Effects of Leaf Surface Roughness and Contact Angle on In Vivo Measurement of Droplet Retention

Droplet retention during pesticide application is a serious problem because run-off droplets flow out of the target area and pose a hazard to human health and the environment. The present study was conducted with the aim to measure the droplet retention of sprayed droplets on crop leaves in vivo using a constructed test system. In the measurement, three crop species with different surface properties (tomato, chili pepper, and winter wheat) were selected for droplet retention determination, and the variations in the time intervals of maximum retention and stable retention were determined. Contact angle and surface roughness (R-a), which are the most important surface properties of crop leaves, were used as independent variables. The R-a values of tomato, pepper, and winter wheat were 24.73 mu m, 5.28 mu m, and 17.59 mu m, respectively, while the contact angles of tomato, pepper, and winter wheat were 97.67 degrees, 70.07 degrees and 131.98 degrees, respectively. The results showed that the curves of droplet retention on sprayed tomato and wheat leaves had similar patterns over time and could be divided into four periods (rapidly increasing period, slowly increasing period, collapsing period, and stable period). The maximum droplet retention on tomato leaf surface was R-max = 0.169 g . cm(-2), and the stable retention was R-st = 0.134 g . cm(-2). The maximum droplet retention on the surface of winter wheat leaf was R-max = 0.244 g . cm(-2), and the stable retention was R-st = 0.093 g . cm(-2). However, droplet retention on pepper leaves was different from that on tomato and wheat leaves. The curve pattern of droplet retention on pepper leaves over time showed two peaks and two valleys. Moreover, the maximum retention, R-max, was in the range of 0.149 similar to 0.151 g . cm(-2), and the stable retention was R-st = 0.077 g . cm(-2). It is expected that the obtained results can be used to characterize the properties of crop leaves and that this study can contribute to the improvement of droplet retention for effective chemical application and the reduction in the environmental pollution caused by agricultural pesticides.

Automated summary

This study aimed to measure the droplet retention on crop leaves during pesticide application and analyze their surface properties. The results showed that droplet retention varied among different crop types, with different curve patterns. This study has important implications for improving the effectiveness of chemical application and reducing environmental pollution caused by agricultural pesticides.