Department of Soils and Agricultural Chemistry, Orissa University of Agriculture and Technology, Bhubaneswar, Orissa, 751003.
Jon exchange equilibria involving K-Ca was studied in the kaolinite dominated Suakati (Oxic Paleustalf) and illite dominated Motto soil (Vertic Halaquept). Both the soils showed a greater preference to K over Ca. Between the two soils, preference to K was greater in case of the kaolinite dominated Suakati soil than the illite dominated Motto soil as indicated from the higher selectivity coefficient and greater - ΔGo values in the former. Selectivity coefficient values decreased in the order of KV > KN > KJ Differences among KV, KN and KG values were higher at lower K saturation levels (below 40 per cent in Motto and 50 per cent in Suakati) than at higher K saturation levels. K specificity of the soils decreased with increase in K saturation to 40 per cent in Motto and 60 per cent in Suakati above which binding energy of the K-adsorption sites remained almost constant.
Exchange isotherm, selectivity coefficient, activity coefficient of adsorbed K, ΔGo of K-Ca exchange
