Soil Organic Carbon
Carbon saturation, the RothC model, and the "4 per 1000" reality check
FYM tripled soil carbon to ~85 t C/ha — but it took 120 years to plateau
Why This Matters
This dataset calibrated and validated the RothC model — the benchmark for IPCC global soil carbon modeling (Jenkinson, 1990). Poulton et al. (2018) showed the COP21 '4 per 1000' target is physically achievable short-term but impossible to sustain. Soils are NOT infinite carbon sinks.
Multi-line SOC Trajectory (1843-2015)
Reality Check
Applying 35 t/ha FYM annually is completely unscalable globally — there isn't enough manure — and causes extreme nitrate leaching.
4 per 1000 Reality Check
Comparing target annual rate (4‰) vs. actual rates achieved on Broadbalk.
The "4 per 1000" initiative, launched at COP21, aims to increase global soil organic carbon stocks by 0.4% per year. However, Broadbalk data shows that while high rates can be achieved initially with massive inputs, they decay as soils reach a new equilibrium.
- Initial burst: FYM first 20 years reached ~18-43‰.
- Diminishing returns: By 60 years, it fell to ~5‰.
- Saturation: At 120 years, it slowed to ~1‰.
Methodology & References
- Poulton, P., Johnston, J., Macdonald, A., White, R., & Powlson, D. (2018). Major limitations to achieving "4 per 1000" increases in soil organic carbon stock in temperate regions: Evidence from long-term experiments at Rothamsted Research, United Kingdom. Global Change Biology, 24(6), 2563-2584.
- Jenkinson, D. S. (1990). The turnover of organic carbon and nitrogen in soil. Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences, 329(1255), 361-368.
- Johnston, A. E., Poulton, P. R., & Coleman, K. (2009). Soil organic matter: its importance in sustainable agriculture and carbon dioxide fluxes. Advances in Agronomy, 101, 1-57.