| As one of the four significant water loss and soil erosion areas in Changjiang upper stream and being featured by complex geomorphic type, the three gorges reservoir area is a significant factor which seriously harms the ecological environment and hinders the development of social economy. As the main field type of soil erosion in the three gorges reservoir area, the sloping fields shall easily runoff totally or form skeleton soil which shall result in declining productivity of land. By establishment of Three Gorges reservoir, the contradiction between human and land became sharper as facing the double pressure of ecological environment construction focusing on water and soil conservation as well as sustainable social economic development. Thus comprehensive management measures of water loss and soil erosion complying sustainable development are urgently needed.By taking the region representation into full account, the small watershed in Nanshan bridge groove, Kai County, Chongqing city was selected as pilot. In the three gorges reservoir area this watershed is typically featured by general deforesting, high coefficient of cultivated land and serious steep slope farming.By focusing on the treatment measures of different forest and grassland and on the basis of field investigation and sampling, laboratory analysis and statistical analysis, this study has analyzed the physical and chemical properties of runoff, sediment and soil under different treatment measures of forest and grassland, as well as the content variation of soil organic carbon and soil active organic carbon fractions. In addition, it discusses on the water loss and soil erosion discipline, presentation features, soil fertility and anticorrosion of typical plants in the three gorges reservoir area by establishment of treatment type, as well as the influence on content change of soil organic carbon and soil active organic carbon fractions of different forest and grass treatment measures. In accordance with above results, forest and grass treatment measures with better effect on prevention and control of water loss and soil erosion shall be selected thus provide important scientific basis for the prevention and control of water loss and soil erosion as well as construct rational water and soil conservation defense system. Furthermore it shall provide significant scientific support for the social economy development of the three gorges reservoir area. The main study achievements are as follows:1. The organic matter content of soil0-20cm under different treatment measures of forest and grassland is the highest. Meanwhile there exists significant variation between the organic matter of surface soil0-20cm under each kind of treatment measures of forest and grassland (excluding bare land control plot) and the soil layer below. The organic matter content of the three soil layers namely soil section of0-10cm、10-20cm、20-30cm under Koelreuteria bipinnata+Cassia suffruticasa and hedgerow as well as closed forest measures have been significantly improve than that of relevant soil layers of bare land control plot. According to the horizontal comparison, the best effect of improving the organic matter content of soil shall be obtained via Koelreuteria bipinnata+Cassia suffruticasa measure.The average content of total nitrogen of soil under different treatment measures of forest and grassland is0.264-0.634g·kg-1. The full N average content of0-30cm soil layer is highest under Koelreuteria bipinnata+Cassia suffruticasa measure while the hedgerow and closed forest measures take the second place. The variation trend of total nitrogen content of each soil layer section and the total organic carbon are almost consistent. There is not obvious change in available nitrogen in traditional planting and bare land control plot while available nitrogen declines from the surface to bottom in other treatment measures of forest and grassland.The total phosphorus content distribution of soil section shall be of certain difference due to different treatment measures of forest and grassland thus shall show great fluctuation with the increasing of soil layer. The distribution of soil total phosphorus content is similar with that of organic matter and total nitrogen under different treatment measures of forest and grassland. At the same time, available phosphorus content shall decline with the increasing of soil layer (excluding bare land control plot) thus the available phosphorus content of each soil layer under hedgerow measure is greater than that of other treatment measures of forest and grassland.2. The percentage composition of non-water stable aggregates under different treatment measures of forest and grassland is:greater than5mm>5-2mm>1-0.5mm>2-1mm>0.25-1mm>0.5-1mm>smaller than0.1mm. Comparing the different treatment measures of forest and grassland, traditional planting and bare land control plot, the soil micro-aggregates with greater grain diameter (0.25-0.005mm). Generally, the treatment measures of forest and grassland have better effect on aggregation of soil composition. Through further aggregation effect the content of aggregates shall be higher than that of traditional planting and bare land control plot.Test result of water-stable aggregates under different treatment measures of forest and grassland shows that it is beneficial for the increasing of>0.25mm water-stable aggregates. However, different treatment measures of forest and grassland shall gain different effects. Oelreuteria bipinnata+Cassia suffruticasa measure owns the best performance in0-30cm soil layers where the mean-weight diameter is0.37-1.59mm indicating that it has relatively stronger soil composition stability and anti-erosion ability. The changing range of fractal dimension characteristics is2.404-2.85. the soil composition fractal dimension characteristics shall be the higher than other measures excluding bare land control plot indicating that traditional planting has higher destruction rate than other measures