Field Performance of 21 Alfalfa (Medicago sativa) Varieties Under Saline Irrigation: Dry Matter Yield, Mineral Composition and Soil Salinity.

California has been facing a drought in the last four years that is changing the state’s agriculture. Good quality water will likely be dedicated to high value, salt-sensitive crops (fruit, nut and vegetable production) and forages will increasingly be irrigated with lower quality (more saline) water. Seed companies are aware of this trend and have developed more salt tolerant varieties of alfalfa (Medicago sativa). Mass and Grattan (1999), classified alfalfa as moderately salt tolerant with a yield loss threshold of 2 dS/m ECe (soil salinity). However, preliminary data from our studies suggest that this threshold is too conservative. A variety trial evaluating the field performance of twenty-one new alfalfa varieties bred for salt tolerance was initiated in October 2014 in the western San Joaquin Valley of California. Low (LS) and high salinity (HS) irrigation water, averaging 1.05 and 10.0 dS/m ECw, respectively, were applied in the first year of the three-year trial. Variety performance was assessed based on shoot dry matter yield in each of the five cuts taken in 2015. Shoot sodium and potassium are also being measured to correlate the yield response with the Na/K ratio. Soil sampling (0-90 cm in 30 cm increments) was conducted in May and October. During year 1, all varieties yielded well in the saline condition and the relative yield (LS/HS) ranged from 75.1 to 100% (average of 86.5%). Data from EM-38 surveys indicated that the high salinity basin had more spatial variability in soil salinity than the low salinity basin. Based on field data currently available from Year 1, it appears that these new alfalfa varieties, bred for salt tolerance, are indeed much more tolerant than the Maas Hoffman salinity tolerance coefficients would suggest.