Exchange equilibria of potassium in some red, black and alluvial soils of India .II. Effect of temperature on K⁺-Ca²⁺ exchange

Abstract

Potassium-calcium exchange equilibria in red (kaolinitic), black (smectitic) and alluvial (illitic) soils of India were studied at 25°C, 40°C and 65°C. The different selectivity coefficients increased in all the soils when the temperature was raised from 25°C to 40°C. Out of seven soils, only in three cases did the exchangeable potassium percentage (EPP) increase with rise in temperature from 25°C to 40°C. When the temperature was further raised to 65°C, EPP as well as selectivity coefficients in the different soils decreased to values less than those observed at 25°C. Similar inferences regarding K selectivity were drawn from normalized exchange isotherms. The sequence of variation in selectivity coefficients with increasing K saturation was Kv > KKDO > KN >KG, where the coefficients are those of Vanselow (Kv), Krishnamoorthy, Davis and Overstreet (KKDO), Gaines and Thomas (KN), and Gapon (KG). The sequence of the coefficients was unaffected by increasing the temperature from 25°C to 65°C. Potassium-calcium exchange was more spontaneous at 40°C than at 25°C. It was non-spontaneous at 65°C in all but the smectitic soils.