Is the topsoil carbon sequestration potential underestimated of agricultural soils under best management?

Enhancing soil carbon (C) sequestration has been globally advocated as a nature-based solution for climate change mitigation. Best management practices (BMPs) can increase soil organic carbon (SOC) content and improve soil structure in the topsoil. However, when estimating changes in SOC stock under BMPs, a default soil depth is often used without considering that BMPs may alter the topsoil depth (through volume expansion in line with the changes in bulk density), potentially leading to an underestimation of C sequestration. To achieve a more robust estimate of SOC stock change, it is necessary to rectify soil depth. In this study, our findings indicate that using a fixed-depth approach to estimate SOC stock may result in a 25.2 % underestimation of SOC stock increase under BMPs. This suggests that under BMPs, using the calibrated-depth approach based on equivalent soil mass can estimate SOC stock more accurately by considering soil depth changes. Additionally, we propose further validation of the calibrated-depth approach's applicability and emphasize that robust soil depth and precise bulk density measurements should be followed to assist more accurately monitoring SOC stock changes. • BMPs increase SOC stock and expand topsoil depth. • Fixed-depth approach underestimation C sequestration under BMPs. • Calibrated-depth approach can better monitor SOC stock changes.