Interest in biochar stems from its potential agronomic benefits and carbon sequestration ability. Biochar application alters soil nitrogen (N) dynamics. This review establishes emerging trends and gaps in biochar-N research. Biochar adsorption of NO₃⁻, up to 0.6 mg g⁻¹ biochar, occurs at pyrolysis temperatures >600 °C with amounts adsorbed dependent on feedstock and NO₃⁻ concentration. Biochar NH₄⁺ adsorption depends on feedstock, but no pyrolysis temperature trend is apparent. Long-term practical effectiveness of inorganic-N adsorption, as a NO₃⁻ leaching mitigation option, requires further study. Biochar adsorption of ammonia (NH₃) decreases NH₃ and NO₃⁻ losses during composting and after manure applications, and offers a mechanism for developing slow release fertilisers. Reductions in NH₃ loss vary with N source and biochar characteristics. Manure derived biochars have a role as N fertilizers. Increasing pyrolysis temperatures, during biochar manufacture from manures and biosolids, results in biochars with decreasing hydrolysable organic N and increasing aromatic and heterocyclic structures. The short- and long-term implications of biochar on N immobilisation and mineralization are specific to individual soil-biochar combinations and further systematic studies are required to predict agronomic and N cycling responses. Most nitrous oxide (N₂O) studies measuring nitrous oxide (N₂O) were short-term in nature and found emission reductions, but long-term studies are lacking, as is mechanistic understanding of reductions. Stable N isotopes have a role in elucidating biochar-N-soil dynamics. There remains a dearth of information regarding effects of biochar and soil biota on N cycling. Biochar has potential within agroecosystems to be an N input, and a mitigation agent for environmentally detrimental N losses. Future research needs to systematically understand biochar-N interactions over the long term.

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.