This article links to the main piece on HealthySoil which explains the broader shift in biochar markets and carbon credits. Here, we focus on what that shift means for soil systems and the Biochar–Humus Complex (BHC).
The key issue for soils
Carbon markets are pushing production toward high-carbon biochar.
However:
Soil systems do not optimise for carbon metrics alone—they optimise for functional interaction.
This does not mean high-carbon biochars have no role in soils. In many cases, their stability and structure may be beneficial. The key point is that soil performance depends on matching material characteristics to system needs.
Biochar is a material class, not a single soil input
Biochar properties used in soils emerge from the interaction of:
- feedstock
- process conditions
- post-processing or conditioning
Treating biochar as a single product obscures how differently materials can behave in soil systems.
Stop saying “biochar improves soil”
Biochar does not act in isolation. Its behaviour depends on:
- interaction with soil biology
- nutrient cycling
- moisture dynamics
- aggregation and structure
The Biochar–Humus Complex (BHC) framing reflects that biochar function emerges through interaction with organic matter, microbes, and soil structure.
Feedstock reality matters
Materials such as compost oversize woody fractions:
- contain mineral fractions (clay/sand)
- have higher moisture
- are biologically pre-processed
These may not maximise carbon credits, but they can:
- integrate effectively into soil systems
- support biological function
However, these materials require appropriate screening, contamination control, and process matching to ensure suitability for soil use.
System efficiency vs carbon efficiency
A material that underperforms in carbon-credit terms may still perform effectively within soil systems.
This is particularly relevant where:
- circular use of biomass is important
- local feedstocks dominate
- soil biological function is a priority
The risk
If production shifts entirely toward carbon optimisation:
- soil-relevant materials may be excluded
- circular feedstocks may be underused
- system performance may be reduced
The correct approach
Define the soil function first, then design the biochar.
This includes:
- matching material to soil type
- integrating with compost and humus
- focusing on system outcomes, not just carbon metrics
Link to main article
For the full discussion on carbon markets, feedstock constraints, and production trade-offs, see the main article on HealthySoil.
Summary
Biochar in soils is part of a system, not a standalone product. The future lies in designing biochar for interaction within soil ecosystems, recognising that carbon optimisation and system optimisation are not always the same.