摘要：

Biochar amendment to soil has been proposed as a mechanism to mitigate climate change through an array of mechanisms; one being the mitigation of soil nitrous oxide (N2O) emissions. Yet the extent and mechanisms through which this may be achieved in temperate agroecosystems is uncertain. We used a pine chip biochar produced at a moderate temperature (550 °C, \\{PC\\} biochar) and a walnut shell biochar produced at a higher temperature (900 °C, \\{WS\\} biochar). Biochar was applied at 10 Mg ha−1 to a working commercial wine grape system in North-Central California. The effects of biochar were assessed over two years at two distinct functional locations: the berm and row, which differed in N application and irrigation. \\{N2O\\} emissions and ancillary soil properties (NH4+, NO3, water filled pore space (WFPS), and pH) were closely monitored following management and precipitation events. Soil bulk density, cover crop yield and soil C and N were measured annually to address longer term changes in cropping system and soil properties. In the \\{PC\\} biochar treatment, annual cumulative \\{N2O\\} emissions were significantly higher than the control treatment each year (p < 0.05); 4.14 ± 1.14 kg N2O-N ha−1 yr−1 versus 2.00 ± 0.66 kg N2O-N ha−1 yr−1 in year one, and 4.24 ± 0.74 kg N2O-N ha−1 yr−1 versus 1.60 ± 0.28 kg N2O-N ha−1 yr−1 in year two. Emissions of \\{N2O\\} in the \\{WS\\} biochar treatment were also higher than the control each year, but differences were not significant. The effect of biochar on \\{N2O\\} emissions was more pronounced in the row location where annual emissions were significantly higher than the control in one and both years for the \\{WS\\} and \\{PC\\} biochars, respectively (p < 0.05). In the \\{PC\\} biochar treatment, we observed increased \\{N2O\\} emissions at both functional locations, however increases were more pronounced in the row location where they were in part attributable to increased cover crop N inputs. Differences between treatments in NH4+, NO3− and \\{WFPS\\} were mostly not significant. The \\{WS\\} biochar significantly raised soil pH relative to the control (p < 0.05), however in the berm location only, and increased soil pH in this treatment did not correspond to changes in \\{N2O\\} emissions. Since neither biochar amendment reduced \\{N2O\\} emissions, our results demonstrate the need to evaluate \\{N2O\\} emissions at a cropping system scale (e.g. encompassing changes in N inputs and cycling) and in systems where nitrification processes may dominate emissions.

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