Study On The Soil Erosion Assessing Indexes System Of Purple Soil

The quantitative assessment of soil erosion is geography problem which including mixed factors,mixed levels, mixed scales.There has been no unanimous conclusion on the quantitative assessment indexes and their thresholds for Purple Soil soil erosion.In view of existing internal situation the study on soil erosion assessing indexes system and their grades of Purple Soil is weak.The study area is located in XieJiaWan ,a small watershed in the Experimental Station of Soil and Water Conservation of SuiNing City ,SiChuan Province,study about building the soil erosion assessing indexes and their grades of Purple Soil in a small watershed.Combinating of theory, method,technology, study in a deepgoing way .With the principles of combination of qualitative and quantitative analysis ,macroscopic and microscopic analysis,through field investigation, soil sampling,analysis of soil and experiment,analysis soil erosion factors influence ,apply the statistics method ,choose the soil erosion assessing indexes in XieJiaWan small watershed ,especially study in a deepgoing way on soil factors assessing indexes,identifying their grade and weigh by AHP,build up the soil erosion assessing indxes system.The samples verifying shows that the accurate of the assessment system is 83.3%.The results of the study are followed:(1) Soil erosion assessing factors and assessing method .Analysis climatical factors,topography factors, vegetable factors, soil factor and manual factors .With the principles of the main fators,combination of qualitative and quantitative analysis , divergence and handled easily, identify the soil erosion assessing indexes ,and its weight is drawn by AHP method.(2)Study on soil anti-erodibility indexes.Choose soil content of medium, organic mater, soil aggregate,soil micro-aggregate and more indexes, statistics method ,the result show that ,the destroyed aggregate, 0.1~0.05mm content,the organic mater and <0.002mm content , their R value is 0.834,0.938,0.960,0.971. So this text choose the destroyed aggregate,0.1～0.05mm content,the organic mater and <0.002mm content regard as the assessing indexes.(3) Study on rainfall infiltration .The lasted time of start runoff and the rainfall intensity, slope.the lasted of time of start runoff changes smaller with the rainfall intensity.Slope and the rainfall intensity effect the infiltration .The stable rate of infiltration and sina (a is slope) is index function .Under the same slope, the changing carve of infiltration ratio with time is the same regulation. The stable rate of infiltration changes bigger with the rainfall intensity changes bigger.(4)Divide the grades of soil erosion assessing indexes.Divide the gradation of the cover rate of vegtable according to the Water Department . The useland of grades is basid on the actually value ,the fruit graden is 1 grade , grass is 3 grsde , no useland is 5 grade ,plough is 4 grades.Correlation analysis of soil erosion grade with the destroyed aggregate,0.1～0.05mm conten,the organic mater and <0.002mm content,get the simulate curves ,gain the their thresholds.(5)Build and verify the soil erosion assessing indexea system. According to the assessing indexes in XieJiaWan small watershed, the weight is drawn by AHP method; build up the soil eroson assessing indexes system, The samples verifying shows that the accurate of the assessment system is 83.3%.