Wind tunnel evaluation of spray nozzle and droplet size effects on spray penetration inside soybean plants

Authors: CASTILHO THEODORO, JOSE GABRIEL - The Ohio State University; OZKAN, ERDAL - The Ohio State University; Zhu, Heping; Jeon, Hongyoung; CAMPOS, JAVIER - The Ohio State University; WOMAC, ALVIN - University Of Tennessee

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2025
Publication Date: 1/20/2025
Citation: Castilho Theodoro, J., Ozkan, E., Zhu, H., Jeon, H., Campos, J., Womac, A. 2025. Wind tunnel evaluation of spray nozzle and droplet size effects on spray penetration inside soybean plants. Journal of the ASABE. 68(1): 71-79. https://doi.org/10.13031/ja.16174.
DOI: https://doi.org/10.13031/ja.16174

Interpretive Summary: Protecting soybeans against attacks from pests and diseases is critical for growers to obtain profitable yields. Adequate pesticides must be delivered to middle and lower positions of soybean canopy to achieve effective pest management. In this research, different types of commercially-available nozzles were tested to determine the influence of spray droplet sizes on spray penetration into soybean canopies. These nozzles produced four different droplet size classes (medium, coarse, very coarse and extremely coarse) and they were evaluated in an open-circuit laminar-airflow wind tunnel with a constant wind speed. Soybeans at the growth stage that pods were filled with green seeds were placed with a row space of 0.38 m (or 15 inch) on the wind tunnel floor to simulate soybeans commonly grown in the field. Spray deposition levels were accessed at three heights inside soybean plants at five locations downwind the spray nozzles. Test results showed that the top soybean surface received the highest spray deposition as expected while the lower part of canopy received significantly low spray deposits regardless of droplet size classes. That is, spray penetration to the lower part was a challenge regardless of the nozzle selection. In general, however, nozzles producing medium and coarse droplets achieved relatively higher spray coverage on the top and middle of canopy than those producing very coarse and extremely coarse droplets. Therefore, this research suggests that among currently available nozzles those to produce medium or coarse droplets should be used to obtain optimal spray application effectiveness for soybean production.

Technical Abstract: Adequate spray deposition and penetration of pesticides reaching the lower part of soybean canopy can increase the chance of success to protect plants from diseases and insects, especially when soybean foliage are matured. Therefore, selecting the nozzle type with the most appropriate droplet size plays a significant role in providing the right amount of spray deposition to the right place in plant canopy. The objective of this study was to evaluate the most effective spray nozzle and droplet size distribution to achieve more spray coverage within the soybean canopy under a 2 ms-1 wind tunnel-controlled-wind speed at 0.38 m row spacing. An open circuit wind tunnel with laminar airflow was used to avoid the uncontrollable outdoor weather conditions that often vary when similar experiments are conducted in the field. Four commercial spray nozzles (droplet size): XR11004 (medium), TTJ6011004 (coarse), AITTJ6011004 (very coarse), and AI11004 (extremely coarse) were operated at 275 kPa pressure and sprayed for 3 s to increase the spray droplet density to detect their effects in the soybean canopy. Eleven pots of soybean plants were placed in the wind tunnel test section in three rows along the direction of airflow to simulate the 0.38 m soybean row spacing. For each test run, water sensitive papers (WSP) were placed at three different heights of the soybean canopy (top, middle and bottom) within 5 soybean plants located 0.15, 0.70, 1.25, 1.80 and 2.40 m downwind from the spray boom. After plants were sprayed, WSP samples were collected to determine the spray coverage. The top of the canopy received the greatest amount of spray coverage followed by the middle position. Regardless of the nozzle and droplet size, significantly lower amount of spray deposition was found at the bottom part of the canopy at all the sample collection points along the wind tunnel test section. Overall, the nozzles that generated medium and coarse droplet sizes provided higher levels of spray coverage on the top and middle part of the soybean canopy. Providing adequate coverage in the bottom part of the canopy remained as a challenge, which must be addressed in the future studies to evaluate additional nozzle types with different droplet size classes under different wind speed and row spacing settings.