NONEXCHANGEABLE POTASSIUM RELEASE KINETICS IN ILLITIC SOIL PROFILES

The kinetics of initially nonexchangeable K released to H-resin were i nvestigated on Gurdaspur loam (Udic Haplustalfs), Nihalkhera sandy loa m (Typic Comborthids), and Tulewal loamy sand (Ustochrepts) representi ng three agroclimatic regions of the Punjab state. Calcium-saturated s oil samples were equilibrated with H-resin for 0.25 to 96 h. The kinet ics of K release were evaluated using Elovich, power-function, first-o rder diffusion, zero-order, and parabolic diffusion equations. Potassi um release from nonexchangeable pool to H-resin on all three soils con formed 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 det ermination (R2) and lowest values of standard error (SE) of the estima te. The Elovich equation and power-function equation also described th e data satisfactorily. The zero-order equation did not describe the da ta well as shown by higher SE and lower R2 values than those found wit h the Elovich, first-order, diffusion, and power-function equations. T he values of rate constants or the nonexchangeable K release coefficie nts (kr) exhibited a great variation in their magnitude, which is attr ibuted to the mineralogical differences among these soils. The kr valu es 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 magni tude of kr suggested the medium rates of nonexchangeable K release fro m the three soils.