Full explanation
SOM components: (1) live biomass 1–5% (roots, microbes, mesofauna); (2) active organic matter 10–25% (plant residues <5 years); (3) stable humus 70–85% (20–2000 year turnover). SOM is measured as Loss on Ignition (DSTU ISO 10694:2015) or by the Walkley-Black method. Each +1% SOM in chernozem delivers: +150–200 m³ water/ha (drought tolerance), +30–50 kg/ha mineralized N per season, +5–15% CEC, +8–15% cereal yield. Practices to build SOM: minimum tillage (−0.5–1% per generation versus intensive), cover crops in rotation (+0.1–0.3% over 5 years), and 5–10 t/ha compost annually. EU CAP's carbon-farming programme measures depth-weighted SOM to 60 cm — the key metric for EUR 40–90/t CO₂-eq payments.