THE KINETICS OF NONEXCHANGEABLE POTASSIUM RELEASE IN COASTAL PLAIN SOILS
Martin, Harris W.
University Of Delaware
The kinetics of nonexchangeable K release using H-saturated resin were investigated on a Kenansville soil (Arenic Hapludults) and on a Kalmia soil (Typic Hapludults) from the Delaware Coastal Plain. The mineralogy of the <2ēm clay fraction of the two soils was largely kaolinite with substantial quantities of chloritized vermiculite. Both soils contained most of their total K in the mineral form. Kinetics of nonexchangeable K release in the soils was investigated from 6 min to 40 days. The data were found to conform well to first-order kinetics. Release rate coefficients (k2) ranged from 1.1 to 2.2 x 10-3 hour-1. The low k2 values indicated slow rates of K release as would be expected. The parabolic diffusion law also explained the data well with apparent diffusion rate coefficients (k2/) ranging from 1.7 to 2.6 x 10-2 hour-1/2. Thus, diffusion appeared to be the major rate limiting step in the rate of K release.
After 40 days of H-resin extraction the <2ēm clay fraction of the soils revealed no apparent clay mineral deterioration; thus, the use of H-saturated resin in evaluating the kinetics of nonexchangeable K release is justified.