Interactions and coupling between emissions of methane and nitrous oxide from animal husbandry

The gases methane (CH4) and nitrous oxide (N2O) contribute to global warming, while N2O also affects the ozone layer. Sources of greenhouse gas emissions in animal husbandry include animals, animal houses (indoor storage of animal excreta), outdoor storage, manure and slurry treatment (e.g., composting, anaerobic treatment), land application and chemical fertilisers. Although in many countries emphasis is put on reduction of environmental pollution by nutrients, ammonia emission and odour nuisance, reduction of the emission of greenhouse gases will become equally important in the near future to meet integrated sustainability criteria (1997 Kyoto protocol). Emissions of greenhouse gases differ in origin. Methane from animal husbandry is for a large part endogenous, and may be hard to reduce in intensive animal production. Methane emission reduction strategies should focus on its use as fuel or preventing its formation, mainly during on-farm storage (indoor, outside) or treatment through control of critical processes (degradation of organic matter) and critical factors (e.g., temperature). Nitrous oxide is mainly produced during the aerobic storage and treatment of animal excreta, as well as after land spreading. As N2O basically is an intermediate product of complex biochemical processes (nitrification, denitrification), optimal process conditions are the key issues in N2O emission reduction strategies from animal husbandry.