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Impact of three water deficit treatments in vegetative, flowering and grain filling stages along with optimum irrigation as control were evaluated on grain yield and agronomic characteristics of 8 sunflower cultivars (Hysun 33, Hysun 25, Farrokh, Record, Aravirski, Lakumka, Master and SHF 81-90) as a strip plot design with three replications in Khoy Agricultural and Natural Resources Research Station. Different water regimes had significant effect on growth period, plant height, stem and head diameter, seed yield and its component. Stem diameter, plant height and seed number per head were affected considerably by drought stress in vegetative stage, while head diameter by drought stress in flowering stage and growth period and seed weight by water deficit in seed filling stage. Water deficit in flowering and vegetative stages had the highest (38%) and lowest (25%) negative effect on grain yield, respectively, so flowering stage and vegetative stage established as the most sensitive and tolerant stages to water deficit, respectively. Farrokh hybrid with highest seed yield in different irrigation treatments (3686, 2856, 2256 and 2506 Kg/ha in control and water deficit in vegetative, flowering and grain filling stages, respectively) revealed as the most drought tolerant cultivator while Hysun33 lowest seed yield showed maximum drought sensitive.

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In order to study the effect of sulfur and Thiobacillus on some qualitative and quantitative traits of sunflower (cv. Hisun 25), an experiment was conducted as factorial based on Randomized Complete Block Design with three replications on research farm of the Gonbad Kavous University in 2013. The sulfur rate factor was in four levels: 0, 200, 400 and 600 kg sulfur per hectare and Thiobacillus bacteria factor was in four levels: 0, 10, 20 and 30 kg Thiobacillus per hectare. Results showed that the sulfur had a significant effect on plant height, 1000-seed weight and seed yield at 5% and on plant dry weight, oil percentage and oil yield at 1% probability. Effect of Thiobacillus on 1000-seed weight and seed yield at 5% and on plant height, plant dry weight, oil percentage and oil yield at 1% was significant. The maximum values of all traits were obtained from the highest amounts of sulfur and Thiobacillus. The highest plant height, 1000-seed weight, plant dry weight, seed yield, oil percentage and oil yield obtained from consumption of 600 kg S/ha. The maximum plant height, 1000-seed weight, plant dry weight, seed yield, oil percentage and oil yield belonged to consumption of 30 kg Thiobacillus/ha. The results of this study showed that effect of sulfur and Thiobacillus on some morphological traits, seed yield and yield components was less than percentage and yield of oil. This maybe has happened because of the sulfur role in oil production.