Exchange equilibria of potassium in some red, black and alluvial soils of India .I. Effect of displacing cations

Abstract

Exchange equilibria of K+ versus Ca2+, NH4+ and Na+ were studied in seven benchmark soils representing red, black and alluvial soil groups of India. At low K saturation, illitic (alluvial) soils showed higher K selectivity than smectitic (black) and kaolinitic (red) soils. Fine textured smectitic soils maintained high K selectivity even at high K saturation. Potassium was usually preferred to Ca2+ throughout the range of K saturation encountered, except in one kaolinitic and one illitic soil, where cation preference was reversed at higher K saturation. In the K+-NH4+ exchange system, all the soils in general preferred NH4+ to K+. Smectitic soils preferred K+ to Na+, whereas kaolinitic and illitic soils preferred Na+ to K+. With an increase in K saturation, the activity coefficients of adsorbed Ca2+, NH4+ and Na+ always decreased, but that of K+ initially increased and then decreased to unity. The relative escaping tendency of K from the adsorbed to the solution phase was greater in the K+-Ca2+ system followed by the K+-NH4+ and K+-Na+ systems.