The Kinetics of Soil Potassium Desorption
1987
Sharpley, Andrew N.
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 (Kd) 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, Kd = k K₀ tᵅ Wᴮ where k, α, and β are constants. The kinetic constants, k (r² = 0.91), α (r² = 0.91), and β (r² = 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.
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