The effects of electrolyte concentrations on calcium-sodium exchange equilibria in two soil samples of india

Abstract

The effects of total electrolyte concentrations of the equilibrium solutions (t.e.c.) on Ca 2+-Na + exchange equilibria in two soil samples (high and low in organic matter, clay content and CEC) were studied. Homoionic (Na +-saturated) soil samples were equilibrated with solutions having a large range in sodium adsorption ratio (SAR) at 25, 50, 75 and 100 meq. 1 -1 t.e.c. The exchange equilibria data were analysed, using a thermodynamic approach and the selectivity coefficients of Gapon (1933), Vanselow (1932) and Krishnamoorthy et al. (1948) (K G, K V and K KDO). At a given proportion of Ca 2+: Na + in the equilibrium solution, the development of the exchangeable sodium percentage (ESP) in both soil samples increased with the increase in t.e.c. At a given SAR, the effect of t.e.c. on the development of ESP was less on a soil sample with high organic matter (O.M.), clay content and cation exchange capacity (CEC) than on a soil sample with low O.M., clay content and CEC. The values of exchange selectivity coefficients decreased with the increase in t.e.c, and did not remain constant throughout the exchange isotherm for any of the t.e.c. tried.