Modelling approach of spray retention on rice in plant protection using unmanned aerial vehicle

Spray technology of plant protection Unmanned Aviation Vehicle (UAV) is the highly efficient pesticide application in agricultural aviation, particularly for the zero growth of pesticides. The number, application area and scope of plant protection UAVs are ever increasing in China in the past 10 years. The application performance has also attracted much attention in recent years. Taking the DJI T30 plant protection UAV as the research object, this study aims to investigate the effect of rotor wind field of plant protection UAV and adjuvant on the droplet retention on the rice plant. The pure water, 1% Maifei, and 0.5% Maitu Target adjuvant formulation were taken as the spray formulation. The aviation wind tunnel and Particle Image Velocimetry (PIV) were utilized to measure the spray flow field under the action of the rotor wind field of UAV. Some parameters were evaluated, including the dynamic surface tension, viscosity, and density in the formulations, as well as the dynamic contact angle of droplets on the surface of rice leaves. A quantitative analysis was made to clarify the effect of the rotor wind field on the droplets movement velocity and the retention of droplet on rice, the influence of adjuvant on formulation properties, the nozzle atomization performance, the droplet wetting and spreading performance on the rice leaves. A prediction model of droplet retention on the rice plant was established in the field of plant protection UAV spray technology, especially combining with the droplet interception and the droplet impact model. A field validation test was then conducted to verify the model. The results showed that the adjuvant formulation posed a significant effect on the droplet size, the formulation properties, the nozzle atomization performance, the wetting and spreading performance of the droplets on the surface of rice leaves, as well as the retention of the droplets on the rice plants. The surface tension values of 1% Maifei and 0.5% Maitu Target adjuvant formulations were reduced by 46.81%, and 62.21%, respectively, compared with water; The static contact angle of the droplets on the rice leaves was reduced by 27.74%, and 46.37%, respectively; The retention on the per hectare rice increased by 800.78% and 1 051.49%, respectively. The droplet size increased by at about 9.3%. There was a significant effect of UAV rotor wind field on the droplet movement velocity and the droplet retention on the rice. The droplet movement velocity increased significantly, after the rotor system was turned on and more quickly reached the stable velocity. When the UAV rotor speed increased from 0 to 1 000 and 1 800 r/min, the droplet movement velocity increased by 366.67%, and 663.67% in turn. Compared with the droplet retention on the rice when the rotor system was turn off, the droplet retention of 1% Maifei and 0.5% Maitu Target adjuvant formulation decreased by 26.78%, and 29.75%, respectively, after the rotor system turn on. The accuracies of the retention model were 48.59%, 79.07%, and 79.29%, respectively, in order to predict the retention of the three solutions on the rice plants. © 2022 Chinese Society of Agricultural Engineering. All rights reserved.