Shift From Promotion to Inhibition: Factors Affecting Soil Organic Carbon Sequestration in Intensive Croplands of the N orth C hina Plain

Soil organic carbon (SOC) dynamics are critical to maintaining the productivity and stability of cropland ecosystems. Intensive agricultural regions face risks of SOC loss due to high‐ intensity farming. As a core grain‐producing area and a typical intensive agricultural system, the North China Plain (NCP) requires a clear understanding of the long‐term evolution patterns of SOC to support sustainable carbon management. However, continuous long‐term dynamic datasets and mechanistic drivers—particularly interactions at the interannual scale—remain scarce. This study integrates historical data (1980s) with a 13‐year continuous dataset (2007–2020) from a network of 2463 fixed sampling sites to quantify changes in SOC stock across the NCP. Using Random Forest models, Structural Equation Modeling, and time‐series analysis, we identified a 40‐year SOC stock increase of 16.27 Mg C ha −1 , with an average sequestration rate of 0.407 Mg C ha −1 year −1 , exceeding prior model estimates (0.35 Mg C ha −1 year −1 ). Crucially, the role of precipitation as a driver underwent distinct phase transitions: Mean annual precipitation (MAP) positively promoted SOC accumulation during 2007–2010 but shifted to become the strongest negative driver in 2011–2015 due to alternating extreme rainfall and drought events, ultimately transitioning to indirect regulation via synergistic climate‐nutrient effects from 2016 to 2020. These findings indicate that sustaining SOC accumulation under intensive agriculture requires climate‐adaptive dynamic management strategies, including demand‐based irrigation. The results reveal temporal transitions in SOC sequestration mechanisms, providing a scientific basis for climate‐resilient carbon management strategies.