THE FEEDING POWER OF PLANTS FOR THE POTASSIUM IN FELDSPAR, EXCHANGEABLE FORM, AND DILUTE SOLUTION

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Abstract
Plants were grown in quartz sand cultures supplied with feldspathic K, exchangeable K, and dilute solutions of water soluble K. The nature of the K in the expressed sap of plants was also studied. Corn, rape, buckwheat, peas, sorghum, sudan grass, soybeans, and oats were poor feeders on feldspathic K; alfalfa, alsike clover, red clover, and sweet clover were relatively good feeders. The K content of the good feeders receiving feldspathic K was significantly increased; that of the poor feeders was not. With flowing cultures buckwheat required 3 p.p.m. of K for good growth; 1 p.p.m. sufficed for red clover. The feeding power of plants for feldspathic K seems to be related to their ability to utilize K in dilute solution. The potassium in exchange form is readily available, but this availability decreases with a decreasing degree of saturation of the exchange material with K. The K in the expressed sap and macerated tissue of different plants is practically all in dialyzable form, or in a form which readily hydrolyzes on dialysis. Differences in feeding power do not appear to be related to the internal condition of the K.