Determination of the yield response factor for field crop deficit irrigation

The irrigation network of Taleghan Dam Reservoir was used to determine yield response factor for maize (Zea mays), winter wheat (Triticum aestivum), and barley (Hodeum vulgare) in the Qazvin Plain of Iran. Dependent variable actual crop yield and independent variables including climate data were obtained from Qazvin Plain Irrigation Company. Data were gathered from five fields in Qazvin province between 2002 to 2009. Potential evapotranspiration was calculated by the Penman-Monteith method. Actual evapotranspiration (ETa) was measured based on the irrigation requirement at the fields. Yield response factor (Ky) was obtained for four crop stages including vegetative, flowering, grain filling, and ripening, and calculated for the total growing period. The Ky values for maze, winter wheat and barley in different stages of their growth periods including vegetative, flowering, grain filling, ripening and total growing period were equal to (0.48, 1.45, 0.55, 0.29 and 1.55), (0.60, 0.68, 0.87, 0.69 and 1.20) and (0.50, 0.82, 0.75, 0.57 and 1.10), respectively. The bias error less than 15% between averages of estimated and observed yields verified the results. These results were compared with Ky obtained by FAO and other studies separately. There is a satisfactory correlation between Ky calculated using this research and other studies.   Key words: Yield response factor, actual and maximum evapotranspiration, actual and maximum yield.