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

TLDR

Nitrous oxide emissions from grazing animal excreta account for 1.5 Tg of the 6.7 Tg of anthropogenic N₂O, highlighting the need to understand and mitigate these emissions. The study aimed to assess how incorporating biochar into pasture soil affects N₂O emissions from bovine urine patches and pasture nitrogen uptake and yield. The authors applied 0–30 t ha⁻¹ of biochar to soil and measured resulting N₂O fluxes, pasture N uptake, and yield. During an 86‑day trial, 30 t ha⁻¹ biochar reduced N₂O fluxes from urine patches by >50 % and lowered the emission factor by 70 %, while also decreasing early NO₃⁻‑N concentrations, yet had no effect on pasture yield or nitrogen recovery.

Abstract

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.