بررسی اثر تنش کم آبی بر روی عملکرد و کیفیت علوفه خشک ارقام یونجه در شرایط آب و هوایی خوزستان

In order to investigate the effect of water deficit on yield and water us efficiency (WUE) of four alfalfa cultivars, an experiment was conducted as a split plot design in randomized complete block with 3 replications in Agriclture and Natural Resources Research Center of Khuzestan during 2011-2012. Main plots were 4 irrigation regimes (I1: traditional irrigation, I2: irrigation in loss of 5%, I3: irrigation in loss of 65% and I4: irrigation in loss of 80% AWC) and subplots were four cultivars of alfalfa (V1: Baghdadi, V2: Mesasirsa, V3: Yazdi and V4: Hamedani).The result showed that Baghdadi and Mesasirsa cultivars with the 25 percent water deficit only 10 percent decreased on yield, especially on stem yield and had the higher biomass production under stress conditions when compared to other cultivars. Therefor, in drought stress conditions the rate of dry hay yield decreased but the quality of forage increased because in this stage fiber decreased but protein and DMD increased. The consideration of physiologic and anatomic response releated to drought stress which has been studied revealed that the Baghdadi and Mesasirsa cultivars for the reason of higher in using of mechanism against drought stress were the most tolerant in response to drought stress. Some of the characters of these cultivars are: Had higher maintained of (RWC) Relative Water Content that have been directly with the adjusting osmotic potentioal, had the lower electrolyte leakage under stress conditions when compared to other cultivars and also had more proline accumulation.Those cultivars had the lower electrolyte leakage under stress conditions when compared to other cultivars. The size of stomata was smaller but their number was higher. The size of leaves became small in the water deficit conditions but they were biger than to other cultivars, that is important to have a higher photosynthesis.Key words: Medicago sativa, RWC, proline, electrolyte leakage, stomata, forage quality