Effect of Deficit Irrigation on Water Use and Water Use Efficiency of Alfalfa

Abstract. An alfalfa field study was established in 2011 at the University of Wyoming Research and Extension Center in Powell, WY. The objectives of the study were to determine: a) the daily and seasonal ET_c and water use efficiency (WUE) of alfalfa grown under different irrigation strategies and b) the yield response of alfalfa to limiting water. The experiment was a strip plot with 4 irrigation treatments and three alfalfa cultivars with four replicates. Reference evapotranspiration and crop coefficients were used to estimate the irrigation water amounts. A neutron probe, to a depth of 100 cm, was used for water balance estimations. The WUE was estimated as the ratio of the dry matter (DM) yield to ET_c. Significant differences (P<0.05) on water use and WUE were found between irrigation treatments while no differences were found between varieties. A strong relationship (R² = 0.81) was found between ET_c and total yield. The daily ET_c ranged from 5.5 to 0.7 mm d^-1 and the seasonal ET_c ranged from 737 to 191 mm for the fully irrigated and 25% irrigated treatments, respectively. DM yield was as high as 15293 kg ha^-1 and as low as 3,900 kg ha^-1 for the fully irrigated and the 25% irrigated treatments, respectively. The WUE was as high as 3 kg m^-3 and as low as 1.17 kg m^-3 for the fully irrigated and the 25% irrigated treatments, respectively. Further steps include studying the effects of limiting water on the forage quality of alfalfa and the development of irrigation scheduling strategies.