Effects of woodchip biochar on temperature sensitivity of greenhouse gas emissions in amended soils within a mountain vineyard

Abstract

The utilization of biochar as a soil amendment holds promise for long-term carbon sequestration due to its elevated carbon content and persistent chemical structure. This characteristic has positioned biochar as a proposed nature-based solution for climate change mitigation. Nevertheless, the impact of biochar on soil greenhouse gas (GHG) emissions remains a subject of ongoing debate. In the present investigation, we evaluated the influence of conifer wood biochar on the fluxes of three GHGs, namely carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄), in a vineyard soil subjected to biochar-alone treatments (at rates of 25 and 50 t ha⁻¹) and in combination with green waste compost (at a rate of 45 t ha⁻¹). The experimental field was situated in northern Italy and was organized in a randomized block design. Soil GHG fluxes were monitored for two and a half years. Monthly flux measurements were conducted using a high-resolution multi-gas analyzer for 24 hours. Fluxes were, therefore, correlated with soil temperature to assess the influence of treatments on the sensitivity of GHG emissions to this pivotal environmental parameter. The findings demonstrated diminished temperature sensitivity in the initial experimental year across all GHG fluxes in soils amended with biochar and biochar-compost combination, in contrast to treatments lacking biochar (i.e., control and compost-alone treatments). Notably, the attenuation was most pronounced for N₂O emissions, suggesting a potential role of biochar in mitigating the release of this gas. However, this effect did not persist in the second and third years of the experiment. Overall, biochar significantly contributed to a reduction in N₂O fluxes and an increase in CO₂ fluxes, but the effect was limited and temporary. Furthermore, biochar had no impact on CH₄ fluxes. The discerned fluctuation in the impact of biochar over time can be attributed to the processes of biochar aging and/or the interannual variability in soil moisture.