Biochar Incorporation into Pasture Soil Suppresses in situ Nitrous Oxide Emissions from Ruminant Urine Patches

Nitrous oxide (N 2 O) emissions from grazing animal excreta are estimated to be responsible for 1.5 Tg of the total 6.7 Tg of anthropogenic N 2 O emissions. This study was conducted to determine the in situ effect of incorporating biochar, into soil, on N 2 O 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 N 2 O fluxes, N uptake by pasture, and pasture yield. During an 86‐d spring‐summer period, where irrigation and rainfall occurred, the N 2 O fluxes from 15 N labeled ruminant urine patches were reduced by >50%, after incorporating 30 t ha −1 of biochar. Taking into account the N 2 O emissions from the control plots, 30 t ha −1 of biochar reduced the N 2 O emission factor from urine by 70%. The atom% 15 N enrichment of the N 2 O emitted was lower in the 30 t ha −1 biochar treatment, indicating less urine‐N contributed to the N 2 O flux. Soil NO 3 − ‐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 15 N applied in herbage. Incorporating biochar into the soil can significantly diminish ruminant urine‐derived N 2 O 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 N 2 O fluxes.