Ionic exchange interrelationships in soils and crops. Ion selectivity in soils.

Abstract

The relative displacing power of various exchangeable cations in soils depends on the difference between the ion activity in the outside solution and the inside micellar-ion activity of the clay minerals. Theoretical calculations on the relationships between exchange capacity and distribution of ions with different valencies are shown in a graph. Evidence for the presence of Donnan systems is provided by results of chemical studies of temperate, tropical and subtropical soils. The ratio of divalent and monovalent exchangeable cations and the Ca/Mg ratio in soils depend chiefly on the degree of base saturation of the soil colloid. Highly leached acid tropical soils contain more monovalent cations relative to divalent and more Mg relative to Ca than do illuvial, base-saturated soils, indicating that both a valence effect and an effect of activity coefficients play a part in the ion-distribution problem of soils. (Abstract retrieved from CAB Abstracts by CABI’s permission)