Influence of leaf surface wettability on droplet deposition effect of rape leaves and their correlation

The wettability of plant leaf surface reflects the hydrophilic ability of leaves, and influences the spreading and retention behavior of liquid on leaf surface directly, which resulted in the affection of droplet deposition effect as well. In this study, contact angle was used to characterise leaf surface wettability, the influence of vegetable oil addition on leaf surface wettability and droplet deposition effect was investigated, and the correlation models between leaf surface wettability and deposition amount were established. Besides, the photolysis rate and elution recovery rate of tartrazine 85, allura red, ponceau 2R and methylene blue were compared. As a result, with the increase of vegetable oil addition in spray indicator, the contact angles of spray indicator on rape leaf surface decreased sharply at first, then slowly and tended to be stable, while the deposition amount showed a trend of sharp rise and then fluctuated in a certain range. Meanwhile, the droplet deposition amount on rape leaves was positively correlated with surface wettability, the correlation from good to bad was: tartrazine 85 (R = 0.9299), allura red (R = 0.9244), ponceau 2R (R = 0.9202), methylene blue (R = 0.8748). In combination with the photolysis rate and elution recovery rate of four spray indicators, tartrazine 85 and allura red performed better than ponceau 2R and methylene blue for their low photolysis rate and high elution recovery rate, which were more suitable for farmland spray applications.