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 454 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 effective and comparatively cost-efficient way is to avoid losses from spreading of manure. Hence exposure to the atmosphere must be kept as short as possible. This is ensured by close-to-soil linear spreading (trailing hose) followed by fast incorporation into soil or by using a grubber (immediate incorporation) for liquid manure on fallow agricultural crop land. Such incorporation is not possible if manure is spread onto crops or grassland. For this case injection procedures and the slurry cultivator technique are available which, however, have rarely been used in Germany so far.
Emissions from storage can be avoided by covering storage systems for slurry or digestate as gastight as possible and by not storing excrements in the housing, e.g. underneath slatted floor. A floating plastic cover, for instance, reduces emissions by about 85 % compared to an uncovered storage system.
In housing systems for pigs and poultry, ammonia can be extracted from the air with air scrubbing systems. As in Germany cattle is mostly kept in ventilated pens, air scrubbing would have no effect.
Application of mineral fertilizer causes NH3 emissions as well. Urea has a particularly high emission potential. A reduction in emissions could be achieved if another type of fertilizer, e.g. calcium ammonium nitrate, were used instead of urea. According to the current fertilizer ordinance, from February 2020 urea may only be applied in combination with emission-reducing measures (addition of urease inhibitor or incorporation within four hours).