EVAPORATION AND WIND DRIFT LOSSES DURING SPRINKLER IRRIGATION INFLUENCED BY DROPLET SIZE DISTRIBUTION

Irrigated agriculture is often criticized for its poor resource-use efficiency in the case of sprinkler systems in comparison with localized irrigation. Water losses due to evaporation of droplets during flight and wind drift of droplets out of the target area are often generalized regardless of the context in which they were measured, and may reveal the evaporation capacity of the measurement facility rather than that of the irrigation system itself. Using an approach combining in situ measurement (rainfall, electric conductivity) and simulations, losses were estimated according to droplet size distribution. Droplets less than 1 mm in diameter displayed the highest losses. Losses due to evaporation represented 30-50% of total loss; the remaining 50-70% were due to wind causing small droplets to drift outside the target zone. With a Rain Bird 46 sprinkler, total losses for the different periods of the day should not represent more than 20% at any time, or less than 4% for a 24-h irrigation period in the climate conditions that prevail in summer in the south of France. Copyright (C) 2011 John Wiley & Sons, Ltd.