Abstract:
Abstract: Pesticide wastes have caused serious pollution to the air, water, and soil in recent years. It is a high demand to clarify the spreading behavior of pesticide droplets on the plant leaves, particularly for the better utility efficiency of pesticides. Among them, the maximum spreading area of pesticide droplets on the plant leaves can dominate the action range, evaporation time, and foliar absorption of active ingredients in the pesticides. This study aims to explore the influence mechanism of droplet size, surfactant concentration, and leaf inclination on the maximum spreading area of droplets on the corn leaves. The leaf inclination angles were set as 0°, 15°, 30°, 45°, 60°, and 75°. The droplet sizes were 548, 675, 756, 877, and 973 μm. A droplet generator was used to produce the droplets of different sizes, further to reach the plant leaves at the free velocity. The solutions were utilized the 0, 0.1%, 0.01%, and 0.005% of OP-10 surfactant. A full factorial experiment was designed with a total of 120 tests. The results show that there were significant effects of droplet size, surfactant concentration, and leaf inclination on the maximum spreading area (P<0.001). The influencing factors were ranked in the order of the surfactant concentration > droplet size > leaf angle. The partial-eta squares were 0.857, 0.473, and 0.073, respectively. A linear relationship was observed between the droplet size and the spreading area. The spreading area also increased with the increase of the droplet size, leaf angle, and solution surfactant concentration. Once the droplet size increased from 548 to 973 μm, the spreading area increased by 71.2% on average. When the leaf inclination angle was 75°, the average spreading area was 1.512 4 mm2. The spreading area increased by 18.0%, and 11.9%, compared with the 0° and 45°. The spreading area of 0.1% OP-10 on the maize leaves increased by an average of 572.7%, compared with the deionized water. Therefore, the droplet size increased the maximum spreading area of the droplets on the corn leaf surface with the same increased efficiency under different leaf inclination angles. Furthermore, the relationship between the droplet size and the maximum spreading area was y=0.001 7x+0.022 3, where the goodness of fit R2 was 0.969. It infers that the maximum spreading area of the droplet increased by 0.17 mm2 on average, particularly for every 100 μm increase in the droplet size. The highest value of 4.13mm2 was achieved in the maximum spreading area of 973 μm droplets at 0.1% concentration, when the leaf inclination angle was 75°. By contrast, the average level of the spread area was significantly higher at the 0.1% concentration, compared to the rest groups. The Pearson correlation analysis was carried out between the surface tension, contact angle, adhesion work, and spreading area of the solution. It was found that there was a significant positive correlation between the adhesion work and the spreading area (r=0.995, P=0.009). The adhesion work was well represented by the spreading area trend of the droplets on the leaf. Correspondingly, the surface tension of the liquid medicine was lower than the critical surface tension of the leaves in actual agricultural production. Furthermore, a greater surfactant composition was required for better wetting after atomization in the liquid medicine, compared with the critical micelle concentration. The 0.01%-0.1% OP-10 solution can be expected as a reference surfactant for higher spreading efficiency and better performance at a high level. The findings can provide a strong reference to understanding the spreading mechanism of pesticide droplets on the plant leaves. The particle size of pesticide droplets and the concentration of surfactants can also be adjusted for better spreading performance at the different leaf inclination angles.