A scenario-based framework linking biophysical soil carbon modeling to illustrative economic signals

Soil organic carbon (SOC) sequestration offers climate mitigation potential in agriculture, yet linking biophysical soil carbon dynamics to policy-relevant interpretation remains challenging. This study develops and demonstrates a transparent, scenario-based framework to explore how alternative carbon policy signals could translate into relative, illustrative economic responses in temperate agricultural systems: A Plot-Scale Case Study. SOC dynamics were simulated over 20 years (2025–2045) for Conservation Agriculture (CA), Conventional Tillage (CT), and Organic Farming (OF) in a temperate Andosol region of Niigata, Japan, under two CMIP6 climate pathways (SSP2–4.5 and SSP5–8.5). Modeled SOC changes were translated into illustrative economic signals using three carbon pricing instruments: carbon tax, subsidy, and cap-and-trade, and assessed through a Net Present Value (NPV) framework with discount rate sensitivity analysis. Under moderate climate forcing (SSP2–4.5), CA, CT, and OF sequestered carbon at 0.09, 0.08, and 0.06 t C ha−1 yr−1, respectively. CA consistently generated the highest NPV across pricing scenarios ($286 ha−1 at 3% discount rate under a moderate price trajectory). Under the high-emissions SSP5–8.5 scenario, the model projected differential responses across systems. These varying responses are directly related to the calibrated fractions of inert organic matter, rather than empirically validated differences in climate vulnerability.