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The high nitrogen pollution in Europe has many negative consequences: nitrogen dioxide and ammonia worsen air quality, nitrogen deposition in soils reduces biodiversity and leads to the eutrophication and acidification of lakes and seas, and nitrate pollute groundwater. But how can the amount of nitrogen in the environment be reduced? Under the "Farm to Fork" (F2F) strategy of the "Green Deal," the EU Commission aims to reduce nutrient losses by 50% by 2030 by requiring EU countries to cut chemical fertilizer use by 20%.

As in Nature Food, a research team from the Helmholtz Centre for Environmental Research (UFZ) has calculated that such a uniform reduction in fertilizer use would not be sufficient.

Nitrogen is essential for life—for plants, animals, humans, and the ecosystem as a whole. But excess nitrogen in the environment becomes a problem. Over-fertilization can lead to a lack of oxygen in lakes, rivers, or seas. This results in the mortality of fish, the loss of species, and a decline in bathing water quality. Sensitive plants that depend on nitrogen-poor soils disappear. Nitrogen oxides from traffic and industry produce ground-level ozone and particulate matter while the use of fertilizer releases nitrous oxide (laughing gas).

Excess nitrate from agriculture enters drinking water via the groundwater while nitrogen compounds such as ammonium and nitrate acidify soils and water bodies.

Excess nitrogen in the environment is reflected in the soil surplus, which is calculated as the difference between inputs (e.g. fertilizers, animal manure, or atmospheric deposition) and outputs (e.g. plant growth). This nitrogen surplus has increased rapidly in Europe as shown by data first published by a UFZ research team in a in 2022.

"While the nitrogen surplus was relatively low until the mid-20th century, it increased considerably after the Second World War and reached its peak in the mid-1980s because of the increased use of synthetic fertilizers," says Masooma Batool, UFZ data analyst and lead author of both the current paper and a related study published three years earlier.

At the end of the 1980s, the nitrogen surplus decreased noticeably as a result of the EU Nitrates Directive, reforms to the Common Agricultural Policy (CAP), and economic and political changes. There have also been technological advances such as more precise fertilization. However, the nitrogen surplus has remained at a high level since the 2010s.

The origin and extent of the nitrogen surplus vary greatly from region to region

For the current study, the UFZ researchers analyzed the annual nitrogen surplus in Europe between 1850 and 2019 and clustered it into four categories based on its origin and extent. According to this classification, countries such as the Netherlands and Denmark belong to the "manure" category because high livestock densities lead to dominant manure inputs and a high nitrogen surplus.

Central European countries such as Germany and France, where more mineral fertilizer is applied than animal manure, belong to the "synthetic fertilizer" category. Many Eastern European and Mediterranean countries fall into the "Moderate use of manure and synthetic fertilizers" category, while Northern European countries such as Norway, Sweden, and Finland, where less mineral fertilizer and animal manure are applied than elsewhere, belong to the "Natural landscapes" category.

"By delineating these four categories, we can assess how effective the Farm to Fork strategy of the EU is," says Ph.D. student Batool.

Are the EU targets sufficient to halve the nutrient surplus by 2030?

To find out, the researchers developed future scenarios for the four regional categories. Their calculations are based on the nitrogen surpluses for 2015–2019 and the existing requirements of the Food and Agriculture Organization (FAO) of the UN or the Green Deal.

According to the calculations, if EU states implemented the F2F strategy with at least a 20% reduction in the use of mineral fertilizers, the nitrogen surplus in soils would be reduced—not by half as hoped but rather only by 10–16%. In none of the four regional categories is the nitrogen surplus reduced by the desired 50%.

According to Dr. Rohini Kumar, co-author and UFZ hydrosystem modeler, "The agricultural regions of Europe differ in terms of land use, the intensity of nitrogen use, and the technologies used. Therefore, according to our calculations, a uniform EU-wide reduction in mineral fertilizers as anchored in the F2F strategy will not lead to the desired result."

Even the most ambitious scenario of the FAO, which stipulates an EU-wide reduction of 43% in synthetic fertilizers and 4% in animal manure—combined with modern technologies and management measures—would reduce the nitrogen surplus by only 30–45%.

"According to our calculations, five countries—Sweden, Denmark, Latvia, Lithuania, and the Czech Republic—would halve their nitrogen surplus in this scenario," says Dr. Andreas Musolff, UFZ hydrogeologist and co-author.

On the other hand, countries with a high nitrogen surplus (e.g. Germany and the Netherlands) would be well below the target of 50%.

But how could countries like Germany halve the nitrogen surplus? "According to our calculations, German farmers would have to reduce mineral fertilizer use by 20% and manure use by an additional 50% provided that modern technologies and management measures are used," says Batool.

If they do not modernize technologies and cultivation, they would have to spread 67% less animal manure. However, this reduction would also entail yield losses—17% with modern technologies and management measures and 25% with the current ones. This means that less food and feed would be produced.

"With these scenarios, decision-makers can analyze the consequences of the gradual reduction of mineral fertilizer and/or animal manure on the production of food and animal feed if the nitrogen surplus is to be halved," says Kumar. This would enable them to develop strategies for achieving environmental goals and ensuring sufficient agricultural production.