Accurate measurement of wind drift and evaporation losses could improve water application efficiency of sprinkler irrigation systems − A comparison of measuring techniques

Wind drift and evaporation losses (WDEL) are some of the major sprinkler-irrigation losses which exist even in a well-managed irrigation system. Several research studies found a wide range of WDEL under different and nearly similar configurations of sprinkler irrigation systems under similar weather conditions but using different methodologies to measure the WDEL. The specific objective of this research was to evaluate the three most commonly used measuring techniques (standard catch-can tests (CC), an electrical conductivity method (EC), and a physical-based mathematical approach (PM)) for WDEL on a common sprinkler irrigation system under the same climatic conditions. We conducted 33 experiments from May to September of 2018 near Prosser, Washington. Twenty-two of these experiments were during the daylight hours, and 11 were during the night. We used catch-cans of 29.3 cm diameter and rain gauges (diameter of 10 cm) to collect water to measure the irrigation water's electrical conductivity. Mass and heat transfer approaches were used in the PM technique. The results showed that the three techniques yielded statistically different mean WDEL. The highest WDELs were in CC (22.8%), followed by EC (17.5%) and PM (6.8%) techniques. The CC WDELs were better correlated with PM than the EC approach. The mean nighttime WDEL for the EC and CC methods were not statistically different (p > 0.05). The CC WDELs were more closely related to wind speed than the vapor pressure deficit. The EC and PM approaches have a higher correlation to the vapor pressure deficit. The overall conclusion disclosed that the more we use indirect measurement methods, the more the chances of erroneous numbers. The EC and PM approaches are likely limited to measuring droplet evaporation as the latter includes several assumptions. The CC approach is a direct measurement of the WDEL.