Dynamics of Desorption of Labile Potassium from Chernozems

Abstract

The dynamics of desorption of the easily exchangeable and nonexchangeable potassium (K) have been studied in chernozem samples taken from a field trial with a single-time application of different rates of potassium fertilizers after a long period of the absence of fertilizers in Voronezh oblast. The desorption of the easily exchangeable K is adequately described by the zero-order equation of reaction; several mechanisms participate in it. The reaction rate constant regularly increases with an increase in the rate of applied K fertilizer. Taking into account the high correlation between the amounts of K released into the soil solution and absorbed by plants in the course of the dynamic experiments, we may conclude about a significant improvement of plant nutrition conditions even in the case of a single application of K fertilizer at a small rate. The desorption of nonexchangeable K is approximated by the equation of irreversible reaction of the first order. The parameters of this equation, as well as of the equation of diffusion and of the Elovich equation, do not change in dependence on the rate of applied K fertilizer. The reaction rate constants in the equations of the first and zero orders describing the desorption of nonexchangeable and easily exchangeable K from chernozems are three to five times higher than those for soddy-podzolic soils and other soils of humid regions. This can be explained by the differences in the number and nature of exchange centers in the organic matter and on clay minerals of these soils.