Control of Potassium Release and Reversion Associated with Changes in Soil Moisture

The changes in exchangeable K that occur when soils are dried and rewet, and the affect of organic additives on these changes were determined with 20 soils from the North Central Region of the USA. The release of K associated with drying was essentially eliminated by adding dextrose to the soils before drying. The use of dried samples for the determination of the exchangeable K in field‐moist soils will be limited to some extent, however, because some soils fix K when they are dried and dextrose does not prevent fixation. In most cases, a decrease in exchangeable K occurred when air‐dry soils were rewet. A greater decrease in exchangeable K was attained with all soils when the air‐dry, rewet samples were redried in the presence of octanol. In some cases, only the reversion of K released by drying was involved, and the decrease was not enough to reduce the exchangeable K level to that in undried soil. In others, K fixation occurred and the heated soils contained less exchangeable K after treatment than they had in their field‐moist state. Nevertheless, the octanol treatment resulted in improved estimates of plant‐available K and of exchangeable K in undried soil samples over those obtainable with either air‐dry or air‐dry rewet samples.