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

TLDR

Low‑temperature pyrolysis of biomass yields biochar, a material promoted for carbon sequestration that can alter soil nitrogen cycling, and intensively managed pastures are a major source of nitrous oxide from ruminant urine patches. The study tested whether incorporating biochar into pasture soil would reduce the soil inorganic‑N pool available for N₂O production. In a laboratory experiment, 20 Mg ha⁻¹ biochar was mixed into soil and bovine urine (760 kg N ha⁻¹) applied, with treatments of soil alone, soil + biochar, soil + urine, and soil + biochar + urine, to measure N₂O‑N and NH₃‑N fluxes and inorganic‑N transformations. Biochar addition did not reduce the inorganic‑N pool or cumulative N₂O emissions over 53 days, and while N₂O fluxes were initially higher in the biochar‑plus‑urine treatment, they converged with urine alone after 50 days; NH₃‑N fluxes were slightly increased (~3 % of applied N) with biochar.

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 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 higher 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.