Soil Formation Rates And Its Regulation In Sichuan Basin

In the long geological epoch, soil is the near-surface natural medium which is developed by the weathering product of bedrock and all kinds of loose sediment (soil parent material) under physics, chemistry and the biological function. Because of climate, topography, time and human activities, and other external factors, which will affect the mother of weathering and the rate of soil formation, chronosequences vary greatly. To fix quantify the influence of time on the soil formation, namely the establishment of soil rate model, it seems simple but is actually very complex issue. In recent years, many scholars abroad were introduced the models into soil formation process, through quantitative model research the soil formation rates were more accurate. However, the model estimates required a combination of soil conditions, characteristics of the natural environment and the level of productive forces, in the determination of the need for more correction, it is need for more correction in the determination. Most previous studies described the pedogenesis from the natural conditions, but the impact of man-made on the soil formation process was usually neglected. This paper applies the quality of balance method, PROFILE model and Barth model to estimates the formation rates of the soil developed the purple parent materials in Sichuan Basin, then selects a suitable model of the purple soil formation. At the same time, it is determined the study area of man-made soil and mensurated the content elements in soil and its distribution. In this basis, it is analyzed the impact of the artificial perturbation on the soil formation rates and the taxonomy characteristic. The main achievements of this study are as follows:1. Three models are sensitive to external environment. The purple soil formation rates is 0.2115 keq ha^-1 a^-1 by the quality of balance method, is 0.1815 keq ha^-1 a^-1 by PROFILE model and is 2409.75 t km^-2 a^-1 by Barth model. The estimated results of the three models have certain relativity in the soil developed by J₂s, J₃p and J₃sn and have some difference in the soil developed by J₃zl and K₂j. It is because that the environment of soil formation rock is sensitivity to the choice of sampling site. The soil formation rate has very uncertainty and the error may reach 40%. It can only used in the soil individual, still can't use in the large-scale. Barth model required a combination of soil conditions, characteristics of the natural environment and the level of productive forces, in the determination of the need for more correction, it is need for more correction in the determination. The quality of balance method is more stable when the external environment condition was changed. So it is more suitable used in Sichuan basin.2. The relation of the soil character and the composing of parent rock elements are close. The distribution of K, Ca, Mg, Fe and other elements in Three Gorges Reservoir district are governed by the inheritance of parent rock. The difference of the parent rock elements caused the nutrient element content in soil. The results show that the ranking of the average contents of elements is that Si>Al>Fe>K>Mg>Ca>Na. The contents of Fe,Ca,Mg,Na,K are higher than the back-ground values of soil elements of China and the world, and A1 is intervenient, and Si is lower. It can be showed that the contents of Ca,Mg,K are the highest in the soil developed by limestone and are the lowest by sandstone. Among the soil developed by clastic rock, the contents of weathering elements developed by mudstone are higher than siltstone and sandstone. And it developed by siltstone is in the middle. The ranking of the leaching of parent rock is that: Ca>Mg>Al>Si>K>Fe>Na. Na is one of the lowest of them as the contents of Na in soil could be supplied by Na in parent materials. The degree of soil weathering in semi-tropical region could be not illustrated by CIA, CIW, A, B, ba, etc., calculated from the contents of weathering elements in soils. The silica-alumina molecular ratio and silica-sesquioxide molecular ratio of the fraction in soils on soil weathering are only used in at early developed soil, or at early weathering parent materials.3. After covering the soil, the migration of Ca and Fe is strong. The change of the soil physics structural causes the parent rock breaked and accelerates the soil formation rate. The ranking of the average contents of the soil formation elements is SiO₂> Al₂O₃> Fe₂O₃> K₂O> MgO> Na₂O> CaO. Compared with the soil background value in Three Gorges Reservoir Region, its Ca content was obviously low. This is mainly because that the soil is developed by the residual deopsit of J₂s and J₃p, its degree of the shower bath is strong. The migration degree of Fe was more obvious after imported the soil from other places.lt indicated that the change of the soil physics character mainly leaded to the leaching of Fe after the soil covering with other soil for melioration. At the same time, the soil leaching coefficient and soil formation rate have the better relevance. The soil density and volumeweight have certain extent reduction. Compared with before covering the soil, the porosity and the absorptivity have raised. After covering the soil, the grain content of The J₂s parent rock (<5mm)increased 5.70% and the content of grain (<2mm) increased 10.99%. But the J₃p parent rock was more obvious, they were increased 29.80% and 11.19%. The original arable land's surface has covered by the 10cm thick loose topsoil, so its hydrothermal condition has had the change, which was advantageous to the soil moisture infiltration, and can promote to supplement of the soil moisture. In addition, after covering the soil, it obtained good maintenance to the all-in-one of soil structure, which has the decisive function to the evaporation of soil moisture. Therefore, we can see that thickness of soil had increased and hydrothermal condition of soil had improved after human disturbance. That to accelerate the soil formation is the logical step of the process.In the genetics and in the diagnostics soil classification system, it does not have the detailed description of Anthrosol. But the research of Anthrosol many are the artificial cultivation, applies fertilizer, measures, irrigation and so on. But the influence is getting bigger and bigger along with the artificial function to the soil, the research is also very weak such as the industrial pollution soil, the filling soil, the industry and life solid trash and so on. So it is necessary to define the artificial soil and take enhances its research level. It can be provide the scientific basis for the evaluation of artificial soil, the engineering use and the environment improvement. It makes the contribution for the sustainable development of human society.