The effect of potassium on the growth and chemical composition of some tropical and temperate pastrure legumes. II. Potassium, calcium, magnesium, sodium, nitrogen, phosphorus, and chloride

Abstract

Seven 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 were recorded. From the latter, data and discussion are presented for two groups of nutrients: cations (potassium, calcium, magnesium, and sodium) and nitrogen, phosphorus, and chloride. The multiple analyses permitted (a) an assessment of the effect of potassium chloride treatment on the above elements in the various plants, (b) a check of nutrient sufficiency at all levels of potassium treatment, and (c) the partial mineral characterization of those species. Species used were Phaseolus lathyroides, P. atropurpureus, Desrnodium intortum, D. uncinatum, Stylosanthes humilis, Lotononis bainesii, Centrosema pubescens, Medicago sativa, M. truncatula, Trifolium repens, and T. fragiferum.

Within the cation group, potassium application had little effect on the plant potassium concentration at low treatment levels, despite large increases in growth; at medium to high application rates, potassium concentration increased in the plant tissue. Potassium treatment caused decreases in calcium, magnesium, and sodium in the plant tissue, but these effects were not general for all species.

In P. lathyroides, P. atropurpureus, and M. sativa the effect of added potassium chloride on plant calcium was relatively small compared with that for the remaining species. In C. pubescens, M. truncatula, and T. fragiferum there was little to no effect of potassium chloride on magnesium concentration; in other species the uptake of magnesium was depressed. Sodium concentrations in D. intortum, D. uncinatum, and C. pubescens were not affected by potassium chloride additions; in other species there were substantial reductions. In both cases, magnesium and sodium, the species which did not show any interaction with potassium chloride were relatively low in magnesium and sodium respectively.

There was little effect of treatment on total cation contents. Potassium chloride applications had no effect on plant nitrogen concentration but increased the concentration of chloride and decreased that of phosphorus; these effects, however, were also conditioned by species. The Desrnodium species were depressed in growth by high chloride.