Model construction and verification of vegetation cover and management factor in southern red soil region of China

Studying the change characteristic of vegetation cover factor in the red soil region and constructing vegetation cover factor calculation model can provide valuable information for regional soil erosion control and dynamic monitoring. Based on more than 200 field rainfall events in Soil and Water Conservation Experimental Extension Station of Wuhua County in Guangdong province, this study analyzed the quantitative relationship between the soil erosion modulus and factors which affected soil erosion. The plants were mainly Pinus massoniana Lamb., Eucalyptus gran dis Hill, Citrus maxima (Burm.) Merr., Schima kwangtungensis Hung T. Chang,Rosa sericea Lindl., Dicranopteris dichoto ma (Thunb.) Bernh., Eriachne pallescens R. Br. and so on. The soil field water holding capacity was 26.7%-36.7%. The soil organic matter was 078%-1.69%. The artificial rainfall simulation device was used to produce rainfall. The effective rainfall area was 2 m by 3 m. The rainfall intensity was 0.5-2.5 mm/min. The rainfall dimeter was 0.6-2.2 mm. The rainfall uniformity was 81.5%-93.6%. This study obtained the vegetation cover factor values under different underlying surfaces based on the Chinese Soil Loss Equation, and constructed the quantitative model between the vegetation cover factor value and vegetation cover. The model was established based on data from 98 rainfall tests in 2016 and 2018, from 81 natural rainfall events in 2016 and from 29 natural rainfall events in 2017. Furthermore, the tested data were used at two spatial scales to verify the calculation accuracy of the model. The verification data was from 33 natural rainfall events in 2019 at Wubeihe station. In addition, data from Wuhua county was also used for model verification. The following key results were obtained: 1) The negative power function could be used to describe the relationship between the soil erosion modulus and vegetation cover, and the fitted equation reached a significant level (P=1.11×10-6). There was a significant positive logarithmic function relation between the soil erosion modulus and the soil moisture at 0-15 cm soil depth before each rainfall event (P=9.34×10-16). The soil erosion modulus increased firstly and then decreased with the increase of slope gradient. The soil erosion modulus increased significantly with the increase of the individual rainfall amount, the individual rainfall erosivity and the runoff depth (P≤1.08×10-13). 2) Based on the comparison of the statistics of fitted equations, the second-order exponential decay model was determined to quantitatively characterize the dynamic relationship between vegetation cover factor and vegetation cover. The fitted equation between vegetation cover factor and vegetation cover based on the second-order exponential decay model reached to a significant level (P=0.003), and the coefficient of determination and Sutcliffe efficiency coefficient were 0.947 and 0.876. The point scale verification result showed that the relative error of 90% verified samples were less than 0.30. The regional scale verification results showed that the absolute relative error of 70%-80% verified samples was less than 0.1. In summary, the calculation accuracy of the model was relatively ideal. The research results above could provide a useful method for in-depth understanding of the soil erosion characteristic and dynamic monitoring in red soil regions.