The behavior of added and native potassium of five Tennessee soils and factors affecting its availability

Much research has been conducted to determine the relationships among potassium, the soil and the plant. Although our knowledge of these relationships has greatly increased, our understanding of the mechanisms responsible for soil potassium release and the processes involved in soil potassium reactions has only started. The fact that the total potassium in a soil is not a reliable index of the capacity, of a soil to supply potassium to plants has been known for some time. As early as 1894 (4), it was observed that part of the potassium added as fertilizer was converted to a form not readily available to plants.

Investigations agree that the quantities of potassium removed by chemical and biological methods cannot be absolutely categorized as exchangeable or available potassium because the quantity removed is a function of multiple variables.

The use of radioactive isotopes has contributed significantly to the solutions of soil problems. They enable the distinction of potassium added as fertilizer potassium from native soil potassium through the technique of isotopic dilution.

The objectives for this study were to determine the behavior of potassium added as fertilizer and native soil potassium of five Tennessee soils and the factors affecting the availability of potassium to plants. Native potassium is that potassium in the soil prior to sampling which may or may not include potassium applied by man. Experiments were conducted to study: the influence of alternate wetting and drying and of clay mineralogy on fixation and release of native and added potassium in the soil; the relation of several chemical extraction techniques to available potassium in the soil; the contributions of potassium from sand, silt and clay to the total and available potassium content of the soil; the effect of added potassium on the replacement of calcium and magnesium; the uptake of potassium by sudangrass; and the equilibria of native and added potassium in the soil by the radioactive tracer technique.