Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Proceedings
Publication Acceptance Date: 7/19/1999
Publication Date: N/A
Citation: Interpretive Summary: Most agricultural pesticides are applied by over-the-row boom sprayers using hydraulic nozzles. These treatments are susceptible to wind creating off-target spray drift and have difficulty producing uniform in-canopy deposits. Recently, manufacturers have been marketing air-boom sprayers as a means of improving spray delivery in field crops. However, little effort has been directed at understanding the effect of many parameters related to air-assisted spray delivery. This research involved wind-tunnel experiments to determine effects of airjet outlet speed, droplet size, wind speed and plant variety on canopy spray deposits and off-target losses. It was found that droplet size played a critical role in determining where spray was deposited. Compared to conventional sprayer operation, air-assisted delivery resulted in keeping more material on the crop and on the ground under the crop. Even the slowest airjet speeds tested significantly reduced spray losses through the air compared with cases without air-assist. Higher wind speeds during spraying increased off-target losses but air- ssistance was shown to significantly reduce these losses. While air- ssisted applications still resulted in large differences between deposits in the top and bottom of the canopy, these differences were reduced. These findings will be useful to equipment manufacturers looking for research information to aid in the design of improved spray delivery systems. Spray applicators will find evidence through these studies that shows how to put more spray where it is needed and to reduce the environmental impact of their applications.
Technical Abstract: Recent EPA funded research was directed into defining the drift risk posed by conventional, over-the-row, boom sprayer applications. Equipment manufacturers have begun to offer alternatives to conventional application techniques, such as air-assisted spray delivery, in searching for ways to improve spray delivery techniques. However, little research has been conducted to document the effect of operating parameters on the performance of air-assisted sprayers. The objective of this research was to determine the effect of the airjet speed, droplet size, plant variety and wind speed on spray deposits within and under a canopy as well as airborne spray losses. A uniform droplet generator was used to provide control of the droplet sizes being evaluated. Droplet size was shown to be a critical factor in determining where spray would be deposited. Larger droplets (300 #m) were deposited more easily into the canopy or to the ground under the canopy than smaller droplets, even under the highest wind speed conditions (4 m/s). Air-assistance was shown to be important in reducing off-target airborne spray losses, particularly for small droplet sprays. In no experiments was it found that air-assistance eliminated off-target airborne spray losses. Higher spray deposits were found on the ground under the canopy and more material was recovered in the bottom of the canopy for the air-assisted applications. However, there were still large differences between deposits found on upper- and under-side leaf surfaces. Changes in the shape or open area of the airjet outlet did not reduce airborne spray losses for small droplet treatments.