1 Jul 2025

Black carbon fell 19 to 43 percent in an 11-year biochar field trial

Climate and environment
AI illustration · Illustrative scene, not a photograph of the specific device or experiment.

What was demonstrated

In a long-term field experiment near Bayreuth, Germany, started in 2010 on a sandy loam Cambisol with 507 mm mean annual precipitation, pine-wood biochar applied at 31.5 Mg per hectare raised black carbon stocks about threefold, to 15 to 20 Mg C per hectare. Between years 3 and 11, black carbon fell by 43 percent in the biochar-only treatment and by 19 percent where biochar was applied with compost. The Results describe the 43 percent decline as significant and the 19 percent decline as not significant, and the authors report no statistically significant difference between the two treatments. Biochar metabolites (BCm) made up less than 3 percent of total black carbon according to the abstract, and the authors conclude that BCm is a negligible loss pathway over this period.

Why it matters

Biochar carbon removal claims depend on how long black carbon stays in soil. This field measurement from one site suggests that black carbon stocks can fall measurably within about a decade. The authors attribute the loss mainly to lateral and vertical transport driven by rainfall, tillage and soil fauna.

Caveats

  • The abstract says black carbon 'decreased slightly after 11 years in both treatments', while the Results describe the 43 percent biochar-only decline as significant. This record uses the Results figures.
  • This is a single site with three of five replicate plots per treatment. The authors say the findings might only transfer to similar regional contexts.
  • The authors state that it remained unresolved why BCm stocks decreased after biochar was added, and that BCm release could play a larger role over longer timescales. The metabolite share is given as under 3 percent in the abstract and under 1 percent in the conclusion.
  • Bulk density was estimated with a pedotransfer function, so stock values carry additional uncertainty.

Technology profiles

Sources

  1. peer reviewed paper
    Relevance of biochar metabolization: evidence from a long-term biochar field experiment
    Arthur Gross, Marko Šolić, Bruno Glaser et al.. Frontiers in Sustainable Food Systems, 1 Jul 2025. DOI: 10.3389/fsufs.2025.1578363.

Last reviewed 21 Oct 2026.