Comparative responses to calcium of five tropical and four temperate pasture legume species

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Abstract
A low humic grey soil grossly deficient in calcium was used to ascertain the relative effects of calcium carbonate additions on the growth, calcium and nitrogen contents, nodulation, and calcium deficiency symptoms of five tropical legumes (Desmodium uncinatum (Jacq.) DC., Indigofera spicata Forsk., Centrosema pubescens Benth., Stylosanthes bojeri Vog., and Phaseolus lathyroides L.) and four temperate legumes (Medicago tribuloides Desr., M. sativa L., Trifolium fragiferum L., and T. repens L.). In the absence of added calcium the five tropical legumes did not show any visual symptoms of calcium deficiency, and the respective yields on the nil treatments were 25, 40, 52, 64, and 68% of their maximum yields in the presence of added calcium carbonate. The four temperate legumes showed visual symptoms of calcium deficiency. and the respective yields on the nil treatments were 0.2, 1.5, 2.0 and 6.5% of their maxima. Calcium, nitrogen, and nodulation data are quoted and discussed. It is considered that the effect of added calcium carbonate in this soil is primarily one of calcium nutrition of the species, and that the differences between the two groups of legumes may be due to restricted uptake. There is evidence that the process of nodule formation is calcium-sensitive in the tropical species as well as in the temperate species. It is suggested that the superior ability of the tropical species to nodulate at low calcium levels is primarily related to their superior ability to extract calcium from the soil.

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