Unweathered Wood Biochar Impact on Nitrous Oxide Emissions from a Bovine‐Urine‐Amended Pasture Soil

Low‐temperature pyrolysis of biomass produces a product known as biochar The incorporation of this material into the soil has been advocated as a C sequestration method. Biochar also has the potential to influence the soil N cycle by altering nitrification rates and by adsorbingNH 4 +or NH 3 Biochar can be incorporated into the soil during renovation of intensively managed pasture soils. These managed pastures are a significant source of N 2 O, a greenhouse gas, produced in ruminant urine patches. We hypothesized that biochar effects on the N cycle could reduce the soil inorganic‐N pool available for N 2 O‐producing mechanisms. A laboratory study was performed to examine the effect of biochar incorporation into soil (20 Mg ha −1 ) on N 2 O‐N and NH 3 –N fluxes, and inorganic‐N transformations, following the application of bovine urine (760 kg N ha −1 ). Treatments included controls (soil only and soil plus biochar), and two urine treatments (soil plus urine and soil plus biochar plus urine). Fluxes of N 2 O from the biochar plus urine treatment were generally higher than from urine alone during the first 30 d, but after 50 d there was no significant difference ( P = 0.11) in terms of cumulative N 2 O‐N emitted as a percentage of the urine N applied during the 53‐d period; however, NH 3 –N fluxes were enhanced by approximately 3% of the N applied in the biochar plus urine treatment compared with the urine‐only treatment after 17 d. Soil inorganic‐N pools differed between treatments, with higherNH 4 +concentrations in the presence of biochar, indicative of lower rates of nitrification. The inorganic‐N pool available for N 2 O‐producing mechanisms was not reduced, however, by adding biochar.