Determination of Water Production Function - Nitrogen Fertilizer and Evaluation of Indices of Onion Production in Zahak Sistan and Baluchestan Region

In order to determine the production function of water and nitrogen fertilizer for onion plant in Three irrigation methods, an experiment based on split plot design was carried out with three replications at research farm in Zahak for two years. The research factors included irrigation by three methods (furrow irrigation, surface drip and subsurface drip), four levels of irrigation water (120, 100, 75 and 50persent water requirement) and four levels of nitrogen fertilizer 100, 75, 50 and 25% nitrogen). In order to determine the optimum depth of water and fertilizer, the best function of onion production was selected from four production functions (linear, logarithmic, quadratic and transverse) for all three irrigation methods. In all three irrigation methods, the quadratic function was selected as the superior production function. The average final production index relative to the depth of irrigation water in furrow irrigation, surface drip irrigation and subsurface drip irrigation was 0.23, 0.34 and 0.37 ton/ ha respectively, and the final production index relative to nitrogen was 0.09, 0.21 and 0.22 ton/ha respectively. The ratio of the technical replacement rate of nitrogen fertilizer instead of the amount of irrigation water was determined to be 39.9, 0.61 and 0.6 kg respectively.