Potassium-calcium exchange in some New Zealand soils

Abstract

The preference of some New Zealand soils to retain potassium over calcium under simulated field conditions has been measured by using Gaines and Thomas selectivity coefficients. All samples showed a preference for potassium over calcium (and magnesium), although the soils contained much more exchangeable calcium than exchangeable potassium. The preference for potassium decreased as more potassium was added to the samples. Oxidic, allophanic and ultic soils had the least preference for potassium; brown soils, formed mainly in loess, had the greatest preference, and this was probably due to the presence of many potassium-selective sites on vermiculite and mica clays in the soils. The results suggest that calcium, rather than potassium, is likely to be leached from all of the soils tested. This was consistent with data from laboratory leaching experiments using an allophanic soil.