Estimating soil organic carbon deficits at the continental scale using legacy-data-driven dynamic baseline and attainable projections

• This study developed a novel soil-carbon stock modeling framework to estimate attainable and current deficit stocks. • Attainable carbon-storage thresholds may have shifted and have lower carbon sequestration target. • Extensively cultivated Mollisols and Alfisols currently have lower attainable steady state. • Time-adjusted soil-carbon framework sets recalibrated carbon sequestration targets for effective policy implementation. Soil organic carbon (SOC) stocks vary temporally, across land use, climate, and soil type, making it challenging to model current stocks (SOC cs ). The attainable steady-state stock (SOC at ), the practically achievable under optimal soil, climate, and management conditions, remains dynamic because soil-loss processes continually modify the biophysical limits on maximum storage, causing SOC at to shift over time. Robust methods are required to integrate temporal dynamics, model and extrapolate SOC cs and SOC at , and quantify current deficits (SOC def ), the unrealized sequestration capacity. We used legacy SOC observations along with time-adjustment and data-driven modeling to generate spatially explicit projections of 2024 SOC cs . We estimated SOC at by selecting the maximum SOC value from a spatially constrained similarity matrix of projected SOC cs , then used both reference layers to derive location-specific SOC def . The resulting maps revealed extensive heterogeneity among the land use types and across regions. Mean SOC def of 3.46 kg m –2 was noted for all croplands in continental United States. Larger deficits clustered on soil orders of Mollisols and Alfisols in the Midwest region, but were lower than anticipated, alluding to depleted SOC cs and SOC at . Degraded grasslands showed similarly reduced SOC at , underscoring the need to recalibrate sequestration targets based on current projected steady states. The results underscore the framework’s novelty as it effectively integrates temporal dynamics of soil carbon stocks and converts soil-carbon storage processes into actionable, farm-level sequestration targets. By generating empirically derived, region-specific SOC cs –SOC at –SOC def benchmarks, the framework offers precise reference points that align management incentives, climate-smart policies, and site-specific restoration strategies.