Study On The Changes Of Paddy Soil Organic Carbon Storage In Qingtian County Based On Dndc Model

Qingtian County is located in the mountain area of southern Zhejiang Province. The topography of the county is mainly occupied with Low Mountain and small hill. Perennial terraced farming was mainly used for agricultural production in the county. There were several serious problems for agricultural activities:almost no crop straw returning back to the field, low soil organic matter content, serious soil acidification, imbalanced soil nutrients status, increasing inhibiting factors, increasing compaction degree, narrow plow layer depth and significantly decreasing soil fertility. This county was one of the typical representatives of the great potential terraced hills and mountains area. Therefore, study on the long term effect of soil organic carbon storage changes and field management on soil carbon cycle in the county could not only provide scientific basis for contributing soil carbon sequestration capacity, improving soil quality and increasing crop yields, but also provide technical support for climate change mitigation and scientific mitigation option development. At the meantime, it also could contribute to achieving a long-term purpose of agricultural sustainable development and ultimately achieve a "win-win" goal. In this study, on the basis of information and data offered by Agricultural Bureau in Qingtian County, firstly, we verified the feasibility of DNDC model applied to hilly agricultural area at Qingtian County, and carried out the model to estimate the paddy soil organic carbon storage in Qingtian County, and then forecasted soil organic carbon stock change in the future. Several main conclusions were shown as follows:(1) the database of DNDC model for regional mode included one database of geographic information system (GIS) data and general information data. For the implementation of paddy soil organic carbon storage simulation in Qingtian County, GIS database and common database of paddy soil in Qingtian County need to be established. DNDC model read the input information of the entire area from these databases and carried out the simulation. In order to verify whether DNDC model was suitable for paddy field in Qingtian County, the simulation results and measured data were compared with each other. In this study, the measured data in1985offered by Agricultural Bureau in Qingtian County was used as the input database of DNDC model, and then the simulation was carried out for25years, subsequently, correlation analysis between the simulation results of paddy soil organic carbon storage in2010and the related measured data in2010was implemented and determination coefficient r was0.454, p<0.01. The results showed that There was statistically significant correlation between the simulated and the measured organic carbon content in2010, thus verifying the feasibility of DNDC model in this region.(2) In the process of regional mode of DNDC model in2010, the model run four times for each cropping system per polygon. The four parameter combinations were the maximum sensitivity soil parameter plus irrigation, the minimum sensitivity soil parameter plus irrigation, the maximum sensitivity soil parameter plus non-irrigation and the minimum sensitivity soil parameter plus non-irrigation. DNDC model simulated each cropping system, each polygon per year one by one until the end of the database. Simulation results showed that soil organic carbon content in the0～20cm plow layer was the same under two scenarios of adequate and without irrigation plus the maximum sensitivity soil parameter, the value was ranged from9.77to37.79g/kg, average value was20.97g/kg, while soil organic carbon content in the0-20cm plow layer was the same under two scenarios of adequate and without irrigation plus the minimum sensitivity soil parameter, the value was from5.81to24.40g/kg, average value was13.15g/kg. Under the conditions of the existing production level, the soil organic carbon storage in the plow layer in paddy field in Qingtian County was in the medium level in2010.(3) the storage of paddy soil organic carbon pool in2010and2035was simulated based on the measured database in1985and meteorological database from1985to2010, subsequently, the organic carbon density and organic carbon storage in plow layer of paddy soil in Qingtian County were estimated according to the simulation results. The results showed average paddy soil organic carbon density in the plow layer in2010and2035was3.84kg/m2and3.48kg/m2respectively. The total paddy soil organic carbon storage in the plow layer in2010and2035was0.95Tg and0.89Tg respectively. The measured average paddy soil organic carbon density and organic carbon storage in the plow layer in2010was3.72kg/m2and1.00Tg respectively while the average paddy soil organic carbon content, soil organic carbon density and organic carbon storage in1985was13.78g/kg,3.10kg/m2and0.80Tg respectively. The average paddy soil organic carbon density in2010and2035 increased20%and12.26%respectively compared with that in1985, while the average paddy soil organic carbon density in2035decreased6.32%compared with that in2010. It could be seen that paddy soil organic carbon storage in plow layer in Qingtian County showed the trend firstly increasing and then decreasing, and gradually stable in the future under the conditions of the existing production level in1985-2035. The prediction of soil organic carbon storage based on DNDC model would have a great significance to guide the improvement of paddy soil sustainable farming ability in Qingtian County.