Umweltbundesamt
Click to enlargeNitrogen is an essential nutrient for all living organisms. The use of mineral and organic nitrogen fertilizers to increase yields is therefore common practice in agriculture. Careful and needs-based application is crucial. Excess nitrogen can pollute water and land ecosystems and adversely affect the climate, air quality, and biodiversity.
Nitrogen (N) is fundamental for all living organisms.
Nitrogen compounds pass through the soil, air, and water. However, human-induced overload and disruption of the natural nitrogen cycle and sensitive systems can lead to environmental and health impacts. More than 50 percent of reactive nitrogen compounds in Germany enter the environment through agriculture. Further inputs come in roughly equal parts from industry, transport, and private households. Nitrogen is used in agriculture as a fertilizer to achieve high yields of good quality, to supply sufficient nutrients, and to maintain soil fertility. The nitrogen surpluses in agricultural soils, which are still significantly too high, arise when more fertilizer is applied than is removed by the plants. The target value of the German government's national sustainability strategy to limit the nitrogen surplus to 70 kilograms (kg) N per hectare (ha) on a five-year average by 2030 has not yet been achieved. On average for the years 2018 to 2022, the nitrogen surplus from the total balance for Germany was around 77 kg N/ha LF. In addition to land use (80 percent), livestock farming (19 percent) and biogas production (1 percent) also contribute to the nitrogen surplus in agriculture. The surplus calculated from the overall balance shows an average value for the entire agricultural area in Germany and does not reflect regional differences. Current figures on the spatial distribution of nitrogen surpluses from the land balance for Germany at the district level can be found here.
An excess of nitrogen and its transfer to sensitive ecosystems can have serious environmental impacts.
If the nitrogen fertilizer applied is not taken up by the plants, it can be carried into groundwater and surface water or into the air. There, it endangers groundwater as nitrate and contributes to the over-supply of nutrients (eutrophication) in surface waters and terrestrial ecosystems. Ammonia is carried through the air into sensitive ecosystems, where it has an eutrophicating and acidifying effect. The resulting greenhouse gases also have a negative impact on the climate. This has adverse consequences for landscape quality and biodiversity.
Nitrogen surpluses and nitrogen inputs into fragile ecosystems can engender environmental damage.
Nitrogen fertilizer that is not absorbed by crops can, after being converted into nitrates, end up in neighbouring waterbodies or in the air, where it is hazardous to groundwater and drinking water and contributes to the eutrophication of surface waterbodies and terrestrial ecosystems. Nitrate air emissions provoke the eutrophication and acidification of fragile ecosystems and contribute to greenhouse gas formation. This in turn has a negative impact on landscape quality and biodiversity.
Nitrogen can be found in the soil in various forms. In its ammonium form (NH4), it is initially bound to soil particles. Over time, however, it is converted into nitrate (NO3) by soil microorganisms. Nitrate is highly mobile in the soil and can be transferred to the groundwater with seepage water, especially in autumn after the harvest and during heavy rainfall. Under certain conditions, nitrate in groundwater—and subsequently in drinking water—can be converted into nitrite, which is harmful to health. The limit value for nitrate in drinking water was therefore set at 50 mg/l throughout the EU in 1991. The latest survey of groundwater quality in accordance with the EU Water Framework Directive in 2021 showed that 32.7 percent of groundwater bodies are in poor chemical condition. The main cause of this is diffuse nitrate pollution (22 percent of all groundwater bodies). The main sources are nitrogen surpluses from fertilization, feeding protein-rich concentrates, and the mineralization of organic matter. When grassland is plowed, large amounts of nitrate are also released in a short period of time due to the mineralization of organic soil matter. In some regions of Germany, particularly in the livestock farming regions of northwestern Germany, where large quantities of animal manure are produced, this limit is sometimes exceeded significantly. The reason for this is often the improper use of manure, i.e., manure that is not adapted to the plants' needs in terms of timing and quantity. This situation is exacerbated by the growth in biogas plants in livestock farming regions in recent years, which has been driven by the Renewable Energy Sources Act (EEG). In addition to a small proportion of manure, these plants mainly use corn as a fermentation substrate for electricity generation, with the result that the feed required for livestock farming is increasingly being imported. The resulting fermentation residues are rich in nutrients and are spread on the fields in addition to the farm manure that is already produced.
