Spray deposition on soybeans and airborne drift from nozzles on a moving boom in a wind tunnel

Authors: CASTILLO THEODORO, JOSE - The Ohio State University; Zhu, Heping; OZKAN, ERDAL - The Ohio State University; Jeon, Hongyoung

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2025
Publication Date: 12/23/2025
Citation: Castillo Theodoro, J.G., Zhu, H., Ozkan, E., Jeon, H. 2025. Spray deposition on soybeans and airborne drift from nozzles on a moving boom in a wind tunnel. Journal of the ASABE. 68(6):1041-1052. https://doi.org/10.13031/ja.16442.
DOI: https://doi.org/10.13031/ja.16442

Interpretive Summary: Protecting the middle and bottom parts of the soybean canopy from pests is an imperative task for pesticide applications. Testing spray applications in a field is the best way to evaluate different techniques and nozzles for delivering spray in the middle and lower canopy parts. However, conducting comprehensive tests for spray penetration into the soybean canopy with various application techniques in a field is not feasible due to unpredictable weather conditions and inconsistent crop conditions. Thus, various application techniques, particularly four spray nozzles with different droplet sizes, were evaluated for their performance in penetrating spray into dense soybean canopies in an open-circuit wind tunnel with three different wind speeds. Potted R5-stage soybean plants were placed close to each other in the tunnel to simulate a high-density soybean field while each nozzle discharged sprays to achieve a spray volume of 150 L/ha. During the tests, spray deposit and coverage at three different canopy depths of the soybean plants, and spray drift at the end of the tunnel were collected to evaluate their canopy penetration performance. The spray deposit and coverage data showed that, regardless of the nozzle being used, penetrating the soybean canopy to deliver sprays to the inside of the soybean plant canopies was a difficult task with merely changing nozzles, although the top part of the soybean plant canopy had sufficient spray coverage and deposit. However, the data showed that achieving the reduction of spray drift by selecting nozzles was possible. US soybean farmers can use these results to select nozzles that reduce spray drift to prevent unintended crop injuries to neighboring crops.

Technical Abstract: Adequate spray deposits and coverage in the middle and lower parts of the canopy are essential to protect soybean crops from disease and insect attacks. Additionally, uncontrollable weather conditions can influence the effectiveness of spray applications. Thus, the objective of this research was to evaluate the effect of the wind speeds of 0, 2.4, and 5.1 m s-1 on the spray coverage and deposition discharged from travelling nozzles with different droplet sizes under wind tunnel-controlled conditions. An open-circuit wind tunnel, equipped with a moving spray boom placed 0.5 m above the top of the soybean canopy and operating at a speed of 0.9 m s-1 , was used in this study. To achieve the application rate of 150 L ha-1, pulse width modulation solenoid valves were coupled with the nozzles at a duty cycle of 19% and an operating pressure of 276 kPa . Four types of same color-coded 110° flat-fan spray nozzles (XR11004, TTJ6011004, AITTJ6011004, and AIXR11004) were used to determine the effects of spray droplet size spectra on spray deposition and coverage inside the soybean canopy. Container-grown soybean plants at the R5 growth stage were placed on the test section floor in two rows to simulate 0.38 m soybean row spacing. Spray coverage and deposits were measured at the top, middle, and bottom of the plants, and airborne spray drift was captured at the exit of the wind tunnel. Regardless of wind speeds and droplet sizes generated from the nozzle type, the top of the canopy consistently received the highest spray deposition, with coverage ranging from 22.0% to 35.8% and deposits ranging from 0.76 to 1.27 µL cm-2. Delivering an acceptable level of spray deposition and coverage in the canopy's middle and bottom remained a challenge for the XR, TTJ60, AITTJ60, and AIXR nozzles. Airborne spray drift increased as the wind speed increased from 2.4 to 5.1 m s'¹. XR and TTJ60 nozzles produced greater airborne spray drift than AIXR and AITTJ60 nozzles due to significant differences in droplet sizes. Nozzles that produced ultra-coarse droplets reduced airborne spray drift risks. The dense soybean canopies and overlapping foliage of crops limited the spray droplet penetration capability of the hydraulic nozzles.