Study On The Characteristics Of Soil Iron Morphology And Its Relationship With Soil Magnetism In Dadugang, Xishuangbanna

Iron is abundant in the earth's crust.Iron in the soil exists in many forms,such as oxides,hydroxides and hydrates.The activity of iron oxide in soil is strong,and it is easy to be affected by various factors to change its form.It can record many kin ds of information such as soil forming conditions,climate change and land use change.Iron oxide in soil is also an important adsorbent,which is closely related to soil carbon cycle and the migration of soil pollutants.The type and content of iron oxide minerals in iron oxides are also the determinants of soil magnetism.Therefore,it is of great significance to study the morphological characteristics of iron oxide in soil,its influencing factors and its relationship with magnetism.In this paper,16 so il profiles of Dadugang tea garden,cornfield and forest in Xishuangbanna were collected,the depth of profile was 140cm,and 176 samples were collected.The total iron content,free iron content and active iron content of the samples were measured.The fr ee degree,active iron content and active iron content of the samples were calculated.The low-frequency magnetic susceptibility,frequency magnetic susceptibility and non hysteresis remanence magnetic susceptibility were measured Three kinds of soil magnetic parameters,TOC,p H,WC,BD,EC and 10 kinds of major chemical elements were measured.In this paper,the profile characteristics of various forms of iron were analyzed in detail,and the effects of soil physical and chemical properties on soil iron oxides and the relationship between various forms of iron oxides and soil susceptibility were analyzed by correlation analysis,multiple linear regression,systematic clustering and principal component analysis.The main results and understandings are as follows:(1)The average values of total iron,free iron and active iron Fe _o in tea garden,corn field and forest were similar,but the vertical distribution characteristics of different forms of iron between profiles were quite different.The total iron,free iron and free degree of most soil profiles increased slowly with the in crease of soil depth,and the profiles located at the foot of slope and local depression decreased with the increase of soil depth.The differences of their contents between profiles are mainly affected by the parent material and the degree of soil develop ment.The active iron and the degree of activation of the soil are larger in the surface layer,and decrease with the increase of soil depth,and finally tend to be stable.The total iron content,free iron content and free degree of soil in 0-30cm layer increased with the change of corn field or tea garden.(2)The main related factors of Fe_t content are the content of Sa and P,the secondary related factors are the content of TOC,p H,TN,Ti,Zr and S in soil;the main related factors of Fe_d content are Ti,P and Sa,the secondary related factors are TOC,TN,p H,S and weathering leaching coefficient ba;the main related factors of Fe_o content are TN,BD,WC and S,and the secondary correlation factors were TOC,EC and P.(3)The correlation between Fe_t,Fe_d and soil low frequency susceptibility?_lf,frequency susceptibility?_{f d} and non hysteresis remanence susceptibility?_{A R M} was not significant,while Fe_o was positively correlated with all three susceptibility(P<0.01).And had a high coefficient of de termination R²,indicating that there were more weak crystalline ferromagnetic minerals in active iron in Dadu hillock soil of Xishuangbanna,and most of them are single domain,pseudo single domain and superparamagnetic particles.There was a significant positive correlation between soil activation degree(Fe_o/Fe_d)and?_lf,?_{f d} and?_{AR M}(P<0.01),while the correlation between soil free degree(Fe_d/Fe_t)and three magnetic susceptibility was poor,which indicated that the active iron content was the key factor to determine the magnetic strength of soil in the study area.(4)The contents of TOC,N,P,S and water content WC were positively correlated with Fe_o and?_lf(P<0.01),while BD was negatively correlated with Fe _oand?_lf(P<0.01).These parameters may affect the magnetic properties of soil by affecting the content of active iron in the soil.(5)The soil profile was divided into two groups by cluster analysis:group a and group b.The magnetic susceptibility of group b was significantly higher than that of group a.The relationship between?_lf,Fe_o and main physicochemical parameters of the two sections was analyzed by principal component analysis.The results showed that?_lf and Fe_o in group a were closely related to soil nutrient elements,weathering leaching and water content,while?_lf and Fe_o in group b were more closely related to each other.The possible mechanism of positive correlation was that N,TOC,P and S increased the magnetic susceptibility by promoting t he formation of Fe_o.