Nutrient Management Research Database

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−1to 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−1yr−1versus 2.00 ± 0.66 kg N2O-N ha−1yr−1in year one, and 4.24 ± 0.74 kg N2O-N ha−1yr−1versus 1.60 ± 0.28 kg N2O-N ha−1yr−1in 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 N2Oemissions 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.

This study took place in a commercial wine grape vineyard, located in northern Lodi, and was conducted over two years between 2010 and 2012.

• The study plots were 500m2 and consisted of four vine rows and 3 rows with cover crops.  Each plot had two functional locations, the berm and the row. 
• Treatments included walnut shell biochar (WS), pine chip biochar (PC) and control, and there were three replicates of each treatment.  Biochar was applied at a rate of 10 Mg ha^-1 and rows were disked to 15cm on the same day of application.
• Plots were under hanging drip irrigation and fertilizer was delivered through drip lines.  Synthetic N was only applied in the spring/summer of the first year (9.6 kg N ha^-1).  In the second year a total of 66.4 kg N ha^-1 was applied in 5 applications.
• A cover crop mixture of sweet pea, vetch, faba bean and barley was planted in the rows each fall and mowed in April.
• Soil samples were taken before the incorporation of biochar, and at 12 months and 18 months after incorporation.  Soil was assessed for gravimetric moisture content, macro and micro nutrients and cation exchange capacity.
• N20 and CO2 gas was measured one day before management and rain events and then for 7-10 days afterward. Soils were also sampled at the time of daily gas measurements near each gas sampling chamber for nitrate, ammonium, dissolved organic carbon and pH.

• Neither walnut shell or pine chip biochar decreased N20 emissions.
• In year two, N20 emissions were higher in the berm where pine chip biochar was applied when compared to the control. N20 emissions were also higher for both years in the pine chip biochar treatment rows than in the control.
•  Walnut shell biochar increased pH when compared to the control treatment.
• Pine chip biochar increased total berm soil C after 12 and 18 months relative to the control, and both biochar treatments resulted in higher total soil C in vine rows when compared to the control after 18 months.
• Pine chip biochar increase cover crop yield by 155% in the first year.