Biochar amendments mitigate soil greenhouse gas emissions by shifted soil properties, enzyme activities, and nitrogen cycling processes

Abstract Amending agricultural soils with biochar has emerged as a promising approach to sustainably mitigate soil greenhouse gas (GHG) emissions, but information on mechanisms underlying biochar-induced emission dynamics of GHGs remains limited. Our study aimed to comprehensively explore the significance of biochar mediated changes of soil properties, enzyme activities, and nitrogen cycling processes, for mitigating GHG emissions and lowering the concomitant global warming potential (GWP). For this purpose, we conducted a meta-analysis of 78 published studies investigating the effects of biochar amendments on soil properties in agricultural systems worldwide. Biochar amendment significantly increased soil porosity, moisture and total carbon (+ 57% to + 62%), but also soil organic carbon (+ 24%) and total nitrogen (+ 26%). Additionally, salinity, cation exchange capacity, base saturation, and C:N ratio increased (+ 20% to + 29%), while bulk density, labile organic carbon, ammonium- and ammonia–nitrogen, nitrate- and nitrite-nitrogen decreased (− 8% to –38%). Biochar negatively affected the activities of key soil enzymes, such as β-glucosidase, N-acetyl glucose-aminidase, and acid phosphatase (− 14% to − 34%), enhanced ammonification and biological nitrogen fixation (+ 11% to + 13%), while suppressing denitrification and nitrification (− 6% to − 12%). These shifts contributed to significant reductions in GHG emissions: carbon dioxide (− 24% on average), methane (− 36% to − 22%), and nitrous oxide (− 33% to − 39%). Consequently, global warming potential (GWP) was lowered, with the extent of reduction depending on biochar properties and management practices. High pyrolysis temperatures (> 400 °C), long-term application (100-year scale), and higher biochar doses (≥ 40 t·ha⁻ 1 ) induced the greatest reductions in GWP (− 83% to − 66%). Among cropping systems, rice fields benefited most from biochar application (lowest greenhouse gas emission intensity, − 53%), while maize systems contributed most to GWP among analyzed crops. Therefore, strategic biochar deployment, optimized for specific cropping systems and pyrolysis conditions, offers a powerful and scalable pathway towards climate-positive agriculture. Graphical Abstract