Salt water has long been an enemy of the farmer, but a new study suggests it need not be.

Plant physiologists at the University of California at Davis succeeded in growing barley in sand dunes irrigated with water from the Pacific and now are studying the use of salt water for wheat and tomatoes.

In a report in a recent issue of Science journal of the American Association for the Advancement of Science, Dr. Emanuel Epstein and graduate student J.D. Norlyn estimated their experiments with barley produced a yield equal to about 1,000 pounds of grain per acre - half the national average.

"A thousand pounds to the acre on soil that is normally not used for cropping, with water that would never be put on agricultural soil, is not too shabby." Norlyn said in a telephone interview.

Epstein and Norlyn noted that although salt water will kill conventional crops, there is no fundamental biological incompatibility between plant life and highly saline conditions.

Marine algae and plants that grow on beaches, in salt marches and in saline desert soils are proof that plants can thrive in salty conditions.

The two researchers said that although nearly all crop plants are sensitive to salinity, there is much genetic variability in salt tolerance among various strains of plants.

"The leads that this evidence provides for selection and breeding for salt tolerance have not been pursued on any scale even remotely commensurate with their promise," the scientist wrote.

Norlyn said barley is one grain that has shown some salt tolerance. To select the best strains of barley for the salt water experiment, Epstein and Norlyn subjected specially selected seeds and plants to saline solutions in thelaboratary to see which would survive.

Of 2,800 seeds if one highly crossbred, for example, 9.2 per cent completed their whole life cycle with salt water, growing from seed to plant and then producing seed.

Then, after selecting the most salt-tolerant strains, Epstein and Norlyn planted barley in sand at a marine laboratory at Bodega Bay, on the Pacific 50 miles north of San Francisco.

The plots were irrigated with conventional furrows fed by ditches lined with plastic sheets. Each plot was fertilized before planting. Some rows were irrigated by pure salt water, others by diluted salt water and some by fresh water. Dilution by rain water was minimal.

The crops were harvested last summer and the salt water-irrigated barley was smaller than that fed fresh water, but the grain was a satisfactory feed quality and the seed was usable.

Barley, grows virtually everywhere around the world and there are 22,000 different strains of it. Epstein and Norlyn said selections for salt tolerance followed by a breeding program can be expected to increase yields from salt water irrigation.

Evidence already at hand indicates that this genetic approach to saline crop production is applicable to crops other than barley," they said.