Ammonia is formed by the breakdown of nitrogenous organic compounds. Being volatile, it is easily released into the atmosphere, where it contributes to fine-dust formation. Furthermore, it is transported within the atmosphere and deposited on soils or surface waters, where it can pollute ecosystems through over-fertilisation and acidification. After its release into soil and water it is converted via nitrification and denitrification, which may produce the greenhouse gas nitrous oxide. Agriculture is far and away the greatest contributor to ammonia emissions, which originate chiefly in the animal production sector, from animal housing and from the storage and spreading of farmyard manures (slurry, dung).
The agri-environmental indicator ‘ammonia emissions’ (kg-N per hectare of utilised agricultural area) is calculated with a tool based on the model ‘Agrammon’ and uses ALFAM2 to calculate emissions from slurry application. The tool covers mineral fertilizer applications and the following components associated with emissions from animal production:
- housing and exercise yard;
- storage of farmyard manures;
- application of farmyard manures.
Calculations are based on soluble nitrogen.
Ammonia emissions from cattle depend on the type of housing: more ammonia is emitted in free-stall housing, where excrement is distributed over a greater surface area, than in tied-housing systems. In addition, housing type influences the relative proportions of dung and slurry produced. This is important, since slurry and dung emit different amounts of ammonia. The absolute quantity of dung and slurry produced also depends on the time spent by the animals on pasture or in the yard.
The most important factor influencing ammonia emissions from stored slurry is whether or not the store is covered. With regard to spreading, the weather as well as the technique used are important. Emissions are higher if the slurry is spread on particularly warm days. Emissions are lower when a band spreader is used rather than a splash plate. With manure spreading, the speed with which the manure is worked into the soil is of decisive importance; if the process is accomplished quickly, ammonia emissions can be significantly reduced.
Plant production also makes a small contribution to ammonia emissions, since the use of mineral and recycling fertilisers releases ammonia. In previous versions of Agrammon, moreover, it was assumed that plants and soils additionally emit 2 kgN per hectare of utilised agricultural area. Meanwhile, however, the assumption that ammonia uptake and release by plants is in balance has gained currency (EMEP/EAA 2016).