| Soil, near-surface natural medium, developed from weathering products of bedrocks and loose sediments (soil parent material) by physical chemistry and biological function in long geological epoch. So, soils are a non-renewable resource on a human time scale. Human activities are responsible for a huge amount of soil damage through soil compaction and sealing, erosion, salinisation, acidification, pollution, and other impacts. In addition, agricultural and other land use practices and climate global change will also affect soil evolution. If we want to be able to adapt reasonable practices (and other land use and management activities) to protect soil, ones need to be able to predict the impact of such practices, and of environmental change on soil evolution. Meanwhile, as a complex system composed of a set of interconnected physical, chemical and biological factors that function as a whole, the researches of soil formation and pedogenises is still a challenge for soil scientists. And only a little research has been devoted to studying pedogenises. In recently, researches on science of soil formation have been focus on qualitative description converted to quantitative and modeling. Considered on the complex of soil system, soil scientists have experimented with the application of modern mathematical and statistical models to its quantification, but the researches is still little and incomplete. Thus, taken soil basic properties, major elements, landform characteristic, and land use types as object, the formation and evolution of profile in Sichuan basin and chemical weathering degree and transfer of major elements in the Three Gorges Reservoir Area was studied by Al2O3-CN-K2O map (or chemical index) and mass balance model. Based on that, the pedogensise in landscape was recognized and expressed combined with parent material types, landform characteristic, and land use types. The main results showed as follows:1. The distribution and transfer of major elements in soil profile:formation and evolutionBased on the distribution of soil basic properties and major elements content, the soil chemical weathering degree was studied by Al2O3-CN-K2O weathering trend map. In profile of SCSI 1, the properties of A and AB layer were different to that of BC and C layer. If taken A and AB layer (or BC and C layer) as whole, the well characteristic of soil evolution was observed. Thus, we can confer that the SCSI 1 profile was constituted of two independent soil profiles, due to burying by dilapidation and land slide or artificial earthing. In profile of SCSI 2,3,6,9,11, and 14, the properties in A, B (AC or BC) and C layer were similar, but the chemical weathering degree in surface layer was weaken than that below, which was considered as the inversion of soil profile. Considered the landform and erosion status of this area and the quickly weathering of purple rock, it couldn't be a converted profile and the most possible was the synthesized results of continuous supplying of weathering residues from parent material and the erosion in surface layer. In profile of SCSI4,7,12, and 13, these were in the process of normal evolution due to the content of Ti. But considered by other soil properties, the weathering degree in C layer was stronger than that in above. If no other parent material mixed, the mostly possible process, cause this phenomenon, was the effect of groundwater. In profile of SCSI 5 and 10, no obvious difference was found among soil basic properties and major elements content and has no consistent distribution trend, the thickness of A layer was relatively less, no significant weathering difference, and pedogensis characteristic was not obvious. In profile of SCSI 15, the illuvial layer was observed in the 33～55 cm depth, with Fe-Mn colloid material, and weathering degree was stronger and the difference among layers was little, which suggested that these profiles was affected by human activities. Meanwhile, the results, which came from the mass balance model, showed that the element was lost in profile of SCSI 1,2, 3,8,9,13, and 14 and enriched in profile of SCSI 4,5,6,10, and 12. The main losing source was Ca in profile of SCSI 1, Al and Fe in profile of SCSI 9, Si in profile of SCSI 13 and 14, and Si, Al, and Fe in the other profile. The main enriching element was Si in profile of SCSI 4,5,6,10, and 15 and Al and Fe for profile of SCSI 12. To certain extent, the distribution of soil properties and ratio among major elements can reflect the formation and evolution, and the results also suggested that the soil profile was influenced by climate and human activities.2. Pedogensis in landscape:the spatial distribution of major elements and chemical weatheringIn the Three Gorges Reservoir Area, the soil contained at mean of 63.13% SiO2,14.34% Al2O3, 5.13% Fe2O3,2.54% K2O,2.52% CaO,1.92% MgO,1.05% Na2O, and 4410 mg·kg-1Ti. The spatial distribution of Si/Al, Si/Fe, and Si/R2O3 in surface soil layer was similar, with relatively higher value in north of Quma basin, Hongyan basin, a part region of Xinmiao basin and Choushou basin, and anticline region in study area, and relatively lower value in the Wushan old strata, a part of Fuling old strata and the riverside in range of Yunyang to Wanzhou, which indicated the enrich of Al in these regions. The spatial distribution of CIA and PWI of surface soil layer also was similar, with distributed in cincture, and the CIA and PWI value in the riverside of Yangtze River was lower than that in the other region. The results also indicated that the weathering degree was strongest in Fengjie and Yunyun region, and followed by in part region of Xinmiao basin and Hongyan basin, which suggested the losing of Ca, Mg, K, and Na was much severely.The bedrock underlying in study area contained at mean of 62.49% SiO2,14.15% Al2O3,5.25% Fe2O3,2.60% K2O,1.65% CaO,1.76% MgO,1.09% Na2O, and 4807 mg·kg-1Ti. The spatial distribution of Si/Al, Si/Fe, and Si/R2O3 was similar, with relatively higher value in a part region of Quma basin and Xinmiao basin, and relatively lower value in the Wushan old strata, a part of Fuling old strata. The spatial distribution of CIA and PWI of surface soil layer also was similar, with distributed in cincture. The results showed that the chemical weathering degree was relatively lower in south of Yuyang basin, Wushan old strata, and a part region of Fuling basin and higher in Quma basin, a part region of Xinmiao basin, and anticline region in study