Use of ultrasound anemometers to study the influence of air currents generated by a sprayer with an electronic control airflow system on foliar coverage. Effect of droplet size

Abstract

Air assistance and droplet’s characteristics influence on the pesticide deposit and its distribution over the intended target during the spray application process. The present research work is focused on the characterization of the leaf coverage and the overall spray distribution within the whole canopy by combining different settings of air assistance with different nozzles, generating different droplet’s sizes. A new designed air-assisted orchard sprayer was tested, presenting a wireless remote-regulation system to control the airflow rate from the fan by adjusting the blade pitch. In this way, five airflow rates were obtained by combining the gearbox position and the blade pitch. For each one of these five air settings, three droplet sizes (F-Fine, M−Medium, and C-Coarse) were combined and evaluated over a set of artificial apple trees. The evaluation was divided in two parts: a) a whole characterization of the airstream generated by the five air settings was performed for the two sprayer’s sides using a 3D-ultrasonic anemometer and placing the sprayer in front of the artificial trees and b) a coverage tests for each nozzle-air settings combination by using water sensitive papers (WSP) placed at different heights and depths evenly distributed across the canopy, the WSP’s were analyzed by a processing image software. The results demonstrated that ultrasonic anemometers were helpful to characterize the airstream and to analyze its effect on leaf coverage. Experimental data showed that a higher airflow rate and a larger droplet size generated a more homogeneous coverage on both sides of the sprayer. In this line, the turbulence intensity data suggest that larger variations in the air velocities increase the drag coefficient. Which meant that the canopy resistance to the air stream increased. In addition, an increase of turbulence intensity generated higher spray coverage. Therefore, a higher turbulence intensity did not imply a better spray coverage. It was also observed that the droplet size was critical on regulating the airflow influence on spray coverage. Coarse droplet size did not present any relation with the airflow changes. While the fine droplet size presented a high dependency on airflow conditions.