The calcium and pH components of lime responses in tropical legumes

Abstract

Pot experiments with nodulated tropical pasture legumes on a soil low in calcium and with a pH of 5.3 showed wide variation between species in response to lime applications. Further experiments with Lotononis bainesii which showed a small response to lime, and Glycine wightii which showed a large response, allowed the lime effects to be resolved into calcium and pH effects. This was done by supplying calcium in a number of forms, and by altering the soil pH with a variety of compounds. The yield of Lotononis was affected only by pH, in spite of large variation in the calcium content of the plant resulting from varying the calcium supply. Glycine responded to both calcium and pH. The pH effect did not involve molybdenum supply or the alleviation of manganese and aluminium toxicities. Yield responses to low levels of calcium nitrate could not be attributed solely to pH effects, and suggest that a nodular dependence on favourable pH may have been circumvented. A calcium content of only 0.2% in the shoot is apparently sufficient for Lotononis, and the soil used was able to supply this.