Surface charge characteristics of a variable charge soil (Rhodic Ferralsols) in the Central Highlands

Abstract

Variable charge soils (VCS) predominantly contain minerals with variable surface charge density, such as kaolinite, gibbsite, goethite, hematite and amorphous minerals. The charge characteristics differ between profile horizons, the topsoil normally possesses net negative surface charge whereas the subsoil may have net positive surface charge and are largely dependent on soil pH. The soils pose a particular challenge to sustainable management in terms of low cation exchange capacity (CEC) at soil low pH and may develop appreciable anion exchange capacity (AEC) under acidic conditions. A full understanding of the variation of charge with soil pH, before establishing strategies for sustainable management of these soils, is essential.