Sodium-calcium and magnesium exchange equilibria in soils

Natrium - (Calcium + Magnesium) - Austauschgleichgewichte in Böden . Beckett's approach has been used to describe the Na-(Ca + Mg) exchange isotherm in twenty soil samples that differed in texture and salinity. The data obtained from the isotherms were compared with the values of exchangeable sodium obtained by ammonium acetate and the concentration ratios (Na/ °Ca+Mg) calculated from the saturation paste extract. The Na-Q/I relation was always linear for each of the studied soils with no curvature at the lower values of concentration ratio. Values of - Δ Na₀ obtained from the isotherms were highly correlated with exchangeable Na (r² + 0.89). The equilibrium concentration ratios of the isotherms were similar to those obtained from the saturated paste extract in the non-saline soils, and were much lower in the case of the salt affected soils. The slope of the Na-Q/I relation appeared to be a soil characteristic not affected by either Na depletion from the soil or Na addition up to 5 me./100 g. soil. The PBC^Na values were highly correlated with the C.E.C. values of the soil (r² + 0.97).