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

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 N-15 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) of biochar reduced the N2O emission factor from urine by 70%. The atom% N-15 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 N-15 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.