Dynamics of Water Droplet Impact

Abstract

<abstract> Soybeans are often sprayed to prevent significant yield loss from damage by insect pests and plant diseases. Understanding interactions of spray droplet reactions on soybean plant surfaces can lead to development of improved application strategies to enhance efficacy of pesticides. In this research, dynamics of impact and spread of water droplets of 185 to 693 μm at 1.85 to 6.4 m s^-1 impact speeds and 28° to 75° impact angles on two soybean leaf surface orientations (horizontal and 30° inclination) were investigated with two high-speed digital video cameras and a mono-sized droplet generator under laboratory-controlled conditions. Within the test ranges of the variables, droplet rebound was not observed after impact on leaf surfaces, while droplets larger than 300 μm were observed to slide on the 30° inclined surface. Droplet spread factors increased with droplet diameters and impact speeds but decreased with impact angles. Isoline distributions of droplet spread factors on a horizontal surface were established to provide visual observations for estimating spray coverage areas with different droplet impact speeds and impact angles. At similar impact speeds and angles, droplet spread factors on inclined leaf surfaces were greater than those on horizontal surfaces. These discoveries elucidate that careful selection of controllable spray parameters to maximize droplet spread area and retention on soybean plants is possible for efficient soybean spray applications with minimal amounts of spray mixtures.