Large quantities of nitrogen compounds from agriculture enter surface waters via groundwater and runoff from agricultural land. This leads to excessive nutrient levels in rivers, lakes, and seas, causing eutrophication of the affected waters. An oversupply of nitrogen in water bodies leads to an increase in primary plant production, for example algae. This in turn can lead to a significant oxygen deficiency in the water and to conditions that are hostile to animals and plants. However, the effect that excessive nitrogen input has on surface waters also depends on other growth-limiting nutrients such as phosphorus. The ratio of nitrogen to phosphorus is crucial for plant growth conditions. The natural biological ratio of 16 (nitrogen):1 (phosphorus) in water bodies has shifted in favor of nitrogen due to high nitrogen inputs. While nitrogen is the growth-limiting factor in the oceans and therefore crucial for nutrient effects, phosphorus (also largely originating from agriculture) can be blamed for excessive plant growth in most rivers, lakes, and coastal waters. Oxygen depletion and the displacement of native plants and animals that are less well adapted to the new living conditions lead to a loss of biodiversity in the waters.
In nature-orientated terrestrial (forest) ecosystems, an oversupply of nitrogen (eutrophication) can have long-term negative effects on vegetation and species composition. Plants and animals that are adapted to nutrient-poor living conditions can be displaced by nitrogen-loving species, which then spread more rapidly. This can lead to a homogenization of vegetation and a decline in biological diversity.
Furthermore, nitrogen overfertilization causes excessive growth in length and soft, spongy shoots, cells, and tissues in crops and trees. They become more susceptible to frost and heat, the shelf life of harvested products decreases, and plant pests as well as bacterial and fungal diseases can spread more easily. This can result in yield losses in agricultural crops and windbreak damage in forests.
The proportion of ammonium (NH4) contained in farm manure in relation to total nitrogen (N) is around 15 percent in farmyard manure, around 60 percent in slurry, and almost 95 percent in liquid manure. During the storage and application of farm manure, the ammonium is converted into ammonia (NH3) and can escape into the atmosphere. Ammonia is also emitted from large agricultural livestock facilities. In the case of synthetic nitrogen fertilizers, large quantities of ammonia can escape, especially when ammonium-forming urea fertilizers or ammonium-containing AHL solutions are used – up to 15 percent of the total nitrogen content.
The amount of ammonia lost during application depends on numerous soil and weather conditions. A high pH value, low buffer capacity, low soil moisture, high temperatures, and wind promote ammonia volatilization. In order to reduce or prevent this, the Fertilizer Ordinance (DüV), which was amended in 2020, contains a number of requirements for the proper application of farm manure and urea fertilizers. For example, farm manure must be worked into the soil on uncultivated farmland immediately and no later than four hours after application. From 2020, the application of liquid farm manure on cultivated farmland and from 2025 on grassland will only be permitted using low-emission application techniques (drag hose, drag shoe, injection method). From 2020, urea fertilizers may only be applied if a urease inhibitor has been added to them or if they are incorporated within four hours at the latest.
Ammonia is a precursor to secondary particulate matter that is harmful to health. Ammonia also has a damaging effect on adjacent ecosystems. Mosses and lichens, for example, react to even low atmospheric concentrations of ammonia with changes in their species composition. The deposition of ammonia in sensitive ecosystems can lead to risks for biodiversity.
