Biochar is widely promoted as a tool for improving soil health and storing carbon, but its effectiveness can vary greatly from one field to another. A new global study reveals that the amount of nitrogen already present in soil is a key factor controlling both how much carbon biochar stores and how that carbon becomes stabilized.
"Our findings show that soil nitrogen status is not simply a background condition. It determines how microorganisms respond to biochar and which pathway ultimately protects carbon in soil," said corresponding author Xuejun Liu. "This knowledge can help move biochar management from a one-size-fits-all approach toward strategies tailored to local soil conditions."
Researchers from China Agricultural University conducted a comprehensive meta-analysis using 932 paired observations from 173 peer-reviewed studies involving cropland soils worldwide. They examined how biochar affected soil organic carbon, microbial biomass carbon, dissolved organic carbon, and microbial necromass carbon.
Microbial biomass carbon represents carbon contained in living soil microorganisms. Microbial necromass carbon comes from dead microbial cells and residues, which can become an important and persistent component of soil organic matter.
The researchers divided soils into low-nitrogen and high-nitrogen groups based on their initial total nitrogen content. Biochar increased all major carbon pools in both groups, but its effects were substantially stronger in nitrogen-poor soils.
In low-nitrogen soils, biochar increased soil organic carbon by 47.9%, microbial biomass carbon by 37.4%, dissolved organic carbon by 29.7%, and microbial necromass carbon by 14.0%. In high-nitrogen soils, the corresponding increases were 29.4%, 22.7%, 11.0%, and 6.15%.
The analysis also uncovered two distinct carbon storage pathways.
In high-nitrogen soils, microbial biomass was closely linked to particulate organic carbon. This indicates that biochar-supported carbon was stored mainly through physical protection within soil particles and aggregates.
In low-nitrogen soils, microbial necromass was strongly associated with mineral-bound organic carbon. Here, long-term storage depended more heavily on microbial residues attaching to mineral surfaces, a process that can protect carbon from decomposition.
The factors controlling biochar performance also differed between soil types. In high-nitrogen soils, microbial biomass responses were strongly influenced by biochar application rate, temperature, and the soil carbon-to-nitrogen ratio. Microbial necromass depended more on experimental duration, biochar carbon content, and soil pH.
In low-nitrogen soils, microbial biomass responses were driven mainly by initial soil carbon, soil depth, and treatment duration. Microbial necromass accumulation was more closely related to biochar application rate, biochar carbon content, and the length of the experiment.
The results suggest that farmers and land managers should assess soil nitrogen before selecting biochar materials and application rates. Nitrogen-poor soils may offer particularly strong opportunities for biochar-based carbon sequestration, but the most effective biochar properties and management practices will depend on local soil conditions.
The study provides a scientific basis for precision biochar management, helping agriculture store more carbon while improving the efficiency of climate-smart soil practices.
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Journal Reference: Shen, S., Zhou, R., Wu, L. et al. Soil nitrogen level controls biochar's enhancement of microbial-derived carbon sequestration. Biochar 8, 127 (2026).
https://doi.org/10.1007/s42773-026-00643-7
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About Biochar
Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.
