Abstract: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 on 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 field 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.

The wind drift and evaporation losses (WDEL) are high in arid, semi-arid and windward areas, and reduce the efficiency of the sprinkler irrigation system; therefore, this study was carried out in order to achieve a practical criterion and provide a relationship for accurate estimation of the wind drift and evaporation losses in different atmospheric conditions. The experiments were done at the Meteorological Station of the Faculty of Agriculture of Ferdowsi University of Mashhad using a line-source sprinkler irrigation system based on the single sprinkler installation method. To achieve the objectives of this plan, factorial experiment was performed on PGP sprinkler with regard to the two factors, the pressure of the sprinkler function (with three levels 1.6, 2.5 and 3.4 bar) and the diameter of the nozzle (with three levels of 4, 5 and 6 mm) with three replications (morning, noon and night). Assessing the result of the data variance analysis showed that the effects of pressure, aperture diameter, and time on the wind drift and evaporation losses are not significant. Investigating the main effects of these factors showed that the effect of aperture diameter on irrigation losses is significant at the level of the 1%. In order to further investigate, the comparison of mean losses data in three aperture diameter was done using Duncan′s test. The results indicated that aperture 4 with the losses of 44% had a significant difference with other diameters. This result suggests an increase in losses for smaller diameters due to the small droplets and the increase in wind drift. Also, the comparison of the mean losses data in three times showed that irrigation at noon with the losses of 44% had a significant difference compared to other times due to a significant increase in temperature and radiation of the sun and saturation vapor pressure deficit, and there is no significant difference between morning and evening irrigation. Also, analysis of variance showed that the effect of water pressure change between 1.6 and 4.3 bar does not have a significant effect on the WDEL in this sprinkler. In general, the results showed that increasing wind speed increases the losses of evaporation and wind. Also, this study suggested that changing the irrigation time in areas with hot and dry days, from day to night in summer, leads to a significant reduction of the wind drift and evaporation losses.

The performance and efficiency of classical fixed sprinkler and wheel move irrigation systems were compared in the Dehgolan Plain, north‐west Iran. The field and laboratory experiments were conducted with 10 classical fixed and 10 wheel move systems. Christensen coefficient of uniformity (CU), distribution uniformity (DU), potential application efficiency of low quarter (PELQ) and application efficiency of the lower quarter (AELQ) were used for the purpose of this assessment. The results showed a low efficiency due to improper design and management of classical fixed systems. Also, the results indicated that the wheel move systems used in the Dehgolan Plain performed well. The average mean values of the above coefficients (i.e. 12.6, 19.8, 21.5 and 14.5%) were higher in wheel move systems in comparison to those of classical fixed systems. Additionally, the average mean value of wind drift and evaporation losses (WDEL) and percolation losses (DP) were 0.45 and 1.17% lower in the wheel move systems, respectively, in comparison to those of classical fixed systems. The adequacy of irrigation (ADirr) of the wheel move systems was 16.3% higher than that of classical fixed systems. Generally, the results showed that wheel move systems in the Dehgolan Plain have a substantially higher efficiency than the classical fixed systems. © 2020 John Wiley & Sons, Ltd.