Potential runoff and erosion comparison of four center pivot sprinklers

The operational characteristics of center pivot sprinklers are well documented but few studies have been conducted to evaluate the effects that operating characteristics of a particular sprinkler have on infiltration, runoff, and erosion of specific soil types. The objective of this study was to evaluate potential runoff and erosion from common commercial center pivot sprinklers on three widely distributed, south central Idaho soils. A modified commercial irrigation boom system was used to emulate center pivot irrigation on experimental runoff plots. Sprinklers used in the study were: 1) Nelson R3000 with brown plate, 2) Nelson R3000 with red plate, 3) Nelson S3000 with purple plate, and 4) Senninger I-Wob with standard 9-groove plate. There were significant differences in measured runoff percentages and measured erosion rates between center pivot sprinkler types for the soils tested and experimental conditions. The magnitude of the differences among sprinklers was equal to or greater than the differences between the soils tested. The I-Wob and S3000 sprinklers exhibited the greatest measured runoff percentages and measured erosion rates and the R3000 sprinklers exhibited the least runoff and erosion for the three soils tested. In general, sprinkler types that visually appear to more evenly distribute sprinkler droplets over the wetted area with respect to time exhibited the greatest measured runoff and measured erosion rates. The relative ranking of the sprinklers in terms of measured runoff percentages and measured erosion rates was consistent when four and six irrigation events were used to apply 75 mm of water. The relative differences in runoff between the sprinklers tested were not directly proportional to sprinkler droplet kinetic energy per unit water volume applied. This outcome is in conflict with conventional theory on soil surface sealing from droplet impact. Possible explanations include incorrect representation of sprinkler droplet kinetic energy, conventional soil surface sealing theory does not apply to the soils used in this study, or some unknown factor is dominating the infiltration and runoff process for the study conditions