Classification And Reference Of Purple Soil In ST And WRB

Classification is an important way to understand natural things.Soil classification is the basis for soil evaluation,rational development and utilization of soil,exchange of soil science research results and transfer of regional soil production and management experience.Purple soil not only exists in China,but also widely distributed all over the world.However,due to historical inheritance and geographical limitations,different countries and regions have different names for purple soil,which makes it difficult to understand,use and improve purple soil internationally.As the most widely distributed soil type in Chongqing,purple soil plays an important role in agricultural production.Therefore,clarifying the position of purple soil in Chongqing in international soil classification and establishing the reference between different classification systems will help to promote the process of quantitative classification of purple soil and provide data reference for further improving Chinese Soil Taxonomy.In this paper,field soil surveys were conducted to specify 41 soil profiles of the purple soils in Chongqing,and obtain soil-forming conditions and soil morphological characteristics of the profiles.Soil samples were collected from the profiles by horizon for analysis of physical and chemical properties.According to the classification principles and methods of Soil Taxonomy(ST)and World Reference Base for Soil Resource(WRB),the tested soils was attributed in ST and WRB level by level,and the references between ST,WRB and CST were established for purple soils at the subgroup level.The main conclusions are as follows:(1)Based on the analysis of the soil-forming environment,profile morphological characteristics and physicochemical properties of the tested soils,the differences in topography,parent material,elevation and human activities have great influence during the development of purple soil.The altitude distribution of the soil samples ranged from224 to 1027 m,and most of the tested soil profiles were developed into cultivated land.The texture of the tested soils varied greatly,and the gravel content of some soils was high.The hue of purple soil is 2.5 R?2.5 Y.The hue of soil in most sections is basically the same as that of parent rock.Only a few sections are affected by the soil forming environment,and the hue of soil is significantly different from that of parent rock.The contents of organic carbon,total nitrogen and total phosphorus in the surface layer of the tested soil were higher than those in the surface layer,but there was no significant difference in total potassium.There were significant differences in p H,Ca CO₃ equivalent content and lime reaction among different soil profiles.(2)According to Keys to Soil Taxonomy(Twelfth Edition,2014),four diagnostic horizons,including ochric epipedon,albic horizon,argillic horizon and cambic horizon,and five diagnostic characteristics,including abrupt textural change,free carbonates,paralithic contact,soil moisture regimes and soil temperature regimes,were identified in the 41 soil profiles.And the 41 purple soil profiles were sorted into 3 soil orders(Alfisols,Inceptisols and Entisols),3 soil suborders(Udalfs,Udepts and Orthents),4soil great groups(Hapludalfs,Eutrudepts,Dystrudepts and Udorthents),8 soil subgroups(Ultic Hapludalfs,Typic Hapludalfs,Aquic Dystric Eutrudepts,Arenic Eutrudepts,Dystric Eutrudepts,Typic Eutrudepts,Typic Dystrudepts and Typic Udorthents).Topography,altitude and parent rock are important factors affecting the classification of purple soil in ST.(3)According to World Reference Base for Soil Resources(2015),four diagnostic horizons,including argic horizon,cambic horizon,ferric horizon and hortic horizon,and five diagnostic properties and materials,including Abrupt textural difference,continuous rock,stagnic properties,albic material and calcaric material,were diagnosed for the tested soil profiles.And the 41 tested soil profiles were sorted 4 reference soil groups(Anthrosols,Luvisols,Cambisols and Regosols).In the second level,each tested soil profile has its own a set of principal and supplementary qualifiers.Among them,the principal qualifiers are leptic,skeletic,calcaric,dystric/eutric,and the supplementary qualifiers are aric,loamic,ochric,ferric,etc.The 41 tested soil profiles were classified into 28 secondary units.Topography,altitude,human activities and parent material are important factors affecting the attribution of purple soil in WRB.(4)According to the attribution reference of purple soil in CST,STand WRB,it can be seen that purple soil has its own characteristics in each systematic classification,but there are also similar parts.The main part,especially the soil order,can basically correspond one by one,and some diagnostic indexes are similar,which indicates that the soil classification of purple soil tends to be unified in international exchanges.However,CST and WRB pay more attention to the impact of human activities on soil classification than St.both of them have anthropogenic soil classes.At the same time,in the lower level of taxon,the classification of purple soil is higher.In addition,the classification results of purple soil in soil systematic classification and numerical classification are both identical and different.When numerical classification is applied to soil classification,the key to correct soil classification is to select appropriate soil index.