Simulate Study On Soil Erodibility Of Purple Soil In Hilly Region

Soil erodibilty is an important indicator to evalue the sensitivity of soil erosion,also an important parameter to the soil erosion model.Soil erosion and water loss in purple hilly region is very serious,because of the fragile ecological environment,high panting rate,many sloping land and so on.Studding on the purple soil erodibility is the base to comprehend and master the mechanism of soil erosion.Artificial rainfall simulator and analysis of soil physical and chemical properties were used in this research.The mechanical characteristics of simulated rainfall,soil erosion and water loss were studied in the paper.Purple soil erodibility and the relationship between soil properties and soil erodibility was also studied as to investigate and measure the value of soil erodibility,to further study the mechanism of purple soil erosion,to provide theoretical foundation of soil erosion model.The results show that:(1) The maximum rainfall intensity of field artificial simulation was 62.86mm h^-1,and the minimum was 33.20 mm h^-1,the maximum 30 min rainfall intensity Was at 42.14～81.40mm h^-1,the rainfall duration was about 60 minutes.The minimum uniformity coefficient of simulate rainfall was.0.796,and the maxinum was 0.921.The coefficient meets the requirement of uniformity.Filter paper splash procedure was used to measure the raindrop diameter during the rainfall.The minimum median diameter D₅₀ of the raindrop was 1.09mm,the maximum was 3.65mm.The simulated rainfall nozzle diameter determines the size and distribution of the raindrop.The natural rainfall data was analysis by nonlinear procedure of SPSS to discuss the similarity between simulate and natural rainfall.The similarity test model was set up:e'=5.039+14.372 logI'.The results showed that simulate rainfall intensity and raindrop kinetic energy in line with the e'-I' model which was set up by natural rainfall.So the simulate rainfall was similar to natural rainfall. The process of runoff amount,sediment amount and sediment concentration had a certain amount of undulation.(2) Tbe soil in the pilot area was sandsilt soil.The sand(1～0.05mm) was 36.69%,silt (0.05～0.005mm) was 41.15%,and clay(＜0.005mm) was 22.16%.Cubic spline interpolation method was used to change the particle size distribution system into the United States system,the results showed a good interpolation.Soil organic matter content averaged 10.37g kg^-1,soil pH at 8.2～8.4,indicating the soil was calcareous purple soil.Air dry soil aggregates content of＞0.25mm was 94.59%,but＞0.25mm water stable aggregates content was 45.03%,the structural destroy rate was 52.39%;aggregate stability index(ASI) was an average of 1.76,indicating the soil aggregate stability in the experiment area was bad.The average infiltration rate of soil in the beginning 5 min was 15.33 mm min^-1,stability infiltration rate was 2.98 mm min^-1.The infiltration process was in line with the y=ax^b power function,the simulation of equation was significant.(3) Based on universal soil loss equation,the rainfall,runoff and sediment records were used to calculate the soil erodibility value.The maximum value of the purple soil erodibility was 0.0317, the minimum was 0.0025,the average was 0.0121t hm² h MJ^-1 hm^-2 mm^-1(0.09518sht h 100ft^-1 sht^-1 in^-1)under 10 numbers of simulate rainfall.The soil properties data was used to calculate the soil erodibility.Results showed that the average erodibility value based on nomogram equation was 0.0521,EPIC model estimated value was 0.0468,Shirazi calculated the erodibility value was 0.0438.The estimated soil erodibility value was much larger than the measured value.The estimated and measured value of soil erodibility had a good linear relationship.So the linear equation could be set up to modify the estimate values.According to the data information need and the fitting accuracy,the EPIC model may estimate soil erodibility better.(4) Correlation analysis method was used to study the relationship between soil erodibility and soil texture,organic matter content,soil structure and permeability.Principal component analysis was used to extract 4principal components;the 4 principal components cumulative contribute the 89.73%of the variances.The first component contained the soil organic matter content,soil particle size distribution and micro aggregates information.The No.2 component main stood for the water stable aggregates characteristic of soil structure.The third component main extracted the soil infiltration characteristics.The fourth principal component extracted scattered information,mainly the clay content of soil particle size distribution.Based on the principal component analysis,the clay content of particle size distribution(CLAY),organic matter content(OM),＞0.5mm water stable aggregates content(WSA_＞0.5) and stable infiltration rate(INF_sat) were analysis to set up the linear equation:K=0.003CLAY-0.054OM-0.001WSA_＞0.5-0.027INF_sat+0.638 or K=G.619CLAY-3.692OM-0.203WSA_＞0.5-2.965INF_sat(p=0.015).The purple soil erodibility could be calculate by using the soil particle size distribution,organic matter content, aggregates characteristic and infiltration data.(5)Artificial simulate rainfall has been widely used in the soil erodibility study.The similarity of simulate rainfall and scale simulation model should be considered in the study.The simulate rainfall could simulate the soil erosion and water loss under natural rainfall only when the rainfall intensity and raindrop was in the same scale of the natural rainfall.Soil erodibility,as an important evaluation indicator of soil sensitivity to erosion,was dynamically changed by the effects of soil physical and chemical properties.The observation data of standard field runoff plots should be strengthen collated and analysis,combing with artificial rainfall to determine soil erodibility value range and the dynamic characteristic,to provide an accurate parameter of the soil erosion model.