What is the H:Corg test for biochar, and why 0.7?
H:Corg is the molar ratio of hydrogen to organic carbon in biochar, measured by a lab. A lower ratio points to more fused aromatic carbon, which microbes break down slowly. Verra VM0044 v1.2 accepts biochar for soil use only at 0.7 or below, tested on every batch.
What the number tells you
Pyrolysis turns plant carbon into aromatic rings that fuse into larger structures. The more fused they are, the longer the carbon lasts in soil. Verra's draft VM0044 v2.0 explains that H:Corg measures this indirectly, and that higher temperatures and longer reaction times give more fused structures.
The rule in VM0044 v1.2
- Soil use: H:Corg must be 0.7 or lower (applicability condition 10b).
- Frequency: each batch produced at the facility.
- Method: IBI Biochar Testing Guidelines or EBC production guidelines.
- Lab: accredited or approved by the relevant national agency.
- Soil biochar must also meet IBI, EBC or national limits for heavy metals and organic contaminants.
Where the draft v2.0 goes further
The July 2026 draft keeps the 0.7 limit for soil use and uses each lot's H:Corg to work out how much carbon counts as permanent, adjusted for the soil temperature where the biochar is spread. Under v1.2, permanence still comes from production temperature.
A batch above 0.7
It cannot be credited for soil use under v1.2. Check that batch's kiln temperature and burn time first: the draft v2.0 links lower temperatures and shorter reaction times to less stable carbon.
What Senseible does here
On a Senseible project, each batch carries its lab result next to its kiln sensor temperature logs, and the automatic flags with kiln at least 450 C, H:Corg at most 0.7, spreading inside the plot and transport distance catch a failed batch on the spot. A failed lab test is never marked complete.
- What a biochar lab test checks
- Kiln temperature records
- CO2 in a tonne of biochar
- Carbon removal projects
Sources: Verra, VM0044 v1.2 methodology document: applicability conditions 9 to 14, Section 7 (additionality), Tables 3 and 4, Section 9 (monitoring), Verra, Draft VM0044 Biochar Use in Soil and Non-Soil Applications, v2.0 (15 July 2026)
Last reviewed 2026-11-02.