Water Productivity and Virtual Water of Barley Cultivars under Different Irrigation Regimes

To remain viable in facing with increasing costs, farmers need to increase irrigation Water Productivity (WP) and save Virtual Water (VW). To evaluate the WP and VW for five barley cultivars (Reyhan, Nimrooz, Valfajr, Zehak, and Yusof) under different irrigation regimes [well-watered (100% Field Capacity; FC), mild water stress (75% FC), severe water stress (50% FC), and extremely severe water stress (25% FC)], a two- year field experiment was laid out in Darab, Fars Province, Iran, during 2014 and 2015 growing seasons. Results showed that change in moisture stress from well-watered to extremely severe water stress, was associated with a significant increase in WP and Economic Water Productivity (EWP) for straw and biological yield. A positive linear relationship was found between grain yield and VW, and the lowest VW was found in the range of 3,314 to 3,451 kg ha^-1 of grain yield. Interestingly, for all irrigation regimes, Zehak and Yusof cultivars had greater WP for the grain yield. Furthermore, VW for biological yield of Yusof cultivar sharply decreased from 0.410 m^3 kg^-1 in well-watered treatment to 0.164 m^3 kg^-1 under extremely water stress conditions in both years. Comparison of Zehak and Yusof cultivars with Reyhan, Nimrooz and Valfajr showed that under water stress conditions, the first two cultivars showed significantly lower VW for the grain yield than the other cultivars. Indeed, Yusof and Zehak cultivars showed the lowest Economic Virtual Water (EVW), which was in the range of 0.054 to 0.091 m^3 1,000 Rials^-1, under extremely water stress conditions. Thus, to achieve optimum EWP and EVW and attaining stable yields under semi-arid conditions, suitable barley cultivars such as Zehak and Yusof could be irrigated with less water (i.e. 25 to 50% FC).