A SPRINKLER WATER DROPLET EVAPORATION AND PLANT CANOPY MODEL .2. MODEL APPLICATION

A model that combines water droplet evaporation and three-dimensional droplet trajectory equations with a comprehensive plant environment model is validated under field conditions for a solid-set sprinkler irrigation system by comparing field measurements of air temperature and vapor pressure with predictions for a mature corn canopy. Irrigation water temperature was significant in determining evaporation loss of droplets during flight. Although direct evaporation loss of water droplets was minimal (< 1%), a total amount of energy equivalent to 24% of the net radiation during irrigation was transferred from the plant-environment to the water droplets as they were warmed during flight and after they impacted the canopy and soil. Substantial errors in computing the energy balance of the plant-environment can be made by assuming that all droplets are at the wet bulb temperature when they reach the canopy. For the case study in this article, about 8% of the applied water was evaporated during irrigation, but only 3% of the water applied by an overhead sprinkler system was truly lost to the plant during the day of irrigation because transpiration and soil evaporation would have occurred even without irrigation. This indicates that irrigation efficiencies can be higher than previously expected with large solid-set irrigation systems.