A Study On The Dynamic Changes Of Cropland Soil Organic Carbon In Hilly Region Of Southwest China Based On DNDC Model

As the global warming, carbon cycle has become a common concern of the international community as well as one of the three research hotspots about the global change.The soil organic carbon can be both source and sink of CO2.The soil organic carbon and its dynamic change of certain region can influence the carbon cycle greatly. The soil in the cropland ecosystem was disturbed seriously by human activities, meanwhile it can be artificially adjusted in a relatively short timescale which provides a potential mechanism to reduce emissions of carbon into the atmosphere. The study on the regional soil organic carbon of cropland soil can not only provide basic data for the research on the carbon cycle and carbon balance of terrestrial ecosystem, but also guide the use and protection of the existing soil resources scientifically and maintainament of the sustainable use of the land resources.This study simulated the dynamic changes of SOC in cropland soil of Liangping County from 1981 to 2010 based on the DNDC modle and GIS, analyzed the change of SOCD spatial distribution as well as the changes in different land uses, different soil types and different crop systems.The main conclusions are as follows:(1) The annual mean value of SOCD in cropland soil of Liangping County increased from 2.55 kg C/m2 to 2.90 kg C/m2 with a growth rate of 13.96% during 1981 to 2010.The tendency of the change showed that the cropland soil of Liangping County played the role of carbon sink in the carbon cycle.(2) The spatial distribution and its change of SOCD in cropland soil of Liangping County were apparently different. The SOCD in cropland soil is higher at the center of the Liangping dam and in the piedmont alluvial plain where the elevation is lower, and it was lower at the hill where the elevation is higher. The SOCD decreased with the increase of altitude, the high and low SOD distributed crossly with the cross distribution of parallel valley-and-ridge. The SOCD increased fastest in the center, northeast and southwest of the Liangping dam, and faster in the southwest of Hucheng syncline and the middle of the Jin-ji syncline.(3) The SOCD varied with the soil types. The SOCD in different subtypes ranks from the lowest to the highest as follow: river alluvial soil, brown purple soil, purple paddy soil, alluvial paddy soil, yellow paddy soil. The average SOCD in yellow paddy soil is the largest,and followed by dark purple paddy soil.The SOCD of soil genus in brown purple soil differs a little with a tiny change in 30 years. The SOCD in yellow soil was medium with tiny change in 30 years.(4) The soil in different land use produced different influence to the procedure of carbon sink. The average SOCD in paddy rice soil of 2010 was 2.82 kg C/m2, and 2.71 kg C/ m2 in dry land. The SOCD in each land use were increasing slowly, and the SOCD ranked from highest to the lowest as paddy field, rained paddy field, dry land. The tendency of the change illustrated that the cropland soil especially which in the paddy fields of Liangping were carbon sink in the carbon cycle. It is beneficial to sequestrate carbon and fertilize soil.(5) The SOCD aslo varied with the crop systems. The SOCD is the largest in paddy field planted paddy rice-wheat crop system than that planted other crop systems. In the rained paddy field, the SOCD which planted bean-corn-cassava cropping system is the largest, followed by rapeseeds- cassava cropg system which increasing faster than that planted wheat- cassava, bottomed the vegetable-vegetable-vegetable cropping system. In the dry land, the SOCD planted bean-corn-cassava cropping system is the largest, followed by that planted wheat-cassava and rapeseeds-cassava.