Less ammonia in the air makes a decisive contribution to cutting harmful air pollution and reducing nitrogen deposition in sensitive ecosystems. Cost-effective measures to reduce ammonia emissions from agriculture exist and have already been implemented. A number of measures have been documented and evaluated in a series of reports. The choice of measures to be taken at farm level depends on a number of factors. The UN Economic Commission for Europe (UN ECE Task Force on Reactive Nitrogen) Framework Code of Agricultural Practice describes helpful techniques as well as housing and storage systems to reduce ammonia emissions.
Ammonia emissions from slurry can be cut by reducing the exposed surface area of slurry or other liquid manure in storage. Possible measures:
Solid manure should be stored as dry and as covered as possible. A small surface area of the solid manure stack, e.g. through a side wall, also helps to reduce ammonia emissions.
It is very important to minimise nitrogen losses during fertilisation in the field so that the ammonia that was previously prevented from volatilising in the barn or during storage is not lost here. Emission-reducing application techniques cover the slurry with soil directly at or immediately after application, or reduce the exposed surface of the fertiliser. These techniques include:
Farm fertilizer usually has a higher pH value and is alkaline. By acidifying the slurry to a neutral level or to a pH value of 6, the outgassing of ammonia is reduced by at least 50 percent. This is achieved in conventional agriculture by adding sulphuric acid. A process for the automatic addition of sulphuric acid during application is already on the market and is used throughout Denmark.
The procedure must at all times take care to avoid any risk to personnel, animals and the environment. The efficiency increases the sooner the acid is added. Acidification in the barn is therefore widely discussed in Germany.
In ruminants, protein surpluses and N excretion depend heavily on the crude protein content of the feed. The feed composition and feed management thus have a strong influence on the resulting ammonia emissions per livestock unit or per production unit (e.g. 1 l milk). If it is ensured that farm animals are not fed with more protein than is necessary to achieve the desired performance level, N excretion can be reduced. The reduction of emissions per production unit requires good animal husbandry to ensure optimum feed utilisation. Animal genetics, living conditions and animal care knowledge are prerequisites for good animal health.
The following feeding methods help to reduce ammonia emissions.
Ammonia losses from ammonium nitrate (NH4NO3) are generally only in the range of 0.5 % to 5 % of the total nitrogen applied. Ammonium nitrate therefore has an advantage over other mineral fertilizers. Ammonium phosphate, ammonium sulphate, urea and urea ammonium N can have much higher losses and thus emissions. According to the German fertiliser ordinance (amendment 2017), urea fertilisers must be provided with a urease inhibitor which prevents the formation of ammonia. Alternatively, these can also be incorporated or injected immediately. In general, field irrigation following fertilisation helps to "wash" the fertiliser into the soil and prevent nitrogen losses.
Fertilisation recommendations based on soil and plant analyses provide guide values for assessing the nutrient requirements of arable crops and grassland. In this way, overfertilisation, which would lead to emissions, can be avoided. The farm gate balance is the difference of all nitrogen inputs to the farm (fertiliser, feed, litter, animals, as well as N fixation by legumes and atmospheric N deposition) minus the total nitrogen removal in products (plants, animals, manure) leaving the farm. Since 2018, the material flow or yard gate balance has applied to all farms with more than 30 ha of usable area if their animal stocking exceeds 2.5 GV/ha or if they have more than 2,000 pig fattening places.