Optimization of Deficit Irrigation and Nitrogen Rates on Bread Irrigated Wheat at Northwest of Iran

ABSTRACT: Limitation of water resources, relative much land and little of water productivity (WP) are the specifications of agricultural irrigated areas. So, optimization of WP and expanding cropping area, led to improve WP and increase total wheat production. This field experiment (during 2000-2002) on a deep clay silty soil in Northwest of Iran was conducted for four deficit irrigation levels (rainfed, 1/3, 2/3 and full irrigation) combined with N rates (0, 30, 60, 90 and 120kg.N.ha-1) on Alamout wheat variety. With irrigation and nitrogen, crop responses were generally significant up to 90kg.N.ha-1. An addition of 34 percent reduction of water use related to full irrigation (2/3 of F.I) significantly increased yields and obtained maximum water productivity. Use efficiency for both irrigation water and N levels were greatly increased by deficit irrigation. Nitrogen use efficiency (NUE) over two crop seasons increased from 2.63-25.04 kg.N-1.ha-1 for grain yield. The WPirr over two seasons increased from 15.08-27.92 kg.mm-1.ha-1 for total grain yield and 8.43-20.56kg.mm-1.ha-1 for increase grain yield compare to rainfed condition. Optimum level of deficit irrigation was realized with 2/3 of full irrigation treatment (27.3 percent decreases in full irrigation water use = 160mm) which led to maximum irrigation water productivity and with 4467kg.ha-1 grain yield. Water productivity based on irrigation water alone (WPirr) and both irrigation plus rainfall (WPrain+irr) at 90kg.N.ha-1 over the two seasons were 9.58 and 27.92kg mm-1 respectively. Although it reduced 19.8 percent of grain yield comparison with full irrigation, but it got maximum water productivity, 37.5 percent increase in cropping area and mentioned 10.2 percent increase in total yield production. Thus, with 66% of full irrigation and 90kg.N.ha-1, combined with appropriate management, wheat output could be substantially and consistently increased in the semi arid climate zone.