Characterization and influence of biochars on nitrous oxide emission from agricultural soil.

Extensive use of biochar to mitigate N(2)O emission is limited by the lack of understanding on the exact mechanisms altering N(2)O emissions from biochar-amended soils. Biochars produced from giant reed were characterized and used to investigate their influence on N(2)O emission. Responses of N(2)O emission varied with pyrolysis temperature, and the reduction order of N(2)O emission by biochar (BC) was: BC200 ≈ BC600 > BC500 ≈ BC300 ≈ BC350 > BC400. The reduced emission was attributed to enhanced N immobilization and decreased denitrification in the biochar-amended soils. The remaining polycyclic aromatic hydrocarbons (PAHs) in low-temperature biochars (300-400 °C) played a major role in reducing N(2)O emission, but not for high-temperature biochars (500-600 °C). Removal of phenolic compounds from low-temperature (200-400 °C) biochars resulted in a surprising reduction of N(2)O emission, but the mechanism is still unknown. Overall, adding giant reed biochars could reduce N(2)O evolution from agricultural soil, thus possibly mitigating global warming.