thus is unfavorable for increasing of soil aggregates and soil composition stability.The mean value of soil bulk density under different treatment measures of forest and grassland is1.42g·cm-3and it is smallest under Koelreuteria bipinnata+Cassia suffruticasa measure excluding bare land control plot while greatest under traditional planting in the10-30cm soil layer. The greater capillary porosity is, the greater the storage content of effective water in soil is. Under different treatment measures of forest and grassland, the capillary porosity of each soil layer shall increase to some extent than bare land control plot. Among which it shall increase to the highest extent under natural recovery. Closed forest measure shall take the second place while the traditional planting takes the last place. The greater the non-capillary porosity is, the permeability of soil shall be better and the rainfall storage shall be greater. Under different treatment measures of forest and grassland (excluding closed forest), non-capillary porosity of soil shall be bigger in10-20cm soil layer than that of0-10cm. and the rest shall reduce with the increasing of soil depth. Stronger declining of non-capillary porosity of soil shall appear in20-30cm soil layer.3. Under different treatment measures of forest and grassland the soil management process and soil property shall change to some extent and then the organic carbon shall change. The organic carbon content shall decrease with the increasing of soil depth and its indicator is changing. In vertical direction, there is relevance between organic carbon and soil depth and its indicators shall decline with the increasing of soil depth.According to the section, the organic carbon content has increased249.76%,207.24%,123.09%,57.12%,46.74%and39.54%in0-10cm layer under oelreuteria bipinnata+Cassia suffruticasa, hedgerows, closed forest, natural restoration, economic forest, traditional planting exceeded bare land control plot. And the organic carbon content has increased199.46%,153.08%,120.93%and13.94%in10-20cm layer under Koelreuteria bipinnata+Cassia suffruticasa, hedgerows, closed forest, natural restoration, economic forest, traditional planting exceeded bare land control plot.Under different treatment measures of forest and grassland the C/N ratio value shall decline with the increasing of soil depth and changes greatly in different soil layers. Generally, the highest C/N ratio appears in oelreuteria bipinnata+Cassia suffruticasa measure, the hedgerows measure takes the second place and the lowest ratio appears in traditional planting and bare land control plot.The organic carbon content in soil aggregates shall increase with the soil layer depth under different treatment measures of forest and grassland showing obvious change of gradient. The organic carbon content in soil aggregates is lowest in0-10cm soil layer under traditional planting and bare land control plot while that in20-30cm is obvious lower than that in0-20cm. and there is not obvious variation than that in0-20cm. In accordance with the relevant analysis with the water-stable aggregates>0.25mm under different treatment measures of forest and grassland with the organic carbon content, there is positive correlation relation between them and reached up to highly significant level.4. The active organic carbon content is in the order of Koelreuteria bipinnata+Cassia suffruticasa> hedgerows> closed forest> natural restoration> economic forest> traditional planting> bare land control plot. Under the same treatment measures of forest and grassland, the content of POC, ROC, DOC and MBC shall decline with the increasing soil depth among which the content of organic carbon and active organic carbon in0-10cm soil is significantly high than that in20-30cm soil.There is negative correlation relation between active organic carbon under different soil depth and soil erodibility K-factor indicating that soil property shall be changed via different treatment measures of forest and grassland which shall influence the resistance to corrosion of soil.5. According to the monitoring result of natural rainfall in field under the prevention and control measures of different forest and grassland during the whole year, the prevention and control measures of forest and grassland shall greatly influence the runoff erosion amount of sloping farmland via influencing rainfall erosion power. Among the prevention and control measures on forest and grassland, the greatest runoff and sediment appeared in bare land control plot while the smallest appear in the measure of Koelreuteria bipinnata+Cassia suffruticasa and hedgerow thus the obvious effect of water and soil reservation shall be obtained. There is positive correlation relationship between slope runoff erosion power expressed with peak flow modulus as well as runoff depth and erosion and sediment amount which means the runoff erosion power shall favorably imitate erosion power. Furthermore, the influence of different treatment measures of forest and grassland on erosion result expressed by runoff erosion power/volume shall be the index for assessment on regulatory effect of vegetation erosion power.6. In accordance with relevant analysis, analysis on main composition and path coefficient, there is certain relativity between active organic carbon composition and soil physicochemical indexes under different treatment measures of forest and grassland. Via main composition analysis it is assured that organic matter, available nitrogen, available phosphorus, C/N, unit weight, total porosity, capillary porosity, clay content, MWD and fractal dimension characteristics are the simplified soil physicochemical indexes under different treatment measures of forest and grassland. Furthermore, the analysis indicates that there indexes have great direct or indirect influence on active organic carbon, organic matter, total porosity and available nitrogen in four types of soil. |
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