Efficiency and uniformity of the LEPA and spray sprinkler methods: A review

Application efficiencies and uniformity coefficients reported for the low e nergy precision application (LEPA) and spray sprinkler irrigation methods a re reviewed and summarized. The relative sizes of the water loss pathways f or the two sprinkler methods are also summarized. With negligible runoff an d deep percolation, reported application efficiencies for LEPA are typicall y in the 95 to 98% range. Measurements such as chemical tracers, weighing l ysimeter catches, and energy balance modeling are believed to be more accur ate than small collector measurements for estimating spray application effi ciency. Spray application efficiencies based on these other measurements ex ceed 90% when runoff and deep percolation are negligible. Because of the st art and stop nature of mechanical move irrigation systems, uniformity coeff icients for LEPA and spray are measured both along the irrigation system ma inline and in the direction of travel. Along the mainline, reported uniform ity coefficients are generally in the 0.94 to 0.97 range for LEPA and in th e 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 d iking 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 i rrigation because the basins prevent runoff and average the applications du ring 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 nonbeneficial c anopy evaporation.