Soybean Foliar Deposition and Airflow Distribution Interrelated to Nozzle Type and Boom Travel Direction in Wind Tunnel

Spray deposition and coverage within soybean canopies remain critical challenges for achieving effective pesticide applications, particularly under windy conditions. This research investigated the influence of wind speed, boom travel direction relative to wind direction, and nozzle type on droplet deposition, coverage uniformity, canopy penetration, and airflow distributions inside soybean canopies under controlled wind-tunnel airflow. Spray deposition, analyzed using a fluorometric tracer, and coverage, quantified with water-sensitive papers, were assessed in R3-stage soybeans in an 18-m wind tunnel using XR (perpendicular spray) and 3D (38° angle) flat fan nozzles under varying air speeds and boom travel directions in the wind tunnel. Potted plants were placed in the wind tunnel to mimic soybeans grown in field conditions. Droplet sizes of the nozzles were measured using a laser imaging particle sizing system. Airflow velocity and turbulence within the soybean canopy were investigated with a 3-D hot-film anemometer system. The results indicated that wind and boom direction were the main influential factors for spray coverage and deposition. The top canopy position, exposed to the highest air-turbulence intensity, received the greatest deposition, whereas the middle and bottom positions, characterized by lower turbulence, exhibited sharp declines in both deposition and coverage regardless of treatment. The 3D nozzle provided greater coverage and deposition than the XR nozzle only under no-wind conditions; however, under wind conditions, equivalent performance was observed from both nozzles. Therefore, it was essential to incorporate wind conditions and canopy structures into consideration when choosing nozzles to maximize spray penetration and achieve efficient and effective spray applications for soybeans.