effects of water stress at different growth stages on yield and water use efficiency of some wheat cultivars

concerning limitation of water resources, determination of the least water that can lead to the maximum yield is of great importance in crop production. in order to evaluate effects of deficit irrigation on grain yield and water use efficiency of some wheat )triticum aestivum) cultivars under different climatic conditions, two similar field experiments were conducted in 2004 in agricultural research stations of azad university of karaj and torbat-jam (central and eastern part of iran, respectively). the experiments were conducted as a randomized complete block design in a factorial arrangement with four replications. first factor was consisted of 9 different irrigation regimes, including a control treatment (irrigation at 40% soil moisture depletion), and irrigating when 60 and/or 80 percent of soil moisture was depleted from stem elongation to ripening, from the start of flowering to ripening, only at flowering stage, and irrigation termination at flowering and grain filling stages. the second factor was consisted of three wheat cultivars, including chamran, marvdasht and gaspard. results showed that yield, harvest index and water use efficiency were affected by water stress, as plants in control treatment produced the highest grain and biological yields, harvest index and water use efficiency. water use efficiency varied from 0.17 to 1.34 kg m-3 between irrigation regimes. deficit irrigation and drought stress at the end of season influenced yield and wue extremely, whereas limited irrigation at early growth stages had no significant effects. responses of wheat cultivars to irrigation regimes varied between two locations and warmer and drier conditions in torbat-jam lead to more water consumption and lower water use efficiency. among measured characteristics, seed yield had the most direct effect on wue and following that, total water used was accounted reasonably for the rest of variation in wue. thus it seems that wheat irrigation management, especially during late of growth season, is so important, and should be involved climatic conditions of each location as an effective variable.