SOME EFFECTS OF POTASSIUM UPON THE GROWTH OF SUGAR CANE AND UPON THE ABSORPTION AND MIGRATION OF ASH CONSTITUENTS

Abstract

Sugar cane plants of the variety H 109 were grown in quartz sand cultures and supplied with the following amts. of potassium: 87.9 p.p.m.K, 39 p.p.m.K, 3.9 p.p.m.K, no K + Na, no K and no Na. Symptoms of K starvation, which began to appear in 3 weeks, were depressed growth of the entire plant, discoloration of leaves, and dieback of the leaf tips. The development of red midribs, which occurred on the plants deficient in K, was shown to be a secondary rather than a primary symptom of K deficiency, developing when phloroglucin and sufficient sulphate occur within the plants. The source of phloroglucin suggested is the decomposition of tannic acids, a possible result of K deficiency. The sulphate came from an excess of ferrous sulphate used as the source of Fe. Growth was proportional to amount of K supplied. Because the plants totally deprived of both Na and K equalled or surpassed those supplied with Na but no K. it is concluded that Na does not even partially replace K in the nutrition of sugar cane. During the first month the absorption of K was limited by size of plant; after the first month the amt. absorbed was directly proportional to amt. supplied. Since equal amts. of K were absorbed by day and by night, absorption was not affected by light. Plants deficient in K absorbed more P and Fe than the controls, during the first 7 months. They also absorbed more Ca, Mg, and Si during the first couple of months. The addition of K to deficient plants caused a rapid absorption of K, increased growth, decreased absorption of P and Mg, and caused some of the Fe which had accumulated in roots and stems to pass up into the blades. K migrated from dying leaves to the living top. Because the amt. of migration showed a closer relationship to moisture % than to K content, it is shown that the translocation of K is not an adaptation in K-deficient plants but occurs there more than elsewhere only when those plants at the same time have the lowest moisture content.