Control of Gaseous Emissions from Livestock Buildings and Manure Stores

Abstract

Agricultural animal production is increasingly regarded as a source of gases which are both aggravating and ecologically harmful. An overview of the origin, number and quantity of trace gases emitted from animal housing and from manure stores is presented and possible means of preventing or reducing them are discussed. Of the 136 trace gases in the air of animal houses, ammonia and methane present the greatest risk to the environment. Quantitative information on concentrations found in air is available for only 23 of these gases. The gases are emitted principally from freshly deposited and stored excreta, from animal feed and from the animals themselves. Future work should determine sources and quantities of the gases emitted from animal housing more precisely and should aim to investigate the potential of these gases to cause damage to man, animals and environment. Total ammonia emissions from animal production in the former West Germany are estimated as approximately 300 000 to 700 000 t/a. It is calculated that between 10 and 23 kg/ha of nitrogen a year enters the soil via the air from these sources, the average of which is higher than the average "critical loads" for most natural habitats. However, there is still a shortage of satisfactory information on the extent of emissions, in particular on those from naturally ventilated animal houses. Ammonia has a direct effect on the trees in the area surrounding animal houses and is also transported long distances through the air causing eutrophication and acidification of water and soil. This frequently results in changes in plant ecology, hence reducing plant diversity. Reduction measures must begin with the housing and manure removal systems and with feeding and management. Factors such as the protein content of feeds, the pH value of slurry and feed additives, air temperature, air exchange rate and litter affect the extent of ammonia emissions from animal housing. Sustained reduction of emissions from outdoor stores is possible by using various coverings. The greatest research need is perceived to be in the area of feed practices which reduce nitrogen and the development of low emission housing and manure removal systems as well as in a detailed compilation of emission factors. As regards the environment, probably the most important carbon-containing gas is methane, which contributes to the "greenhouse effect". Emissions from animal husbandry in Germany are estimated at about 2Mt/a. This corresponds to 0·15% of the assumed global emission from all sources. There is still little knowledge about the quantities of the greenhouse gas nitrous oxide (N 20) released from agricultural animals. It is estimated that agriculture in Germany emits between 5 and 23 kt/a. It will take some time for reduction measures to be put into practice and the possibility of reducing livestock numbers should also be included in the discussion. Ammonia emissions from animal production represent a considerable loss in valuable fertilizer nitrogen. A reduction in emissions is therefore necessary not only for environmental protection but also to minimize economic loss.