Utilization of non-exchangeable soil potassium in relation to soil type, plant species and stage of growth

Abstract

The stage of growth at which three plant species, a grass, a legume and a cereal, absorbed initially non-exchangeable potassium (Kn) from two soils, a red podzolic and a krasnozem, was examined by sequential harvesting in a glasshouse experiment. Large amounts of Kn were removed from the red podzolic soil, which contained greater amounts of micaceous material, in the order setaria > maize > lucerne. Uptake of Kn appeared insignificant after exchangeable Kn as measured on the bulk soil, had been depleted by about 60%, and its contribution to total plant uptake thereafter was independent of species. For setaria and maize, plant K concentrations at this time were above the critical level, so that Kn represents a potassium resource that can be exploited during normal growth of an appropriate species. Uptake of Kn from the krasnozem was relatively small. The red podzolic soil yielded much more Kn than a similar soil in earlier experiments. This was attributed to differences in clay mineralogy, possibly associated with differences in the weathering stages reached by the two soils. Thus, it is not possible to infer the pattern of release of Kn simply from a knowledge of Great Soil Group and parent material.