| Soil carbon pool is the most active in the surface the Earth circle, which can directly affect greenhouse gas concentrations in the atmosphere. Farnland is the soil carbon which is closely related to human activities. Around 10% of the land was used for agricultural production all over the world. Soil for greenhouse gas emission reduction and sequestration has great potential in agricultural ecosystem. In recent years, the concentration of CO2 in the atmosphere has been increasing, causing the attention around the world. Countries around the world are looking for ways to reduce emissions and increase sequestration on CO?. Against this background, the carbon sinks of farmland ecological system which is closely related to human survival and development for its specificity and distribution of large area become hot topic in the global academic research. Zhenlai County as an important food production base in Jinlin Western, because of their special geographical environment and land management measures implemented to reduce land salinization, increasing paddy field area which had significant impac on soil organic carbon storage. In this paper, organic carbon storage and changes of farmland ecosystem in Zhenlai as the research object has important significance.The study based on the National Natural Science Foundation"The impact and driving mechanism of LUCC on soil organic carbon during the past 50 years", by interpreting remote sensing images on the land use/cover changes from 1996 to 2008 in wstern Jilin Province, simulated soil organic carbon storage and changes in 1996,2000,2004 and 2008 in Zhenlai county using DNDC model, analyzing the trends of soil organic carbon storage and changes during 12 years and carbon sequestration capacity of different soil types. Based on the meteorological data, soil data and Farmland management information in 2008, the different scenarios were set to explore the effect of temperature change and cropland management changes for soil organic carbon. Firstly, satellite images of the study area in 1996,2000,2004 and 2008 were purchased and were processed by the steps of geometrical correction, images mosaic, unsupervised classification and interactive visual interpretation. On the basis of getting the land use data, the distribution and area of farmland can be extracted further. By combining the figures of farmland distribution with the soil type map and the administrative under GIS, small grids were formed. Every grid was given its own attribute value, such as meteorological data, soil properties and farmland management information. Riquirde database was established for the DNDC model.Secondly, the measured datas in three years from 2006 to 2008 were compared to the simulation results which could get by inputing actual parameters to verify the model's credibility.soil organic carbon content was tested by potassium dichromate sulfuric acid method. Then soil samples were tested their bulk density and water content. Compared the calculation with simulation values,results showed that:The correlation coefficient of simulation values and measured values were 0.9536 and 0.9152 in 2006,0.9429 and 0.9831 in 2007,0.9762 and 0.964 in 2008, respectively. So Simulation result was well, indicating that the DNDC model can reflect the actual situation of the study area.Thirdly, soil organic carbon storage in 1996,2000,2004 and 2008 was estimated using DNDC model, analyzing the spatial and temporal changes.of soil organic carbon storage in four years. Input datas came from the pre-build database file. Total organic carbon storage and units organic carbon content were the highest in 2008, total organic carbon strorage(0-20cm) was 17,709.6×106kg in the areas of 240,460hm2 and an average was 73,649.0 kg in per hectare. Total organic carbon storage was the lowest and was 10,893.4×106kg in the areas of 183,284hm2 in 2000 year. The unit of organic carbon content was the lowest in 1996 year, total organic carbon storage (0-20cm) was 11,852.3×106kg in the areas of 199,808hm2, an average was 59,318.8 kg·hm-2. In 2004, total organic carbon storage (0-20cm) was 19,544.4106kg and an average was 66129.0 kg·hm-2 in the areas of 241,111hm2. After farming in a year, soil organic carbon storage had increased by 337.4x106kg, 369.8x106kg,475.6x106kg,488.3×106kg respectively in 1996.2000,2004 and 2008 in Zhenlai County, soil carbon balance was positive, as a sink of atmospheric CO2. For different soil types, soil carbon sequestration demonstrated great differences. Carbon sequestration capacity of different soil types followed by chestnut soil, swamp soil, meadow soil, chernozem, chernozem light, sandy, alluvial soil, alkaline soil, saline soil. Analysing simulation datas, the results showed that soil organic carbon storage had an increasing trend from 1996 to 2008 in the study area. From 1996 to 2000, soil organic carbon storage appeared a modest decline, the reason was reduction of farmland area in 2000 in Zhenlai county, resulting in the loss of soil organic carbon storage. The average carbon stock of various soil types showed the same trend from 1996 to 2008. A separate analysis of each year demonstrated that all kinds of soil carbon sequestration had the same law. Carbon sequestration capacity of each type of soil was enhanced in different year.Finally, based on the meteorological data, soil data and Farmland management information in 2008, considering the actual situation of the study area, the different situations were set to explore the effect of temperature change and cropland management changes for soil organic carbon. The results showed that:soil organic carbon accumulation has negative effects, if the temperature rise, not organic fertilizer. The measures such as increasing straw ratio into soil, moderate amount of chemical fertilizer, increasing organic fertilizer application rate can effectively increase the accumulation of SOC.This paper researched soil organic caron storage and change of agroecosystem in Zhenlai county, using RS data nearly 12 years, combining advanced environmental simulation technology with soil monitoring experiment. The study has important scientific value and practical significance on finding out law of soil organic carbon change, assessing carbon storage and so on.
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