Effects of Supplemental Irrigation and Nitrogen on Correlation Coefficient and Drought Tolerance Indices for Rainfed bread Wheat

In order to study correlation coefficients and path analysis for grain yield, an experiment was conducted as a split- plot in a randomized complete block design (RCBD) with three replications during three crop seasons (1999-2002) on rain fed wheat cultivar at Maragheh agricultural research station of DARI, Iran. The treatments were included four levels of supplemental irrigation (rainfed, 95, 151 and 207mm of irrigation) as main plots and five nitrogen rates (0, 30, 60, 90 and 120-kg.N.ha-1) as sub plots. Grain yield, straw and stubble, biological yield, harvest index (H.I.), plant height, kernel number per spike, spike number per square meter and Thousand kernel weight (TKW) were determined. The results showed that positive and significant correlations of grain yield with all traits: biological yield (r = 0.96**), plant height (r = 0.93**), straw yield (r = 0.92**), kernel number per spike (r = 0.87**), spike number per square meter (r = 0.84**), TKW (r = 0.52**) and harvest index (r = 0.49**) respectively. Path analysis results showed that increase in grain yield was resulted from increase in kernel number per spike, plant height, straw and spike number per square meter. Drought tolerance indices of (Tolerance Index, Mean Productivity, Geometric Mean Productivity, Stress Tolerance Index and Harmonic Mean) showed that 33% of full irrigation treatment combined with 60 Kg-N.ha-1 substantially increased water productivity.