evaluation of effective drought stress on yield, yield components and harvest index of sunflower hybrid iroflor at different levels of nitrogen and plant population in urmieh climate conditions

this research was conducted to study the effects of water deficiency stress, nitrogen application rates, and plant population on water use efficiency and nitrogen of oily sunflower in 2007-2008 agriculture and research center of west-azerbaijan. the study was consisted split-split-plot experiments using randomized complete block design 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 field capacity, 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 population of 5.55, 6.66 and 8.33 plant m-2.the results indicated that water deficiency stress, nitrogen and plant population on grain and biological yields, seeds per head, head diameter, kernel percentage to seed, 1000 grain weight, plant grain yield and harvest index were significant. the maximum grain yield (4200 kg/ha) was related to optimum irrigation treatment. severe drought stress reduced the grain yield by 44% compared to the optimum irrigation condition. grain yield increased with nitrogen application rate. the response of grain yield to increase in plant population was positive. all yield components were responded to the changes in plant population. the harvest index decreased with increasing severe drought stress and plant population. according to this research derived results application of 220 kg n ha-1 and plant population increase in optimum conditions and moderate drought stress is recommended for suitable yield, although nitrogen consumption and plant population increase has a little impact on grain yield in severe drought stress conditions.