| The upper of Hanjiang River and Jialing River are located in the south of Qinling Mountains,which are the intersection of East Asian summer monsoon and winter monsoon in China,and the environmental change has unique regional characteristics.There is a large area of thick loess distributed in the basins of the upper of Hanjiang River and Jialing River,and the soil developed on loess is the main local soil resource.However,the degree of research on these soils is relatively low,and the existing data are mainly based on the study and elaboration of soil genetic classification,and the soil taxonomy is lack of due research.Lijiahe(LJH)and Yangjiashan(YJS)profiles were selected as typical loess parent materials in the upper of Hanjiang River and Jialing River.And their macro morphology,physical and chemical properties(chromaticity,magnetic susceptibility,loss on ignition(LOI),pH,CaCO3 and particle composition),aggregate,geochemistry and micro morphology were studied.On this basis,the differences of soil weathering and pedogenesis in different areas,and the status and attributes of soil in Chinese Soil Taxonomy were discussed deeply.Through systematic research,this paper obtains the following main understandings:(1)The parent soil of loess in the upper of Hanjiang River has an Ap-AB-Bt-C profile structure,while the loess parent soil in the upper of Jialing River has an A-AB-Bt-Bk-C profile structure.(2)The change trend of soil physical and chemical properties in the upper of Hanjiang River and Jialing River are very similar,in which a*,magnetic susceptibility and LOI show the characteristics of Bt(Bk)>A(Ap)?AB>C,while L*,b*and CaCO3 show the characteristics of A(Ap)?ABAl2O3(153.1 g·kg-1)Fe2O3(57.2 g·kg-1)>K2O(25.9 g·kg-1),and those in YJS profile in the upper of Jialing River are SiO2(542.6 g·kg-1)>Al2O3(124.3 g·kg-1)>Fe2O3(46.1 g·kg-1)>K2O(23.2 g·kg-1).The active elements in LJH profile were:MgO(18.2 g·kg-1)>CaO(10.2 g·kg-1)>Na2O(9.8 g·kg-1),and YJS profile were MgO(22 g·kg-1)>CaO(102.9 g·kg-1)>Na2O(12.7 g·kg-1),which was higher than the former,indicating that the soluble elements in LJH profile were deluged in large quantities.(4)The content of large aggregate in A layer of LJH profile(83.73%)was significantly higher than that of YJS section(69.72%),while that of Bt layer was slightly lower than that of the latter(71.27%),and the two profiles of C layer were close(59.18%,56.55%).Large aggregates with the size of>2,1?2 mm have stronger aggregation,which has a more important contribution to the maintenance of soil stability.Silt,organic matter,iron and aluminum oxides are important factors to promote the formation of soil macroaggregates and maintain their stability.(5)The coarse grains in LJH profile are mainly quartz and feldspar,while YJS profile contains a large number of secondary calcite and other unstable minerals.in LJH profile,the average grain size of each occurrence layer is Ap?AB>C>Bt,while YJS profile is A?AB>Bk>C>Bt.There are many types of pores in the Bt layer of LJH profile,and the pore walls are very smooth,with the dominant pore channels and pores;a large number of sedimentary clays strongly contaminated by iron and manganese oxides are developed,and more iron manganese agglomerates and iron manganese nodules are distributed.The pore morphology of Bt layer in YJS profile is irregular,and the pore wall is relatively rough;it is mainly residual clay,with a small amount of colloidal film and nuclear iron manganese oxides.(6)The characteristics of soil weathering in the upper of Hanjiang River and Jialing River are obviously different.The intensity of soil weathering in the former is significantly higher than that in the latter,which shows that the former experienced a moderate weathering process from the strong weathering of plagioclase to the micro enrichment of iron and aluminum elements,while the latter is in the late stage of weak weathering to the early stage of medium weathering.The K2O/Na2O(2.63),residual index(5.51)and CIA(71.73)of soil in LJH profile were higher than those in YJS profile(1.83,1.26,65.04),while the SiO2/(Fe2O3+Al2O3)(3.14)and leaching coefficient(0.3)were lower than those in YJS profile(3.18,1.12);The loss rate of Ca and Na in LJH profile is higher than that in YJS profile,and the clay minerals such as muscovite,montmorillonite and illite produced by weathering are more than those in YJS profile.(7)In the Chinese Soil Taxonomy,the position of soil in the two regions is different.In the middle of LJH profile(30?140 cm)and YJS profile(20?78 cm),there were Argic horizons(Bt).The clay content of the former(17.35%)is 9.05%higher than that of the leaching layer(8.3%),while that of the latter(13.64%)is 4.09%higher than that of the leaching layer(9.55%),so both of them are Argosols.There are a lot of clay film and ferromanganese film on the pore wall and structural plane of Bt layer in LJH profile,and iron-manganese nodules appear,which is consistent with the characteristics of claypan.Finally,it is classified as Eutric Claypani-Udic Argosols.There is a Calcic horizon(Bk)in the lower part of YJS profile(78?100 cm),and the content of CaCO3(202.78 g·kg-1)is 74.89 g·kg-1 more than that of overlying soil(127.89 g·kg-1),and finally belongs to Typic Calci-Ustic Argosols.Due to the different topography around the two profiles,there are differences in the influence of the East summer monsoon,so the pedogenic degree is different,forming different types of soil. |
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