Submitted to: Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2015
Publication Date: 7/28/2015
Citation: Ferreira, J.F., Cornacchione, M.V., Liu, X., Suarez, D.L. 2015. Nutrient composition, forage parameters, and antioxidant capacity of alfalfa (Medicago sativa, L.) in response to saline irrigation water. Agriculture. 5:577-597. doi: 10.3390/agriculture5030577.
Interpretive Summary: Alfalfa is the most important forage legume used in dairy cattle feed in the United States. California is the main national alfalfa producer and almost 100% of the crop in the state is irrigated to provide enough biomass for animal feed. However, high cost and increasing scarcity of high quality water will lead to increasing use of degraded or drainage waters to irrigate this crop. These waters generally have elevated to high levels of salts. Although alfalfa is moderatly tolerant to salinity compared to forage grasses, the effects of saline irrigation waters on alfalfa nutritional value and forage quality are not fully understood. Also, the literature lacks data on the effect of saline waters on the antioxidant capacity of alflafa, which could add to the list of benefits to livestock fed with the crop. This work evaluated four commercial cultivars of alfalfa, irrigated with a range of waters with increasing salinity levels, and with a salt mixture designed to simulate drainage water compositions of the California Central Valley. Plants were harvest in September of 2011 (2nd harvest) and in April of 2012 (7th harvest), and evaluated for their shoot biomass, mineral composition (macro and micronutrients), forage quality, and for shoot antioxidant capacity. Regarding macronutrients for animal production, increased salinity led to significant increases in magnesium (Mg), phosphorus (P), sulfur (S), and nitrogen (N), but to significant decreases in calcium (Ca) and potassium (K). Micronutrients in alfalfa also increased or decreased with salinity, but to levels that did not raise concerns regarding toxicity or deficiency to livestock. Sodium (Na) also increased significantly. Salinity improved forage quality by significantly increasing crude protein (CP), total digestible nutrients (TDN), net energy of lactation (NEL), and relative feed value (RFV). Although shoot biomass decreased significantly at the second harvest, biomass was not affected at the seventh harvest, after the crop was established. All four cultivars maintained their antioxidant capacity, regardless of the salinity level of the irrigation waters. Our results indicate that the alfalfa cultivars evaluated in this work, once established, can tolerate moderate to high levels of salinity in irrigation waters without detrimental effects to forage nutritional value and with benefits to forage quality, thus meeting the standards required for alfalfa forage used as dairy cattle feed. The information generated in our work is of high interest to alfalfa producers who can only count on drainage waters and soils with moderate to high salinity to produce alfalfa as a forage for livestock.
Technical Abstract: Although alfalfa is moderately tolerant of salinity, the effects of salinity on nutrient composition and forage parameters are poorly understood. In addition, there are no data on the effect of salinity on the antioxidant capacity of alfalfa. We evaluated four non-dormant, salinity-tolerant commercial cultivars, irrigated with saline water with electrical conductivities of 3.1, 7.2, 12.7, 18.4, 24.0, and 30.0 dS/m, designed to simulate drainage waters from the California Central Valley. Alfalfa shoots were evaluated for nutrient composition, forage parameters, and antioxidant capacity. Salinity significantly increased shoot N, P, Mg, and S, but decreased Ca and K. Alfalfa micronutrients were also affected by salinity, but to a lesser extent. Na and Cl increased significantly with increasing salinity. Salinity slightly improved forage parameters by significantly increasing crude protein, the net energy of lactation, and the relative feed value. All cultivars maintained their antioxidant capacity regardless of salinity level. The results indicate that alfalfa can tolerate moderate to high salinity while maintaining nutrient composition, antioxidant capacity, and slightly improved forage parameters, thus meeting the standards required for dairy cattle feed.