Will Biochar Suppress or Stimulate Greenhouse Gas Emissions in Agricultural Fields? Unveiling the Dice Game through Data Syntheses.

With the increasing popularity of biochar as a soil amendment worldwide in recent years, a question of concern arises as to whether the application of biochar would suppress or stimulate greenhouse gas (GHG) emissions. In this study, published data extracted from independent individual studies were systematically selected, statistically processed, graphically presented and critically analyzed to understand biochar's influences on the emissions of CO₂, CH₄ and N₂O—the three major GHGs emitted in agricultural fields. The results revealed not only the significant importance of biochar's pyrolysis temperature for its impacts on GHG emissions, but also the dissimilar influences on the generations of different GHGs. The application of biochar, in general, stimulated the emissions of CO₂ and CH₄ to various extents. With biochar pyrolyzed under relatively lower temperatures (e.g., <500 °C), higher application rates generally resulted in more stimulated CO₂ and CH₄ emissions; whereas those pyrolyzed under relatively higher temperatures (e.g., >550 °C) became less stimulative (and sometimes even suppressive) for CO₂ and CH₄ emissions, especially when applied at higher rates. Nevertheless, the response of N₂O emission to biochar application contrasted with those of CO₂ and CH₄. The results may contribute to better regulations for biochar application in combating GHG emissions in agriculture. [ABSTRACT FROM AUTHOR]