Abstract: Drought seriously affects the growth and production of forage crops and has long been one of the most important limiting factors for animal husbandry in the Loess Plateau of China. Understanding of forage response to water deficit can help to optimize grassland management and improve productivity. This study was carried out in a greenhouse with alfalfa (Medicago sativa) under four water levels of 35%, 50%, 65% and 80% field saturated water capacity (FWC) to clarify the influence of water deficit on forage yield and quality. It was found that: 1) With increasing water stress, the height and fresh and dry weight per plant of alfalfa decreased significantly (P<0.05), although fresh and dry weight per plant did not differ between 65% FWC and 80% FWC. 2) The neutral detergent fiber content (NDF) of alfalfa at 50% FWC was significantly lower than that under 65% FWC (P<0.05), but did not differ from NDF at other water levels. The crude protein content at 35% FWC and 80% FWC were significantly higher than those at 50% FWC and 65% FWC. There was no significant difference in digestible dry matter, total digestible nutrient, digestible dry matter intake and relative feeding value among various levels of water deficit. 3) Copper and Fe concentrations initially increased and then decreased with increasing water stress, while Mg and Mn concentrations showed an opposite trend and Zn concentration increased. The accumulations of five trace elements tested differed little among the different levels of water stress, except that Mg and Mn accumulations were significantly higher at 80% FWC than at 35% FWC and 50% FWC. In summary, mild water stress was conducive to the improved yield and quality. At 50% FWC, alfalfa forage showed lower fiber content and higher nutritional value, while at 65% FWC, alfalfa showed higher yield. Trace elements Mn, Mg, Cu and Fe can reflect the quality characteristics of alfalfa to a certain extent.

Key words: drought, alfalfa, quality, trace element