mdw7fc/soil-n-carrying-capacity: v2.0 — v5 model with N immobilization, root C, SOC equilibrium

Code and data accompanying:

Wallenstein, M. D. (2026). Soil feedback dynamics amplify the consequences of nitrogen supply disruptions. Nature Food.

Changes from v1.0

• N immobilization feedback: iterative yield-residue-immobilization loop accounts for mineral N drawn into SOM when high C:N residue is incorporated
• Root carbon inputs: belowground C enters SOM independent of residue retention, with regional root:shoot ratios (0.6-1.0)
• Regional CRE calibration: each region's carbon retention efficiency calibrated so initial SOC is at approximate equilibrium under current management
• SOC corrections: Sub-Saharan Africa corrected to 9 t C/ha (cropland-specific, not landscape average); FSU corrected to 35 t C/ha (cultivated chernozems)
• Recalibrated decay constants: k_slow = 0.03705, k_passive = 0.000728

Key results

| Scenario | Static loss (yr 0) | Dynamic loss (yr 10) | Amplification | |---|---|---|---| | Uniform 20% | 4.5% | 5.7% | 1.27x | | Trade-dependency | 5.0% | 6.3% | 1.27x | | Price-mediated | 5.9% | 8.1% | 1.36x |