Biochar incorporation into pasture soil suppresses in situ nitrous oxide emissions from ruminant urine patches

Abstract

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 of biochar 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.