Evaluation and Improvement of Crop Production Functions for Simulation Winter Wheat Yields with Two Types of Yield Response Factors

Water is an important item of crop production and Irrigation water is limiting for crop production in arid and semi-arid areas. On the other hand, considering the population growth and increasing the water and food needs and also limited resources of water, the optimization of water consumption, especially in section of agriculture is important. For this purpose, in first step, the production function of expected products in any region should be obtained acceptably, because in this case, the models are totally dependent on the production function. Thus, finding the optimal production function has the lowest error in the estimation of risk-taking and decision-making power in the future will be important. So this study was conducted in Esmaeil Abad in Qazvin plain in Iran in the growing season of 2009-2012. Deficit Irrigations applied on different growth stages of winter wheat. The maximum evapotranspiration 641 mm and maximum attainable yield 5847 kg/ha was determined. After that the different production functions were studied and these methods have been tried to improve a new method with the least error. On the other hand yield response factor (Ky) per month was defined as either one of the standard values by FAO and the other using correction values by Najarchi et al. (2011). The result showed that the new model in this study is normalized with yield response factors of Najarchi et al. (2011) with 5% normal root mean square (NRMSE) has the lowest error. Therefore this technique for estimating water deficits of winter wheat in the Qazvin Plain was suggested.