The effect of phosphorus on the growth and chemical composition of some tropical pasture legumes. II. Nitrogen, calcium, magnesium, potassium, and sodium contents

Abstract

This paper describes the effect of phosphorus on nitrogen concentration and on the total and individual concentrations of the cations calcium, magnesium, potassium, and sodium in the plant tops of 10 tropical legumes and one temperate legume when grown on two soils of different type, a light-textured solodic soil and a gley soil. Species used were Phaseolus lathyroides, P. atropurpureus, Stylosanthes humilis, Centrosema pubescens, Glycine javanica, Lotononis bainesii, Medicago sativa, Desmodium uncinatum, D. intortum, Vigna luteola, and Leucaena leucocephala.

The nitrogen concentrations in the plant tops were increased by phosphorus supply, and good correlations were established between the nitrogen and phosphorus concentrations in the plant tops.

When sodium dihydrogen phosphate was used as the source of phosphate, the sodium concentration in V. luteola, M. sativa, and L. bainesii was increased. Other species were not affected. Increasing phosphate supply as monocalcium phosphate had little effect on plant calcium concentration, but brought about an increase of magnesium in P. lathyroides and P. atropurpureus. In the solodic soil particularly, increases in phosphate supply in most species caused reductions in the potassium concentration, partly compensated by increases in the magnesium and calcium concentrations.

Concentrations of the cations in the plants reflected the soil exchangeable cation composition. Plant species differed in their cation status. P. atropurpureus and P. lathyroides were relatively high in magnesium, L. bainesii and D. intortum in potassium, V. luteola, L. bainesii, M. sativa, and P. lathyroides in sodium, and C. pubescens and S. humilis in calcium.