Evaluation Of Morphological Characteristics Development And Taxonomy Of Karst Soil Profile In Hunan Province

This essay,taking advantage of the project of "soil series survey and compilation of soil flora in Hunan Province",thirty two soil profiles(twenty one representative dry land soil profiles and eleven paddy soil profiles)developed from calcareous rock were selected in the karst area of Hunan Province.Based on the study on the soil forming environment,profile morphological characteristics description and analysis,indoor physical and chemical analysis and other steps,the soil development index was used to explore the differences of profile morphological development degree of different karst soils,and compared the soil color of dry land and paddy soil,then according to the Chinese Soil Taxonomy(Third Edition),ascertain the attribution of the thirty two soil in Chinese soil taxonomy.This study in theory can be provided a scientific basis for a comprehensive understanding of the occurrence and development process of karst soil and the sustainable utilization of karst soil in Hunan Province,and to verify,supplement and improve the current China’s karst soil systematic classification system.The main results are as follows:(1)From the perspective of soil morphological characteristics,the collected soil was generally thick,and the soil profile was obviously differentiated.The dry land soil hue were mainly 10 YR,7.5YR and 5YR,and the color of the dry soil in the same profile section is relatively consistent;the section configuration was mostly A-B-C type;the soil surface structure was mainly massive and prismatic structure,and the middle and lower layers were mostly massive structure.The soil neovasites were mainly iron fierce stripes,clay glue film,iron manganese oxide glue film,etc.The color of paddy soil profile changed greatly,and the colors were mainly grayish yellow brown,turbid yellow orange,light yellow,etc.the soil hue were mainly 10 YR,7.5YR and 2.5Y.The structure of the paddy soil in the same profile is relatively consistent,mostly were massive or prismatic structure,clay film and iron manganese soil neovasites were commonly existed on the surface of paddy soil structure.(2)Quantitative analysis of soil morphological characteristics and soil development degree: the depth change of soil redness rating index(RR)profile was complex,which was greatly affected by soil parent material,the effect of desiliconisation and aluminum was weak,the differentiation regular pattern of paddy soil profile was not obvious,and the color change of soil profile was greatly affected by artificial Hydroponics.The soil profile depth change of hbrizon index(HI)was relatively steady,and the maximum value almost appeared on the soil surface,indicating that the soil pedogenesis was obvious on the surface,and the biological small cycle had an important impact on soil formation.In this study,weighted profile development index(WPDI)ranges from 0.55 to 0.81,dry land is generally larger than paddy field,and the overall profile development of paddy field soil is relatively poor.A series of changes in the morphology of the soil after flooding may occur in the dry land.The spatial distribution of WPDI index generally showed a decreasing trend from southern Hunan to central Hunan to Western Hunan,which was significantly positively correlated with the annual average temperature,annual average precipitation and annual average ground temperature at the sampling point,and significantly negatively correlated with altitude.The climate is relatively warm and humid,which is conducive to the development of morphological characteristics of karst soil profile.It is a simple method to quantitatively describe the development degree of soil profile.(3)According to "the Keys to Chinese soil taxonomy(third edition)",four diagnostic surfaces were retrieved in the study area(including moilc,umbric,ochric,hydroponic epipedons),and five diagnostic subsurface horizons: low activity iron rich layer,viscous layer,embryonic layer,hydroponic redox layer and cultivated sediment layer;totally 11 diagnostic characteristics were identified: lithological characteristics of carbonate rock,Incubation characteristics,calcareousness,quasi rocky contact surface,soil moisture status,redox characteristics,soil temperature status,humus characteristics,iron characteristics,aluminum phenomenon and calcareousness.Five soil classes were divided into leached soil class,rudimentary soil class,iron rich soil class,neodiagenetic soil class and artificial soil class.There were six subclasses: normally wet leached soil,wet leached soil,wet embryonic soil,wet iron rich soil,wet newly formed soil and hydroponic man-made soil.Thus,11 soil groups,18 subgrous,27 soil family,and 32 soil series are classified.(4)Comparing the soil development index results of the tested soils in soil taxonomy,it can objectively reflected the differences and similarities of the properties of karst soils in Hunan Province,but there were also some differences.Soil profile D18 was divided into neodiagenetic soil class.Compared with its soil development index,it is not the profile with the lowest degree of soil development.The HI and WPDI index is 0.61 and RR index is 4.The analysis showed that it may be related to the terrain of the sampling point was high hill and steep slope.Due to the influence of surface soil loss and underground leakage under the condition of slope,the soil here has the characteristics of thin soil layer and rapid renewal for a long time,so it showed the characteristics of young soil.The topographic position should be considered for the classification of soil system and soil class.