| Soil CaCO3 eluviation and deposition process is the most important development and evolution process of soil, from parent material to mature soil in the Loess Plateau, arid and semiarid area. CaCO3 not only affects soil physical and chemical characteristics but also causes CO2 change in the air, because CaCO3 is main components among the total pool of inorganic carbon of soil. This paper systematically summarized and analyzed general development characteristics of soil profile CaCO3 in Loess hill gully area including source, content, forming-condition, distribution and illuviation- depth of CaCO3, which will have the most important significance for the further studies on global soil and climate change.Soil CaCO3 eluviation-illuviation is a relatively complicate process, soil CO2 is one of the important effect factors, which influences soil CaCO3 through controlling soil pH value and CaCO3 solution capability. The study on soil CO2 concentration redounds to understanding and illustrating the inner mechanism of CaCO3 deposition process and provides experiment data for CaCO3 deposition model development.Based on the two years located research and out-door investigation in Zhuanyaogou watershed, Hequ county, the north west of Shanxi province. The distribution and change pattern of soil CO2 concentration in soil profile data are analyzed as well as its effect factors. A model for soil CaCO3 eluviation-illuviation is developed based on mechanism of soil chemical thermodynamic principle and applying other modeling experience for reference.The research results are as follows:1. The relationship of soil CO2 concentration and CaCO3 content presents positive correlativity. Meanwhile, owe to different land use, it leads to moisture and CaCO3 content in soil profile obvious difference, but its effect on PH value is minor. According to statistics analysis, the result indicates the relationship of PH value and CaCO3 content presents nonlinear positive correlativity, regression equation is PH=(-7.26+8.98x)/x, correlation coefficient r=0.9997,the formula manifests: in the certain range of CaCO3 content with the increment of CaCO3 content, soil PH value is increased, however beyond this range effects of CaCO3 content on soil PH will obviously decrease and even disappear.2. According to the weighted average, soil CO2 concentration is 0.58-13.29 times of that in atmosphere and is relatively lower than similar research, Meanwhile, Soil CO2 concentration in profile varied irregularly, which possibly is due to the chemical and physical characteristic of Loess soils, season change and arid climate etc. The variation of soil CO2 concentration in profile is mainly controlled by soil temperature and soil moisture, in contrast with soil temperature, the control role of soil moisture is minor.In conclusion, in order to have a good command of the distribution and change rule of soil profile CO2 concentration as well as its effect factors, multi-point and successive location experiment should be made, meanwhile establish indoor soil-pillar monitoring experiment. The model should be coupled with other model such as random rainfall model, evapotraspirationmodel etc, and avoid subject factor effect. The aim is to evince accurately general law of CaCO3 deposition, provide scientific basis for making strategic decisions on soil management and environment protection.
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