The Interplay Between Bioeconomy and the Maintenance of Long-Term Soil Organic Carbon Stock in Agricultural Soils: A Systematic Review

Crop residues' potential for the bioeconomy is often limited well below its full extent to prevent soil organic carbon (SOC) depletion. However, when processed in the bioeconomy, biomass carbon can often be partially recovered in a stabilized degradation-resistant coproduct. This study reviews and interlinks the fundaments between these coproducts' process-dependent characteristics and the use of soil models to predict SOC turnover by replacing fresh crop residues with bioeconomy coproducts after processing. Different modeling approaches to incorporating stabilized organic matter into soils were investigated, as well as the input data requirements of a variety of soil models. Stemming from a revision of over 600 datasets, we synthesized and proposed average conversion coefficients from biomass C to coproduct (CC‾) and their inherent recalcitrance in agricultural soils (CR‾) for pyrolysis (CC‾: 48 %, CR‾: 95 %) and gasification (CC‾: 20 %, CR‾: 95 %) biochar, hydrochar (CC‾: 31 %, CR‾: 83 %), digestate (CC‾: 36 %, CR‾: 68 %) and lignocellulosic bioethanol solid (CC‾: 44 %, CR‾: 42 %) and liquid (CC‾: 21 %, CR‾: 46 %) coproducts. This review thus represents a stepping-stone towards i) setting the fundaments for adapting soil models to the dynamics between crop residue harvest and return of C under multiple forms and ii) exploring future scenarios involving coproduct return as a strategy to increase the supply of renewable C for the bioeconomy while ensuring the maintenance of SOC stocks.