Here we present a two year study examining the impact of a high temperature (∼950 °C) walnut shell (WS) and moderate temperature (∼550 °C) pine chip (PC) biochar, applied at 10 Mg ha-1, on soil N2O emissions and fertility. Soil gas fluxes were measured daily following key management and precipitation events and otherwise, weekly, with all analyses performed at two functional locations, the berm (directly below the vines) and the row (space between vine rows). This is the first study to report annual gas emissions. Differences in cumulative N2O emissions were not significantly different in the first year, however in the second year; cumulative N2O emissions were significantly higher in the PC biochar treatment, relative to the control and WS biochar treatment, with emissions of 4.94, 2.37, 1.81 kg N2O-N ha-1 year-1, respectively. Proximal N2O drivers; NH 4+, NO3-, water filled pore space (WFPS), dissolved organic carbon (DOC) and pH were measured in conjunction with soil gas fluxes. In the berm, N2O emissions positively correlated with NH4+ concentrations for all treatments, however only the control significantly correlated with the remaining N2O drivers. At both locations, differences in NH4+, NO3-, WFPS or DOC between treatments were rarely significant and could not explain the differences in N2O emissions. Distal N2O drivers; bulk density, soil aggregation, water retention curves and field capacity measurements were taken every six or 12 months. Increases in soil aggregation, field capacity and cover crop yield were observed in the PC biochar treatment, potentially leading to changes in water and nutrient availability that promoted N2O production. Grape yield was unaffected by biochar amendment. Soil C, K and P concentrations improved following biochar amendment, but correlated with initial biochar concentrations. Our results question the validity and capacity of biochar to ameliorate temperate soils and reduce N2O emissions, and warrants further investigation.
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