KINETICS OF POTASSIUM DESORPTION BY ALFISOLS OF GREECE

Kinetics of K desorption was studied on Alfisol Haploxeralf samples of central Greece. Calcium-saturated samples were equilibrated with diff erent potassium concentrations and pH for 96 hours at pH 5.0, 6.0, 7.0 and 8.0 and initial potassium concentrations of 7, 35, 54 and 112 ppm . Samples were continuously leached with 0.01 M CaCL2 until K was not detected in the leachate. Desorption was nearly complete in approximat ely 3 to 4 hours for the Alfisol Haploxeralf. When the initial K conce ntrations varied between 0-7, 7-35, 35-54 and 54-112 ppm, then approxi mately 95-97%, 93-98%, 75-96% and 18-75%, respectively, was subsequent ly desorbed from Alfisol Haploxeralf samples. Three mathematical model s (first order, power function and parabolic diffusion) were used to d escribe cumulative potassium release at different values of pH and ini tially adsorbed K. Comparisons of coefficients of determination (r2) i ndicated that the first order, power function and parabolic diffusion equations adequately described cumulative potassium release for all st udied pH and initially adsorbed potassium. Apparent potassium desorpti on rate coefficients (k) ranged from 4.3 x 10(-3) to 11.4(-3) x 10(-3) min-1. The magnitude of the k values decreased as adsorbed potassium and pH increased. Finally all the studied models were transformed to p H-dependent forms.