Potassium response of various crops on a high-lime soil in relation to their contents of potassium, calcium, magnesium, and sodium

The K response of seven different crops grown on a K-deficient high-lime soil of the Webster series was determined in the greenhouse, using two rates of K fertilization. The crops were analyzed for K, Ca Mg, and Na in order to determine if the variations in the K response of the different crops on high-lime soils might be explained by differences in their normal absorption of Ca, Mg, and Na in relation to K. Large responses to K fertilization were obtained with corn and sorghum, whereas only slight to moderate responses were obtained with flax, oats, and soybeans. Sweet clover gave no response and that of buckwheat was negative. Of the various crops studied, only flax and oats absorbed appreciable amounts of Na. It appears that these crops respond but little to K fertilization because the Na which they absorb substitutes for K in the plant and thereby lowers the crop demand for K. In the case of those crops which absorb only small amounts of Na, it was found that their K responsiveness on the high-lime soil studied varied with their normal contents of Ca and Mg in relation to K. Sweet clover and buckwheat, which gave no K response, are crops which ordinarily use large amounts of Ca and Mg in relation to K, whereas the highly responsive crops, corn and sorghum, normally use small amounts. Soybeans occupy an intermediate position as regards K response and contents of Ca and Mg. These results are explained on the basis that (a) K absorption by crops on high-lime soils is repressed by high concentrations of Ca and Mg in the soil solutions, and (b) that those crops which require considerable amounts of Ca and Mg for normal growth show low response to K fertilization because they lower the ratios of Ca and Mg to K in the soil solution sufficiently to reduce or remove the repressive effects of Ca and Mg on K absorption.