NONEXCHANGEABLE POTASSIUM RELEASE KINETICS IN ILLITIC SOIL PROFILES

Abstract

The kinetics of initially nonexchangeable K released to H-resin were investigated on Gurdaspur loam (Udic Haplustalfs), Nihalkhera sandy loam (Typic Comborthids), and Tulewal loamy sand (Ustochrepts) representing three agroclimatic regions of the Punjab state. Calcium-saturated soil samples were equilibrated with H-resin for 0.25 to 96 h. The kinetics of K release were evaluated using Elovich, power-function, first-order diffusion, zero-order, and parabolic diffusion equations. Potassium release from nonexchangeable pool to H-resin on all three soils conformed well to the first-order (R2 = 0.936–0.987; SE = 1.0–3.30 x 10-3) equations as evidenced by the highest values of coefficient of determination (R2) and lowest values of standard error (SE) of the estimate. The Elovich equation and power-function equation also described the data satisfactorily. The zero-order equation did not describe the data well as shown by higher SE and lower R2 values than those found with the Elovich, first-order, diffusion, and power-function equations. The values of rate constants or the nonexchangeable K release coefficients (kr) exhibited a great variation in their magnitude, which is attributed to the mineralogical differences among these soils. The kr values varied from 0.025 to 0.034 h-1 in Gurdaspur, 0.030 to 0.049 h-1 in Nihalkhera, and 0.018 to 0.036 h-1 in Tulewal soil profiles. The magnitude of kr suggested the medium rates of nonexchangeable K release from the three soils.