POTASSIUM DYNAMICS IN SOIL DURING, STEADY FLOW

Abstract

Using a limited number of reasonable assumptions regarding the a priori unknown parameters, a model describing the dynamics of soil K during steady flow calibrated to experimental K/CaCl2 breakthrough curves obtained at relatively high flow rates from 2 columns packed with a sandy loam and a loamy sand, respectively. The model combines the effect of hydrodynamic dispersion and 1st-order mass transfer between the mobile and immobile regions with instantaneous, nonlinear cation exchange in both regions. The fraction of exchange sites in dynamic equilibrium with the mobile solution and the 1st-order mass transfer coefficient should be regarded as a priori unknown. The mass transfer coefficient for chloride ions was significantly higher than that for cations. Other transport parameters could be estimated independently of K transport, using chloride ion as a tracer. In soils with low cation exchange capacity, the sensitivity of the model to the cation exchange parameters is relatively high, thus necessitating a careful experimental determination of these parameters.