Effect of Elimination of Irrigation in Terminal Stages of Growth on Yield and Water Use Efficiency of Five Wheat (Triticum aestivum L.) Genotypes in Mashhad

In order to optimize use of water resources with selection of suitable wheat genotype(s) and irrigation schedule, in this experiment, the effect of elimination of irrigation at terminal growth and development stages of five wheat genotypes was investigated in two successive growing seasons (2002-03 and 2003-04) in the agricultural research station of Torogh Mashhad. Split plot experiments were used based on randomized complete block design with three replications. Irrigation treatments were allocated to the main plots as: W₁: irrigation at stem elongation, flowering, milky, and doughy stages; W₂: irrigation at stem elongation, flowering, and milky stages; and W₃: irrigation at stem elongation and flowering stages. Five wheat genotypes including: C₁: Toos, C₂: C-78-4, C₃: C-78-8, C₄: C-79-6, and C₅: C-79-16 were assigned to the sub plots. Results showed that the effect of irrigation treatments on biological yield (BY), grain yield (GY), thousands kernel weight (TKW) and water use efficiency (WUE) were significant. Elimination of irrigation in grain filling period i.e. milky and soft dough stages, decreased BY (4.17% and 12.1%, respectively) and GY (5.14% and 11.9%, respectively). The mean GY of bread wheat genotypes under W₁, W₂, and W₃ irrigation treatments were 5834, 5549, and 5215 kg/ha, while WUE values were 1.022, 1.426 and 2.346 kg.m^-3, respectively. Although elimination of irrigation in the critical periods of developmental stages (grain filling) of wheat had positive effects on WUE, it had negative effect on GY and, therefore, is not recommended. C₄ and C₅ genotypes had the highest GY and WUE (1.814 and 1.748 kg.m^-3, respectively). However, C₄ and C₅ genotypes were more tolerant to terminal water stress.