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Dynamics of water droplet impact and spread on soybean leaves

Weidong Jia, Heping Zhu
Transactions of the ASABE 2015 v.58 no.4 pp. 1009-1016
Glycine max, droplet studies, droplets, generators (equipment), leaves, soybeans, spray coverage, spraying, video cameras
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 rebounds were not observed after impact on leaf surfaces and droplets larger than 300 µm slid on the 30° inclined surface. Droplet spread ratios increased with droplet diameters and impact speeds but decreased with impact angles. Isoline distributions of droplet spread ratios were established to provide visual observations as a baseline for choosing optimal droplet diameter, impact speed and impact angle to maximize spray coverage areas. At similar impact speeds and angles, droplet spread ratios 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 essential for efficient soybean spray applications with minimal amounts of spray mixtures.