Assessment of spray patterns and efficiency of an unmanned sprayer used in planar growing systems

Authors: KANG, CHENCHEN - Pennsylvania State University; HE, LONG - Pennsylvania State University; Zhu, Heping

Submitted to: Precision Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2024
Publication Date: 7/15/2024
Citation: Kang, C., He, L., Zhu, H. 2024. Assessment of spray patterns and efficiency of an unmanned sprayer used in planar growing systems. Precision Agriculture. 25: 2271–2291. https://doi.org/10.1007/s11119-024-10166-5.
DOI: https://doi.org/10.1007/s11119-024-10166-5

Interpretive Summary: Plants in the two-dimensional planar growing system are shaped into a flat canopy wall, offering easy worker access and automation opportunities for modern orchard and vineyard managements. However, conventional orchard air-blast sprayers are commonly used to apply chemicals to protect these flat plants from pest attacks, causing significant chemical waste to the non-target areas. In this research, an unmanned ground vehicle sprayer was investigated for its spray deposition quality in a vineyard and an apple orchard. The sprayer was automatically navigated with a real-time kinematic-global positioning system along predefined routes set via a smartphone application. The sprayer also consisted of two spray jets on each side to direct spray patterns with automatic vertical and horizontal angle adjustments. Field experiments demonstrated that mathematical models developed as a decision-support tool for adjusting sprayer settings achieved adequate spray coverage on the two different crop types. However, achieving uniform coverage across the entire targeted area remained challenging for the unmanned sprayer due to uneven terrains in the field and GPS errors to the vehicle navigation. Integrating the laser sensor intelligent spray system into the sprayer might be the solution to significantly mitigate these challenges.

Technical Abstract: Automated technologies in precision agriculture enable unmanned systems to precisely target areas with chemicals through controlled nozzle movements. Quantitative assessment of these sprayers can enhance spraying strategies, catering to different canopy sizes, row spacing and coverage objectives. This research assessed an unmanned sprayer equipped with pan-tilt nozzles for targeted area control and spray coverage adjustment. The spray cloud path on the canopy, as the nozzles moved vertically and the sprayer advanced, was simulated mathematically. A model was developed to determine the swing angle based on orchard/vineyard geometrical parameters. This model was then applied in field tests in a vineyard and an apple orchard. Various nozzle-heading angles, driving speeds, and flow rates were determined, using average coverage and droplet density as the evaluation criterion. The findings showed that the developed model offered an effective method for determining the swing angles. Lowering driving speeds and increasing flow rates were found to notably enhance coverage. A 45º nozzle-heading angle proved more effective in vineyards, whereas a 90º angle yielded better results in apple orchards, reflecting the variations in canopy size and row spacing. The unmanned sprayer demonstrated great potential for autonomous spraying in vineyards and orchards.