Comparative responses to manganese excess of eight tropical and four temperate pasture legume species

Abstract

Eight tropical legumes and four temperate legumes were grown in water culture and their response to excess manganese was determined by comparing relative dry matter production (tops and roots), manganese, calcium, and nitrogen percentages in the dry matter. The tropical legumes as a group were as much affected by excess manganese as the temperate legumes. There were varying degrees of tolerance within each group. The growth of the different species varied over a wide range but this had nothing to do with sensitivity to manganese. The concentrations of manganese in the roots of two species representing the most tolerant and the least tolerant species were examined. They suggested that the relative tolerance of species depends in part on retention of manganese within the root system. Manganese treatments had little effect on the calcium and nitrogen concentrations in the dry matter (tops) of the majority of species examined. The diagnosis of manganese toxicity may be made by comparing manganese concentrations in the tops with toxicity threshold values obtained by the authors and other workers, and used in conjunction with the visual symptoms of manganese toxicity which have been observed for the various species. Toxicity threshold manganese values in the dry matter of the tops obtained in this investigation were: Centrosema pubescens 1600, Stylosanthes humilis 1140, Lotononis bainesii 1320, Phaseolus lathyroides 840, Leucaena leucocephala 550, Desmodium uncinatum 1160, Glycine javanica 560, Phaseolus atropurpureus 810, Trifolium repens 650, Medicago sativa 380, Trifolium fragiferum 510, and Medicago truncatula 560 p.p.m.