Spray evaporation losses from sprinkler irrigation systems

Minimising the loss of water from irrigation systems is important for achie ving water and energy conservation. Water is lost during storage, conveyanc e and field application. In sprinkler irrigation systems, the loss that occ urs in the field is the largest of the three. The above canopy spray evapor ation loss (ACSEL) represents the portion of the water that is lost to the atmosphere during the time it travels from the sprinkler nozzle to the crop canopy. The electrical conductivity (EC) method was used to determine the ACSEL from different types of sprinkler irrigation systems calculated at in creasing distances from the sprinkler nozzles. In this method, the change i n solute concentration and consequent change in EC as the water droplets tr avel through the air was used to calculate the volume lost by evaporation. The travelling gun irrigation systems showed the largest variation in ACSEL . The ACSEL varied depending on whether the water droplets travelled into t he wind or with the wind. Therefore, for measuring ACSEL, it is important t o place the collectors on either side of the travelling gun. The wind direc tion in relation to the average travel direction of the gun also affected t he uniformity of ACSEL. The centre pivot irrigation systems gave the most u niform ACSEL across the different nozzles. Therefore, for centre pivot syst ems, about four to six collectors per row is sufficient to determine ACSEL in the field with a precision of +/- 0.5%.