Nitrous oxide emissions from ruminant urine: science and mitigation for intensively managed perennial pastures

Despite optimising fertiliser practice and nitrogen (N) use efficiency nitrous oxide N2O generation from ruminant-urine deposition prevails due to the concentration of N in the urine excreted. Development and application of mitigation strategies to reduce N2O emissions from grazed pasture systems requires knowledge of production and consumption pathways, and factors affecting these. Soil physical properties regulate the soil aeration status (redox potential) selecting for microbial pathways processing inorganic-N. Mitigation of N2O emissions must initially target the prevention of NO and NO2− during nitrification by inhibiting ammonia oxidation, but must also consider what microbes are being targeted. Biological nitrification inhibition as a potential mitigation option in pasture systems remains under researched. Emerging research demonstrates that previously unrecognised effects of soil organic matter content, soil fertility (phosphorus levels) and non-linear effects of soil temperature on nitrification require a better understanding in relation to N2O emissions and their mitigation.