## 3 Results and Discussion
### Same-nozzle-sprinkler Pipe Sections  
Same-nozzle-sprinkler pipe sections (PSs) of RSPSs distributed the most water around the central axes of PSs, and the applied water volumes declined gradually with increasing distance from the axes (Figure 7). With an increase in nozzle diameter, the coverage width of PSs increased, and the irrigation intensities also increased. When the sprinkler intervals increased to 4.5 m, the continuities of water distribution along the axis of the PS appeared to decrease, and regions of higher and lower spraying volumes appeared alternately along the PS axis. The PSs of FSPSs tended to distribute most water over both sides of the PS axis, while the area around the PS axis received less water (Figure 8). This became more apparent with increases in nozzle diameter and sprinkler interval (Figure 8). When the sprinkler intervals increased to 4.5 m, the continuities of water distribution along the axis of the PS appeared to decrease, which appeared as a continuous circular water distribution along the axes, with lower water volumes in the center of the circle and higher water volumes to the exterior of the circle. In all cases, the cross-sectional view (perpendicular to PS axis) of water distribution characteristic of FSPS PS is trapezoidal in shape, showing a plateau of quite high sprinkling intensity and a sharp decrease at the edges of the PSs. The height of this plateau increased in value as the nozzle diameter increased and sprinkler intervals decreased, and the width of this plateau increased in value as the nozzle diameter and sprinkler intervals increased. In addition, it is should be noted that the FSPSs have fairly high application intensity compared to RSPS PSs under same nozzle diameters and sprinkler intervals. A higher application intensity could bring problems of runoff and soil erosion [51]. Figure 7: Water distribution characteristics of same-nozzle-sprinkler pipe sections with rotating spray plate sprinklers (RSPSs). The figures in different columns and rows indicate different nozzle diameters (2.78, 4.76, and 6.75 mm) and sprinkler intervals (1.5, 3.0, and 4.5 m): RSPS—2.78—1.5 (**a**), RSPS—4.76—1.5 (**b**), RSPS—6.75—1.5 (**c**), RSPS—2.78—3.0 (**d**), RSPS—4.76—3.0 (**e**), RSPS—6.75—3.0 (**f**), RSPS—2.78—4.5 (**g**), RSPS—4.76—4.5 (**h**) and RSPS—6.75—4.5 (**i**). The water distribution was not symmetric with respect to the PS axes when nozzle diameter was 4.76 mm and 6.75 mm, especially for FSPS PSs. The sprinkler was suspended below the beam of center pivot simulator by a hosepipe. The perfect state is where the sprinkler is strictly perpendicular to the ground. However, in reality, it is inevitable that the sprinkler will incline a little, because of the strain of hosepipe, imprecise screw thread, and the imbalance gravity along the suspended parts (including hosepipe, pressure gauge, pressure regulator and sprinkler). These are also common in a real center pivot. The inclined position of sprinkler will lead to the asymmetrical water distribution to some extent. Moreover, the influence could be more significant as the discharge rate (nozzle diameters) increases. In addition, the water distribution of PSs were based on the measured water distribution of single sprinkler, therefore leading to the asymmetrical water distributions with respect to the PS axes in Figure 7b,c,e,f,h,i and Figure 8b,c,e,f,h,i when the nozzle diameters were 4.76 and 6.75 mm. The sprinkling uniformities of the PSs suggested that, when the nozzle diameters were 2.78 and 4.76 mm, the _CUCs_ of RSPS PSs were 5.8%-9.7% and 4.0%-6.4% higher than those of FSPS PSs (Table 6), respectively, and when the nozzle diameters were 6.75 mm, the _CUCs_ of RSPS PSs were 5.8%-13.3% less than those of FSPS PSs (Table 6). Possible reasons why the RSPS PSs showed poorer uniformity than the FSPS PSs with larger-diameter nozzles included that RSPSs concentrated most water volume around the axis region of the PS, generating a relative narrow water belt with high application rate (Figure 7c,f,i).