The Characteristics Of Soil Genesis And Taxonomy Of Yellow Soil In Chongqing

Soils played an important part in the production and life of humans,and soil taxonomy was of significant to the recognization of the physical-chemical properties and fertilizer supply capacity of soils.After long-term development of soil science,the Chinese Soil Taxonomy which depended on quantification and standardization had become the main stream.Nowadays,our country was still in the stage of the Chinese Soil Genetic Classification dominate in soil classification system,and meanwhile the Chinese Soil Taxonomy developed rapidly.From now on,the compilation work of Soil Series of China was in the process of development which was led by Institute of Soil Science,Chinese Academy of Sciences.The workers of soil science from some provinces had deeply studied some kinds of soils,and great achievement had been made.There are large area of zonal soil—yellow soil distributed in Chongqing,and little studies were about this period.In order to make up the shortfall,and gain the full understanding of this kind of soil,from the point of Soil Genetic Classification,15typical yellow soil profile was selected in Chongqing as objects,and the soil-forming environment,the morphological characteristics,the physical-chemical properties were studied,depending on the typical principle of Chinese Soil Taxonomy,the retrieval of higher category partition and the basic taxon level was executed.The soil series were built,and the reference between Chinese Soil Genetic Classification and Chinese Soil Taxonomy in different level was studied,in order to deeply explore the location of Chinese Soil Taxonomy of yellow soil in Chongqing,and meanwhile,according to the analysis of physical-chemical properties,the study could comprehend the iconic soil-forming process of yellow soil in Chongqing,which could be used to judge whether the soils were typical or not.These series of research could supplement the productive data of yellow soil in Chongqing,which could lay a foundation for Chinese Soil Taxonomy to be in line with the world,and could also provide basis for the further improvement of Chinese Soil Taxonomy.Followed by the main results:?1?The parental material types of typical yellow soil in Chongqing were quite diverse,here as followed:sediment of Qp;weathered residual sediment of sandstone of T₃x;weathered slope deposits of shale of O;weathered residual sediment of slate of Qb;weathered residual sediment of dolomite,slate and sandstone;weathered residual sediment of yellow sandstone of J₂xt;weathered residual sediment of yellow sandstone of J₂s;weathered residual sediment of flint limestone of?;weathered residual sediment of purple sandstone of J₂s.And in Chongqing,the altitude of tested yellow soil profile was distributed among 200 m to 1200 m,but mostly distributed in the range of 400-800m.The land use was mostly dry land,there were woodland and wasteland,too.The color of soils was mostly yellow or yellowish brown.The structure was mostly granular of lump,only one profile of structure was prismatic.The new growth included Argillan,Humus film and Ferromanganese markings.The soil texture ranged from sandy to clay.According to the analysis of chemical properties,the pH of were low,which were between acidic to neutral.The content of SOC were high,the C/N of surface soil ranged from 8-10,only the C/N of Y15 was lowest,the reason might be that the profile had been changed from paddy field to dry land,the strong drying-wetting actions decreased the soil SOC content,but CEC of this profile was higher,this might because that after the drying-wetting actions,the soil had been abandoned,which meant that the natural vegetation could quickly restore the productivity of topsoil,compared with SOC,CEC was more sensitive to soil fertility.?2?According to the analysis of SiO₂/Al₂O₃,the yellow soils whose parental material were limestone,J₂?especially the J₂xt and J₃p?and sandstone of T₃x distributed in the lower altitude had experienced Desilication and Aluminization,and the yellow soil which developed from sandstone of T₃x distributed in the higher altitude?more than 1200 m?,because of the high altitude,they could not reach to the proper Hydrothermal condition,and there were no Desilication and Aluminization occurred in the soils.And the Desilication and Aluminization did not occurred in the soils developed from Qp,either,besides,these kind of soils mostly distributed in the lower altitude,usually distributed in the 200 m,which could not reach to the proper Hydrothermal condition,either.These two kinds of soils were not typical yellow soils.?3?According to the Keys to Chinese Soil Taxonomy?3rd edition?and Classification Standard of Soil Family and Soil Series,among the 15 tested soils,one diagnostic surface horizons of Ochric epidedon three diagnostic horizons of Glossic horizon,Cambic horizon and Argic horizon,nine diagnostic characteristics of Paralithic contact,Udic,Perudic,Stagnic and Aquic soil moisture regime,Redox features,Mesic and Thermic soil temperature regime,Humic property,Ferric property,Alic property,Glossic evidence,Eutric and Dystric Base saturation were found.And the 15 tested soils could be sorted into two Orders of Argosols and Cambosols,four Suborders of Perudic Argosols,Udic Argosols,Perudic Cambosols and Udic Cambosols,seven Group of Hapli-Perudic Argosols,Ferri-Udic Argosols,Stagni-Perudic Cambosols,Acidi-Peridoc Cambosols,Ali-Udic Cambosols,Ferri-Udic Cambosols and Hapli-Udic Cambosols,eight Subgroup of Alic Hapli-Perudic Argosols,Mottlic Ferri-Udic Argosols,Albic Ferri-Udic Argosols,Typic Stagni-Perudic Cambosols,Ferric Acidi-Peridoc Cambosols,Xanthic Ali-Udic Cambosols,Typic Ferri-Udic Cambosols and Typic Hapli-Udic Cambosols.15 soil families and 15 soil series.?4?According to the reference of Chinese Soil Genetic Classification and Chinese Soil Taxonomy,there were no one-to-one correspondence between them,the yellow soil subgroup of Chinese Soil Genetic Classification corresponded to 4 subgroup of Chinese Soil Taxonomy,and 9 soil species of Chinese Soil Genetic Classification corresponded to 15 soil series of Chinese Soil Taxonomy,which meant that Chinese Soil Taxonomy had higher discrimination,and could also avoid the same name contrasted to the different soil type or the same soil type contrasted to the different name.But Chinese Soil Taxonomy had its own disadvantages,the naming method was complex,especially the name of soil families,meanwhile,this naming method was beneficial for the English description,which could promote the international exchange of soil information.