Abstract
AbstractCalcium–sodium exchange equilibria were studied at 15 and 25 °C in 2 smectite dominant soils belonging to Typic Haplustalf (Bundi Series) and Typic Pellustert (Chambal series) of Chambal Command Area of Rajasthan (India). These soils had preference for Na+ over Ca2+; however, the soil of Bundi Series at low Na saturation (10%) showed a preference for Ca2+ at lower temperature only. Higher specificity for Na+ in Chambal Series was related to the presence of zeoloites. The relationship between exchangeable sodium ratio and sodium adsorption ratio was nonlinear, and Chambal Series could maintain relatively lower sodium adsorption ratio even at higher exchangeable sodium ratio. Among different calculated selectivity coefficients, Gapon selectivity coefficient (KG) registered the lowest coefficient of variation. The values of thermodynamic equilibrium constant (K) were greater than unity indicating higher preference for Na+, especially in Chambal Series. The Ca↔Na exchange reaction was associated with an increase in the entropy of the system in these soils.
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