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The dry matter yield of 11 tropical legumes, 10 temperate legumes and 11 tropical grasses was examined in pot experiments on a clay soil with increasing levels of sodium chloride. A mathematical model was fitted to the yield-salt level curves for each species and both the half yield soil salinity level and zero yield soil salinity level were estimated. Species were ranked in relation to their salt tolerance at half and zero yield and these values were expressed in terms of the electrical conductivity of the soil saturation extract. Grasses showed a greater ability to persist at high salt levels than the legumes. The most tolerant grasses were Chloris gayana, Panicum coloratum, Pennisetum clandestinum, Sorghum almum and Digitaria decumbens. Medicago sativa, which was included in both temperate and tropical groups, was the most tolerant legume of both groups. The tropical legumes Macroptilium lathyroides and Macroptilium atropurpureum were almost equivalent to M. sativa in their salt tolerance. The least tolerant grass was Setaria anceps and the least tolerant tropical and temperate legumes were Desmodium uncinatum and Trifolium semipilosum respectively. Both Na and Cl percentages in the plant generally increased with increasing salt but no consistent relationship was found between plant salt tolerance and Na and Cl content. The field implications of the high salt tolerance of certain grasses is discussed in relation to the establishment of permanent grass-legume pastures on saline-sodic soils. |
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