Soil organic carbon simulation under conservation tillage using DNDC model coupled with remote sensing technology

Farming practices can contribute to the soil organic carbon storage in the carbon budget of farmland ecosystems. This study aims to determine the dynamic response pattern of conservation tillage to the soil organic carbon. The density of soil organic carbon under conservation tillage was collected from the cornfield in Jilin Province, China from 2000 to 2020 at the county and grid scales. The "golden corn belt" in Jilin Province was taken as the study area, and the spring corn was selected as the research object. Remote sensing inversion was used to couple the Denitrification-Decomposition (DNDC) model. Firstly, the crop residue coverage was inverted using remote sensing. The input parameter of the model was selected to optimize the residue management module in the DNDC model. Secondly, the local soil properties were combined with the meteorology and farmland measure data. Regional simulation was implemented using two division units, in order to accurately depict the spatiotemporal dynamic evolution of soil organic carbon density under conservation tillage. In addition, the potential of conservation tillage was further explored to increase the soil carbon pools. The simulation was finally performed on the growth potential of soil organic carbon density under different straw return scenarios, according to the parameters of crop residue coverage in the DNDC model. The results show: 1) The DNDC model was feasible in this case. The R² value reached 90% for the soil organic carbon under different farmland measures, and the relativer root mean square error values were all within 10%. The relatively better performance was used to simulate the local soil organic carbon density and long-term forecasts. 2) Soil organic carbon storage in cornfields increased significantly over the past 20 years, from 6.08×10⁸ to 1.22×10⁹ t. The reason was closely related to the expansion of the cultivated land area. The soil organic carbon density varied between 4.46 and 98.09 t/hm2 at the county scale, while there was a variation between 3.34 and 139.2 t/hm² at the grid scale. The overall density of soil organic carbon showed a spatial distribution pattern of high in the central region and low in the northern region. 3) Conservation tillage posed a more significant impact on the organic carbon accumulation in the surface soil. The highest growth rate of soil organic carbon density in the 0-10 cm soil layer was 4.4%, while only 0.09% was found in the 10-20 cm soil layer. 4) The huge growth potential of soil organic carbon was observed in the southwestern and central regions in the growth range from 0.24 to 0.57 t/hm², particularly with the increase of crop residue coverage. 5) The fineness of the unit division dominated the simulation. There were slightly different values of the simulation under different units. But there was no spatial distribution of the research subjects. Compared with the spatial distribution after simulation at the county level, the grid scale was indicated in much more detail. In summary, the conservation tillage significantly increased the soil organic carbon in cornfields. The farmland ecosystem shared great potential for carbon sequestration in the future. However, there are local differences in the response of soil organic carbon to the conservation tillage. Therefore, the finding can provide an important reference for the decision-making on conservation tillage tunable for local conditions and carbon budget in farmland ecosystems.