THE NITROGEN DILEMMA
[This English translation was generated using an automated translation tool based on ChatGPT, without any manual correction.]
About a third of the seaborne fertilizer trade worldwide is conducted through the Strait of Hormuz. However, due to the blockade by Iran and later also by the USA, this route was hardly passable in March and April, which disrupted supply chains and also increased the price of nitrogen-based mineral fertilizers. This also affected the EU, which has to import 30 percent of its nitrogen needs. Trade organizations and aid agencies warned of the global consequences for agriculture, especially for poorer regions in Africa, Asia, and South America. But why is the element with the chemical symbol 'N' also so important in plant research?
"Nitrogen is the nutrient that the plant needs the most," says Ricardo Giehl, head of the working group "Molecular Plant Nutrition." Nitrogen is used in agriculture as a fertilizer to supply nutrients and maintain soil fertility. It is an essential component of important biomolecules – from DNA to chlorophyll to all proteins. It is especially important because it has a significant effect on yield.
- Image: IPK Leibniz-Institut/R. Giehl und N. Narisetti
Insufficient nitrogen supply inhibits plant growth and leads to yellowing of older leaves in crops such as barley.
Nitrogen also brings some problems. With excessive use, it can overload ecosystems, disrupt natural cycles, and thus lead to environmental issues. A crucial factor in this is agriculture.
A milestone for the large-scale production of synthetic fertilizers is the Haber-Bosch process, developed in the early 21st century by German chemists Fritz Haber and Carl Bosch. At its core, it involves producing ammonia from water and nitrogen from the air under high pressure (up to 300 bar) and high temperature (up to 500°C). Ammonia is then the starting material for the production of chemical compounds such as nitrate, ammonium, and urea, which can be absorbed by plants.
However, the effort is enormous. It is estimated that up to two percent of the world's energy and three to five percent of the world's natural gas are consumed for the production of nitrogen fertilizers. And agriculture has a very high demand. "Wheat requires up to 250 kilograms per hectare under high-yield conditions," says Ricardo Giehl. This has consequences. According to the Federal Environment Agency, more than 50 percent of reactive nitrogen compounds in Germany enter the environment through agriculture. "The challenge is to find mechanisms and ways to achieve high yields with unchanged high quality using less fertilizer." This is being researched at the institute in several working groups.
"Ultimately, it is about breeding new plants that can absorb nitrogen better and more efficiently," explains Ricardo Giehl. This can either increase the absorption capacity or improve the contact of the roots with the available nitrogen in the soil. "This is where our working group, as well as Hannah Schneider's, comes in, and we deal with the physiology, architecture, and structure of the root system," explains the IPK researcher. "Plants have mechanisms to recognize and respond to nitrogen availability in the soil, but often these are not optimally designed to efficiently absorb the fertilizer applied to the fields."
- Image: IPK Leibniz-Institut/L. Wu
The research at IPK investigates how nitrogen uptake can be genetically improved. The images show how root growth is stimulated in the area with nitrogen fertilizer (dashed
frame). An AI method is used for the automatic analysis of thousands of root images.
What influence nitrogen has on the change of root architecture is being investigated by Ricardo Giehl and his colleagues in the SMARTROOT project, which runs until 2028 and is funded by the Federal Ministry of Agriculture, Food and Home Affairs. They also use the PhänoSphäre of the IPK for this purpose. In root observation boxes, called rhizotrons, the growth of the roots can be observed and documented precisely. Later, the nitrogen content in the shoot will be measured. The Collaborative Research Center "Plant Proteoform Diversity," in which the IPK working group "Molecular Plant Nutrition" is also involved, is investigating a protein variation in a subproject that is important for root growth under low nitrogen conditions.
However, there are already concrete results: Just recently, a research team involving the IPK discovered a molecular mechanism in the model plant Arabidopsis that allows plants to adjust their root growth to better reach and utilize nitrate occurrences in the soil. The results published in the journal "Nature Plants" open up new perspectives for sustainable agriculture. But it is also needed, as the pressure for action is enormous given the many problems.
In the past, the nitrogen surplus in agriculture was so high that the target value of the National Sustainability Strategy was clearly missed. At least: In 2023, it was possible for the first time to limit the surplus to an average of 70 kilograms per hectare over five years.
However, the fundamental problem remains. Nitrogen fertilizers that are not absorbed by the plants in the field end up in groundwater and surface waters. There, as nitrate, it endangers our groundwater and contributes to eutrophication, meaning an oversupply of nutrients.
Nitrate is very mobile in the soil and can be leached into groundwater, especially in the autumn after harvest and during heavy rainfall. In groundwater - and subsequently in drinking water - nitrate can be converted into health-hazardous nitrite under certain conditions. The limit value for nitrate in drinking water was therefore set at 50 mg/l across the EU in 1991. Evaluations of data on nitrate levels at 1,147 measuring points have shown that in 2024, 15.7 percent of the measuring points reported values significantly higher than 50 mg/l. This groundwater cannot be used for drinking water production without further treatment.
Nitrogen compounds also enter surface waters with groundwater and from runoff from agricultural land. This leads to increased nutrient levels in rivers, lakes, and seas. This results in an increase in primary production of plants, such as algae, and can lead to massive oxygen depletion in the waters.
Excessive fertilizer application can ultimately also contribute to accelerated soil acidification. This is associated with changes in soil structure and living conditions for soil microorganisms. According to the Federal Environment Agency, this affects soil fertility, yields, and the quality of plant products. The challenges are therefore significant not only for farmers and ecologists but also for science.
The challenge is to find mechanisms and ways to achieve high yields of consistently high quality with less fertilizer.
Ricardo Giehl
Therefore, the topic will also be discussed at the International Symposium (“Nitrogen 2026”), which will take place from August 23 to 27, 2026, at the IPK. Leading international scientists will be present, covering all facets of the topic. It is about nitrogen in the soil and in water, but especially about genetic aspects and molecular processes of nitrogen uptake and nitrogen cycling in plants. “Of course, fertilizers can also be improved, but our starting point is the plant, where we still see a lot of potential for improvement,” says Ricardo Giehl.
“Our ability to achieve many of the UN Sustainable Development Goals is closely linked to an improved use of nitrogen fertilizers and the expansion of the supply of protein-rich foods, which are mostly derived from plant raw materials,” says Nicolaus von Wirén, Managing Director of the IPK and Chairman of the Organizing Committee, which also includes Ricardo Giehl and Hannah Schneider.
The nitrogen dilemma will therefore also occupy the experts at the IPK in August.
More information:
- Image: IPK Leibniz-Institut/S. Balyberdin