| Rocky desertification as land degradation processes typical karst area of southwest China, became the most prominent karst field of environmental issues and research focus by the party and the state and governments at all levels attach great importance, concerned with the research of many scholars, but also related to hotpot and difficulty of karst area of social and economic development and people’s lives. Due to the limitations of its study methods and means, the theoretical study of desertification and Countermeasures seriously out of line, so rocky desertification countermeasures far beyond its theoretical studies. Therefore, the application of new research methods for the exploration of karst rocky desertification area is of great significance.Study on soil magnetism is a new field of soil research, as an important part of the environmental magnetic, magnetic characteristics in our main soil types, soil magnetic geographical distribution law, made extensive research in China in the main soil types of soil magnetism magnetic characteristics, geographic distribution, soil magnetic minerals and evolution of modern city, soil pollution and air pollution, soil erosion and soil and water loss, the ancient environment and climate. Because of its unique climatic conditions, bedrock and parent material in tropical and subtropical areas, soil type is numerous, provide plenty of material for the study of soil magnetism, is an important regional soil magnetism research in china. At present, soil magnetism research focuses on the the strongly disturbed soil unaffected by human activities, as well as due to the problem of pollution caused by soil magnetic anomaly, less soil magnetic studies under intense disturbance of human activities. In this study, taking this as the breakthrough point, choose the tropical and subtropical karst rocky desertification area soil as research material, using magnetic analysis method, research in the area of soil magnetic variation, not only take advantage of the magnetic method of karst rocky desertification area research, will be doing an understanding of magnetic changes in the soil under the influence of human activities strongly.Through the research, preliminary draw the following conclusions:(1)Soil magnetism variation characteristics of studied area of rocky desertification in fallow for the overall performance of extraterrestrial, soil magnetic susceptibility increased with rocky desertification area of rocky desertification degree decreased, showing a tendency of negative correlation between the two, the study area pedogenesis in the initial stage, the formation of the ferromagnetic materials and less agglomeration. The soil magnetic susceptibility value is higher, basically in more than10%, indicating a higher degree of soil development in the study area, the SP particle content in the soil has a certain abundance, the overall changes of characteristics except for the extraterrestrial, rocky desertification area of soil magnetic susceptibility with rocky desertification degree decreased. This is consistent with the study area of soil magnetic susceptibility changes, there is obvious correlation between the two index, correlation coefficient R2=0.2058. The correlation is low, Showing that the soil frequency variations in the susceptibility of the study area may be affected by factors other than the degree of soil development, Strong human disturbance and dissolution. Changes in characteristics of the soil magnetic susceptibility can be reflected to some extent the degree of rocky desertification.(2)Soil properties of the study area indicators findings, in the region, soil particles finer particles of clay content component is much higher than the coarser particles of sand component, showing heavy clay soil texture phenomenon, as in the rocky desertification, soil clay content gradually increased soil particle composition, sand content decreased; the overall change tendency of soil organic matter content showing, with the enhancement of the rocky desertification, its content decreased gradually, showed positive correlation with the soil magnetic susceptibility, frequency dependent susceptibility; free iron oxide content in the soil varies with the rocky desertification having an increasing trend, and negatively relation with soil magnetic and magnetic susceptibility, except for the abandoned land.(3)Soil magnetic characteristics of the study area of abandoned land and other land use types showed significant differences, the soil magnetic susceptibility variation characteristics and tendency to increase with increasing the rocky desertification in karst rocky desertification, magnetic frequency was demonstrated by a low-high trend, the trend of organic matter content and the content of free iron oxide is similar in both the dry land and forest land. The analysts believe that the abandoned land uncultivated, anthropogenic disturbance is reduced, the soil magnetism is effected by soil conditions and the process of soil, increase the content of organic matter, soil secondary magnetic minerals increased with an increasing soil magnetism; upland soils due to human aging or tilling, regional a unique hydrothermal climate conditions in karst rocky desertification, there are some erosion of soil, and is accompanied by the loss of water and soil, magnetic material loss in the soil to a certain extent, show soil magnetism with rocky desertification degree decreased, soil texture, clay, organic matter content is reduced accordingly; woodland soil vegetation cover is relatively better, and less human disturbance, soil magnetic characteristics change completely changed by the changes in the external environment conditions. Showing that karst rocky desertification area of human activity is very serious, the combination effect of natural factors and human activities, not only to a certain extent, changed the development environment of the local soil, but also affect the changes of soil physical and chemical properties, the sustainable use of land and its development has a serious effect.(4)Because of the influence of parent rocks and the unique characteristics of the climate, the soil is shallow,, and the boundary between soil and bedrock is clear. Study on the properties of the soil profile shows, abandoned land in human disturbance, after long-term natural evolution and succession, recovered by natural condition, its physical and chemical properties of soil improvement comes to be better, increasing the content of organic matter, soil structure is relatively stable, and there is a certain degree of herbaceous vegetation cover, which can effectively reduce the soil erosion and soil and water loss, have certain inhibition effect on the rocky desertification process. Dryland farming by human strength, change greatly hot water steam condition of soil, soil organic matter decomposition intensifies, so the soil organic matter content was the lowest, which in turn, affect the soil physical and chemical properties, enable the rapid destruction of good soil structure, its rich soil contains organic matter erosion easily, soil fertility decline sharply, soil have some erosion. Returning farmland to forest and grassland, reducing tillage and human disturbance, is conducive to the accumulation of soil organic matter, helps to reduce soil erosion to a certain extent, in some degree, which can reduce the rocky desertification. |
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