a1 ALTERRA, Wageningen University and Research Centre, PO Box 47, 6700 AA Wageningen, the Netherlands
a2 Department of Agroecology and Environment, University of Aarhus, PO Box 50, Tjele, Denmark
a3 AgResearch Ltd, Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand
a4 Livestock Research, Wageningen University and Research Centre, PO Box 65, 8200 AB Lelystad, the Netherlands
Herbivores are a significant source of nitrous oxide (N2O) emissions. They account for a large share of manure-related N2O emissions, as well as soil-related N2O emissions through the use of grazing land, and land for feed and forage production. It is widely acknowledged that mitigation measures are necessary to avoid an increase in N2O emissions while meeting the growing global food demand. The production and emissions of N2O are closely linked to the efficiency of nitrogen (N) transfer between the major components of a livestock system, that is, animal, manure, soil and crop. Therefore, mitigation options in this paper have been structured along these N pathways. Mitigation technologies involving diet-based intervention include lowering the CP content or increasing the condensed tannin content of the diet. Animal-related mitigation options also include breeding for improved N conversion and high animal productivity. The main soil-based mitigation measures include efficient use of fertilizer and manure, including the use of nitrification inhibitors. In pasture-based systems with animal housing facilities, reducing grazing time is an effective option to reduce N2O losses. Crop-based options comprise breeding efforts for increased N-use efficiency and the use of pastures with N2-fixing clover. It is important to recognize that all N2O mitigation options affect the N and carbon cycles of livestock systems. Therefore, care should be taken that reductions in N2O emissions are not offset by unwanted increases in ammonia, methane or carbon dioxide emissions. Despite the abundant availability of mitigation options, implementation in practice is still lagging. Actual implementation will only follow after increased awareness among farmers and greenhouse gases targeted policies. So far, reductions in N2O emissions that have been achieved are mostly a positive side effect of other N-targeted policies.
(Received March 28 2011)
(Accepted August 22 2011)
(Online publication October 10 2011)