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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.

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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 (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]

Variable-rate irrigation (VRI) can effectively improve the irrigation efficiency. In this study, we evaluated the two key indicators, irrigation uniformity and accuracy for a three-span center pivot VRI system with the combination of two sprinkler types, i.e., the Nelson D3000 (a fixed spray plate sprinkler, FSPS) and the R3000 (a rotating spray plate sprinkler, RSPS), two sets of irrigation depths designed for four management zones (zones 1–4) of 10, 8, 15, and 20 mm and 10, 15, 20, and 25 mm, and three cycle times (CTs) of the solenoid valve of 30, 45, and 60 s, with constant-rate irrigation (CRI) as a reference. In addition, the radially affected lengths of irrigation depths in zones 1–4 under various VRI treatments were further determined. The radial (mean CU H = 90.8%) and circumferential application uniformity (mean CU H = 95.6%) as well as radial irrigation accuracy (mean NRMSE = 15.3%) of the R3000 were superior to those of D3000 under VRI. The irrigation uniformity and accuracy of each management zone were less impacted by the designed irrigation depth and CT, but more affected by the location of the management zone. The irrigation uniformity and accuracy of VRI were close to those of CRI, indicating that the VRI system tested could guarantee the same application performance as the CRI system. Changing the D3000 sprinklers to R3000 sprinklers in the VRI system effectively reduced the radially affected lengths of management zones. The radially affected lengths of D3000 under various treatments were primarily distributed from 3–6 m, whereas those of R3000 were 0–3 m. Thus, it was recommended to select RSPSs in the design of the center pivot VRI system, and the transition zone and CT in relation to R3000 sprinklers were suggested to be 0–3 m and 60 s, respectively. This research provides the recommendations for better implementation of VRI. • Rotating spray plate sprinkler can minimize the radially affected length in VRI. • Uniformity and accuracy of VRI are less affected by irrigation depth and cycle time. • Irrigation effect of the R3000 is superior to that of the D3000 under VRI. [ABSTRACT FROM AUTHOR]