Taxonomic Classification Of Paddy Soil In Chongqing

With the development of soil science,soil classification is growing.Currently,the quantificational,standardized diagnostic classification had become the main stream of national soil classification.In China,the study of soil classification is still in the stage of which soil genetic classification dominated,and soil taxonomy develops rapidly.Since 1995,Chinese Soil Taxonomy(Revised proposal)had been published,soil researchers have done a lot of research on national and regional soil taxonomy,and have received a series of impressive achievement.The paddy soil in Chongqing is a type of soil genetic classification,so far,there is none report about the soil taxonomy of paddy soils.In order to break the backward and understand the type of paddy soil in Chongqing,the study selected 42 paddy soils as tested soils,to study the soil-forming environment,soil profile properties and physic-chemical characteristics,and based on the principle and method of Keys to Chinese Soil Taxonomy to determine the ascription,and the reference of soil genetic classification.This can accumulate the data of paddy soil in Chongqing,promoting and improving the work of soil taxonomy in Chongqing,providing scientific basis for rational utilization and evaluation of regional soil resources,and also providing reference data to perfect Soil Taxonomy.Here are the main results:(1)Paddy soil has changed the original soil appearance to a certain extent because of the effect of long-term hydroponic ripening.Soil parent material,topography,soil moisture and the influence of human activity make a great influence on the morphological characteristics and physicochemical properties of the paddy soil profile.The main source of the parent material of paddy soil in Chongqing are purple sand(paging)rock and limestone weathered residual and slope deposits.Most of the paddy soil profiles have the Plow bottom bccause of long maturation Hydroponics.The seasonal variation of water has a strong influence on the form and distribution of iron in soil.The main color of the soil profile is dark red brown,brown,brown,light brown,gray yellow orange and yellow turbid turbid.Most of the structure of paddy soil is large blocky and angular blocky.(2)According to Chinese Soil Taxonomy(3rd edition),forty-two tested Paddy soil profiles identified one diagnostic surface horizon: Fimic epipedon,three diagnostic subsurface horizons: Albic horizon,Cambic horizon and Hydragric horizon,eight diagnostic characteristics: Lithic contact,Paralithic contact,Soil moisture regimes,Gleyic features,Redox features,Soil temperature regimes,Ferric property and Calcaric property.(3)According to Chinese Soil Taxonomy(3rd edition),forty-two tested Paddy soil profiles were divided into three Orders: Anthrosols,Gleyosols and Cambosols,four Suborders: Stagnic Anthrosols,Orthic Gleyosols,Aquic Cambosols and Udic Cambosols,nine Group: Gleyi-Stagnic Anthrosols,Fe-leachi-Stagnic Anthrosols,Fe-accumuli-Stagnic Anthrosols,Hapli-Stagnic Anthrosols,Hapli-Orthic Gleyosols and Ochri-Aquic Cambosols,Acidi-Udic Cambosols,Ferri-Udic Cambosols and Hapli-Udic Cambosols,sixteen subgroup.The taxonomy of tested soils were determined according to Chinese Soil Taxonomy,and the references to Genetic Soil Classification,the results showed that,the sixteen subgroups in Chinese Soil Taxonomy was sorted into five subgroups and nineteen soil genus in Genetic Soil Classification.Because of the difference of the two classification system,the corresponding relationship between the same soil type is complex.Usually on the same class the Chinese Soil Taxnonmy has more soil types than Genetic Soil Classification of China.This is because Chinese Soil Taxnonmy take into account both the historical reasons of soil formation,and considering the differences in soil characteristics and properties caused by soil morphological development.(4)According to Criteria for Establishment of Soil Family and Soil Series in Chinese Soil Taxonomy,choosing the size of particles,mineral composition,pH,soil temperature as the basis of Soil Family,the forty-two typical tested Paddy soil profiles have been divided into thirty Soil Families.According to the characteristic of paddy soil profiles and the standard of Soil Series the parent material,soil layer arrangement,soil landscape location,soil profile thickness,the texture of surface soil,the depth and thickness of Gley and Illuviumrock,rock debris content,content of tuberculosis and intrusive body and the color of soil were selected as the basis of Soil Series.The forty-two typical tested Paddy soil profiles were divided into forty-two Soil Series.(5)Some simple thinking comes into being in the paddy soil system classification process.That a lot of paddy soil has the gleyic features from the surface at very first time causes the soil color present blue or gray green.Running up to the standard of iron infiltration in the gleyic anthrosols is not due to iron leaching,but the color of reductive iron,which makes the inaccurate situation in iron infiltration gleyic anthrosols might be retrieved.Therefore,it is suggested to revise iron infiltration sub horizon and increase the description relative to content of the lower.The surface texture is a highly stable natural attribute of soil and is of great influence to the forms of land utilization.In the soil series identification process,the surface soil texture is only divided into four categories as sand,loam,clay loam and clay.In view of its importance to productive practice,suggestions should be given that make the surface soil texture classified into 12 types in accordance with Soil Taxonomy.As a texture of soil which is stable and easily to identify,colors are suitable for use as the identification index of soil series,but the changes of colors are complex and individual difference.Facing to this situation,further studies are still needed on how to utilize colors appropriate to distinguish the soil series.