The Kinetics of Soil Potassium Desorption

The kinetics of soil K desorption from five soils was investigated at different water/soil ratios (10:1–400:1), over a short period of time (30 min), so that the results could be related to K desorption from agricultural soils to rainfall and drainage water. Potassium desorption ( K d ) was logarithmically related to contact time ( t ) at any given water/soil ratio ( W ) and K addition and to W at any given contact time and K addition. Potassium desorption was also directly related to the initial exchangeable K content of soil. The following kinetic equation previously developed for soil P desorption, described soil K desorption, K d = k K 0 t α W B where k , α, and β are constants. The kinetic constants, k ( r 2 = 0.91), α ( r 2 = 0.91), and β ( r 2 = 0.92) were related to cation exchange capacity (CEC). Unlike previous K desorption equations—(i) the uniformity of k , α, and β for a given soil, in accounting for the effects of reaction time, water/soil ratio, and soil K status on K desorption, and (ii) the fact that the constants can be estimated from CEC—may allow application of the equation to the prediction of soil K desorption in surface and groundwater quality and plant nutrient uptake modeling.