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United States Department of Agriculture

Agricultural Research Service

Title: Influence of Crop Canopy on Spray Deposition and Movement: Preliminary Results

Author
item Hoffmann, Wesley

Submitted to: American Society Agricultural Engineers/National Aerial Applicators Assoc
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 3, 2001
Publication Date: N/A

Interpretive Summary: Studies were conducted to investigate the influence that crop canopies, such as corn, cotton, and soybeans, have on spray deposition and movement from an aerial application. Using a fluorescent dye as a tracer, spray deposits were measured at the top of the canopy (TOP samples), at the ground within the crop canopy (GROUND samples), and in a grazed pasture (PASTURE samples). The turbulent air that is present over crop canopies increases the amount of spray materials that deposit on horizontal surfaces. Significantly higher deposits were measured in TOP samples in corn, cotton, and soybeans than for GROUND or PASTURE samples. There were no differences in GROUND and PASTURE samples beyond 25 m (82 ft) from the aircraft flightline. Higher deposits were measured at the TOP of the crop canopy than in the PASTURE samples out to 120 m (394 ft). Leaf area index (a measure of canopy density) and wind speed were not found to consistently influence the spray deposition and movement. These studie will aid ongoing efforts to improve techniques for aerial application of agricultural chemicals that will require lower dosages and thus be more environmentally friendly.

Technical Abstract: Many factors influence the deposition and movement of aerially applied crop protection chemicals. Studies were conducted to investigate the influence that crop canopies, such as corn, cotton, and soybeans, have on spray deposition and movement from an aerial application. Using a fluorescent dye as a tracer, spray deposits were measured at the top of the canopy (TOP samples), at the ground within the crop canopy (GROUND samples), and in a grazed pasture (PASTURE samples). In the near field (0 - 40 m) samples, TOP deposition was higher than the PASTURE samples in corn, cotton, and soybeans, except at 0 and 5 m in cotton. The increased turbulence over crop canopy enhanced the amount of material that was deposited. Lower total amounts of material were detected in the PASTURE samples suggesting that released materials are drifting beyond the distances tested. The GROUND deposition was lower than all TOP samples and PASTURE samples collected 0 ? 25 m from the flightline due to the crop intercepting the spray. After 25 m, droplets may be so small and not have enough mass for gravity to pull the droplets out of the air in which they are entrained and into the canopy to be collected on the GROUND samples or onto the PASTURE samples. The TOP samples had more spray material than the PASTURE samples at 70 - 120 m downwind of the spray line.

Last Modified: 11/27/2014
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