The effect of lime, KCl and parent material on the cation exchange capacity of some acid subsoils of the western Cape

Abstract

Cation exchange capacity (CEC) values obtained by ²²Na dilution for a number of mineralogically diverse acid subsoils reflected positive responses to lime and to treatment with KCl such that: CEC (unlimed, no KCl) < (unlimed + KCl) < (limed, no KCl) < (limed + KCl). Mean CEC values for the kaolinitic granite soils and for the 2:1 mineral-containing Bokkeveld shale (BS) soils were similar. This similarity masked a wider variability in the CEC values observed for the BS than for the granite soils, particularly in terms of response to lime. The Table Mountain sandstone (TMS) soils had a lower mean CEC but a wider variation between treatments. Overall CEC responses to liming and to applied K respectively, were: TMS > BS > > granite; and: TMS > > granite > BS. CEC values per kg clay⁻¹ increased exponentially with decreasing soil clay content, probably as a function of dilution.