Simulating leaching of potassium in a sandy soil using simple and complex models

The objective of this study was to assess the applicability of the Burn's-type model (simple model) and LEACHM (complex model) for describing potassium (K+) leaching in soil. Movement of K+ in a sandy soil using leaching column was examined. Pulse of K+ was applied to the column and then eluted with calcium chloride (CaCl2) solutions of various concentrations (3–15 mM CaCl2). Breakthrough curves for K+ indicated that after the initial adsorption, the concentration of K+ in the leachate would decrease rapidly with K+ retained strongly, so giving an extended tail. The LEACHM model was able to predict approximately the extent of K+ retardation, but K+ was leached a little later than simulated particularly at 5, 10 and 15 mM calcium (Ca2+) concentrations and the model was not able to predict effectively the slow rate of desorption of K+ from the column. Simulations using Wineglass model, described the location of the peak only in some cases and underestimated tailing. Also, the pulse of K+ was simulated to appear a little earlier and less tailed than that measured. Possible causes for the differences between the measured and simulated curves are as follows: the inability of the models to account for kinetically controlled chemical processes, assumption of a constant adsorption coefficient which is not valid as the adsorption coefficient changes as the concentration of K+ and Ca2+ changes during the leaching. The models could be useful tool to simulate leaching of K+ from agricultural land in regions with low quality water for irrigation and to forecast information in decision-making for environmental management.