Influence of Continuous Cropping on the Fixation and Release of Potassium in Three Pennsylvania Soils

Abstract

AbstractThe fixation and release of potassium by three Pennsylvania soils was studied under greenhouse conditions using ryegrass as the indicator crop. The soils studied were representative of the two types of clay mineral distributions determined by a previous mineralogical survey of the soils of Pennsylvania.The potassium fixed by the soils during the greenhouse experiment was measured two ways: the fixation of exchangeable potassium as nonexchangeable, and the fixation of acid soluble potassium as acid insoluble. The amounts of potassium fixed as nonexchangeable and as acid insoluble potassium were approximately the same. The potassium fixed under moist greenhouse conditions was less than that fixed by repeated wetting and drying the soils at 75°C. The difference in the potassium fixation capacities of the soils was related to the physical characteristics of the vermiculite contained in the respective soils.The release of potassium by the soils during the greenhouse experiment was again measured two ways: the release of acid insoluble potassium as acid soluble, and the release of acid soluble potassium as exchangeable. The best indicator of the rate of release of potassium was the acid soluble potassium. The different rates of release of potassium by the soils were related to the hydrous mica content and were responsible for the significant differences in the ryegrass yield of the three soils.