Effect of Drought Stress, Plant Density and Nitrogen Rates on Morphophysiological and Quality Traits of Sunflower in Urmia Climate Conditions

This experiment was carried out to study the effects of water stress, different levels of nitrogen application and plant density on quality traits, phyllochron and leaf appearance rate of sunflower. It was conducted at West-Azarbaijan’s Research Center for Agriculture during growing season of 2011 and 2012. The study consisted of split-split-plot experiment based on a Randomized Complete Block Design with three replications. The main factor was considered to be irrigation treatments including optimum irrigation, moderate and severe stress in which irrigation was done after depletion of 50, 70 and 90% of field capacity, respectively. Three nitrogen levels including 100, 160 and 220 kg N ha^-1 were considered as sub plot with sub-sub plot consisting of three plant densities of 5.55, 6.66 and 8.33 plants m². The studied traits in this research were oil percentage, oil yield, protein percentage, protein yield, grain yield, phyllochron and leaf appearance rate. The combined variance analysis indicated that water deficiency stress, nitrogen and plant density had a considerable impact on oil and protein yield, oil and protein percentage, phyllochron and leaf appearance rate. The maximum oil yield (2213.22 kg ha^-1) was attributed to optimum irrigation and density of 83300 plants ha^-1. Severe drought stress reduced the oil yield by 62% compared to the optimum irrigation condition. Oil yield increased at higher nitrogen application rates. The response of oil yield to increase in plant density was positive. With increasing plant density, oil yield, oil percent, protein yield and phyllochron increased, but protein percent and leaf appearance rate decreased. So, application of 220 kg N ha^-1 and larger plant densities in optimum conditions and moderate drought stress conditions is recommended for suitable oil and protein yield.