IRRIGATION WITH BRACKISH-WATER UNDER DESERT CONDITIONS .9. THE SALT TOLERANCE OF 6 FORAGE CROPS

The response of six forage crops to salinity was investigated in the f ield by means of a double-line source experimental design. The crops w ere Rhodes grass (Chloris gayana Kunth) cv. common, Bermuda grass (Cyn odon dactylon L. Pers.) cv. Suwannee, Kallar grass (Leptochloa fusca L . Kunth), salt (spike) grass (Distichlis spicata L.), seashore paspalu m (Paspalum vaginatum Swartz), and alfalfa (Medicago sativa L.) cv. Gi lboa. The trial was carried out over two growing seasons, 1990 and 199 1. The electrical conductivity of the irrigation water (EC(i)) ranged from 1.2 to 9.5 dS/m, and the mean seasonal electrical conductivity of the saturated soil paste (EC(e)) from 3 to 14 dS/m. The salt toleranc e of the six forage species was found to be: salt grass > Bermuda gras s > seashore paspalum > Rhodes grass > Kallar grass = alfalfa. In the first season, dry matter yields of salt grass, Bermuda grass and seash ore paspalum were not affected by a soil EC(e) of 14 dS/m. In the seco nd season, only the yield of salt grass was unaffected. Rhodes grass h ad, in the second season, exceptionally high annual yields (5.0 kg/m2) with fresh water irrigation. Thus, even though in comparison with mos t other grasses the yield of Rhodes grass was reduced by salinity (abo ut 6% yield reduction with every unit increase in EC(e) above a thresh old of 4.0 dS/m), its yield exceeded that of most species at an EC(e) of 8 dS/m. There was no consistency in the effect of salinity on crude protein, fiber and ash contents among the six forage grasses. In the second season ash content varied from 8% for Bermuda grass to about 15 .5% for seashore paspalum. Crude protein content varied from approxima tely 11.5% for Rhodes grass to approximately 16% for Bermuda grass and 22% for alfalfa. Both Bermuda grass and salt grass had a relatively h igh fiber content (40-42%). When brackish water supply was limited, dr y matter yield of salt grass was double the yield of the other species , indicating an advantage of this species under non-irrigated range-la nd conditions. This work shows that brackish water with an EC(i) of gr eater-than-or-equal-to 10 dS/m may be used for irrigation of certain f orage crops without any yield reduction.