Biochar Soil Carbon Sequestration

Feedstock & Process

Pyrolysis temperature 500 °C

Annual feedstock input 3.0 tC/ha/yr

Mean soil temperature 15 °C

Pools (year 0 / 150)

Biochar-C (pyrolyzed, applied to soil) Labile OM-C (same biomass, not pyrolyzed)

Biochar stock

0.0 tC/ha

Baseline stock

0.0 tC/ha

Biochar MRT

50 yr

CO₂ avoided

0.0 t/ha

How it works

Both pathways start from the same annual carbon input from crop residue or wood waste. One is pyrolyzed (heated without oxygen) into biochar before returning it to the soil; the other is left as raw organic matter. Each soil carbon pool C obeys first-order decay with continuous input:

dC/dt = In − k·C
C(t+1) = C(t)·e^(−k) + (In/k)·(1 − e^(−k))   [exact per-year step]

Pyrolysis temperature sets two things, following the general trend reported in biochar life-cycle studies (Lehmann & Joseph; Woolf et al. 2010; Zimmerman 2010):

Biochar-C yield  Y(T) ≈ 0.55 − 4.2e-4·(T − 300)     [fraction of feedstock C retained as biochar]
Biochar MRT(T)  ≈ 50 · 10^((T − 300)/400) years     [higher pyrolysis T → more aromatic, slower-decaying C]

Both decay rates are temperature-sensitive via a Q₁₀ relationship, the standard way soil science scales decomposition with warming — a 10 °C rise multiplies the rate by Q₁₀:

k(T_soil) = k_ref · Q10^((T_soil − 15)/10)
Labile OM:  Q10 = 2.0   (fresh biomass decomposes fast and is heat-sensitive)
Biochar:    Q10 = 1.3   (aromatic carbon is chemically far more heat-stable)

Pyrolysis temperature — trades yield for stability: higher heat retains less carbon per pass but what remains resists decomposition for far longer.
Feedstock input — the annual carbon supply rate applied to both pools identically, so the comparison stays fair.
Soil temperature — a warmer soil accelerates both pools' decomposition, but hits the labile pool much harder.
CO₂ avoided — the extra carbon held in the biochar column versus the untreated baseline, converted to CO₂ mass by the 44/12 molar-mass ratio — the net additional atmospheric CO₂ this pathway keeps out of circulation.

This is a simplified, illustrative version of the mechanism used in real biochar carbon-credit accounting — actual project methodologies (e.g. IPCC, Puro.earth) also account for pyrolysis process emissions and transport, omitted here to isolate the soil-carbon-pool physics.

1 cube ≈ 2 tC/ha

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