Nitrogen is an essential building block for life, but high nitrogen deposition on natural areas causes biodiversity loss. Wageningen University & Research assists in finding innovative solutions with a view to overcoming the current nitrogen impasse in the Netherlands. We are doing this on the basis of various disciplines: agriculture, economics and nature.

We've put together seven questions and answers on nitrogen:

1. What is nitrogen?

Nitrogen (N) is an important nutrient for plant growth and essential, along with phosphate, for protein formation. For this reason, both are administered in fertilisers. In the Netherlands, very high levels of nitrogen are administered in the form of artificial fertiliser and animal manure, partly as a result of large nitrogen imports in the form of animal feed. This, among other things, leads to large emissions of ammonia (NH3) into the air. In addition, nitrogen oxides (NOx) are emitted, by transport and industry in particular. High levels of nitrogen affect biodiversity and contribute to fine particulates in the air.

2. Are nitrogen oxides and ammonia harmful?

Nitrogen oxides and ammonia land on natural ground, where they raise the nutrient level and contribute to soil acidification. This results in an imbalance in nutrients, including a shortage of calcium, potassium and magnesium, and a surplus of nitrogen. The diversity of plant species declines, and there are knock-on effects on birdlife and other fauna.

Nitrogen in the air leads to the formation of ozone (smog), and it also makes a major contribution to particulates, resulting in negative health effects. The nitrogen policy is aimed in part at limiting emissions of ammonia and nitrogen oxides.

3. What caused the 2019 Dutch nitrogen problem?

The nitrogen problem has in fact existed since the start of the 1980s, when a great deal of attention was being paid to acid deposition, popularly known as "acid rain". Acid deposition occur in wet form (rain) and dry form (gases, particulates). It consists of sulphur dioxide (SO2), nitrogen oxides (NOx) and ammonia (NH3). Apart from sulphur, which has fallen by more than 80% since 1980, the issue then was the same nitrogen problem.

Since then, the Dutch government has also sought to reduce nitrogen emissions. Indeed, since 1990, nitrogen emissions have been more than halved. Nitrogen oxide emissions have been falling steadily for the past thirty years, although the decline in ammonia emissions has stagnated since around 2010.

In 2015 the Dutch government introduced the Nitrogen Action Programme (PAS) to further reduce nitrogen deposition and limit the harmful effects. In May of 2019 the Council of State (RvS) however found the PAS to be inadequate. As a consequence of this 'nitrogen ruling' the Netherlands has to take new measures to reduce nitrogen depositon on nature reserves.

Read more about the sudden nitrogen commotion

European Union member states are now obliged, under the Birds and Habitats Directives, to bring natural areas up to a  "favourable conservation status" (FCS) while improving environmental conditions.

Conditions in the Netherlands are still very much mediocre. Deposition has fallen by ca. 45% since 1990, (ca. 40% for ammonia and over 50% for nitrogen oxides). However, too much nitrogen is still ending up on around three quarters of the surface of the Netherlands. Around 120 of the 160 Natura 2000 areas in the Netherlands show nitrogen deposition above a critical deposition level.

The Nitrogen Action Programme (PAS) was introduced by the government in 2015, but in May 2019 the Council of State (RvS) found that the PAS was inadequate. This ruling means that the Netherlands is now blocked when it comes to building new roads and residential areas without compensating for the additional nitrogen emissions.

An advisory board (Adviescollege Stikstofproblematiek) was set up to advise the minister on how to deal with the nitrogen issue in the Netherlands. Experts from WUR took place in this board. Its final recommendations were published in June 2019 in the report 'Niet alles kan overal' ('Not everything is possible everywhere').

4. To what extent must nitrogen be reduced?

In formal terms, nitrogen deposition must return to the so-called "critical deposition values" (CDV), but these values vary according to the type of nature. Wildflower meadows and marshland can, for example, tolerate less nitrogen than forest or sandy soil.

The critical deposition values vary mostly between 5 and 25 kg nitrogen per ha per year. In most cases, the range is between 10 and 20 kg nitrogen per ha per year, with a range of 5 to 10 kg nitrogen per ha per year for sensitive marshes and dunes.

