EVALUATION OF POTENTIAL RUNOFF AND EROSION OF FOUR CENTER PIVOT IRRIGATION 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 for specific soil types. The objective of this study was to evaluate potential runoff and erosion from four commercial center pivot sprinklers on four widely distributed, south central Idaho soils. A modified commercial irrigation boom system was used to simulate 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 black plate. Significant differences in runoff and erosion between sprinkler types were observed but were not consistent across all runoff tests or soil types. However, on occasions sprinkler types that visually appear to more evenly distribute sprinkler droplets over the wetted area with respect to time produced the greatest soil erosion for bare soil conditions. This functional difference in spatial distribution of water application with respect to time may have caused sediment to remain in suspension in overland flow for a longer duration allowing sediment to be more readily transported down slope and removed from runoff plots. A 50% reduction in sprinkler flow rate reduced runoff and soil erosion 60% to 80% for the same volume of water applied in six irrigations. The practice of reducing sprinkler flow rate early in the growing season prior to crop canopy development could be an effective management tool for reducing center pivot sprinkler irrigation runoff and erosion.