Genetic Characteristics Of Stagnic Anthrosols And Their Taxonomic Implications In Hunan Province Of China

China is at a stage in which the Chinese Soil Genetic Classification System(CSGC)and Chinese Soil Taxonomy(CST)still coexist while gradually shifting to CST.Both classification systems are guided by the principles of soil genetics,and an in-depth study of soil genetic characteristics is conducive to a comprehensive understanding of the soil formation process and a reasonable classification in CST.Stagnic Anthrosols refer to the type of rice field soils in CST and correspond to Paddy soils in the CSGC.The aims of this study were to investigate the genetic characteristics in soils derived from different parent materials and to elucidate how parent materials and pedogenic environment affect the genetic characteristics and reveal the implications for pedogenetics and taxonomy in Stagnic Anthrosols.Our study selects paddy soils derived from granite(GR),plate shale(PS),quaternary red clays(QRC),limestone(LS),purple sandy shale(PSS)and fluvial-lacustrine deposits(FLD)in Hunan Province as research objects,to explore implications on pedogenetics and taxonomy of Stagnic Anthrosols from the perspective of profile morphological characteristics,cation exchange capacity,iron oxide form and its differentiation,and clay mineral characteristics.Main results are presented as follows:(1)In the soil profile tested in this study,Hapli-Stagnic Anthrosols(HSA)and Fe-accumulic-Stagnic Anthrosols(FSA)were the dominant types(soil group)of Stagnic Anthrosols in Hunan Province.There was less distribution of Gleyi-Stagnic Anthrosols(GSA),while Fe-Leachi-Stanic Anthrosols still has not yet been found.The types(soil group)of Stagnic Anthrosols derived from GR were mostly classified as FSA and GSA.Stagnic Anthrosols derived from PS and QRC were mostly divided into FSA;However,the soils derived from LS,PSS and FLD were mainly classified as HSA.FSA and GSA were primarily distributed in Hill-Mesoslope and Hill-Lower Slope,while HSA was distributed primarily in Hill-Bottom and Lacustrine plain-Low terrace.(2)The soils derived from GR,PS and QRC,which are mostly classified as FSA and GSA,are dominated by yellow-related colors(e.g.,dark yellowish-orange,light yellowish-brown,dark yellowish-brown,yellow-brown and etc.)in profile.In detail,the occurrence frequency and abundance(++++)of neogenesis(e.g.,cutans,streaks,nodules and etc.)in the Stagnic Anthrosols are the higher than LS,PSS and FLD;moreover,the exchangeable acidity(EA)content,the differentiation degree(Illuvial coefficient)of iron in the profile are generally higher than those of the Stagnic Anthrosols derived from the LS,PSS and FLD;the contents of 1:1 type kaolinite,vermiculite and illite/vermiculite(I/V)mixed layer mineral were dominantly distributed in GR,PS and QRC.However,the soils derived from LS,PSS and FLD were mainly classified as HSA.The genetic characteristics of Stagnic Anthrosols derived from LS,PSS and FLD generally showed the different trends:Red-related colors(e.g.,brown,dark brown,dark red-brown and etc.)of soil are generally found in the profiles;exchangeable bases(EB),and the differentiation degree(Illuvial coefficient)of iron in the profiles are higher and lower,respectively,and 2:1 type illite/smectite(I/S)mixed-layer mineral and chlorite were mainly observed in LS,PSS and FLD.The differences in genetic characteristics are related to the physicochemical properties(e.g.,p H,sand,silt and organic carbon)of the parent materials.(3)The structure and tightness condition of soil in Anthrostagnic epipedon(Ap)is mostly acinose and loose respectively.The contents of K~+,EA,Fe_oand Fe_pwas substantially higher than that in the Hydragric horizon(Br).Under the influence of artificial seasonal submergence and drainage,the occurrence frequency and abundance(++++)in neogenesis,the contents of the base saturation(BSP),Fe_t,Fe_dand Fe_cin Hydragric horizon(Br)was significantly higher than that of the Anthraquic epipedon(Ap).(4)The genetic characteristics of Stagnic Anthrosols are closely related to the type of parent materials and artificial farming,and show differences in various soil groups and diagnostic horizons.Studying on the soil particle size distribution and p H and deepening its quantitative research could improve the criteria of soil family in CST.In-depth quantitative analysis on the micromorphology,occurrence frequency and abundance of the neogenesis in the Hydragric horizon was significant to improve the criteria of soil suborder within the soil group of Stagnic Anthrosols as per CST.Cation exchange capacity can provide a reference of the lower categories of taxonomic classification for production performance in CST.The illuvial coefficient was a good indicator to distinguish the degree of profile differentiation and the development degree and soil-forming environment.It has better indication significance on the genetic taxonomic for Stagnic Anthrosols.The types and quantities of clay minerals can better reflect the direction and extent of development of Stagnic Anthrosols and can be used as one of the bases for the classification of soil group and subgroup within the soil family of Stagnic Anthrosols as per CST.