CALCIUM-POTASSIUM RATIOS FOR ALFALFA

Abstract

The effect of widely varying Ca-K ratios in the soil exchange complex upon the growth and composition of alfalfa was studied in an expt. designed to have an effect upon the soil equivalent to 10 yrs.'' cropping. Alfalfa was grown through 7 consecutive crops, over a period of 131/2 mos., on a series of soils having exchangeable Ca and K in initial ratios varying between 1:1 and 32:1, and constant amts. of other major and minor nutrients. The varied ratios were obtained by mixing varied proportions of homionically saturated soils. The 7 harvests of alfalfa and the roots were analyzed and the final exchangeable cation content of the soil was detd. Nutrient balance sheets were prepd., showing the nutrient changes in the soil and nutrient removal by the successive crops. The Ca-K, Mg-K, and Ca-Mg ratios in the soil and plant were calculated. The exptl. evidence indicates that, within limits, the absolute amts. of Ca and K in the exchangeable form are more significant than the ratio between them, and that alfalfa can adjust itself to wide variations in the Ca-K ratio in the soil, making normal growth at values ranging "between 1:1 and about 100:1. Abrupt decreases in yield occurred when the Ca-K ratio in the plant exceeded 4:1, the K content was less than 1%, or the Ca content exceeded 2%; under the conditions of the expt. these are considered critical limits.