| The Loess Plateau region is an important ecological barrier and the production base of animal husbandry in China. However, unreasonable human activities lead to serious degradation of grassland, severe soil erosion, and the sustainable development of threaten ecosystem. The vegetation restoration measure which takes advantage of the mutual feedback effect between plants- soil system, recover and rebuild huge adjustment function of soil reservoir, which is the fundamental measure to solve the problem of the regional ecological environment. This study selected different years grassland as the research object, which is in the Yunwu Mountains grassland nature reserve in the loess plateau. In this paper, we use the methods of artificial rainfall simulation, microscopic CT scans and indoor analysis. In this paper, In this paper, we study the change rule of soil physical, chemical and hydraulic properties in the process of vegetation restoration. This paper analyzes the evolution of soil structure characteristics to clarify the mechanism of action of soil structure evolution to rainfall infiltration process. We purpose to provide certain scientific basis of vegetation restoration and reconstruction in loess plateau areas. The main results obtained are summarized as follows:1. The process of returning farmland to grassland is conducive to improving soil physical and chemical properties. Performance to reduce soil bulk density, increase soil porosity, reduce soil sand content, increase the silt and clay content, mainly reflected in the early farmland(< 3 years) and 0 to 10 cm soil layer, but did not cause the change of soil texture. Grain for 3 to 8 years is soil organic carbon, total nitrogen content in recovery stage, from grain for 8 years began to accumulate, conversion of 22-24 years is a rapid accumulation of soil organic carbon, total nitrogen content.0 to 10 cm soil layer soil organic carbon, total nitrogen content, respectively from the field for eight years 22 years is significantly higher than 10 to 40 cm soil layer. Soil organic carbon accumulation speed is bigger than the accumulation of nitrogen.2. The process of returning farmland to grass promotes large aggregate formation, improve the aggregate stability. Performance for the conversion of 8-24 years large aggregate content of water stability significantly increased by 21.34%- 21.34%, conversion of 22-24 years most aggregate stability.0 to 10 cm soil aggregate stability above 10 to 40 cm soil layer. Large aggregate content of water stability directly increase aggregate stability, and stability was significantly positively effect, mainly reflected in the > 1 mm large aggregate water stability. Organic carbon content indirectly boost aggregate stability.3. Three years after returning farmland grassland vegetation restoration is helpful to improve the pore structure stability. Performance is beneficial to the soil in the 0 to 10 cm soil layer 1-5 mm together the increase of the total porosity and the pore of the total reduction. Among them, the capillary porosity(3.25 microns- 20 microns) with gradually reduce, increase of fixed number of year of the farmland conversion of 8-22 years reduced significantly.20 microns- 100 microns ventilation pore porosity with the extension of cultivated fixed number of year of reduced gradually, and > 100 microns ventilation pore porosity increase gradually.> 100 microns ventilation pore porosity is highest, account for more than 99% of the total porosity. Vegetation restoration is advantageous to the increase in long and narrow pore shape factor(0.2) or less porosity, and lower irregular pore(0.2< shape factor < 0.5) and the rules of the pore porosity of shape factor(0.5 or higher). Long, narrow pore porosity is highest, account for more than 99% of the total porosity. Soil silt content is the main influence factors of aggregate pore structure characteristics, and 1-5 mm irregular porosity in the aggregate, rules, porosity and capillary porosity significantly negative correlation(Sig) < 0.001).4. Process of returning cultivated land to grassland significantly improves the performance of soil water and holding water. As the vegetation restoration, soil saturated hydraulic conductivity from the conversion of 4.16 mm·min-1, 3 years to grain for 22 years of 6.74 mm·min-1, significantly increased by 61.9%.Compared with the slope, when the organic carbon content and water stability of large aggregate content increase 1 g·kg-1 and 1% respectively, the saturated hydraulic conductivity increased by 1.2% and 2.4%, respectively. Vegetation restoration is helpful to improve the soil water-holding capacity, mainly reflected in the 0 to 10 cm soil layer, the conversion of 22-24 years water-holding performance improved significantly. Large aggregate stability of soil water content and organic carbon content are the main factors influencing the saturated hydraulic conductivity, and organic carbon content is the most important factors affect the ability of the soil moisture. Organic carbon content increase large aggregate stability by increasing the water content to improve soil structure, thus improve the saturated hydraulic conductivity and water holding capacity.5. Returning farmland to grassland could improve the ability of soil, rainfall infiltration. Show the with vegetation restoration, the initial infiltration rate increase, extend the time of reach the steady infiltration rate. In the process of vegetation restoration infiltration rate increased with the increase of rainfall intensity.1-5 mm aggregate irregular porosity and capillary porosity are the main factors influencing the initial infiltration rate, and negatively correlated with the initial infiltration rate. Moderate rain is strong, the stable infiltration rate and 2-1 mm aggregate negatively correlated with irregular porosity. Heavy rain is strong, the stable infiltration rate and 5-2 mm long and narrow porosity aggregate were positively correlated. |
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