Characterization of soil for potential potassium supplying capacity and release of non-exchangeable potassium during cropping through simulation model

An attempt has been made to develop a method to characterize soils with respect to potential potassium (K) supply capacity and release of non-exchangeable K during cropping and its contribution towards K uptake through a simulation model. The model is based on the equation of continuity (a mathematical statement derived on the basis of principle of conservation of mass of solute and water in a soil element) with the assumption that nutrient flux from soil to root proceeds by mass flow and diffusion and influx into root follows Michaelis-Menten kinetics. Potassium fixation or release in soil has been simulated by incorporating a sink and source function, respectively, to the equation of continuity with the hypothesis that K release takes place in soil when labile K level goes below release threshold level (RTL) and fixation takes place when labile K level goes above fixation threshold level (FTL). Different soil and root parameters required for this model have been determined in solution culture and pot culture experiment, and a computer program has been written in visual basic to run the model. The model was run to characterize a soil with respect to its maximum supply of K to wheat crop from different depths and the contribution of non-exchangeable K, therein, and compared with the data of a field experiment. It has also been shown by simulation that maximum response towards applied K occurs at a particular value of available K, which shifts towards higher value as RTL increases.