Study On Adsorption Characteristics Of Pesticide Droplets On Leaf Surface Of The Typical Target Crops

Pest infestation has brought great harm to agricultural production，which was notconducive to the efficient agricultural production. Therefore, pesticides have been applied toagricultural production long ago in China, in order to ensure agricultural production proceedsmoothly and improve the efficiency of agricultural production. The use of pesticides cansolve pest infestation problems and reduce the loss of food. However, in pesticide useprocess, farmers generally implement rough spraying methods and can not accurately graspthe liquid dose and the characteristics of target crops. This causes problems, such as highinputs of pesticides, weak pertinence, poor adhesion on the leaf surface and so on. In view ofthe above problems, this paper chose three kinds of common pesticides to spray on the leafsurface of typical target crops, we explored the wetting and spreading characteristics of theliquid on the surface of target crops by parameters, such as the surface tension, contact angle,adhesion tension, adhesion work, retention of liquid and so on. Then, the use of dynamiccontact angle and the dynamic droplet diameter reflected liquid dynamic spreading processon the surface of target crops.Research conclusions are as follows:(1) According to the observation of surface morphology characteristic of the target cropleaf, we designed five kinds of leaf surface microstructure models including cylindricalshape, conical shape, square column, hemispheric shape, frustum of a cone. On the basis ofWenzel model and Cassie model, we explored the relation between surface structureparameters and the apparent contact angle of five kinds of models. The studies have shownthat changing the structure parameters α, β and γ could affect the hydrophilic andhydrophobic properties of leaf surface.(2) By determining the surface tension and the electrical conductivity of pesticides withdifferent concentrations, we got the critical micelle concentration of several pesticides. Thecritical micelle concentration of validamycin powder liquor is approximately between0.5518g/L and0.5883g/L, the critical micelle concentration of validamycin agent liquor isapproximately between3.424g/L and3.6364g/L, and the critical micelle concentration ofKresoxim methyl is approximately between0.48538g/L and0.50175g/L. In addition, we cansee that contact angle on the plant leaves reaches the minimum when concentration of pesticides is around the critical micelle concentration. Meanwhile, the wetting and spreading characteristics of the liquid on the surface of target crops are good.(3) Study on adsorption experiment of distilled water on the leaf surface of target crops show that with the time prolonged, water adsorption of six kinds of plant leaves rapidly increases firstly, then slowly increases and finally holds steady. And the water adsorption rate decreases firstly and then tends to be stable with the time prolonged. In general, water absorption capacity of pumpkin leaf is the strongest, eggplant, corn and cucumber leaf take the second place, and rice leaf is the weakest. On this basis, this paper further explored the relationship between retention of liquid on the leaf surface of target crops and many factors including the concentration of pesticide, adhesion force, adhesion work, surface morphology characteristic and so on. Experimental results show that high concentration of pesticide is not conducive to the retention of liquid on leaf surface; Surface morphology characteristic of target crops directly affects the retention of liquid, and the retention of liquid on pumpkin leaf is the biggest, rice leaf is the weakest; Retention of liquid has an exponential relationship with adhesion force; One binary regression equation can be established between retention of liquid on the leaves and adhesion work.(4) The results of experimental study of droplet impact on leaf surface show that:the impact velocity, impact angle, properties of the liquid, solid surface material and other factors has an influence on the spreading factor of droplets on the leaf surface. The effect of kresoxim methyl droplet on pumpkin leaf surface was studied, then we established a quadratic regression model about maximum spread diameter with impact angle and height of free fall.The expression is as follows:dmax=0.35225+0.0001718h+0.0068386θ+0.017136θ2; The results of simulation analysis are the same as experimental results about droplet deposition process on pumpkin surface.