Evaluation of Water Deficit Stress Effects, Different Rates of Nitrogen and Plant Density on Remobilization, Current Photosynthesis and Grain Yield in Sunflower Var. Iroflor

This experiment was consisted in 2007-2008 and 2008-2009 cropping seasons in field Agriculture and Research center of West-Azerbaijan. The experimental design was split-split-plot experiments using Randomized Complete Block Design (RCBD) with 3 replications. The factor main was consisted irrigation treatment including optimum irrigation, moderate stress and sever stress where irrigation was done after depletion of 50%, 70% and 90% of available water, respectively. Three nitrogen levels consisting of 100, 160 and 220 kg N ha 1 were considered as sub plots and sub-sub plots consisted of three plant populations of 5.55, 6.66 and 8.33 plants m . The results of combined analyzes showed that severe drought stress reduced the grain yield by 2 60% compared to the optimum irrigation condition. Comparison of two-year-mean showed that severe drought stress in compared with optimum irrigation dry matter remobilization rate reduced about 30 percent. In level of optimum irrigation with increasing rate of nitrogen dry matter remobilization rate declined and in this condition with increasing plant population dry matter remobilization rate increased. Severe drought stress in compared with optimum irrigation current photosynthesis efficiency reduced about 35 percent. In level of irrigation with increasing rate of nitrogen contribution of remobilization decreased but current photosynthesis contribution increased significantly. In level of irrigation with increasing plant population contribution of remobilization increased but current photosynthesis contribution decreased. Therefore in condition of severe drought stress due to reduction of current photosynthesis rate, current photosynthesis contribution decreased so increasing of contribution of remobilization prevented a mostly from yield reduction.