Release of interlayer potassium in Norwegian grassland soils

摘要

Potassium (K) release from sources that are not initially exchangeable is attributed to depletion of interlayer K of micas and clay minerals or weathering of feldspars. The aim of the present study was to estimate the K release from interlayer K. Soil samples from 17 field experiments in ley on a range of mineral soils in Norway were used in the study. The change in K-fixation capacity was used as an estimate of depletion of interlayer K. It was assumed that the increase in K-fixation capacity during 3 yr of cropping was equivalent to the amount of K depleted from the interlayer positions. Mean K fixation increased in the majority of the soils during 3 yr of grass cropping both with and without K application. The increase in K fixation indicated that without K application, the K uptake from interlayer K amounted to 43%, 28%, and 26% of the K yield for clay soils, high-K sandy soils, and low-K sandy soils, respectively. Including K uptake from exchangeable K in the topsoil and from subsoil, the explained K uptake amounted to 79%, 69%, and 81% for the three groups of soil, respectively. Simple linear-regression analyses showed that the change in K fixation during 3 yr of grass cropping was best explained by the percentage of clay in the soil.