Biochar production under low pyrolysis temperature leads to lesser overall global warming potential and greenhouse gas intensity under lowland and upland short-term condition

Biochar is a carbon-rich black stable solid substance that when utilized as soil amendment can effectively mitigate greenhouse gas (GHG) emission. However, during the pyrolysis process of organic feedstock (i.e. manure) greenhouse gases are released as the feedstock undergo thermochemical degradation. Many studies were reported with regards to the effectiveness of biochar to mitigate greenhouse gas emission and to maintain soil quality via carbon sequestration. However, no clear investigation was done regarding biochar utilization on reducing GHG emission in an integrated perspective that starts from pyrolysis (production) to field application (utilization). To evaluate the integrated influence of biochar utilization on the overall Global Warming Potential (GWP) and (Greenhouse Gas Intensity) GHGI at different temperature, the fluxes of GHGs during feedstock pyrolysis to soil application were calculated. The key components include GHGs released during production processes and biogenic GHG emissions taking place in the soil via short-term incubation experiment in lowland and upland condition treated with biochar pyrolyzed at different temperature. Highest pyrolysis temperature of 700^oC emitted 6.92 Mg CO₂-eq ton^-1 biochar, wherein 8.7% and 91.2% was contributed by Carbon dioxide (CO₂) and Methane (CH₄) effluxes, respectively, during pyrolysis. This GHG emission during pyrolysis at 700^oC was 5.6, 2.2, and 1.5 times higher than at 400^oC, 500^oC and 600^oC, respectively. Meanwhile, biochar produced at lowest temperature (Biochar400) when utilized as soil amendment emitted 43.4 and 38.2 Mg CO₂-eq ha^-1 in lowland and upland condition, respectively. In addition, this emission value under lowland (and upland) condition was 1.38 (1.36), 1.51 (1.56) and 1.86 (1.91) times higher than Biochar500, Biochar600 and Biochar700, respectively. Combining the GWP during the production and the utilization processes in lowland and upland condition reveal that at 400^oC emanates the lowest overall GWP of 93.3 and 88.1 Mg CO₂-eq ha^-1, respectively.  Moreover, under lowland (and upland) condition, overall GWP at 400^oC was noted to be 65.7% (71.7%), 131.6% (140.4%) and 221.9% (237.1%), lower than at 500^oC, 600^oC and 700^oC, respectively. In conclusion, the use of lower temperature during biomass pyrolysis and utilization of its derived biochar could be a practical approach to mitigate GHG emissions.

 

Keywords: Biochar, Pyrolysis, Greenhouse gas, Methane, Global warming potential, Greenhouse gas intensity