In the past few decades, several coefficients of uniformity were developed to express the uniformity of water distribution for different sprinkler irrigation systems. Christiansen’s uniformity coefficient seems to be the most popular uniformity coefficient used by researchers on the global scale. However, more coefficients have also been proposed by other researchers. Therefore, this study focused on evaluating different uniformity coefficients proposed and investigating the effects of field conditions on the results obtained by means of those coefficients. In doing so, sprinkler uniformity tests were conducted by using rain-gauge in order to measure the uniformity coefficients of ten fields irrigated by solid set sprinkler irrigation systems in Dehgolan Plain located in the Kurdistan Province, northwest of Iran. All fields selected differed in prevailing conditions such as the wind speed, size and type of nozzle, raiser height, operating pressure and sprinklers spacing. The coefficient of uniformity for each filed was computed using the 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. The results indicated that should not the field effect 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 suitable only for specific field conditions.
