Testing and Optimizing of Water Distribution Characteristics for End Gun Combination on Center Pivot Irrigation Systems

To solve the problem of no irrigation in the four corners of square fields under center pivot irrigation systems, end guns are typically installed at the end of the overhang to expand the irrigation area, to improve the irrigation uniformity of end guns. The selection and configuration of end guns must match the length and inlet flow rate of the system. Otherwise, the end gun uniformity of irrigation area may decrease, and then potentially reducing the irrigation quality of the center pivot irrigation system. Proper selection and configuration of end guns are essential, as mismatched settings can reduce water distribution uniformity and irrigation quality, impacting the overall performance of the system. In this study, a commonly used center pivot irrigation system with a total length of 131.2 m, including two spans and an overhang in China was taken as the test platform. The AXIS-II rotary damping sprinkler from XCAD USA Company and the Twin101 plus vertical impact sprinkler from Austria's Komet Company were installed at the end of overhang. The two end guns can be worked separately and combinedly, and their corresponding water distribution characteristics were evaluated under various combinations of nozzle diameters and operating pressures. The result of study showed that the irrigation uniformity of the AXIS-II end gun was better than that of the Twin 101 plus. The radial uniformity coefficients for the AXIS-II ranged from 64.1% to 88.6%, and the circular uniformity coefficients ranged from 80.2% to 88.3%. In contrast, the radial uniformity coefficients for the Twin101 Plus ranged from 49.3% to 64.4%, while the circular uniformity coefficients ranged from 79.7% to 86.6%. The irrigation uniformity coefficients can be improved by optimizing the nozzle diameter and working pressure combinations. Specifically, the uniformity coefficients along the lateral pipe could be improved by approximately 10 percentage points for both types of end gun working separately. When AXIS-II and Twin101 plus end guns were combined, the radial and circular uniformity coefficients could be increased to 79.4% and 89.0%, respectively. Correspondingly, the radial and circular variation coefficients were reduced to 35.1% and 15.8%, respectively. When the two sprinklers operated in combination, significant improvements in water distribution uniformity were observed. Irrigation depth increased near the end gun area, especially within 144.2 m of the pivot point, leading to improved water distribution uniformity. The recommended optimal combination of end guns includes the AXIS-II end gun (with nozzle diameter of 15 mm, operating pressure of 200 kPa) and the Twin101 plus end gun (with nozzle diameter of 20 mm, operating pressure of 300 kPa), which is suitable for the center pivot irrigation systems with two spans and an overhang at similar overall length. These results provide the technical support for the selection and optimal design of end guns in center pivot irrigation system. This configuration achieved an irrigation uniformity coefficient (CU_H) of 85%, meeting national standards. And an effective range reached 0.89 times, exceeding the standard requirement of 0.75 times. The research results show that the combination of end guns can effectively improve irrigation performance. When combining the two types of sprinklers, selecting the appropriate nozzle diameter and operating pressure can effectively improve the low irrigation uniformity of end guns on center pivot irrigation systems. Improving the hydraulic performance of end guns can reduce water waste and optimize system performance. In turn, crop yield and quality are enhanced, resulting in significant economic and environmental benefits. Furthermore, this study not only provides a reference for end gun selection and configuration but also offers technical support for the revision of technical standards. The methodologies and results can serve as a basis for future research on optimizing end gun performance and adapting center pivot irrigation systems to different field conditions.