The effects of biochar on wetland and agricultural soil carbon and nitrogen emissions in North Carolina

Biochar is an increasingly popular topic in environmental management due to its potential effects on several ecosystem functions. Specifically, biochar has been linked to significant reductions in greenhouse gas emissions, including nitrous oxide, carbon dioxide and methane when used as a soil amendment. It has also been suggested as a long term mechanism to sequester carbon in soil. The magnitude of such an effect is highly dependent on a variety of environmental factors, as well as the feedstock and temperature at which the char was produced, so it is essential to put biochar studies in specific land use contexts to fully understand its potential impacts. Additionally, naturally occurring char material is a byproduct of prescribed burns and wildfires in fire-adapted ecosystems such as North Carolina peatlands. It is unclear to what extent this naturally occurring char aids in greenhouse gas suppression in these carbon sinks. In order to fully understand the existing and potential role of biochar for land use management in North Carolina, an experiment was designed to quantify the effect of biochar on soil greenhouse gas emission. This experiment looked at agricultural soils, organic peat soils, and heated peat soils. Treatment groups received a 10% by weight char amendment and incubated in the lab for seven months. Gas samples were collected from the headspace to determine gas emissions over time. This study finds modest effects of biochar on greenhouse gas emissions. Char-amended agricultural soils saw reduced nitrous oxide emissions, but increased carbon dioxide emissions. Peat soils saw non-significant reductions in emission rates for all three gases, including a 12% reduction in net methane emission and a 9% reduction in average carbon dioxide emission. Heated peat, which was produced to simulate the effect of a prescribed burn, released large amounts of carbon dioxide and methane in the first sampling date but stabilized to low levels after 17 days. This resulted in heated peat having net positive methane emissions, but lower net carbon dioxide outputs as compared to unheated peat. This study therefore finds evidence that fire regimes in natural peatlands disrupt normal carbon cycling even without igniting the peat, but that the presence of char in the soil contributes to stable carbon storage and greenhouse gas suppression. Effects on nitrogen flux from soils are less clear because changes in emission are driven by difference on individual sampling dates and not any apparent trend over time. Biochar addition to wetland peat soils may be a potential avenue for decreasing greenhouse gas emissions in order to maximize ecosystem services like carbon sequestration from these crucial habitats. However, more research is needed to understand impacts of biochar for agricultural management since results in this study were inconclusive. Additionally, the interaction of soil moisture and biochar on gas flux and a more holistic microcosm study design are recommended as future avenues for research.