## 3 Results and Discussion
### Full Circular Irrigated Area  
Under different sprinkler intervals, the _CUCs_ of RSPS FCIA were 85.8%-91.7%, and those of FSPS FCIA were 85.8%-86.2% (Table 7). The simulated results were consistent with previous reports [33; 52]. Specifically, the _CUCs_ showed no obvious differences between RSPS FCIA and FSPS FCIA with a 1.5-m sprinkler interval. However, _CUCs_ of RSPS FCIA were 3.1% and 5.9% higher than those of FSPS FCIA with 3.0- and 4.5-m sprinkler intervals, respectively (Table 7).  
These results suggested that the 3.0- and 4.5-m sprinkler intervals highlighted the advantages of RSPSs. This indicates that RSPS could accommodate larger sprinkler intervals than FSPS, while maintaining better sprinkling uniformity. Moreover, the _CUCs_ of FCIA at sprinkler intervals of 1.5 m were lower than those at 3.0 m, not only for RSPS but also for FSPS. Possible reasons for this include that the diameters of practically configured nozzles were much larger than the theoretical requirements for sprinklers close to the pivot (Figure 3). Thus, the practical application depth would be much higher than that expected around the pivot, which would reduce the values of _CUC_, according to the algorithm of the Christiansen coefficient of uniformity (Equation 1) [44]. Additionally, the gaps between the actual and expected application depth around the pivot would be greater as the sprinkler interval became smaller. Thus, the _CUC_ of FCIA would be influenced more markedly with smaller sprinkler intervals. In this experiment, the expected application depth was 10 mm. If the values were 20 mm and 12 mm, this could lead to indistinct sprinkling intensities between actual and expected results for the cases of 1.5- and 3.0-m sprinkler intervals, respectively, according to the algorithm of nozzle configuration model [13].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Nozzle Diameter**} & \multirow{2}{*}{**Sprinkler Interval**} & \multicolumn{2}{c}{_CUC_ of PSs with the Same Nozzle Diameter**} \\ \cline{3-4}  & & **RSPS** & **FSPS** \\ \hline \multirow{4}{*}{2.78 mm} & 1.5 m & 47.3\% & 40.4\% \\  & 3.0 m & 46.1\% & 40.3\% \\  & 4.5 m & 51.0\% & 41.3\% \\  & 1.5 m & 48.3\% & 43.9\% \\
4.76 mm & 3.0 m & 48.0\% & 44.0\% \\  & 4.5 m & 48.0\% & 41.6\% \\  & 1.5 m & 45.1\% & 58.0\% \\
6.75 mm & 3.0 m & 44.7\% & 58.0\% \\  & 4.5 m & 45.1\% & 50.9\% \\ \hline \hline \end{tabular}
\end{table}
Table 6: Christiansen coefficients of uniformities (_CUCs_) of same-nozzle-sprinkler pipe sections (PSs) of rotating spray plate sprinklers (RSPSs) and fixed spray plate sprinklers (FSPSs) with differing nozzle diameters and sprinkler intervals.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sprinkler Types**} & \multicolumn{2}{c}{**Sprinkler Intervals and Required Sprinkler Quantities**} \\ \cline{2-4}  & **1.5 m/191** & **3.0 m/96** & **4.5 m/64** \\ \hline RSPS & 85.8\% & 89.3\% & 91.7\% \\ FSPS & 85.8\% & 86.2\% & 85.8\% \\ \hline \hline \end{tabular}
\end{table}
Table 7: Christiansen coefficients of uniformities (_CUCs_) for the full circular irrigated area for the simulated center pivot irrigation system.  
Based on the analysis above, RSPSs showed better sprinkling performance than FSPSs in the center pivot. In practical sprinkler selection for the center pivot, according to the water requirement characteristics and soil characteristics of the irrigated crops, if the demanded application volumes are large and the sprinkler interval is small, then there would be no obvious distinction between RSPSs and FSPSs. It would be reasonable to choose FSPSs considering large sprinkler quantities required (Table 7) and lower costs for purchasing sprinklers. However, if the sprinkler interval is large, and the quality and yield of the irrigated crops are sensitive to sprinkling uniformity leading to significant economic effects, then RSPSs should be used to ensure better high-quality sprinkling irrigation with the center pivot.