In order to evaluate the effect of different levels of defoliation and grain removal on grain yield and photosynthesis rate of sunflower, a factorial experiment was conducted based on randomized complete block design with three replications during 2012 growing season at College of Agriculture, Shiraz University. Treatments were defoliation at 3 levels (0, 50, and 75%) in heading stage and grain removal (without grain removal (control), removal of one half of the grains in inner or side parts) at pollination stage. It appeared that defoliation resulted in reduction of grain yield, 1000 grain weight and grain number. Apparently increased photosynthetic rates of reminder leaves may be considered a response to the reduction of leaf area however it did not generally sufficient to compensate the reduction of leaf area. The highest reduction of grain yield was recorded in 75% defoliation and removal of one-half of the grains in inner parts of head, compared to control. It can be concluded that grain yield of sunflower is more determined by limited source.

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.