Synthesis of soil carbon losses in response to conversion of grassland to agriculture land

The conversion of grassland to cropland is one of the major changes in land use, and it accelerates both soil erosion and the loss of soil organic carbon (SOC). However, the general patterns of SOC loss after grassland cultivation are rarely assessed, and the potential mechanisms remain unclear. Here, a meta-analysis of 81 case studies was performed to show that SOC decreased with soil depths of 0-60 cm after grassland conversion, but no significant differences were found at depths >60 cm. SOC also declined significantly with the duration of grassland conversion. The response ratio of SOC changes tended to reach equilibrium after 20 years of grassland cropping. Our results indicate that reduction in SOC mainly depended on changes in precipitation, soil physical-chemical properties and soil microbes. These conclusions highlight the importance of improving the accuracy of predictions on SOC losses and on the global carbon cycle in the face of land-use changes worldwide.