برهان سهرابی

In order to investigate the effect of different methods, levels and salinity of irrigation water ‎on cotton, a two-year experiment was carried out‏ ‏at the Hashemabad Cotton Research Station ‎in Gorgan city.‎‏ ‏The experiment was performed in a randomized complete block design with ‎three replications. So, four salinity levels of irrigation water (1, 4, 8, 12 dS/m) as main factors, ‎four different levels of irrigation water‏ ‏‎(33, 66, 100 and 133% of water requirements) was ‎considered as the first factor and two irrigation methods (complete irrigation and Partial Root ‎Dry irrigation/PRD) were considered as the second factor. The results showed that compared ‎to control, cotton yield decreased by 41%, 22% and 19%, in 12, 8 and 4 dS/m salinity, ‎respectively. The water use efficiency was reduced at rate of 30, 18 and 16 percent. As the ‎salinity of irrigation water increased, the average weight of the boll, fiber index, earliness and ‎the fibers decreased significantly. As the moisture level increased, the yield of cotton, average ‎boll weight, the number of seed in a boll and the number of bolls increased significantly. In ‎additional the water use efficiency of the 133, 100 and 66% treatments compared to 33 ‎percent decreased by 32, 16 and 10 percent,‎‏ ‏respectively. The cotton yield under133, 100 and ‎‎66% treatments decreased by 32%, 16% and 10%, respectively, compared to the 33% of the ‎water requirement. Although PRD reduced crop yields by 15 percent compared to full ‎irrigation treatment, but the water use efficiency increased by 36%.‎‎‎‎‎‎

Irrigation water and nitrogen fertilizer are two important factors in increasing the yield and yield components of cotton. In order to evaluate effects of irrigation methods, various levels of water and nitrogen fertilizer on yield and yield components of cotton were studied at Hashemabad Cotton Research Station of Gorgan in 2008. The experiment was conducted in split-split plots design with three replications. Furrow and Sprinkler methods were main plots, various levels of irrigation water 0%, 33%, 66%, 100% and 133% of water requirement were subplots plots and various levels of nitrogen fertilizer 0%, 33%, 66%, 100% and 133% of recommended fertilization were sub-sub. The results showed that the effect of irrigation methods were significant on boll weight, seed index, number of seed per boll and lint index but without significant on yield and lint yield. The yield were influenced by various levels of irrigation water and the results showed that the highest yield 1996/60 was obtained in treatment 66% of irrigation water. Levels of irrigation water significantly affected on the entire yield components of cotton except the number of seed per boll. It was also found that the effect of various levels of nitrogen fertilizer showed significant difference on yield, boll and lint yield. The results revealed that yield and lint yield didn’t have significant difference between treatments 133% and 33%, 66%, 100% of various levels of nitrogen fertilizer.

Variable rate water application can be achieved along the length of centre pivot by variable-rate control systems. But to attain a satisfactory level of irrigation efficiency, high water application uniformity over area with same irrigation rate is required. In this research, the water distribution uniformity was evaluated with a modified centre pivot irrigation system that was able to vary the amount of water along the length of centre pivot and vertical to movement direction. Uniformities along the length of centre pivot and vertical to movement direction were calculated at three movement speeds and seven solenoid valve pulsing levels. Results showed that modified centre pivot is able to apply water with acceptable uniformity coefficient (82 to 96%) under different pulsing level and movement speed. Uniformity was increased by increasing pulsing level and decreasing movement speed.