The effect of potassium on the growth and chemical composition of some tropical and temperate pasture legumes. I. Growth and critical percentages of potassuim

Abstract

Eight tropical and four temperate pasture legumes were grown in pots of a potassium-deficient soil, with varying additions of potassium chloride. Growth responses and chemical composition of the plant tops were recorded, and from these, critical percentages of potassium in the plant tops were established. All species responded in growth to potassium additions; however, there was practically no increase in plant potassium concentration over the low treatment range of potassium chloride. Medium to high rates of application increased plant potassium. Critical percentages of potassium in the tops of Phaseolus lathyroides, P. atropurpureus, Desmodium intortum, D. uncinatum, Stylosanthes humilis, Lotononis bainesii, Centrosema pubescens, Glycine javanica, Medicago sativa, M. truncatula, Trifolium repens, and T. fragiferum sampled at the immediate pre-flowering stage of growth were 0.75, 0.75, 0.80, 0.72, 0.60, 0.90?, 0.75, 0.80, 1.2, 1.0, 1.0, and 1.0% potassium respectively in the dry matter. In this work an absolute critical percentage has not been sought, but rather a working value for the rapid diagnosis of nutrient deficiency.