Study On The Influence Mechanism Of Dynamic Evolution Of Maize Canopy Vertical Structure On Rainfall Distribution Process

Rainfall is one of the driving forces of soil erosion,which separates and transports soil particles through raindrop splashing and runoff scouring.Vegetation reduces soil erosion by intercepting rainfall,regulating surface runoff and increasing infiltration.The influence of vegetation canopy on rainfall process is shown in two aspects:first,rainfall redistribution occurs when it passes through vegetation canopy,and the rainfall that is originally uniform will change after passing through vegetation canopy,which is divided into three parts:throughfall,stem flow and canopy interception,and the rainfall will become uneven when it reaches the ground.Secondly,vegetation canopy reduces the kinetic energy of rainfall by reducing the speed,number and falling height of raindrops,and changes the time,space and proportion distribution of raindrops reaching the ground.The morphological structure of vegetation canopy in horizontal and vertical directions can change the process of rainfall redistribution and reduce the kinetic energy of rainfall,thus directly or indirectly affecting the process of soil erosion.However,in practical application,due to the large spatiotemporal variability of the relevant parameters of vegetation canopy morphological structure,the workload of observation is huge.Most studies only consider the horizontal structure of vegetation canopy,less consider the impact of vertical structure of vegetation canopy on soil erosion.Slope farmland is the main source area of soil erosion in the hilly region of China,and crops are the important covering factors on the surface.In the whole growth cycle of crops,the shape of stems,branches and leaves changes rapidly,which causes great changes in the canopy vertical structure of crops,and makes the relationship between the canopy vertical structure of vegetation and rainfall distribution process more complex.Therefore,studying the dynamic evolution characteristics of crop canopy vertical structure and the characteristics of rainfall distribution process under the dynamic evolution of crop canopy vertical structure,quantifying the impact of the dynamic evolution of crop canopy vertical structure on rainfall distribution process is helpful to understand the utilization of rainfall by vegetation,It provides a scientific theoretical basis and technical support for the prevention and control of soil erosion and the optimization of cultivation mode of Sloping Farmland in China.In this paper,maize was selected as the research object.Based on 3D laser scanning technology,3D point cloud data of different growth stages of corn community were obtained.Bilateral filtering method,K-means clustering method,classical restricted Laplacian algorithm,ball pivoting algorithm and other point cloud processing、3D reconstruction methods were used to extract the vertical structure parameters of maize community in different growth stages（plant height,stem height,Leaf area,leaf area index,leaf length,leaf width,leaf angle,stem diameter,crown length rate,crown diameter）were measured and verified by the measured data.The simulated rainfall experiment was used to obtain the rainfall distribution parameters（throughfall under canopy,stem flow,canopy interception,kinetic energy of raindrops reduced through canopy）under the dynamic evolution of maize vertical structure under different rainfall intensities,and the characteristics of rainfall distribution process under the dynamic evolution of maize vertical structure was analyzed.Based on the above research,combined with correlation analysis and partial least square method,quantitative analysis of maize vertical structure parameters on the impact of rainfall distribution process.The main conclusions were as follows:（1）The correlation coefficient R² between plant height and leaf area extracted by classical restricted Laplacian algorithm and ball voting algorithm and the measured data was greater than 0.85,so the applicability of the model was high.The vertical structure parameters of maize showed three different growth trends:plant height,crown diameter,stem height,leaf length,leaf width and stem diameter increased first and then decreased;The crown length rate decreased first and then increased;The leaf angle showed a continuous upward trend.（2）With the increase of rainfall intensity,the throughfall rate,stem flow rate,canopy interception rate and the reduction of raindrop kinetic energy of maize community increased.From seedling stage to decline stage,the average throughfall rate of maize community decreased first and then increased,and reached the lowest value at maturity stage;the average stem flow rate,average canopy interception rate and raindrop kinetic energy reduction of maize increased at first and then decreased,and reached the maximum at maturity.（3）Among the parameters of maize canopy vertical structure,leaf angle,stem height,leaf area,crown diameter and plant height were the main factors affecting the rainfall distribution process.The maize canopy vertical structure index（MCVS）based on throughfall,stem flow and raindrop kinetic energy reduction was constructed((1、(1、(1).Using the regression equation constructed by maize canopy vertical structure index and corresponding rainfall allocation parameters,it was found that:when the value of the(1、(1、(1increases by 0.05,the corresponding throughfall rate decreases by 10.39%～16.02%under different rainfall intensities;the stem flow rate increased by 5.38%～8.37%respectively;the reduction of raindrop kinetic energy per square meter per hour increased by 46.407J～138.34J,respectively.