The Comparison And Classification Of The Properties Of The Soil Developed From Basalt Pyroclastic Material Under Different Soil Forming Environments

The evolution of pyroclastic soil properties has a unique rule,and the diagnostic criteria of different soil system classification systems are different.Basaltic pyroclastic material is mainly composed of basic plagioclase and pyroxene with weak weathering resistance,which is a good material for studying soil genesis and development.The soil samples in this study are from Kuandian,Liaoning Province and Dalai Nur,Inner Mongolia Province.Based on the thoroughly studied of the morphological characteristics,physical and chemical properties and mineralogical composition of the soil samples,the evolution laws of the genetic characteristics of the soils developed by basaltic pyroclastics are analyzed and compared,and judged according to classification standards of different soil systems,compared the results.Research shows:?1?The development soil of basaltic pyroclastic materials has the following common points: with the soil depth increasing,the volume and content of the volcanic debris increase;with the soil depth increasing,the color of the soil changes from deep to shallow;with the increasing of the degree of weathering,the content of small gravel increases and the content of large gravel decreases;the major elements in each profile are SiO₂?Fe₂O₃?Al₂O₃,and alkaline earth metals occur certain leaching loss;with the profile depth increasing,the soil pH?H₂O?increased gradually,the organic carbon decreased gradually,the CEC₇ value decreases,the phosphate absorption first increases and then decreases,reaching the maximum value in layer B;the exchangeable base of soil in the test profile is mainly Ca²⁺,followed by Mg²⁺,K⁺ content is in the third place,and Na⁺ content is the least;the mineral of primary soil in each profile are mainly volcanic glass,and with the increase of soil development degree,it decreases gradually,all these profiles contain quartz,pyroxene,olivine and amphibole;the content of quartz in soil increases with the increase of soil development;the secondary clay minerals include illite,kaolinite,halloysite and boehmite.?2?Compared with the humid climate area,the content of volcanic debris in the arid climate area is less and the particle size is smaller,which shows that the content of large particles and stones is less,and the content of small particles gravel is more;the content of soil that less than 2mm fraction is more,and the content of sand is less,the content of silt and clay is more,and the soil type changes from sand to loam;the sand particles are generally sub round and sub angular,which are smoother than those in the arid climate area,and the number of pores on the surface is reduced,the diameter is smaller,more particles are weathered,iron oxide appears,more quartz is formed by devitrification,and the distribution is wider;the soil structure is relatively mature,the adhesion and plasticity are stronger,the soil becomes acidic,the phosphate absorption capacity is much higher than that in the arid area,the base saturation is lower,and the calcium carbonate in the soil is basically leached out,free iron oxide?Fe_d?is higher than that in the arid area,indicating that it is more weathered and developed,and amorphous iron oxide?Fe_o?is higher than that in the arid area,indicating that the organic matter content is increased,and amorphous iron mainly exists in the form of iron humus complex,rather than in the form of pyrite;the loss of Na,Ca,Mg,K increased,the loss of Si occurred,and the enrichment of Fe and Al is higher;the coefficient of weathering eluviation?ba?is lower and the chemical index of alteration?CIA?is higher,which is in the middle stage of weathering,and the weathering degree is higher than that in the arid area;the content of primary mineral volcanic glass decreased,the content of plagioclase and pyroxene decreased,quartz appeared in each layer and the content increased;the content of kaolinite in clay minerals increased,a small amount of hydroxy aluminum vermiculite appears,the content of boehmite increased,and the content and types of clay minerals increased.In a word,the soils developed from the basalt volcaniclastic materials with similar soil forming time,the development degree of humid climate area is stronger than that of arid climate area.?3?Compared with the long soil forming time area,the content of volcanic debris in the area with short soil forming time is very little,which shows that there are no stones,less large particles and more small particles;the content of soil that less than 2mm fraction is much more than that of the area with short soil forming time,the content of sand is less,the content of silt and clay is more,especially the clay part,the soil type is transformed from loam to silty clay loam,silty clay,silty loam and clay;the sand grains are from sub round to sub round-sub angular,almost without edges and corners,with almost no pores on the surface,more iron oxide and rich quartz formed by devitrification;The soil structure is more mature,the adhesion and plasticity are stronger,the soil acidity is enhanced,the phosphate holding capacity is reduced,and the base saturation is increased,the Fe_d is higher than that in the area with short soil forming time,indicating that the weathering is stronger and the development degree is higher,Fe_o is higher indicating the increase of organic matter content,the main amorphous iron in this area is pyrite,which is different from that in the area with short soil forming time;the loss of K,Ca,Na,Mg is more,Si loss a lot,Fe and Al in the soil are highly enriched,and the enrichment rate tends to be stable;the ba value is lower,the CIA index is higher,it is in the late stage of weathering,and the degree of weathering is higher than that in the area with short soil forming time;the volcanic glass content of the primary mineral in the soil decreased,there was no plagioclase or pyroxene,and the quartz content increased;The content of kaolinite in clay minerals increased,the content of hydroxy aluminum vermiculite disappeared,mica and pyrite appeared,the content of boehmite decreased,and the content and types of clay minerals increased.In a word,for the soils with similar soil forming climate,the development degree of the areas with long soil forming time is stronger than that the areas with short soil forming time.?4?The soils developed from pyroclastic materials were searched by three different soil system classification standards: Keys to Soil Taxonomy?KST?,World Reference Base for Soil Resources?WRB?and Keys to Chinese Soil Taxonomy?Third Edition??CST?.The results are as follows: the soils in arid climate area do not conform to Andisols under the retrieval of KST,WRB and CST standard: in humid climate area,the soil with relatively short soil forming time meets the Andisols standard under the retrieval of KST,WRB and CST,while the soil with relatively long soil forming time only meets the Andisols standard under the retrieval of WRB.It shows that retrieval results of different classification standards are different.In view of the fact that the content of Andisols in CST retrieval is relatively lagging behind,the expression of diagnostic standard language is not concise enough,the drawings are insufficient,and it is difficult to apply in practice,it is suggested that the quantitative standard of Andic soil properties in CST should be revised with reference to KST version 12.