Nitrous oxide (N2O) is a highly potent greenhouse gas with a global warming potential 265 times that of carbon dioxide (CO2). Agriculture is responsible for around 80 percent of nitrous oxide emissions in Germany. The main source of N2O emissions is emissions from agricultural soils. The level of these emissions is largely determined by nitrogen management: the application of organic and mineral fertilizers and the incorporation of crop residues. The decisive factors here are the amount of N input and location factors such as soil properties and weather conditions. In addition to direct nitrous oxide emissions from nitrogen fertilization, there are also indirect N2O emissions caused by the discharge of nitrate and ammonia into other ecosystems.
Improper, excessive fertilization, especially with acidic fertilizers (such as ammonium sulfate), can contribute to accelerated soil acidification. The nitrate (NO3) produced during nitrification is particularly mobile. If it is not absorbed by plants but washed into the groundwater (base leaching), soil acidification accelerates. This is accompanied by changes in soil structure and the living conditions for soil microorganisms. This can subsequently affect soil fertility and the yield and quality of plant products. Mineral fertilizers, especially phosphate fertilizers, but also organic waste fertilizers such as sewage sludge, also contain heavy metals (especially uranium and cadmium).
In order to improve the state of the environment and reduce the input of reactive nitrogen compounds, European and national environmental policies have adopted guidelines and strategies with defined environmental quality objectives and measures.
The EU Nitrates Directive was adopted in 1991 to protect groundwater and surface water from nitrate pollution from agriculture. It provides for the monitoring of groundwater and surface water, the designation of vulnerable areas, and the establishment of rules of good agricultural practice. It describes measures that must be implemented by Member States on the basis of strategies and action programs. In order to assess the success of the measures implemented to reduce nitrogen, Member States must evaluate the status of their surface waters and groundwater resources every four years and submit a nitrate report to the EU Commission. In Germany, the Nitrates Directive is essentially transposed into national law by the Fertilizer Ordinance (DüV). Germany and some other Member States apply the measures of the Nitrates Directive throughout their entire territory and therefore do not designate vulnerable areas. This means that the rules of good agricultural practice laid down in the Fertilizer Ordinance apply to the entire federal territory and must be observed by all farmers.
The current Nitrates Report from 2024 shows that there has been very little change in groundwater pollution over the past 10 years. Nitrate levels in near-surface groundwater in the representative EEA groundwater monitoring network and in the so-called pollution monitoring network have only fallen slightly in the last two reporting periods (2016-2019 and 2020-2022). This means that the “good status” of groundwater in Germany required by the Water Framework Directive has not yet been achieved across the board. The status is therefore unsatisfactory and improvement is very slow. According to the Nitrates Directive, this means that the German government is obliged to take further, more effective measures to achieve the desired goal. Germany has not sufficiently fulfilled this obligation in the past, which is why the EU Commission initiated infringement proceedings against Germany in October 2013 for insufficient implementation of the EU Nitrates Directive and filed a lawsuit with the European Court of Justice (ECJ) in October 2016. In June 2018, the ECJ ruled that Germany had violated its obligations to protect groundwater under the Nitrates Directive. Although the ruling referred to the 2006 Fertilizer Ordinance, it also had implications for the comprehensively revised fertilizer legislation that had just come into force in 2017. This was because it was already clear from the grounds for the judgment that even these changes would not be sufficient to fully implement the Nitrates Directive. This meant that a further revision of the fertilizer legislation was necessary, which was completed in spring 2020. The infringement proceedings were then discontinued by the EU Commission in June 2023.
In 2009, the Federal Environment Agency developed an “Integrated Strategy for the Reduction of Nitrogen Emissions,” which outlines concrete measures for the emitting sectors. The 2014 technical brochure “Reactive Nitrogen in Germany – Causes, Effects, Measures” summarizes the latest findings on this topic and presents them on a new database. Agriculture is considered to have the greatest need for action, but also the greatest potential for reduction. In addition, the greatest synergy effects in achieving water and climate protection as well as air pollution control goals can be exploited here.
The UBA’s motto, For our environment (“Für Mensch und Umwelt”), sums up our mission pretty well, we feel. In this video we give an insight into our work.
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