Salt tolerance of some tropical pasture legumes with potential adaptation to cracking clay soils.

Cracking clay soils or vertisols occur in large areas of the subhumid regions of north-eastern Australia and frequently contain appreciable levels of salt in their subsoils. The comparative salt tolerance of some tropical pasture legumes was studied in pots with NaCl added to a clay soil to achieve electrical conductivities (saturated extract, ECe) over the range 2.0- 20.0 dS m-1. Tolerance, based on EC, at 50% of maximum growth (in parentheses) was in the order: Macroptilium atropurpureum cv. Siratro (10.6)> Macroptilium lathyroides cv. Murray (9.9) > Vigna trilobata (9.7) > Indigofera spicata (9.5) > Desmanthus subulatus (9.3) > Arachis pintoi (7.9) > Clitoria ternatea (6.4) > Stylosanthes scabra (5.6) > Indigofera schimperi (5.4) > Psoralea tenax (5.3) > Rhynchosia minima (5.1). The grass Panicum coloratum cv. Bambatsi was markedly more tolerant than any of the legumes studied, with 50% yield at an EC, of 16.4 dS m-1. Patterns of Na+ and Cl- uptake with increasing level of salt differed between species, but were not related to the degree oftolerance observed. The results are discussed in terms of the reported salinity tolerance of legumes generally and their implications to the search for persistent legumes for clay soils.