This study was conducted to determine the yield response factor (Ky) of wheat with respect to deficit irrigation at different growth stages. The experiment was conducted in Shahrekord in three crop growing seasons using randomized complete blocks design with 3 replications. Treatments consisted of five levels of deficit irrigation: E0 (full irrigation), E1 (85%), E2 (70%) and E3 (55%) of potential evapotranspiration of wheat and E4 (no irrigation), and were assigned to six growth stages: T1 (establishment), T2 (tillering), T3 (head development), T4 (flowering), T5 (milk ripeness) and T6 (maturity harvest). Potential evapotranspiration was measured using a lysimeter, which was in conditions (soil texture and structure and plant growth) similar to the field. After harvesting the plants, grain yield was measured and wheat yield response factor was calculated. Results of combined analysis of variance showed that grain yield was significantly affected by deficit irrigation at establishment, tillering, head development, flowering and milk ripeness stages. The highest and the lowest grain yields (6354 and 2203 kg/ha, respectively) were obtained in E0 and E4 treatments, respectively. Potential evapotranspiration of wheat was 641 mm in this area. Yield response factors (ky) were 0.55-0.76 in T1 growth stage, 0.58-0.97 in T2, 0.70-1.43 in T3, 0.75-1.45 in T4, 0.68-0.95 in T5 and 0.52-0.58 in T6. In general, in all plant growth stages, actual and relative yields decrease as relative evapotranspiration decreases.

Keywords: Evapotranspiration, Alvand wheat cultivar, Growth stages.

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