Study On Soil Anti-erodibility Of Different Land Utilization Types In Purple Soil Hilly Region

Purple soil is the important soil resource of the Three Gorges Reservoir Area,and the plowland area of puruple soil takes up of 69.2%area of Reservoir.Most of this region is the traditional agricultural production, and due to the high reclamation index and the obvious contradiction between the people and land,it resulted in soil and water loss and sediment storage.Study on soil anti-erodibility of purple soil has important practical significance in the construction of the ecological environment and soil erosion control and land-use restructuring in purple soil hilly region.In this paper,based on the physical and chemical properties analysis indoor of soil of several main types of land-use in high-efficiency agriculture section of NanTuo town in Fuling District of ChongQing City and teaching experiment base in back mountain of southwest university,the indicators of soil anti-erodibility in purple soil hilly area were selected by principal component analysis,and the soil anti-erodibility evaluation model of different types of land-use and linearity regression model between indicators of soil anti-erodibility and physical and chemical properties were also established,and the changing orderliness of soil anti-erodibility of different types of land-use in purple soil hilly area was quantitative analyzed.The main conclusions are as follows:1.Consideration of situation on the ground combined with principal component analysis of＜0.001mm granule content,structural particle index,the reunion situation,reunion,the rate of spread,＞0.25 mm water stable aggregates,＞0.5 water stable aggregates,water stability index and etc,the best indicators for the evaluation in purple soil hilly area were confirmed:＞0.25 mm water stable aggregates,rate of structure deterioration,＞0.5 water stable aggregates,reunion,the reunion situation,Organic matter,＜0.001mm granule content,＜0.01mm granule content,water stability index.2.＞0.25mm &＞0.5mm water stable aggregate composition of purple soil of different types of land-use were bamboo forest land＞orchard＞traditional farmland＞tree-crop intercropping land.Rate of structure deterioration was tree-crop intercropping land＞traditional farmland＞orchard＞bamboo forest land.＜0.001mm granule content was orchard(15.88%)＞traditional farmland(12.44%)＞tree-crop intercropping land(12.16%)＞bamboo forest land(8.88%).With the Organic matter increasing,the reunion situation was bamboo forest land(13.91)＞orchard(9.7)＞tree-crop intercropping land(8.95)＞traditional farmland(8.35),and reunion was orchard(23.45)＞bamboo forest land(22.92)＞tree-crop intercropping land(20.52)＞traditional farmland(20.16). Water stability index showed a gradually rising trend from traditional farmland,tree-crop intercropping land, orchard and bamboo forest land,and it was 0.469,0.627,0.704 and 0.868 respectively,3.The soil anti-erodibility evaluation model of purple soil hilly area was Y=0.3893Y₁+0.2984Y₂ +0.1324Y₃,and according to the model,the comprehensive indexs of purple soil of different types of land-use were bamboo forest land(75.35)＞orchard(64.83)＞traditional farmland(64.23)＞tree-crop intercropping land(40.62).4.The roots of purple soil were＜0.5mm roots dominated,and the characteristic of root distribution of different types of land-use showed obvious difference.The root length and anti-erodibility indicators had positive correlation,and among four land-uses,＜0.5mm roots of bamboo forest land were the longest.The length of＜0.5mm roots had remarkable correlation with rate of structure deterioration,the reunion situation,＜0.001mm granule content,and＜0.01mm granule content.5.The root length of bamboo forest land of each diameter class and the comprehensive evaluation index of anti-erodibility had same changing trend.However the root length of other three types of land-uses showed same or different changing trend,and the root length of diameter class of 0.5-1mm and 1-3mm showed same changing trend,and the root length of diameter class of＜0.5mm and＞3mm showed different changing trend. Excepting for traditional farmland the comprehensive evaluation index of anti-erodibility had a rising trend with root density and root biomass of 1-3mm root increasing.But the comprehensive evaluation index of anti-erodibility and the root surface-area of＞3mm root had a exactly opposite changing trend.6.The soil elementary permeability rate had remarkable correlation with＜0.01mm granule content and the reunion situation,and the correlation coefficient was -0.54 and 0.45.The steady infiltration rate had remarkable correlation with＜0.01mm granule content,and the correlation coefficient was -0.48.There was a typical power function relationship between soil elementary permeability rate,steady infiltration rate and＜0.01mm granule content,and with＜0.01mm granule content increasing both rates decreased.However,the soil elementary permeability rate can be significantly advanced by the inprovement of reunion situation.7.The mul-tiple regression equations of soil elementary permeability rate and steady infiltration rate with comprehensive index of anti-erodibility were obtained,and it was Y=61.923-2.691I₀+9.568I_n R₂=0.928.The influence of soil elementary permeability rate and steady infiltration rate on soil anti-erodibility was different, and the soil anti-erodibility was mainly determined by soil steady infiltration rate.8.The soil shear strength only had negative correlation with rate of structure deterioration,and had positive correlation with＞0.25 mm water stable aggregates,＞0.5 water stable aggregates,reunion,the reunion situation,＜0.01mm granule content,＜0.001mm granule content,water stability index and organic matter,and had a bigger correlation coefficient of＜0.01mm and＜0.001mm granule content.9.The soil shear strength of waste-grassland was smaller than that of forest land,and the comprehensive index of anti-erodibility of waste-grassland was significantly smaller than that of forest land.There was a typical power function relationship between shear strength and comprehensive index of anti-erodibility,and it was y=2.142x^3.014.That means the comprehensive index of anti-erodibility increased with shear strength rising in purple soil hilly region,and to some exent the shear strength can reflect the strength of soil anti-erodibility.