## 4 Conclusions  
This study focused on the comparisons of sprinkling performance of rotated and fixed spray plate sprinklers (RSPSs and FSPSs) in center pivot irrigation systems (center pivot). The water distribution characteristics of individual sprinkler were observed under field conditions. Then, following the nozzle diameter configuration model, the water distributions of same-nozzle-sprinkler pipe sections (PSs) and full circular irrigated area (FCIA) of the center pivot were simulated to compare the sprinkling performance of RSPSs and FSPSs under different nozzle diameters and sprinkler intervals.  
Water distributions between individual RSPSs and FSPSs showed distinct patterns. RSPSs distributed the most water around the sprinkler, whereas FSPSs distributed most water over a ring-shaped region at periphery of the sprinkler. The radial water distribution showed single-peak and double-peak patterns for RSPSs and FSPSs respectively. The effective wetted radiuses of RSPSs and FSPSs were 4.88-7.05 m and 5.02-6.85 m with 2.78, 4.76 and 6.75 mm diameter nozzles being installed, respectively.  
RSPS PS distributed most water around their central axes, and the applied water volumes reduced gradually with the increasing distance from the axes. FSPS PSs distributed the most water over both sides of their axes symmetrically, and lower volumes were distributed around the axes. When the sprinkler intervals increased to 4.5 m, the continuities of water distribution along the axes of the PSs decreased. The _CUCs_ of RSPS PSs and FSPS PSs were 44.7%-51.0% and 40.3%-58.0% respectively under different nozzle diameters (2.78, 4.76 and 6.75 mm) and sprinkler intervals (1.5, 3.0 and 4.5 m).  
_CUCs_ of RSPS FCIA were 85.8%, 89.3% and 91.7% under sprinkler intervals of 1.5, 3.0 and 4.5 m, respectively, and _CUCs_ of FSPS FCIAs were 85.8%, 86.2% and 85.8% under sprinkler intervals of 1.5, 3.0 and 4.5 m, respectively. The _CUCs_ of RSPS FCIAs were 3.1% and 6.2% higher than that of FSPS FCIAs when the sprinkler intervals were 3.0 and 4.5 m, respectively. In the center pivot, RSPSs could accommodate larger sprinkler intervals in comparison to FSPS, but also maintained a superior sprinkling performance.  
Moreover, works should be conducted to explore the different crop yield, crop quality, soil moisture dynamics and soil moisture distributions between using RSPS and FSPS, under conditions of real commercial center pivots. It might be worthwhile to analyze and compare the cost effectiveness by different types.  
This work was supported by the National Natural Science Foundation of China (No. 51379011). The authors would like to thank the support provided by the staff and technicians associated with the Clover Group Shuangqiao Experimental Base: [PERSON], [PERSON] and [PERSON]. The utilization of certain products in this study does not imply endorsement of any of them.  
[PERSON] and [PERSON] conceived and designed the experiments; [PERSON], [PERSON] and [PERSON] performed the experiments; and [PERSON] analyzed the data and wrote the paper. Both authors read and approved the manuscript.  
The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.