Facts & Figures
Emissions of ammonia from agriculture
Roland Fuß, Cora Vos und Claus Rösemann | 25.05.2022
Emissions of ammonia (NH3) lead, via input of nitrogen, to eutrophication of close-to-nature ecosystems. Through further transformation processes they contribute to soil acidification, groundwater contamination and indirect emission of nitrous oxide (N2O). Moreover, the emission of ammonia causes the generation of particulate matter and thus jeopardises human health.
In the context of an international convention on air quality control (NEC Directive), Germany committed itself to comply with a national maximum amount of emissions of 550 kilo tons NH3 per year as of 2010. Since then, this level has continuously been exceeded by about 20 %. This is shown by the agricultural ammonia inventory, which reports emissions from animal husbandry (housing, storage of manure) and soils (spreading of manure and mineral fertilisers, grazing).
On 8 December 2016 the European Council adopted a new NEC Directive aiming at an even more significant reduction of emissions. In contrast to the previous NEC Directive it does not define a specific amount of emissions, but a percentage reduction of ammonia emissions relative to the base year 2005. According to the current emission data from 2005, from 2030 an upper limit of 423 kt applies. This leads to an increased pressure on policy makers to launch abatement measures. Especially German agriculture faces adaptive challenges as it contributes more than 90% to the national ammonia emissions.
The most important source of emissions of ammonia in agriculture is manure (slurry, farmyard manure, leachate, but also digestate from biogas plants). Manure generally contains high amounts of ammonium nitrogen (NH4+-N) which can rapidly be transformed into gaseous ammonia, in particular on exposure to the atmosphere. In that way it discharges to the air and is lost as a nutrient for crops. Such losses occur in housing systems, manure storage systems and during the spreading of manure and have to be reduced as far as possible.
The most efficient and comparatively inexpensive way is to avoid losses when spreading farm manure. To do this, contact with the atmosphere must be kept as short as possible. A band-shaped application close to the ground (drag hose) with subsequent rapid incorporation into the soil or the use of a slurry cultivator (immediate incorporation) ensures this in the case of liquid farm fertilizers on uncultivated arable land. If the fertilizer is spread in the crop or on grassland, incorporation in this form is not possible. However, there are injection and slurry cultivation methods as well as slurry cultivators, which are rarely used in Germany.
In storage, emissions can be avoided by covering slurry and digestate stores as gas-tight as possible and by not storing the excrement in the barn, e.g. under a slatted floor. A floating sheet, for example, reduces emissions by 85 percent compared to an uncovered storage facility.
In barns for pig and poultry farming, ammonia can be filtered out of the air with exhaust air purification systems. Since cattle in Germany are mostly kept in freely ventilated loose housing, an exhaust air purification system would have no effect here.
NH3 is also formed after the application of mineral fertilizers. Urea has a particularly high emission potential. Emissions could be reduced if another type of low-grade fertilizer, e.g. calcium ammonium nitrate, were used instead of urea. According to the current Fertilizer Ordinance, urea may only be applied in combination with emission-reducing measures (addition of urease inhibitor or incorporation within four hours) from February 2020.