Identifying key parameters for cover crop C sequestration across process-based models

Cover crops build soil organic carbon (SOC) by increasing C input from plant litter to soil. The effects of cover crops on SOC can be studied by long term monitoring or by simulating the key processes. However, many process models have been built over time and they can result in very different SOC outcomes. In this study, we evaluated four simulation models ranging in complexity from a single pool mass balance to networks of connected C pools ( Yasso 20, SOMIC 1.0 ) and finally to a complete agroecosystem simulator ( DNDC.Can 9.5 ). The four models were applied to an on-farm experiment where four farms tested cover-crops for five years (2019–2023) in a paired field trial (n = 40 field years). Yield and vegetation estimated C inputs were used to simulate the change in C pools over time. The simulated C pools were compared to the total C stock and several labile C pools (water soluble C, microbial respiration C, glomalin related soil proteins) measured in 2021–2023. Overall, the models gave similar predictions. They predicted that cover crops would increase SOC, but they also underestimated the overall C loss from the existing SOC stock. The model predictions followed the overall trends of labile C pools predicted too large total pool sizes. The discrepancy between models and measurements could indicate a problem in the estimation of C inputs from yield data, which presents a clear research gap for further studies. Model intercomparison and evaluation against measured labile C pools can help in identifying parameterization problems and can point ways for integrating and harmonizing the different modeling approaches. Cover crops increase soil C across models and observations Cover crop biomass and root biomass are critical for achieving C sequestration More complex models are sensitive to a few key variables enabling simplification