Catch Can Testing of a Variable Rate Irrigation System and Evaluation Using a Time Varying Densogram

Abstract. Site Specific Variable Rate Irrigation (SS-VRI) is a technology that has the potential to improve water use efficiency and facilitate fertigation/chemigation. The precision with which water is applied depends on the relationship between the sprinkler application pattern, overlap, estimation of pivot orientation, and management zone size, and wind speed. A series of catch can tests have been performed on an SS-VRI equipped pivot in the Pacific Northwest under two different wind speeds. A time-varying densogram was used to estimate the expected application depths based on the prescribed application depths. We developed a simple model of the uncertainties introduced by errors in pivot angle measurement, and wind drift. This model was used to modify the densogram to produce an estimated range of expected application depths. The modified densogram was compared to the observed catch can pattern produced using an isotropic spatial application pattern. The densogram model and preliminary results will be presented.