh (F) 68.3% > Inceptisol at Ikem cultivated, Iik (C) 65.5% > Entisol at Nsukka fallow, ENsk (F) 65.2% > Inceptisol at Ikem fallow, Iik (F) 64.7% > Entisol at Nsukka cultivated ENsk (C) 61.8%. From the results of this study it is evident that the colloidal stability and PSDI of dry aggregates and wet-aggregates differ substantially even though their diameters are the same. Hence they will have differing impact on the soils.