Robert R. Sherlock

Nitrous oxide (N2O) emissions from grazing animal excreta are estimated to be responsible for 1.5 Tg of the total 6.7 Tg of anthropogenic N2O emissions. This study was conducted to determine the in situ effect of incorporating biochar, into soil, on N2O emissions from bovine urine patches and associated pasture uptake of N. The effects of biochar rate (0-30 t ha(-1)), following soil incorporation, were investigated on ruminant urine-derived N2O fluxes, N uptake by pasture, and pasture yield. During an 86-d spring-summer period, where irrigation and rainfall occurred, the N2O fluxes from 15N labeled ruminant urine patches were reduced by >50%, after incorporating 30 t ha(-1) of biochar. Taking into account the N2O emissions from the control plots, 30 t ha(-1) ofbiochar reduced the N2O emission factor from urine by 70%. The atom% 15N enrichment of the N2O emitted was lower in the 30 t ha(-1) biochar treatment, indicating less urine-N contributed to the N2O flux. Soil NO3- -N concentrations were lower with increasing biochar rate during the first 30 d following urine deposition. No differences occurred, due to biochar addition, with respect to dry matter yields, herbage N content, or recovery of 15N applied in herbage. Incorporating biochar into the soil can significantly diminish ruminant urine-derived N2O emissions. Further work is required to determine the persistence of the observed effect and to fully understand the mechanism(s) of the observed reduction in N2O fluxes.

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.