Unweathered wood biochar impact on nitrous oxide emissions from a bovine-urine-amended pasture soil

Abstract

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 adsorbing NH₄⁺ or NH₃. Biochar can be incorporated into the soil during renovation of intensively managed pasture soils. These managed pastures are a significant source of N₂O, 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 N₂O-producing mechanisms. A laboratory study was performed to examine the effect of biochar incorporation into soil (20 Mg ha⁻¹) on N₂O-N and NH₃–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 N₂O 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 N₂O-N emitted as a percentage of the urine N applied during the 53-d period; however, NH₃–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 higher NH₄⁺ concentrations in the presence of biochar, indicative of lower rates of nitrification. The inorganic-N pool available for N₂O-producing mechanisms was not reduced, however, by adding biochar.