Methane (CH4) and Nitrous Oxide (N2O) Emissions from Animal Husbandry

Abstract

The greenhouse gases methane (CH 4 ) and nitrous oxide (N 2 O) contribute to global warming. N2 O also affects the ozone layer. The most important sources of greenhouse gas emissions in agricultural animal husbandry are the animals, animal houses (indoor storage of animal excreta), the outside storage of manure and slurry and their treatment (e.g. compost- ing), as well as the spreading of manure and chemical fertilizers. The source of methane emissions from animal husbandry is largely endoge- nous. Nitrous oxide, however, is mainly produced and emitted during the storage and treatment of animal excreta, as well as after spreading. Although in many countries emphasis is already being placed on the re- duction of environmental pollution caused by nutrients, ammonia emis- sion and odour nuisance, the reduction of the emission of greenhouse gases will become equally important in the near future to meet inte- grated sustainability criteria (Kyoto agreement). While ammonia- and odour emissions affect farmers directly, it is currently not absolutely neces- sary to reduce greenhouse gas emissions because no laws governing this field have been enacted yet. As compared with ammonia emission, only a few data regarding the emission of CH4 and N2O from animal husbandry are available in the literature. In addition, these values can be used only to a very limited extent. The literature summarized below shows that reliable data regarding CH4 emissions are more or less available only for animal housing systems. There are virtually no data for N2O, mainly because the measurement of N2O concentrations sometimes causes considerable diffi- culties (detection limits of continuously working measuring instruments, e.g. IR spectrometer). There is a large variation in the emissions rates stated in the literature, which must mainly be attributed to the large number of parameters (e.g. temperature, substrate) that determine the emission of greenhouse gases. For this reason, some normative values, e.g. those used in national and international emission budget calculation, may have to be revised fre- quently based on the outcome of experimental research. As knowledge about source-specific emission rates grows, there is an increasing need for a more detailed description of the emission factors used in national emission budget calculations and of the parameters which influence them.