Efficiency and uniformity of the LEPA and spray sprinkler methods: a review
Application efficiencies and uniformity coefficients reported for the low energy precision application (LEPA) and spray sprinkler irrigation methods are reviewed and summarized. The relative sizes of the water loss pathways for the two sprinkler methods are also summarized. With negligible runoff and deep percolation, reported application efficiencies for LEPA are typically in the 95 to 98% range. Measurements such as chemical tracers, weighing lysimeter catches, and energy balance modeling are believed to be more accurate than small collector measurements for estimating spray application efficiency. Spray application efficiencies based on these other measurements exceed 90% when runoff and deep percolation are negligible. Because of the start and stop nature of mechanical move irrigation systems, uniformity coefficients for LEPA and spray are measured both along the irrigation system mainline and in the direction of travel. Along the mainline, reported uniformity coefficients are generally in the 0.94 to 0.97 range for LEPA and in the 0.75 to 0.85 range for spray. In the direction of travel, the uniformity coefficients are generally in the 0.75 to 0.85 range for LEPA with furrow diking and in the 0.75 to 0.90 range for spray. On start and stop sprinkler systems, basin tillage on a 2 to 4 m spacing is critical for uniform LEPA irrigation because the basins prevent runoff and average the applications during several unequal start and stop times. Runoff is the largest potential water loss pathway for both LEPA and spray irrigation. For the spray method, runoff can exceed either droplet evaporation and drift or non-beneficial canopy evaporation.