area.However, the chemical weathering degree in the Three Gorges Reservoir area was low. In addition, the chemical weathering degree of soil in some region of study area was even weaker than that of bedrock underlying, with the ratio of 77.39% in acreage from the results of CIA. This may due to the complex of parent material and landform. The type of parent material in this region mainly was mudstone, sandstone, and shale, which means that the activities of geological hazard such as debris flow, dilapidation, and land slide in this region would happen more frequently and that induced the parent material were complex, which mean the soil may be developed from many different parent materials. Meanwhile, the human activities also influenced soil chemical weathering and severely caused soil erosion and lose.The results of mass balance model showed that only the mass of Mn was lost in soil except that developed from J1Z-2X strata. From the ratio of the mass change of each element to total mass change, the Si took the main part, followed by Fe and Ca. The Mtotal was similar among soils developed from different strata, with the value in the range from 4.55 to 7.87 kg·m-2, but the significant difference was found among each element. In whole, the MSiO2 and MCaO were the main source for the change of mass in pedon, particularly in soil developed from T1f/T1d/T1j. Although the linear relationships was observed between the mass change of each element and landform parameters (such as elevation and slope in soil developed from J3p strata, plan curvature and elevation), the relationship between them most possible was nonlinear correlation due to the complex of landform which induced the severely erosion and dilapidation and vertical mixed.3. Pedogensis in landscape:soil carbonThe soil contained at the mean of 1.06% of total carbon with in range from 0.19% to 12.95%, 0.46% of organic carbon with in range from 0.08% to 1.91%, and 0.60% of inorganic carbon with in range from 0.02% to 12.27%. The spatial distribution of soil total carbon and inorganic carbon was similar, with the relatively higher content in Wushan and Fuling old strata and lower content in Wuzhou basin. The content of soil organic carbon was low in the study area (less than 1%) and relatively higher in Hongyan basin, Fuling old strata and anticline region of Tiefeng Mountain to Tongcun. The content of soil carbon was influenced by soil parent material types. In soil developed from P and T strata, the content of total carbon and inorganic carbon was higher than that in soil developed from J. The content of organic carbon in soil developed from T2b/T2l was obvious higher than that in soil developed from other T strata. There were strong relationship between chemical weathering degree and content of total carbon, organic carbon, and inorganic carbon and these relationships were connect to parent material types. The content of total carbon and inorganic carbon had negative relationship with chemical weathering degree, and the content of organic carbon had no nearly relationship with that. It indicated that soil total carbon and inorganic carbon mainly influenced by environment factors such as parent martial and organic carbon may impact by human activities. In landform parameters, the elevation was the most important factor. Except in soil developed from P strata, the content of total carbon and inorganic carbon was had significant relationship with elevation in soil developed from the other strata. To certain extent, the content of total carbon, organic carbon and inorganic carbon were influenced by the other landform parameters such as slope, aspect, and topographic wetness index. For organic carbon, its content had no definitely relationship with landform, which suggested that landform was a possible factor but not a main factor. The content of soil total carbon and inorganic carbon was obvious different among land use types in total, but was no significant difference of that among soils developed from different stratum. In conclusion, the content and spatial distribution of soil carbon is the integrated results of parent material, landform, human activities, and so on.4. Weathering and landscape evolutionThe instability principle holds for numerous geomorphic systems or processes. The unstable growth of any geomorphic phenomenon is finite. Geomorphic instability is thus inherently limited by scale and, at certain spatiotemporal scales, any given instability phenomenon may be absent or irrelevant. Because instabilities occur at a range of spatiotemporal scales from the microscopic and instantaneous to planetary and geological, stability and instability are emergent properties that come and go as scales and resolutions are changed. With respect to weathering and its relationship to landform and landscape evolution, certain ranges of spatiotemporal scale can be identified where either stability or instability is likely. At other scales, stability will be contingent on a specific relationship; e.g., the strength of feedbacks between weathering and erosion. Weathering systems at the local/regolith, landscape unit, and landscape scales as defined here are likely to be unstable under most circumstances. At the hillslope scale and under certain circumstances at intermediate spatial scales more generally, stability is possible if weathering-erosion feedbacks are weak compared to external controls on weathering and erosion rates, while instability is likely if the feedbacks are strong. At certain broad scales or in certain situations, stability may be assumed. The distinction between external controls and intrinsic system components, of course, varies with scale.To sum up, the possible evolution processes of pedon in Sichuan basin was discussed by illustrating soil basic properties and major elements and the recognition and expression of pedogenises in landscape was through by the spatial distribution of major elements, chemical weathering, and soil carbon. It conduced to enrich or improve the mechanism of pedogenises in landscape, and also can provide scientific base for improving arable quality and constructing 3D soil map. But in this study, the most was the discussion in cognition and paid little effort to specific pedogensis processes. If to better know the pedogensis in landscape, the specific pedogensis process under particularly environment or human practices should pay more attention.
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