The partition of basic exchangeable cations

Abstract

The sets of basic exchangeable cations in soil samples can be divided into subsets by changing the conditions under which their displacement takes place. Using a large cation (cholinium) in a nonaqueous solvent (alcohol), primary subsets of exchangeable calcium, magnesium and sodium are displaced. When ammonium ion in an aqueous solvent is used after this primary displacement, a conditionally exchangeable subset is obtained. Potassium is almost completely conditionally exchangeable in the soils studied. The conditional subsets may be further divided depending on whether the condition of using a smaller displacing cation (NH4+) or of having water present is met first. The concept of partition by exchange conditions is distinct from a partition based on exchange constants (under unchanged conditions) to which the epithets easily and difficultly exchangeable are appropriate.