The Effect of Wetting and Drying Cycles on Potassium Release in Three Soil Orders

This research was conducted to study the potassium release under ten wetting and drying cycles in three soil orders (Mollisols, Vertisols, and Aridisols) collected from three different locations (Sharya, Semeel, and Kanishrin) in Dohuk governorate in Iraqi-Kurdistan region by using Ca-resin capsules, and K+ desorption (Kd) fitted to four model equations to choose the best equation to describe K+. The results of the experiments showed that flocculated water content wetting and drying cycles increased cumulative K-release from Ca-resin capsules until a tenth of the wetting-drying cycle. Potassium desorption according to the kinetic approach showed a significant effect of time on potassium desorption, and potassium desorption conformed to parabolic diffusion equations kinetics was the best equation to describe the Kd of potassium by using Ca-resin with a high coefficient of determination (R2) and low standard error and the order of the equation in terms of their preference in describing the desorption process is as follows: 1 – Parabolic diffusion, 2 – Power function, 3 – Elovich equation, 4 – First-order. The apparent desorption rate coefficient for the parabolic diffusion equation ranged from 0.1084–0.0877–0.1040 cmol kg-1∙day -1 from Mollisols, Vertisols, and Aridisols respectively. The rate coefficient K+ desorption according to the parabolic diffusion equation had a significant and positive correlation with SO42-, K+, T-CaCO3, HCO3, CEC, and Ca2+ but negatively significant correlated with EC and active CaCO3.