Context-Dependent Effect of Biochar on Soil Greenhouse Gas Emissions.

Biochar application to soil has been proposed as a means for greenhouse gas emissions mitigation, due to both the removal of CO₂ from the atmosphere through biochar production and soil application and potentially through reduction of soil greenhouse gas emissions. The effects, however, of interactions between biochar, moisture and temperature on soil CO₂ and N₂O emissions, and the applicability of lab scale observation, remain poorly understood.  Here we compare the impact of a mixed wood gasification biochar on CO₂ and N₂O emissions under controlled laboratory incubation at three moistures and temperatures, with emissions from field soils under four cropping systems. Biochar reduced N₂O emissions under specific temperatures and moistures in the laboratory and in the continuous corn cropping system in the field. However, the effect of biochar on N₂O emissions was only significant in the field, and no consistent effect on CO₂ emissions was observed. Results were consistent with previous studies showing that, while biochar can be used to reduce soil N₂O emissions under specific conditions, its efficacy is context-dependent. The disparity in N₂O emission responses at the lab and field scales suggests that laboratory incubation experiments may not always accurately predict the impact of biochar at the field scale.