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When a center pivot irrigation system is adopted in a square field, its four corners cannot be irrigated. Therefore, an end gun is often installed at the end of the system to expand the irrigated area; as such, proper selection of the end gun and optimization of water distribution are essential. In this study, we assessed the water distribution characteristics, application accuracies and uniformities under a three-span center pivot with an overhang and end gun without a boost pump. Two typical low-pressure sprinklers of Nelson R3000 and D3000 at two common operating pressures (0.15 and 0.20 MPa) and three representative nozzle diameters (8.73, 10.32, and 11.91 mm) of the end gun (Nelson P85A impact sprinkler) were considered. Additionally, the effects of various factors on the water distribution uniformity and accuracy were evaluated, and the optimal operating parameters of the center pivot with the end gun were proposed. Regardless of whether the end gun was on, the water application uniformity and accuracy of center pivot with R3000 sprinklers were highly significantly (P0.05) inversely proportional to the operating pressure. Taken together, the end gun nozzle diameter of 11.91 mm at an operating pressure of 0.15 MPa under the center pivot with R3000 sprinklers was recommended. This study provides a scientific basis for the optimal design of a center pivot with an end gun for a square field.

When a center pivot irrigation system is adopted in a square field, its four corners cannot be irrigated. Therefore, an end gun is often installed at the end of the system to expand the irrigated area; as such, proper selection of the end gun and optimization of water distribution are essential. In this study, we assessed the water distribution characteristics, application accuracies and uniformities under a three-span center pivot with an overhang and end gun without a boost pump. Two typical low-pressure sprinklers of Nelson R3000 and D3000 at two common operating pressures (0.15 and 0.20 MPa) and three representative nozzle diameters (8.73, 10.32, and 11.91 mm) of the end gun (Nelson P85A impact sprinkler) were considered. Additionally, the effects of various factors on the water distribution uniformity and accuracy were evaluated, and the optimal operating parameters of the center pivot with the end gun were proposed. Regardless of whether the end gun was on, the water application uniformity and accuracy of center pivot with R3000 sprinklers were highly significantly (P <0.01) superior to those of center pivot with D3000 sprinklers. For R3000, the end gun could effectively compensate for the insufficient irrigation defects at the overhang, thereby improving the overall center pivot water application accuracy and uniformity. However, the overall accuracy and uniformity with D3000 sprinklers were greatly reduced. Compared to the three spans and overhang, the water application uniformity and accuracy of the end gun were relatively poor, and these two indicators were highly significantly (P <0.01) proportional to the nozzle diameter of the end gun and nonsignificantly (P >0.05) inversely proportional to the operating pressure. Taken together, the end gun nozzle diameter of 11.91 mm at an operating pressure of 0.15 MPa under the center pivot with R3000 sprinklers was recommended. This study provides a scientific basis for the optimal design of a center pivot with an end gun for a square field. • Irrigation uniformity and accuracy of R3000 exceed those of D3000 under end gun on or off. • End gun compensates for insufficient irrigation of overhang and improves overall irrigation performance. • End gun with larger nozzle diameter and smaller operating pressure is preferred for corner irrigation. [ABSTRACT FROM AUTHOR]