The Effect Of Vegetation Restoration Years On Soil Infiltrition Process Of Different Land Uses

In order to analyze the change of soil physical parameters, the improvement of infiltrition characeristics under revegetation in Loess Plateau and providing a scientific basis for the conversion mechanism of rainfall and moisture, six plots(25,15,9-year forest lands and grass lands) of Guanshan forest in Gansu province were chosen as research areas. Soil physical properties and characteristics of root system were determined; the disc-permeameter was used to measure infiltrition properties, the number of pore(including macropore) and contribution of macropore to total flow of surface soil. Then, 0-30 cm and 0-60 cm undisturbed soil columns were dug and 2g/L bright blue solution was used as the dying tracer to study the whole infiltrition properties. Finally, Hydrus software was used to simulate the infiltrition of 0-60 cm undisturbed soil columns. There were the results that we got:1)The way of ecological restoration and years always affected the soil physical properties which extensively influenced infiltration capacity of soil. In genaral, the soil physical properties became more beneficial to infiltrition capacity with the increase of time. In this article,for the same year, the soil physical properties and root system characteristics of the surface soil(higher than 20cm) of grasslands were more beneficial to infiltrition than that of forests; under 20 cm, the properties of forests were better than that of grassland gradually.2)In the research of disc-permeameter experiment, the hydraulic conductivity of surface soil was improved with increasing over time no matter in forests and grasslands, and the hydraulic conductivity of grasslands were much better than that of forests. Analyzing the number of pores in soils, the pore with equivalent diameter >0.5mm was the important factor affecting the infiltrition capacity, and contribution of macropore to total flow could reach to 70.92~91.58%, which explained that there was a huge contribution of macropre to total flow.3)In the research of infiltrition capacity of two undisturbed soil columns, the results of initial infiltration rate, transient infiltration rate, stable infiltration rate were shown below: 25-year forest land>15-year forest land>9-year forest land,25-year grassland>15-year grassland>9-year grassland. For forest land and grassland which had the same age, infiltration rates of forest lands was lower than that of grassland, but the difference between 60 cm soil columns were smaller than that of 0-30 cm. Accumulative infiltration amount had the same rule with infiltration rates. With the increase of time, the breakthrough time became shorter, which was obviously shown in forest lands and grasslands. In 0-30 cm soil columns, the breakthrough time of grassland were shorter than that of forest land, while there was no Significant differencet in 60 cm soil columns.4)From the percent of external accumulative dyeing area of 0-60 cm soil columns, soil of forest lands was easier dyed than grassland at the same year, and the percent of external accumulative dyeing area became bigger with the increase of times. The existence of macropore was to explain the difference of simulating values of homogeneous and soil containg macropores. Absolute Error and Relative Error were used to evaluate the feasibility of the model, and Hydrussoftware could be feasible in simulating the infiltrition of undisturbed soil columns.The result of this thesis was shown that: the ecological restoration of Loess Region should band seeding and planting trees together, using grassland to give full play to improve physical property of the surface soil, and allowing full play to the reform of forest land to physical property of the deeper soil. The herbage could improve the physical properties of surface soil quickly, which enhanced rainfall retaining ability. While forests were to reform the physical properties of deeper soil, which took the retaining rainfall to groundwater through root pores, improving the infiltrition property. These two sides modified environment of groundwater and surface water in Loess Plateau.