SODIUM‐CALCIUM EXCHANGE EQUILIBRIA IN SALT‐AFFECTED AND NORMAL SOILS

Abstract

SummarySodium‐calcium exchange equilibria in soils with a range of cation exchange capacity (CEC) and surface charge density (SCD), showed calcium preference whether the results were interpreted by a thermodynamic treatment, by an electric diffuse double layer equation, or by an empirical approach. Surface soils preferred Ca more than the corresponding sub‐soils, which was mainly attributed to their higher SCDs and organic carbon contents (OC). Significant correlations between OC and (ΔGo)ca→Na, and OC and SCD, suggest the effect of OC on Ca preference to be mainly through increased SCD rather than to specific ion exchange sites.Significant correlations between ΔGo and SCD, ΔGo and KG (the Capon constant), and between corrected SCD and KG, suggest that all three approaches can be used to describe Na:Ca exchange equilibria in these soils, and that the equilibria are related to intrinsic soil properties.