| Collapse is one of the most severe soil erosion types with enormous damage in the south of China. Domestic and foreign scholars have made a lot of research on the status and management of collapsing hill in red soil region. The comprehensive measures of collapsing management can be summarized as "stopping the upper part, blocking the bottom, cutting the middle part, greening in both internal and external part", ―cutting the middle part‖, which means cutting the collapsing slope, can effectively change the surface topography, slow down the surface slope and reduce the loss of soil and water to a certain extent on one hand. on the other hand, it leads to a huge change of soil physical and chemical properties with massive disturbance of soil mass. Different land use mode and management mode will inevitably lead to the difference of vegetation cover after terracing, effecting on soil nutrient cycling, soil nutrient storage and availability of nutrients directly as well as the physical and chemical properties of soil and the change of land productivity. Therefore, researching effection on soil properties after terracing collapsing hill under different land use patterns and ages will provide theoretical and practical basis for the improvement of soil and the rational use of land.This paper was based on the study of the terracing of Collapsing Hill in Jingouxing small watershed region of Ganxian county, Jiangxi Province and analyzed fractal dimension of soil particle composition, the distribution characteristics of soil water and nutrients and soil comprehensive fertility quality under two aspects between different land use patterns( including grass shrub mixed forest, orange orchard, pear orchard, Paulownia forest, masson pine forest, fir forest, peanut land, abandoned land) and different ages( including years of 16, 12, 10, 6, 4 and 1) in terrace. this study meant to explore the variation characteristics of soil properties under different land use patterns on the terracing as well as the evolution law of soil physical and chemical properties with the growth of ages. The main conclusions were as follows:(1) Fractal dimension of soil particle composition The result of fractal dimension of soil particles in different land use patterns were as follows: grass shrub mixed forest(2.78) > abandoned land, pear orchard(2.77)> orange orchard(2.76)> fir forest(2.74) > Paulownia forest(2.73)> peanut land(2.69)> masson pine forest(2.68), which indicated that the composition of soil particles in the mixed forest of grass and shrub was uniform, and the soil structure was better. The explanation mainly lay in the vegetation coverage of different land use, the loss of fine particles in the surface of terracing soil under flow scouring was different. The fractal dimension of soil particles in different transformation period as well as the control area were as follows: 16a(2.84)>12a(2.81) >10a(2.77) >6a(2.73) >4a(2.71) >1a(2.68). Compared with the control area, the soil structure in the first 4 years of transformation decreased significantly, then the performance of the soil structure improved with the extension of the age, even better than that of the control area. In study area, there was a significant positive correlation of the soil particles fractal dimension with clay content, other than sand and silt content. Soil particle fractal dimension and organic matter, alkali solution nitrogen, total nitrogen, total potassium, available phosphorus, total phosphorus nutrient content correlation all reached a extremely significant level and were positively correlated, while the content of available potassium was less relevant.(2) Soil water characteristics The soil water characteristic curve showed obvious difference Under different land use patterns. By fitting the soil moisture characteristic curve with Gardner model, results showed that water holding capacity of the peanuts land was worst while grass shrub mixed forest and pear orchard was best.The result of soil porosity showed that : grass shrub mixed forest, pear orchard and orange orchard has the better porosity, and the ability of ventilate and holding water were in good harmony. The total porosity of peanut land is relatively low, and the aeration pore is larger, which brought it a better ventilation performance. However, the Properties of water and fertilizer conservation was poor in the mean time. The difference of soil water characteristic curve in different years was obvious, the water holding capacity of the soil was worse than that of the control area in the first 4 years. With the extension of the transformation period, the water holding capacity was gradually enhanced and significantly better than the control area. The distribution of soil pores in different ages showed that the total porosity of soil decreased and the aeration porosity increased as a result that the soil porosity decreased significantly in the early stage of transformation. Pore distribution changed in the fourth year was not obvious compared with the first year, it began to return to the level of the control area in the sixth year. With the prolonged time, the soil total porosity and capillary porosity increased gradually. In the sixteenth year, the porosity of soil improved significantly as well as the performance of soil structure.(3) Soil nutrients, soil fertility quality The contents of organic matter, alkaline hydrolysis nitrogen, total nitrogen, total potassium, total phosphorus and available phosphorus in soil of the terracing were relatively low, which belonged to the middle and lower level, while the content of available potassium was rich beyond the middle level. On the whole, the content of soil nutrients in the study area was low, and the soil fertility was poor.The soil nutrient contents were significantly different in different land use patterns. The quality of soil fertility in different land use patterns was evaluated by the method of soil fertility quality index, and the result from high to low as follows: grass shrub mixed forest > peanut land > pear orchard > orange orchard > masson pine forest > Paulownia forest > abandoned land > fir forest. Nutrient content in soil of the terracing ascended obviously as a whole With the extension of the transformation period, but the soil nutrients were significantly decreased compared with the control area in the early stage of transformation, the nutrient index of fourth years began to return to the level of the control area. The results of soil comprehensive fertility quality assessment showed that the quality of soil fertility decreased significantly in the early stage of terraced fields. With the extension of transformation period, the quality of the soil fertility was significantly improved and obviously better than that of the region without transformation.To sum up, after terracing in the research area, the grass shrub mixed forest land had maintained a relatively good soil quality because of the good species community composition and the micro ecological environment; The fir forest, paulownia forest, masson pine forest and other forest land had serious soil and water loss, poor soil structure and low fertility quality for the reason of low vegetation cover with a bare state; The fertility quality of cultivated land affected by human is relatively high, but the surface soil texture is sandy, and the structure is poor. After planting pear trees, soil fertility status and structure showed some changes along with the period of transformation prolonged. Soil physical and chemical properties decreased significantly in the early stage of transformation. With the extension of the transformation period, the benefit of soil, water and fertility conservation reflected gradually. As the organic matter input to the surface accumulated constantly, soil structure as well as the physical and chemical properties of soil had been improved effectively. |
PDF Full Text Request