| It is one of hotspots in soil erosion researching that how soil erosion affects soil productivity. Generally, its main approach is affecting contents of soil organic matters and nutrient. Through measuring slope forms on the spot, serried sampling, physical and chemical analyzing, and measuring soil erosion from natural and artificial rainfalls, the project researched in the approaches and behaviors of soil erosion affecting contents of soil carbon and nutrient, and the law of soil carbon and nutrient distributing in micro-topographty under influences of soil erosion. In the same time, supported by Geographic Information System, models of soil carbon and nutrient changing with soil erosion have been built, and spatial processes of soil erosion affecting soil carbon and nutrient have been simulated, and annual and long-term changing of soil carbon and nutrient under impact of soil erosion have been estimated and forecasted, and synchronously, a elementary assessment for different soil erosion management has been performed by using the models built in the study. The main objectives of the study are illustrating behaviors, approaches and processes of soil erosion affecting contents of carbon and nutrient in soil, and simulating its dynamic changing in spatial scale, and providing a methods of estimating content changes of carbon and nutrient under the affluences of soil erosion to guide the practices of soil erosion control, management andprogramming.Knowledge and conclusions educed from the study are following: Firstly, actual behaviors of soil erosion on affecting soil quality have been described. Comparisons of landform measurements on the spots, and results of physical and chemical analyzing indicated that micro-iandform, proportions of soil particles sizes, and contents of soil carbon and nutrient have differences of spatial distribution under different conditions of fertilization development, cultivation, slope, and soil erosion management, which are closely related to intensities of soil erosion and sediment deposition.Secondly, approaches by which soil erosion affects soil quality have been illustrated and confirmed. Results of analysis indicated that, erosion increases correspondingly the particles (>0.2mm) of soil, while the particles (<0.02mm) correspondingly decreased. As the particles (<0.02mm) have enriched nutrient, the redistribution of carbon and nutrient is affected by erosion. Experiments of artificial rainfall showed that sediment is the main body of total nutrient loss and runoff is the main body of available nutrient loss when erosion is slight, but sediment become the main body of total and available nutrient synchronously while erosion is intense. Concentration of nutrient in runoff is most likely to be affected by concentration in topsoil. The higher concentration in topsoil is, the more possible nutrient loss by runoff is.Thirdly, present status of effect of erosion on soil carbon and nutrient has been illustrated in spatial scale of the watershed. Based on Geographic Information System, actuality and process of soil erosion in and between land units were simulated, and actuality and process of annual and long term changing of soil carbon and nutrient in each land unit under erosion were sufficiently calculated and illustrated. Results of simulation and illustration showed that, the relative area in which soil carbon, nitrogen, phosphorus and potassium is deceased is 44.1%, 55.8%, 39.2% and 75.7% respectively. All these results remedied the deficiency of spatial relationship in previous studies.Fourthly, critical value of erosive modulus, which may cause soil carbon and nutrient changing, has been taken. The results of simulation showed that different soil nutrient element(C, N, P, K) have different soil acceptable erosive modulus in different land use types. For example, in this study, the critical value for Nitrogen is located in the range of 1500-2000t/km2for forest land, 2000-2500 t/km2 for tillage land, 2500-3000 t/km2 for garden land, and 1000-1500 t/km2. for grassl... |
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