Water relations and use-efficiency, plant survival and productivity of nine alfalfa (Medicago sativa L.) cultivars in dryland Mediterranean conditions

The potential for alfalfa to be a valuable rainfed pasture option that can be used to increase livestock and crop production in central-south Chile is demonstrated for the first time. The persistence, productivity and water use efficiency of alfalfa (Medicago sativa) cultivars was evaluated at four sites in dryland Mediterranean environments of Chile between 2012 and 2015. Nine alfalfa cultivars were evaluated for plant persistence, winter growth, forage yield, shoot water potential (Ψ), stomatal conductance (gs), and carbon (δ13C) and oxygen (δ18O) compositions. The percentage of plant survival after four years varied between 69 and 97% of the established plants. Alfalfa forage yield was >9 t ha−1yr−1 at Yungay (Andes foothills) in year two, and at Cauquenes (interior dryland site) in years three and four. The highest forage yield was obtained in cultivars SARDI Ten and Aquarius and the lowest in WL326HQ. In 2015, the forage yield during late spring and early summer (November 2015-January 2016) ranged from 3170 to 3570 kg ha−1 (average of the nine cultivars), which represented between 29% and 38% of the total production. The response of gs to Ψ was different among cultivars but all cultivars exhibited a strong decline when Ψ was <−1.0 MP. Shoot water potential evaluated in October-November was negatively correlated with δ13C and δ18O in shoot biomass. The apparent water use efficiency (kg DM/ha/mm of rainfall) across the nine cultivars was highest in Cauquenes in the three years evaluated (>16 kg mm−1). It is concluded that alfalfa is a high yielding forage that can extend the growing season into early summer and autumn in dryland Mediterranean environments.