Spatial distribution of medium- and low-yield croplands and soil carbon sequestration potential in China

Spatial distribution of medium- and low-yield croplands is often required for the high-precision assessment of the soil carbon sequestration potential in China. It is still lacking in the characterization for the large-scale production in precision agriculture. In this research, the spatial distribution of such croplands was determined to predict their soil carbon sequestration potential under diverse future scenarios. 31 long-term positioning experimental sites were also selected from the nine agricultural regions using K-prototypes clustering. Multiple source data were integrated to map the spatial distribution of medium- and low-yield croplands at a 500 m resolution. The planting systems and crop types of each pixel were then considered in the secondary agricultural regions. The pixels of croplands within each secondary region were further classified into the high-, medium-, and low-yield using the relative Net Primary Productivity (NPP) values. Meanwhile, the saturated soil organic carbon density (SOCD) was predicted to quantitatively assess the soil carbon sequestration potential of medium- and low-yield croplands over the next four decades (in 2021-2060). The results revealed that the medium- and low-yield croplands were predominantly located in the Loess Plateau, northwestern regions, including Xinjiang and Ningxia. There were scattered distributions in the central North China Plain, the central Sichuan Basin, the Southeast Hilly Region, and the Yunnan-Guizhou Plateau. Under the medium-emission Shared Socioeconomic Pathway 2-4.5 scenario, with 50% straw returning to the field, the average SOCD of these farmlands was projected to reach 54.15 megagrams of carbon per hectare in 2060, indicating a 19.04% increase from current levels. The soil organic carbon storage of the medium- and low-yield croplands was expected to rise by 0.78 petagram of carbon. The carbon sink of cropland soil was relatively high under the low emissions and high carbon inputs. It is projected that the SOCD of medium- and low-yield croplands can increase to a maximum of 57.76 megagrams of carbon per hectare in 2060. Medium and low yield croplands have considerable potential for productivity improvement and carbon sequestration, and are key areas where management measures can be implemented to increase production and sequester carbon, especially in regions such as the northern arid and semi-arid areas, and the Loess Plateau region, where medium and low yield croplands are widely distributed. Climate change and agricultural management measures jointly affect soil carbon sequestration in cropland. Reasonable promotion of straw returning to the field to increase carbon input is expected to raise the yield by 6.1 t/hm²., helping to achieve the dual carbon goals and ensuring food security. The finding can also provide a scientific reference to accurately identify the distribution pattern of the medium- and low-yield croplands in China. Their soil carbon sinks can potentially contribute to carbon neutrality.