Sulphate Retention as Influenced by pH and Soil Constituents in Some Major Soil Groups of Karnataka

Sulphate retention studies with two pairs of Vertisols (pH-independent) and three pairs of Alfisols (pH-dependent) were carried out at the Agricultural Research Station, Gangavati. The soils had a range of properties in respect of pH, organic matter and free iron oxides. Adsorption of sulphate by Vertisols remained largely independent of equilibrium pH and solution concentration and was purely desorption. The negative values of distribution coefficient (K_d) and Freundlich's ‘k’ as a measure of adsorbability and ‘n’ as a measure of energies of adsorption indicated that soils carried predominantly pH-independent chmges. Alfisols representing variable charges recorded desorption (Ranebennur) at lower equilibrium concentration and higher pH value of the solution. All the soils, both surface and subsurface recorded a net loss in adsorption due to removal of organic matter and free iron oxides. Further, a decrease in, adsorption was indicated by ‘K_d’ and Freundlich's ‘k’ and ‘n’ values apart trom marginal reduction in PZC.