Resistance characteristics of broad-leaf crop canopy in air-assisted spray field and their effects on droplet deposition

Abstract

Air-assisted spray technology is widely applied in high-efficiency pesticide applications. The resistance characteristics of the crop canopy reflect its energy dissipation effect on the assisted airflow, connecting the structure of the crop canopy, assisted airflow velocity, and droplet deposition effect. Using a common broad-leaf crop canopy as the research object, the resistance characteristics of the crop canopy in the air-assisted field were investigated in this study by performing theoretical analysis and wind tunnel tests. Further, the feasibility of using the resistance characteristics of the crop canopy was assessed to evaluate its droplet deposition effect. The results showed that under the conditions of different number of leaf layers and initial leaf azimuth angles, the canopy pressure drop experiences a non-linear increasing trend with increasing assisted airflow velocity and that its regression function conforms to the Darcy–Forchheimer function. Moreover, when the initial azimuth angles of single- and multi-layer leaves were 90°–270°, the change rate of the canopy pressure drop with airflow velocity was 7–9 m/s, and there was a critical wind speed. However, with an increasing number of leaf layers in the crop canopy and changes in the initial leaf azimuth angle, the corresponding changes between the maximum canopy pressure drop and resistance coefficient were non-linear. Thus, it is proposed that the resistance characteristics of multi-layer leaves cannot be quantified as the results of the linear superposition of the resistance characteristics of several single-layer leaves—that is, it should be regarded as a whole research object. Combined with the analysis of the influence of the crop canopy resistance on droplet deposition, it is considered that when the crop canopy has multiple leaf layers in the airflow direction, the existing air-assisted spray technology cannot guarantee droplet deposition and canopy penetration simultaneously.

Spray performance of flexible shield canopy opener and rotor wind integrated boom‐sprayer application in soybean: effects on droplet deposition distribution

“…In order to address the issue of difficult pesticide penetration caused by dense canopy during the middle and late stages of crop growth, air-assisted or air-blast spraying techniques are commonly used to improve the uniformity of droplet deposition within the canopy. 8,9 The benefits of air-assisted technology can be seen in two main ways: first it can expand the droplet transportation channels between branches and leaves, and second, it can enhanced ability to change trajectory and speed of droplet motion. 10 The most common method is to add an air duct and axial fan to the boom-sprayer so that the wind flows rapidly downward from the air duct opening to create an air curtain.…”

Wetting and deposition characteristics of air-assisted spray droplet on large broad-leaved crop canopy

“…Spray method, droplet size, and pesticide properties have always been the main influencing factors for improving the deposition performance of mechanized sprays (Ferguson et al, 2016). In previous studies, the air-assisted spray technology was used to fully disturb the canopy of the fruit tree to achieve air replacement and improve the deposition efficiency on both sides of the leaves (Xi et al, 2020;Gu et al, 2022;Wu et al, 2022). Use coarse nozzle to produce coarse droplets to reduce spray drift, and improve droplet size according to the operating conditions to prevent droplets from bouncing on the leaf surface (Hilz and Vermeer, 2013;Alidoost Dafsari et al, 2021).…”