Scope for reducing ammonia emissions

Letting animals graze for longer hours outdoors, low nitrogen feeding and improved nitrogen management are some effective ways to curb ammonia emissions. Photo: Raoul Pop CC BY-NC

By applying already known techniques and agricultural practices, the EU could reduce agricultural emissions of ammonia by more than 30 per cent, figures show in a new report from the International Institute for Applied System Analysis (IIASA).

Agriculture is responsible for 90 per cent of all ammonia emissions in Europe. Under current legislation total EU emissions of ammonia are expected to increase by about three to four per cent between 2010 and 2020. Ammonia contributes significantly to acidification, eutrophication and the formation of secondary fine particles (PM_2.5).  It will be extremely difficult to achieve the EU environmental objectives for these areas, if more is not done to curb ammonia emissions.
In a recent report¹ IIASA assesses the potential to reduce these emissions by full-scale implementation of already available techniques and practices. Overall, IIASA estimates that in 2020 such measures could reduce EU ammonia emissions from agriculture by about 32 per cent (more than 1.1 million tonnes), compared to business as usual.

The potential varies considerably between member states (figure). A few countries already have relatively strict regulations in place and the potential for further action is therefore limited, this applies in particular to the Netherlands. Some abatement measures are difficult to implement on small farms, which affects the potential of member states dominated by small-scale family farming, such as Romania and Hungary. Ireland, which has a higher proportion of grazing animals, also has less scope, since there are no effective measures to further reduce ammonia emissions from this kind of farming.

Germany, followed by France and Spain, has the greatest scope to reduce ammonia emissions both in percentage and in total numbers.

Figure: Agricultural ammonia emissions by country for the year 2020; emissions from current legislation (CLE) scenario and the maximum technically feasible reduction (MFTR) and the percentage reductions from MFTR compared to CLE.

The measures on which the estimates are based are found in all stages of the nitrogen cycle: feeding, housing, manure storage, manure application, fertiliser application and overall nitrogen management. Measures taken early in the nitrogen cycle have the advantage that they also lead to emission reductions in the subsequent stages.

One of the most cost-effective measures is the introduction of low-protein feeding.  Total ammonia emissions from all farm sources may decrease by 5–15 per cent (average 10 per cent) for a decrease in mean protein content by 10 grams per kg in the diet. This also leads to a more efficient use of nitrogen and reduced emissions of nitrous oxide.

For animals housed indoors, there are a range of measures that can be taken, several of which are described in the newly revised guidance document² to the Convention on Long-range Transboundary Air Pollution.  The possible measures partly depend on the species kept. But the principles are similar, reducing the floor area covered by manure, quickly removing manure, keeping the temperature and pH low, drying manure, scrubbing outlet air and increasing grazing time.  Many of the measures are related to buildings and are cheaper to implement for new constructions or as part of major refurbishments of old ones.

Another approach is to let the animals graze for longer hours. Cattle grazing twenty-four hours a day emit half as much ammonia as livestock kept in conventional cubicle housing all day.

For manure storage, there are good opportunities to reduce ammonia emissions, by covering the tank. The no-cost option of allowing the formation of a natural crust on slurries by minimising stirring reduces emissions by 40 per cent. The slightly more expensive solution, to put a tight lid on the reservoir, reduces ammonia emissions by 80 per cent. The nitrates directive requires leak-tight manure storage, but there is not yet any requirement that the reservoir should be covered.

There are several techniques aimed at reducing air exposure and thereby ammonia emissions, when manure is applied to the fields.  One of the most effective ones is injection, where a slit 50–200 mm in length is cut into the soil and slurry is injected into it. For solid manure, direct incorporation by ploughing or light cultivation is the best option. Done directly after application this can reduce ammonia emissions by 90 per cent.

Nitrogen management is highlighted in the report as one of the most important measures, since it both reduces emissions and improves the economy of farms. For example on dairy farms, which is the most common type of mixed farm system in Europe, improving the use of manure and decreasing the use of nitrogen fertilizers is a cost-effective way to decrease excess nitrogen.  

Besides the introduction of new technologies and changes in management, ammonia emissions may be affected by outside influences that lead to changes in the number of animals and level of agricultural activity. Examples include abolishment of milk quotas, animal welfare regulation or changes in diets, but the impact of such changes was not analysed in the study.

The study also addresses emissions of primary particulate matter (PM) from agriculture, which is estimated to contribute about 20 per cent of EU’s total emissions of PM₁₀ and 15 per cent of PM_2.5 emissions. The largest source of agricultural PM emissions is open burning of agriculture waste, despite the fact that this practise has been banned in most EU countries (exceptions are Cyprus, France, Ireland and Slovenia).  But satellite data show that it is still common in large parts of Europe, suggesting that the introduction of laws is not enough, if efforts are not made at the same time to ensure that they are complied with.

The other source of PM emissions is when agricultural soils are stirred up by machines or animals in motion. It is much more difficult and costly to reduce these emissions, than to stop open field burning, but it is possible, for example through the introduction of low-till farming.

The member states with the greatest scope to reduce their agricultural particulate emissions are the Czech Republic, Greece and Romania.

Kajsa Lindqvist

¹ Emissions from agriculture and their control potentials, IIASA, November 2012

² Draft guidance document for preventing and abating ammonia emissions from agricultural sources, UNECE,  April 2011