农药液滴在玉米叶片表面铺展面积的影响因素

农药液滴在植物叶面上最大铺展面积，决定了农药有效成分作用范围、蒸发时间和叶面吸收效果。为了探究液滴粒径、农药润湿性能和叶面倾角对液滴在玉米叶面上铺展面积的影响机理，通过试验方式产生548、675、756、877、973 μm粒径的液滴，利用质量分数为0、0.005%、0.01%、0.1%的OP-10表面活性剂代表润湿性能不同的农药，设定叶面倾角为0°、15°、30°、45°、60°、75°，进行全因子试验。结果表明：液滴粒径、表面活性剂浓度、叶面倾角均对铺展面积影响显著（P<0.001），三者增大均能提高液滴在玉米叶面上的最大铺展面积。在不同角度下，增大液滴粒径和溶液的润湿性能都能增加液滴在玉米叶面上的铺展面积。药液润湿性能差时，铺展面积随叶面倾角的变化不够明显，润湿性能较好时，铺展面积呈现出随叶面倾角先上升后下降的趋势，粒径为548 μm液滴铺展面积的最大值出现在叶面倾角45°左右。通过表面活性剂的单位浓度铺展面积评估了不同浓度的OP-10液滴的铺展能力，发现0.005%铺展能力大于其他浓度，说明在溶液中加入少量OP-10就可以显著改变溶液润湿性能。研究结果有助于理解叶面铺展润湿机理，并为通过调控农药润湿性能和药液粒径来实现农药减量增效提供了理论支撑。

Factors influencing the spreading areas of pesticide droplets on the surface of maize leaves

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.