Effect of drought stress and nitrogen fertilizer on grain yield and nitrogen use efficiency of wheat (Triticum aestivum L. cv. Sirvan) in Fars Province, Iran conditions

In this experiment the effect nitrogen fertilizer levels (0, 75, 150, 225, 300 and 375 kg.ha-1) and four irrigation levels (normal irrigation, irrigation withhold at spike emergenc, grain filling stages and rainfed conditons) were evaluated on grain yield and agronomic traits of wheat cv. Sirvan during 2013-2014 and 2014-2015 at College of Agriculture, Shiraz University, Iran. Results showed that agronomic nitrogen use efficiency (ANUE), water productivity (WP), grain yield and yield components were reduced and protein content of grain increased under rainfed conditions. Grain yield and biological yield under rainfed condition were lower than normal irrigation by 67% and 58% in first and 75% and 65% in second years, respectively. The maximum grain yield and biological yield were obtained in 150 and 225 kgN.ha-1, under normal irrigation condition (5681 and 11950 kg.ha-1 for the first and 4545 and 10158 kg.ha-1 for the second years, respctivley). Irrigation withhold at spike emergence and grain filling stages were associated with reduction in 1000 grain weight, grain yield, biological yield and harvest index and increase in protein content of grain in both years. Nitrogen application up to optimum level (150 kg.ha-1) enhanced grain yield, yield components and water productivity in both years, but as water stress was intensified, the positive effect of nitrogen fertilizer was lowerd. The maximum water productivity was obtained in 150 kgN.ha-1 under irrigation withhold at spike emergence stage (815 and 672 kg.m-3 in first and second years, respectively). ANUE was reduced by increase in nitrogen fertilizer rate and the lowest rate was obtained in 375 kgN.ha-1. The maximum ANUE was obtained in 75 kgN.ha-1 under irrigation withhold at grain filling stage treatment (20.5 and 19 kg.kg-1 in the firast and second years, respectively). Overall, under normal irrigation condition, the application of 211.4 and 195.3 kgN.ha-1 and under rainfed condition, the application of 144.1 and 138.5 kgN.ha-1 (for the first and second years, respectively) were determined as the optimum rate of nitrogen fertilizer for wheat cv. Sirvan.