Clay Research

Desorption kinetics of adsorbed SO₄^2- in the surface soils and subsoils of five Alfisols of Orissa were studied. Desorption progressed at a faster rate for the initial 60 minutes with release of 73.2 to 98.8% of total desorbed SO₄^2—S and then slowed down to attain equilibrium after 48 to 96 hours in different soils. The amounts of SO₄^2—S desorbed at different time intervals and at equilibrium were higher in the subsoils than in the surface soils. The time dependent SO₄²desorption was best described by the Elovich equation followed closely by power function equation. The Elovich desorption rate coefficient and total desorbable SO₄²⁻–S in soil were positively correlated with clay, exchangeable Ca²⁺ + Mg²⁺ and different forms of Fe and Al in the soils. Clay, free Fe₂O₃, free Al₂O₃, exchangeable Ca²⁺ + Mg²⁺, pH and organic carbon combinedly accounted for 96.2% of variations in Elovich desorption rate coefficient, 98.4% of variations in power function desorption rate coefficient and 95.7% of variations in total desorbable SO₄^2-–S in soils.