Current and critical deposition values:

  • The national average nitrogen deposition is around 21 kg nitrogen per ha per year (1500 mol)
  • At an average deposition value of around 14 kg nitrogen per ha per year (1000 mol), a large part of the natural areas would be in the rough vicinity of the critical deposition values

Read more about reduction of nitrogen

An average cut in deposition from 21 kg to 14 kg nitrogen per ha per year may appear a modest target, but in terms of emissions reduction it is extremely ambitious. This is because the national contribution to nitrogen deposition on Natura-2000 areas is only around 60%. The remaining 40% comes in from outside the country. We, for that matter, also export nitrogen to other countries.

Of the current average deposition of 21 kg, the national part is 13 kg (60%) and 8 kg (40%) comes from abroad. If we want to reach the deposition objective of 14 kg nitrogen on average without further reduction from abroad, that leaves room for only 6 kg of Dutch nitrogen.

That would mean a cut in emissions of over 50% (from 13 kg to 6 kg). Reaching the critical deposition values everywhere will for this reason be virtually impossible.

5. How can we best tackle the nitrogen problem?

The nitrogen problem nexus needs to be seen as a hydra-headed monster. Manure excess results not only in ammonia losses to the air, but also in laughing gas, which is a greenhouse gas. Nitrogen, in the form of nitrate, is also in runoff to groundwater and surface water. Apart from the Birds and Habitats Directives, we also have to comply with the Nitrate Directive, the Water Framework Directive and the Paris Accord. So, it is important to think in an integrated way, and when taking measures not to look purely at the effect on nitrogen deposition. Cutting ammonia emissions is the most effective to reach the critical deposition values, but cutting nitrogen oxide emissions has greater health benefits. In the light of this, cutting emissions in all sectors is important.

Read more about tackling nitrogen

The national contribution to nitrogen deposition in Nature 2000 areas is around 60%. Of this, around 20% comes from traffic, industry and consumers. The other 40% comes from livestock farming. So, to arrive at substantial cuts in emissions, both livestock farming and transport will have to be looked at.

Nitrogen deposition from livestock farming:

  • Around 65% from cattle farming
  • Around 20% from pig farming
  • Around 10% from poultry farming

6. How can we structurally reduce ammonia emissions from livestock farming?

Nitrogen in livestock farming causes losses to the air in the form of ammonia (NH3). Over 80% of ammonia emissions in the Netherlands come from agriculture and particularly from manure. Ammonia is created when an animal has eaten protein and manure and urine mix in the stable and when (artificial) manure is spread on the land. Together with dairy farmers, Wageningen University & Research studied reducing ammonia emissions. Considerable cuts can be achieved without major financial consequences. Read more about the (technical) solutions that are readily available and about how WUR measures ammonia in the fold-out below.

Read more about how to reduce ammonia

Solutions to reduce emissons

  • Spraying with water leads to a sharp decline (up to as much as 35%) in stable emissions
  • By using new stall systems in which no slurry is generated, emissions can be considerably reduced
  • Other types of flooring and extraction in stables can lead to lower ammonia emissions
  • Outdoors, diluting manure with water leads to a sharp cut
  • Leaving cows out on pasture for longer also results in lower stable and lower outdoor emissions
  • Choosing the right point - at low temperature and wind speed - to spread manure leads to much lower emissions
  • Less protein in cattle feed can also reduce ammonia emissions

Measuring ammonia emissions

Wageningen University & Research carries out emission measurements at barns and manure application sites at a number of locations in the Netherlands. There, samples (in the barn, in the outside air and in the soil) are used to measure ammonia emissions. From these results, emission factors are derived, which are used to calculate ammonia emissions from agriculture throughout the Netherlands.

At a number of dairy farms in the country, we are also looking into possibilities to measure ammonia emissions at barn level. The advantage of this is that the farmer gets immediate feedback and can thus contribute to reducing emissions through improved craftsmanship.

    7. How/what does WUR advise the government?

    In 2022, the Dutch government announced that the nitrogen emissions in some areas are to be reduced by as much as 70 to 80 per cent. For quite some time now, WUR has petitioned for a regionally focused, local and integrated approach to the three significant challenges for nature and agriculture: nitrogen, water and climate. This should lead to an integrated perspective for farmers and nature. Our researchers are currently calculating what combinations of measures enable farmers to meet the nitrogen, climate and water goals. Thus, we determine what packages of measures are needed for climate-neutral agriculture that spares nature and improves water quality.