Irrigation with brackish water under desert conditions IX. The salt tolerance of six forage crops

Abstract

The response of six forage crops to salinity was investigated in the field by means of a double-line source experimental design. The crops were Rhodes grass ( Chloris gayana Kunth) cv. common, Bermuda grass ( Cynodon dactylon L. Pers.) cv. Suwannee, Kallar grass ( Leptochloa fusca L. Kunth), salt (spike) grass ( Distichlis spicata L.), seashore paspalum ( Paspalum vaginatum Swartz), and alfalfa ( Medicago sativa L.) cv. Gilboa. The trial was carried out over two growing seasons, 1990 and 1991. 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 tolerance of the six forage species was found to be: salt grass > Bermuda grass > seashore paspalum > Rhodes grass > Kallar grass = alfalfa. In the first season, dry matter yields of salt grass, Bermuda grass and seashore paspalum were not affected by a soil EC e of 14 dS/m. In the second season, only the yield of salt grass was unaffected. Rhodes grass had, in the second season, exceptionally high annual yields (5.0 kg/m 2) with fresh water irrigation. Thus, even though in comparison with most other grasses the yield of Rhodes grass was reduced by salinity (about 6% yield reduction with every unit increase in EC e above a threshold 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 ∼11.5% for Rhodes grass to ∼16% for Bermuda grass and 22% for alfalfa. Both Bermuda grass and salt grass had a relatively high fiber content (40–42%). When brackish water supply was limited, dry matter yield of salt grass was double the yield of the other species, indicating an advantage of this species under non-irrigated rangeland conditions. This work shows that brackish water with an EC i of≥10 dS/m may be used for irrigation of certain forage crops without any yield reduction.