| Soil magnetism is a new field of soil research and an important part of environmental magnetic.1980s, Soil magnetic introduced into China and development rapidly. Achieved a wealth of research results in magnetic characteristics of major soil types, soil magnetic geographic Variation of the evolution of magnetic minerals, magnetic response of the soil pollution, and rich research environment for information extraction of the weathering crust. Because the difference climatic, bedrock and parent material strong influenced, Tropical and subtropical regions have many soil types and is an important area of the soil magnetism in China. Weak magnetic bedrock in soils is widely distributed in the Karst Areas of Southwest. Because its magnetic the special nature of evolution, may provide an opportunity to reveal soil magnetic minerals in mechanism and access to environmental changes of southern China.At this stage are more concentrated in the non-human activities affect the soil types and their weathering crust magnetic, as well as the causes of the pollution of soil magnetic anomaly, few studies of human beings under strong disturbance to the soil causes the soil magnetic evolutionin this study as a starting point, the soil under different land use and development of a weak magnetic bedrock for the study, an attempt to understand this issue.This experiment gives the following tentative conclusion:(1) Degree of soil development in the study area is relatively low, overall in the stage of the rich ferromanganese soil under different land use patterns magnetic because into the soil in which environmental conditions are quite different, the magnetic susceptibility change as follows:limestone in soils:shrub> waste-grassland> dry land> forest land> abandoned land> paddy fields, the magnetic susceptibility values of changes of dolomite in soils:dry land> shrub> abandoned land> waste-grassland> forest land. Combination of field surveys and post analysis, the mode soil magnetic variations mainly due to human disturbance, use conversion, the difference of the water situation led to soil magnetic minerals, the content changes, soil magnetic changes with the corresponding soil development environment and soil the degree of development to correspond with each other.(2) According to the analysis of the magnetic minerals,0.1% of the sample by external pollution and human activities affect the abnormal magnetic variations to be removed, the frequency of the magnetic susceptibility and magnetic susceptibility values showed a significant correlation (y=10.21e0.2002x, R2=0.6315, n=98), Show that the strong interference of human activities, the different way the soil is still in line with the general rules of the process of weak magnetic bedrock in soils Fe-Al-soil magnetic maghemite contribution.(3) Paddy soils of the study area showed that the topsoil magnetic properties of rice fields exist with magnetic weakening of soil development and enhance the two processes, long-term flooding paddy soil, soil particle size decreases, the ferrimagnetic grains in the soil graduallyreductive dissolution of amorphous of soil magnetic contribution mainly composed of lepidocrocite, goethite or aluminum substitutes. Another case is the slow drying process of paddy soil, the decomposition of organic matter, free iron content, clay content increased, enhanced magnetic properties with soil development, a new ferrimagnetic minerals to produce. This phenomenon through the study of topsoil magnetic frequency magnetic susceptibility of 5% to distinguish between the former occurs in the case ofχfd>5%, while the latterχfd<5%.Secondary ferrimagnetic minerals in the dry land,χfd>5% of the soil magnetic mainly by the process of soil formation and occurrence of free iron oxide of control, performance gradually increased with the soil development of magnetic.χfd<5% of soil samples, due to human aging or deep plowing, soil magnetic exotic ferrimagnetic mineral and its oxides or needle iron ore aluminum isomorphous substitutes contributed. Abandoned land is mainly affected by soil magnetism as the combined effect of soil conditions and the process of soil, performance of the dry land abandonment with the increase in soil organic matter content, soil secondary iron oxide minerals increased with an increasing soil magnetism. Drying rice fields fallow soil moisture conditions gradually improved, showing the gradual activation of free iron oxide, newborn body of ferrimagnetic minerals to produce. waste-grassland type of soil gradually evolved, the above features are more obvious. Shrub more than in humans can not take advantage of bare rock, soil magnetic contribution to the secondary ferrous minerals by pedogenesis and reflect the degree of development of the study area as a whole soil magnetic. Plantation of the study area reflects the magnetic variation of the artificially strong disturbance of soil magnetic minerals in the soil pedogenesis formed ferrimagnetic minerals maghemite and magnetite may produce coarse-grained level even. Developed in the higher ground of the original woodland is little to show the magnetic evolution of the zonal soil into soil causes ferrimagnetic and antiferromagnetic minerals.(4) Soil burning experiments show that the study area, soil magnetic contribution of maghemite in the soil process, the long-term flooding of paddy soil lepidocrocite higher amount of lepidocrocite in the bamboo forest soil with poor drainage, Theχ-T Curve of contaminated soil samples, show the characteristics of Fe3O4.Different mode of soil E value of magnetic conversion rate better reflects the degree of soil "maghemite", the value of the magnetic conversion rate E is also applicable in the strong interference of the human soil. |
PDF Full Text Request