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Abstract
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In the past few decades, several coefficients of uniformity have been developed to express uniformity of distributed water for different sprinkler irrigation systems. Christiansen’s uniformity coefficient seems to be the most popular uniformity coefficients used by researchers on a global scale. However, more coefficients have also been proposed by other researchers. Therefore, this study focused on evaluating different proposed uniformity coefficients and investigating the effects of field conditions on the results obtained by those coefficients. In doing so, sprinkler uniformity tests were conducted by using rain-gauges in order to measure uniformity coefficients of ten fields irrigated by solid set sprinkler irrigation systems in Dehgolan Plain located in Kurdistan Province, northwest of Iran. All selected fields were different in prevailing conditions such as wind speed, size and type of nozzle, raiser height, operating pressure and sprinklers spacing. The coefficient of uniformity for each filed was computed by equations proposed by Christiansen (1942), Hawaiian Cane Society Specialists Hart and Reynolds (1965), Wilcox and Swailes (1947), Karmeli (1978), Criddle et al. (1956), Benami and Hore (1964) and Beale (1966). Data analysis was performed using the general linear model procedure of Statistical Analysis System Software. Results indicated that should the field effect not be considered in the statistical model, significant differences (P<0.05) would be observed between the aforesaid coefficients; however, by considering the field effect in the statistical model, no significant differences (P>0.05) would be observed. The results of this study conclusively indicated that the application of various coefficients of uniformity depends on the field conditions and as any specific coefficient of uniformity is only suitable for specific field conditions.
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