Influence of salinity on ionic concentration and yield of three tropical grain legumes

Abstract

The relationships between dry matter yield and ion concentration in three tropical grain legumes, viz. guar, cowpea and blackgram, were examined in soil salinized with a range of isosmotic levels of NaCl, CaCl2 and Na2SO4. The shoot yield of guar and cowpea was reduced to 50% of the control, at soil salt levels corresponding to electrical conductivities determined on saturated extracts (ECe,50%) of 11.8 and 11.6 dS m-1 respectively, the response being independent of the form of salt used. Both these species maintained low Na+ in shoots but accumulated moderate levels of Cl- in the presence of Cl- salts. The shoot yield of blackgram was less affected by CaCl2 salinity than NaCl salinity (i.e. ECe,50% = 13.6 dS m-1 compared with 8.8 dS m-1 respectively), whilst the growth response to Na2SO, was intermediate (ECe,50% = 10.8 dS m-1. Blackgram was found to accumulate large quantities of both Na+ (up to 1500 8mol g-1) and Cl- (up to 8 g-1) in shoot tissues. The use of isosmotic levels of different salts enabled the effects on growth of variation in ion concentration of shoots to be assessed, at the same potential level of water deficit. There was no evidence that ion excess was limiting growth of guar or cowpea, since large differences in ion concentration were not related to differences in dry matter yield. There was evidence that high ion concentrations in the shoots of blackgram, in particular high Na+ , limited growth under salinity stress. It is suggested that some benefit may be gained by searching for blackgram cultivars that accumulate less Na+ in shoots.