Diagnosis of the coupling coordination relationships between crop and soil carbon sequestration function for sloping farmland under erosive environments in the Three Gorges Reservoir Area, China.

Soil carbon sequestration, a critical function of the soil, plays a pivotal role in mitigating climate change, improving the soil environment and maintaining the stability of agricultural ecosystems. Changes in soil properties caused by erosion can significantly affect the soil carbon sequestration function and its coupling with crops. However, its application to agricultural production remains unknown. Herein, a 4-year field observations were conducted on sloping farmland in the Three Gorges Reservoir area of China, using the artificial shovel soil test method. Variations of the soil carbon sequestration function (SCSF) in topsoil layer under five erosion conditions (erosion thicknesses of 0, 5, 10, 15, 20 cm) were analyzed (soil management measures were biochar + chemical fertilizer, BF), and the coupling coordination degree between crop and SCSF and the suitability of crop planting on sloping farmland were systematically diagnosed. The results indicated that the main indicators affecting SCSF, such as soil organic carbon and cation exchange capacity, exhibited an overall decreasing trend as the erosion thickness increased. Soil erosion was an important factor that results in low-carbon sequestration function in topsoil layer, with the SCSF of each eroded plot decreased by 4.62 %, 28.06 %, 55.32 %, and 71.22 % compared to the non-eroded plot, respectively. After four years of tillage, the SCSF has been improved under the management measures of BF. However, the speed of soil restoration was far slower than the rate of erosion-induced damage. The coupling coordination state of crop and SCSF underwent a transition from good coordination to basic coordination and then to near imbalance with the erosion thickness increased, reflecting the unsuitability for crop growth in severely eroded plots (erosion exceeding 15 cm). These findings provide a scientific basis for rational diagnosis and regulation of topsoil layer for sloping farmland, the restoration of soil function, and the promotion of sustainable agricultural development.