# Dynamic Changes in and Driving Factors of Soil Organic Carbon in China from 2001 to 2020
## 4 Discussion
### Driving Factors for SOC
#### 4.2.2 Impact of Land Use Change on SOC  
This study quantitatively detected the intensity of land use change and also conducted a land use transfer matrix analysis to elucidate the impact of land use change on SOC. Overall, the impact of land use change on SOC in the past 20 years has been positive, mainly due to the conversion of large areas of grassland to forest land and cultivated land to grassland. Although the area of grassland converted into arable land is also large, the SOC content of arable land can be greatly increased by adopting appropriate management measures in the long term [68]. Therefore, adopting conservation tillage measures such as no-tillage and straw return, on the other hand, can help to maintain the stability of soil aggregates and reduce the loss of SOC [69; 70]. Fundamental changes in land use patterns have more far-reaching effects on SOC; for example, the conversion of forest and grassland to farmland and the expansion of built-up areas significantly reduced SOC content [71; 72; 73]. On the contrary, the adoption of restoration measures for long-term vegetation, such as returning farmland to forest and grassland and afforestation, contributes to the accumulation and recovery of SOC [74; 75].  
However, land use changes in different regions can lead to differences in organic carbon changes. The overall SOCD is declining in northeast China, and although there is also a large conversion of cultivated land to grassland and grassland to forest, it is not enough to compensate for the loss of carbon from the former conversion. Forest clearing to obtain cultivated land is the main reason for the decrease in soil content in the northeast [72; 73; 76]. As reported by [PERSON] et al. (2023), 35 years of tillage led to a decrease in SOC content of about 3.07 g kg\({}^{-1}\) in the northeast, and about 64% of cultivated land had a negative increase in SOC from 1985 to 2020 [72]. In the Golden-Maize-Belt Counties in Jilin Province, northeast China, the maximum decrease in SOC content even reached 24.83 g kg\({}^{-1}\)[77]. In the eastern and south-central regions, the main land use disturbances have been dominated by agricultural activities, and the increase in SOC was mainly due to the adjustment of agricultural planting structure, application of more organic fertilizers, return of straw to the field, conservation tillage, and other measures [69; 70; 78; 79]. In addition to the conversion of large areas of grassland to woodland in the northern, northwestern, and southwestern regions, these three regions also have large areas of barren land converted to grassland, with the most obvious in the northwestern region. The increase in SOCD in these regions is largely attributed to both the reduction in anthropogenic activity intensity and ecological restoration, the former including the control of grazing intensity and the prohibition of logging [59; 80; 81] and the latter including natural vegetation restoration, returning farmland to forest and grassland, and soil and water conservation [74; 82; 83; 84].