Trends in global nitrous oxide emissions from animal production systems

Summary

Wastes from animal production systems contribute as much as 30-50% to the global N2O emissions from agriculture, but relatively little attention has been given on improving the accuracy of the estimates and on developing mitigation options. This paper discusses trends and uncertainties in global N2O emission from animal waste and discusses possible mitigation strategies, on the basis of literature data and results of simple calculations. Total N2O emissions from animal production systems are estimated at 1.5 Tg. Dung and urine from grazing animals deposited in pastures (41%), indirect sources (27%), animal wastes in stables and storages (19%), application of animal wastes to land (10%) and burning of dung (3%) are the five sources distinguished. Most sensitive factors are N excretion per animal head, the emission factor for grazing animals and that for indirect emissions. Total N2O emissions are related to type and number of animals, N excretion per animal, and the management of animal wastes. Projections by FAO suggest that animal numbers will increase by 40% between 2000 and 2030. Mean N excretion per animal head will probably also increase. These trends combined suggest a strong increase in total N2O emission from animal production systems in the near future, which is opposite to the objectives of the Kyoto Protocol. Improving N use efficiency, combined with anaerobic digestion of animal wastes for bio fuel generation are the most feasible options for mitigation, but these options seem insufficient to reverse the trend of increasing N2O emission. In conclusion, animal production systems are a major and increasing source of N2O in agriculture. The uncertainties in the emission estimates are large, due to the many complexities involved and the lack of accurate data, especially about N excretion and the management of animal wastes in practice. Suggestions are made how to increase the accuracy of the emission estimates and to mitigate N2O emission from animal production systems.