A kinetic model for soil acidification in its context with the associated equilibrium model

Abstract

Soil acidification often leads to exchange reactions that increase the concentration of toxic aluminum ions in the soil. Under the assumption of an instantaneous equilibrium these concentrations are computed as solutions of a nonlinear algebraic equation system. Usually these computations involve numerical complications. This paper takes up a kinetic model proposed in 1983. For a fundamental hydrogen-aluminum exchange reaction it is proved that the algebraic equilibrium can be approximated uniformly by the solution of a corresponding differential equation system, in the autonomous case as well as in the case of external periodic pertubations caused by acid deposition and leaching. Since the solutions of the kinetic model can be computed straightforwardly by numerical integration methods, the kinetic approximation should be more convenient for numerical simulation of soil chemistry processes.