Effect of extra nitrogen fertilizer on reduction of drought stress

This research was performed to investigate the role of extra nitrogen fertilizer in reduction of drought stress effects in bread wheat. For this propose, an experiment was conducted as split plot using randomized complete block design with three replications, during 2010-2011. The three different environmental conditions consisted of  normal conditions, terminal drought stress condition with 30% increase in N fertilizer and terminal drought stress condition, were allocated in the main plots and 7 cultivars and lines of bread wheat were assigned in sub plots. The genotypes under investigation revealed significant differences on MP, GMP, TOL, STI and SSI under drought stress and drought stress with extra N fertilizer conditions. Based on the results of correlation between drought tolerance indices and grain yield, GMP and STI depicted positive correlation with grain yield under all environmental conditions. Therefore, GMP and STI indices were considered as the best for the selection of tolerant genotypes under different environmental conditions. The result of cluster analysis which was based on the reaction of the seed in different environmental conditions, and the indices could lead to separated genotypes to three groups under stress condition and stress condition with extra N fertilizer. Comparison of traits on genotypes in these groups revealed that Sepahan, Pishtaz and Line 9 had the highest amount of yield and indices under drought stress condition with extra N fertilizer, however only Pishtaz and line 9 showed the highest amount of different traits under drought stress conditions. There were low reduction in grain yield under stress condition with extra N fertilizer for Sepahan and Rowshan which is mainly related to effect of nitrogen on drought stress adjustment. Nitrogen treatment did not have noticeable effects on the other genotypes. By comparing the percentage of yield reduction under stress environment, it was proved that Sepahan and Rowshan had 9 and 6 percent yield reduction respectively under extra N fertilizer less than the drought stress. T-test indicated that there were significant differences between grain yield under normal and stress conditions for all genotypes, however, Sepahan and line 11 showed significant differences between drought stress and drought stress with extra N fertilizer conditions.