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ARS Home » Midwest Area » Wooster, Ohio » Application Technology Research » Research » Research Project #438488

Research Project: Improve Spray Droplet Retention Capabilities on Targets with Amendment of Spray Solution Properties

Location: Application Technology Research

Project Number: 5082-21620-001-19-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Sep 1, 2020
End Date: Aug 31, 2022

The objective of this research is to determine dynamic impact, retention, rebound and spread process of surfactant-amended spray droplets on plants with different degrees of leaf surface roughness and wettability, in an effort to establish efficient and effective spray application strategies to reduce pesticide waste and protect the environment.

Droplet impact measurements will be made by emitting droplets from a streamed mono-sized droplet generator capable of producing droplets with diameters between 100 and 800 µm. The droplet generator will be mounted on a horizontal linear speed track as it passes over a leaf sample mounted to a glass slide resting on a raised horizontal platform. Constant speeds of 0.5, 1.0, 1.3, 2.0, 2.5, 3.0, 3.5, and 4.5 m s-1 will be used as the droplet generator horizontal speeds in the tests. Droplet size, flight, and impact on the leaves will be captured with a 3-D stereoscopic imaging system consisting of three ultrahigh-speed digital cameras and will be analyzed with 3-D motion analysis software. Tests will be conducted with spraying droplets onto several different leaf types of specialty crops ranging in wettability and roughness, from very-smooth and easy-to-wet to very-rough and difficult-to-wet. Surface roughness will be measured with a 3-D optical surface profiler and roughness parameters will be calculated for arithmetic mean height using 3-D image acquisition, visualization, and analysis software. Wettability is determined by measuring the contact angle between a droplet of distilled water sitting on a leaf sample with an in-house goniometer using the static and dynamic sessile droplet methods. Deposition and retention will be determined by comparing initial droplet size to the amount of liquid residue after impact, and these values will be compared to the measured roughness and wettability. The effect of surfactant concentration and impact velocity on deposition for different roughness heights will be tested by comparing percent deposition on the different leaf types for different surfactant concentrations and initial droplet flight velocities. The spray solution for the experiments consists of distilled water mixed with six different concentrations of surfactants (0.0%, 0.10%, 0.25%, 0.50%, 0.75%, and 1.00%). Relationships among spray droplet impaction, deposition formation on leaf surfaces, and spray parameters will be determined and documented in a large database and will serve as guidelines to choose the optimum operational parameters. Multivariable regression equations will be used to determine these relations and to calculate principal component indices to document the degree of each factor that will increase droplet retention and reduce droplet rebound and runoff.