Effect Of Calculation Methods For Crop Residue Cover On The Calculation Of Soil Wind Erosion In Farmland

Soil wind erosion is an important ecological environment problem in northern China.As a surface roughness factor in the process of wind erosion,crop stubbles can effectively reduce the degree of wind erosion on the surface of farmland.When calculating the soil wind erosion,immediately using the normalized vegetation index（NDVI）to calculate the stubble coverage should not represent the actual stubble coverage on the ground surface.Importing the stubble coverage calculated by this factor into the soil wind erosion model to calculate the soil wind erosion amount will seriously affect the accuracy of the calculation results.Therefore,the accurate calculation of wind erosion in farmland soil objectively requires the accurate acquisition of stubble coverage.The paper takes the Bashang region of Hebei Province as the research area,selects typical crop stubbles from this area,and uses a hyperspectral ground object spectrometer ASD Fieldspec 3 to simulate field experiments.The spectral information of crop stubbles under 0-50%different coverage is measured,and the corresponding crop stubble coverage is obtained using a digital camera.Using hyperspectral data to construct a ratio index,a normalized difference index,and a correlation analysis with the coverage of the corresponding sample,select a crop stubble characteristic band to construct a stubble index.Combining the correspondence between the crop stubble spectral characteristic band and Sentinel-2 multispectral data band information,the crop stubble coverage（FVC）calculated using the stubble index on the GEE platform,At the same time,stubble coverage（VC）is calculated on the GEE platform based on the NDVI index.The spatiotemporal distribution characteristics of stubble coverage calculated by two methods were compared,and the effects of two methods on the spatiotemporal distribution characteristics of wind erosion calculation results were compared using the Modified Soil Wind Erosion Model（RWEQ）.The main research conclusions are as follows:（1）The characteristic wavebands of crop stubbles are（1620nm,2269nm）、（1606nm,2260nm）。Based on the spectral information of multispectral remote sensing data,the final selection of wavelength（1610nm,2190nm）as the characteristic wavelength was made,and the remote sensing estimation model was constructed as FVC=4.6275 x+0.0229,with R²of 0.7596.（2）According to the spatiotemporal distribution characteristics of crop stubble coverage calculated based on the stubble index and the normalized index（NDVI）,it can be seen that in terms of time,the monthly stubble coverage FVC and VC of the wind erosion season（October May）in the study area from 2017 to 2021 were the highest in October,and the monthly average FVC was higher than the monthly average VC.In winter（December,January,and February）,the stubble coverage gradually decreased from autumn to spring.From a spatial perspective,the spatial distribution of residual stubble coverage in the study area is basically consistent,with spatial and regional differences.The areas with high residual stubble coverage are mainly distributed in the southern part of Kangbao,the northern and central parts of Shangyi,the central and eastern parts of Zhangbei,and Guyuan..From the perspective of interannual scale,the5-year average value of FVC is about 49.6%,and the 5-year average value of VC is about 10.57%.The overall stubble coverage in the study area presents a trend of increasing first and then decreasing,with an annual average FVC of about 4 times the annual average VC,indicating that the stubble coverage calculated based on the stubble index is more accurate than the stubble coverage calculated based on NDVI.（3）By comparing the soil wind erosion quantities Q_FVC and Q_VC calculated using FVC and VC,it can be seen that in terms of time,the monthly average soil wind erosion quantity Q_VC in the wind erosion season（October May of the following year）from 2017to 2021 in the study area was higher than that of Q_FVC.Overall,the soil wind erosion quantity was the highest in April and May,and the lowest in October.With the passage of time,the soil wind erosion quantity gradually increased from autumn to spring.From a spatial perspective,the spatial distribution of soil wind erosion in the Bashang area of Hebei Province from 2017 to 2021 is basically consistent,with spatial distribution and regional differences.The soil wind erosion in the central and western regions of the entire research area is relatively large,specifically manifested in the southern part of Kangbao,the northern and central parts of Shangyi,the eastern part of Zhangbei,and the western part of Guyuan.From the perspective of interannual admeasurement,In 5years,the Q_FVC is about 11.98 t·hm^-2·a^-1,and the Q_VC is about 38.23t·hm^-2·a^-1.the total amount of soil wind erosion in the examined area shows a tendency of first decreasing and then increasing.The average annual Q_VCis 3-4 times the average annual Q_FVC.Based on the spectral characteristics of crop stubbles,this component constructs a stubble index for calculating stubble coverage.It compares the spatiotemporal distribution characteristics of stubble coverage and wind erosion calculated based on the NDVI index with this index.The results show that the coverage calculated based on the stubble index can better reflect the actual stubble coverage status on the ground surface,while the stubble coverage calculated based on the NDVI index will overestimate the calculation results of soil wind erosion.