Data collected during field and laboratory experiments to investigate the long-term effects of biochar application to soil on greenhouse gas emissions in a bioenergy plantation (Miscanthus X. giganteus). Analysis included monitoring of greenhouse gas emissions (carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O)), soil physical (bulk density and soil moisture ) and soil chemical analyses (total carbon (C) and nitrogen (N), extractable ammonium and nitrate). Biochar was applied to plots in a bioenergy plantation and emissions of CO2, CH4 and N2O were measured over a two-year period. In addition a laboratory incubation experiment was conducted on soil taken from the Miscanthus field amended with field-incubated biochar to assess the effect on greenhouse gas emissions. Biochar is a carbon rich substances which is being advocated as a climate mitigation tool to increase carbon sequestration and reduce nitrous oxide emissions. Full details about this dataset can be found at https://doi.org/10.5285/e9baffd1-18ad-435e-94e2-01e49c14c547