Evaluation of a Low Volume Agro-Chemical Application System for Center Pivot Irrigation

Abstract

A low volume agro-chemical application system, called Accu-Pulse Precision Applicator was recently introduced. Accu-Pulse features an independently operated spray boom attached to a center pivot or a linear move irrigation system. The unique spray applicators have adjustable discharge volumes [from 8 to 31 mL per pulse (0.27 to 1.05 oz)] and enable applications at low rates similar to ground sprayers and much lower than chemigation and pivot-attached sprayer systems. The low rates are achieved by periodic pulsing of the chemical solution through the applicators on a span-by-span basis. A series of tests were conducted to evaluate the engineering performance of the Accu-Pulse system. Entrapped air caused the most discharge variability, affecting isolated applicators on a branch line. In the absence of entrapped air the discharge variability (CV) was less than 15% for medium to high discharge settings [19 to 31 mL (0.64 to 1.05 oz)] and varied from 13% to 34% at lower settings [below 19 mL (0.64 oz)]. Uniformity of applicator discharge is not synonymous with application uniformity as the wetting coverage tests show. Based on stained water-sensitive papers, much larger droplets were detected under Accu-Pulse than a ground rig sprayer suggesting a greater potential to reduce spray drift. However percent wetting coverage was about one-third to one-half smaller under Accu-Pulse than the ground sprayer For a commercial Accu-Pulse on an eight-tower center pivot, wetting coverage values were in the 40% range as compared to coverage values of about 60% for a ground sprayer From growers' perspective, the uniformity of applied chemical is an important performance criterion. This study does not address uniformity in chemical application, efficacy, or cost but advances the basic understanding of spray pattern, overlap, wetting coverage, discharge uniformity, droplet size, and pulse time characteristics of the Accu-Pulse system. Additional studies are needed to evaluate and compare the performance and efficacy of Accu-Pulse with other agro-chemical systems.