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%.
Click here to see more...