From lab success to field uncertainty: Limits to biochar’s N₂O mitigation

Nitrous oxide (N2O), a potent greenhouse gas and the leading ozone-depleting substance, poses a major threat to climate stability and environmental sustainability. While biochar shows promise for mitigating soil N2O emissions in labs, its long-term field efficacy remains uncertain, limiting its scalability as a mitigation strategy. By synthesizing 874 paired N2O measurements from global soils with and without biochar amendment, we reveal a pronounced lab–field disparity: robust reductions (–31%, 95% CI: –41% to –19%) in incubations but only marginal effects (–11%, 95% CI: –27% to 10%) in the field. Mechanistically, diminished acid buffering from biochar aging and attenuated nitrogen substrate limitation in field soils constrain its capacity to enhance complete denitrification (N2O→N2) and suppress nitrifier activity. These constraints challenge the direct extrapolation of lab-scale results to agriculture settings and underscore the urgent need to refine biochar design and application strategies to unlock its full climate mitigation potential.