Impacts of biochar application to a Douglas-fir forest soil on greenhouse gas fluxes and water quality

Forest management for carbon sequestration is a valuable tool to combat rising greenhouse gas (GHG) concentrations in the Earth’s atmosphere. This thesis examined the use of biochar, a product of the thermal decomposition of waste organic matter in a reduced oxygen environment (i.e. pyrolysis) that is applied to soil, as an option for increasing carbon sequestration in a Coastal Douglas-fir forest soil in British Columbia when applied with and without urea fertilizer at 200 kg N ha-¹. Biochar produced from Douglas-fir forestry slash materials was used in this study to address this from a systems-based perspective. A soil incubation study showed that biochar application at high rates (10% oven dry soil basis) significantly increased CO₂ and N₂O emissions when applied without fertilizer and at both low (1%) and high rates (10%) decreased CH₄ consumption without fertilization. In terms of carbon dioxide equivalent emissions (CO₂e), it was shown that CO₂ accounted for >98% from all treatments. In a field study, GHG fluxes were measured after application of 5 t ha-¹ of biochar to a Douglas-fir forest soil in the first year followed by urea-N fertilization in the second year. The results showed that 5 t ha-¹ of biochar had little effect on GHG fluxes and their total CO₂e fluxes. Applying biochar prior to fertilizer application following industry-standard practices did not significantly change treatment CO₂e fluxes. It was concluded that low rates of biochar application to this forest soil would improve soil C sequestration with or without fertilization. In the field and laboratory experiments, soil pore water was extracted and analyzed for C and N concentrations and dissolved organic carbon using spectral indices. The results showed that low biochar application rates could be beneficial for both increasing C-sequestration and N-retention. Changes in spectral indices measured in the laboratory suggested that alterations in the dissolved organic matter pool could lead to changes in GHG emissions due to changing substrate supply for microbes as application rates increased. There is a recognized need for further studies prior to large-scale industrial applications; however, as result of this work it is possible to provide recommendations for large-scale pilot studies.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat