Pine sawdust biochar reduces GHG emission by decreasing microbial and enzyme activities in forest and grassland soils in a laboratory experiment

This study investigated the effects of biochar soil amendment on greenhouse gas (GHG) emissions in soils. Pine (Pinus koraiensis Siebold & Zucc.) sawdust biochar was produced at 300 and 550 °C with and without steam activation (coded as BC300-S, BC550-S, BC300 and BC550, respectively). They were applied to forest and grassland soils at 1.5% (w/w) rate in a 100-day laboratory incubation experiment. Application of BC550 significantly reduced cumulative CO₂ emission from the forest soil by 16.4% relative to the control (without biochar application), but not from the grassland soil. Biochar application did not have significant effects on CH₄ uptake from either soil. Application of BC550 and BC550-S reduced the cumulative N₂O emission by 27.5 and 31.5%, respectively, in the forest soil and 14.8 and 11.7%, respectively, in the grassland soil, as compared to the control. The effects of BC300 and BC300-S on cumulative CO₂ and N₂O emission was not significant in both soils, except for the significant reduction in cumulative N₂O emission from the forest soil by BC300-S. The effect of BC550 and BC550-S on N₂O emission persisted until the end of the 100-day incubation indicating possible long-term effects of these biochars. We conclude that BC550 and BC550-S had the highest potential to reduce CO₂ and N₂O emission in the 100-day laboratory incubation experiment. These biochars should be tested in long-term field trials to confirm their potential for mitigating CO₂ and N₂O fluxes in real ecosystems with a relevant time frame.