As European agriculture faces a period of profound tension—marked by widespread farmer protests against environmental regulations and the reform of the Common Agricultural Policy (CAP)—another crisis, quieter but equally alarming, continues to intensify: the disruption of the nitrogen and phosphorus cycles.
In January 2025, a joint report from the European Environment Agency (EEA) and UN Environment confirmed that these two nutrients, heavily applied in both mineral and organic fertilizers, are accumulating in ecosystems at levels far exceeding their capacity for absorption.
To better understand the mechanisms at play and the potential levers for action, we spoke with Sylvain Pellerin, Research Director at INRAE. A national reference in the study of biogeochemical cycles of carbon, nitrogen, and phosphorus, he has spent more than thirty years examining the interactions between agricultural systems and the global environment. Drawing on his research, he warns of the urgent need to reinvent farming practices if we are to remain within planetary boundaries.
1. Why are nitrogen and phosphorus essential for agriculture?
Nitrogen and phosphorus are indispensable nutrients for plant development. They play a central role in vegetative growth, protein synthesis, and therefore the entire food chain. As Pellerin explains, “a plant that cannot find the nitrogen and phosphorus it needs in the soil simply cannot grow.” The requirements are substantial: a cereal crop removes between 15–20 kg of phosphorus and 100–200 kg of nitrogen per hectare each year.
Although these elements occur naturally in the environment—atmospheric dinitrogen, for example, represents 80% of the air—they are not directly available to most plants. Only certain species, such as legumes, can capture atmospheric nitrogen through symbiotic bacteria. Phosphorus, while present in soils, is poorly mobile and therefore difficult for plants to access.
This limitation drove the massive use of synthetic fertilizers, especially since the early 20th century, when chemist Carl Bosch developed an industrial process to produce ammonium from atmospheric nitrogen. This breakthrough paved the way for mineral fertilization, which expanded dramatically in the 1960s in response to rapid population growth.
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2. What are the environmental consequences of disrupting the nitrogen and phosphorus cycles?
While agricultural intensification has succeeded in feeding a growing global population, it has also profoundly disrupted the natural cycles of nitrogen and phosphorus. Pellerin emphasizes that nitrogen, in particular, is highly mobile and reactive, cycling easily between air, water, and soil—making it extremely difficult to control. Once applied in excess, nitrogen and phosphorus inevitably end up in unintended environmental compartments, with multiple harmful effects.
The first well-documented consequence is groundwater contamination by nitrates (a form of nitrogen), which degrades drinking water quality. Next comes the eutrophication of aquatic ecosystems, caused by the accumulation of nitrogen and phosphorus in rivers, lakes, and coastal waters.
This process fuels algal blooms, which, as they decompose, consume dissolved oxygen and create so-called “dead zones.” “These inputs trigger an explosion of algal growth, the biomass then dies, depletes oxygen, and fish follow,” he explains.
Additional impacts include air quality issues, as ammonia volatilized from nitrogen fertilizers is a precursor of fine particulate matter harmful to human health. Perhaps most concerning, however, is the emission of nitrous oxide (N₂O), a greenhouse gas nearly 300 times more potent than CO₂. As Pellerin notes, “what was once considered a local agricultural problem has now become a global issue—touching climate, biodiversity, public health, and the stability of ecosystems.”
According to a report published in January 2025 by the European Environment Agency and UN Environment, agricultural inputs of nitrogen and phosphorus exceed the natural absorption capacity of European ecosystems by 30 to 50 percent, driving increasing eutrophication of soils and waters.
3. Can we feed 9 billion people without synthetic fertilizers?
This question lies at the heart of debates on agricultural transition. Fertilizers have enabled agricultural yields to triple within half a century, and their complete elimination would pose serious challenges to food security. Pellerin has modeled a scenario in which global agriculture operates 100% organically, without synthetic fertilizers. The results are striking: “We found a drop in crop production of about –57%,” which would trigger a worldwide food crisis.
That said, a more moderate scenario—in which 60% of agriculture transitions to organic—appears feasible, provided it is accompanied by major changes in consumption patterns. Key measures include drastically reducing food waste (currently about 25% of global production) and rebalancing diets away from resource-intensive animal products.
“A large share of cropland today is used to feed animals,” Pellerin stresses. Cutting meat consumption is not only a climate issue, but also a powerful way to reduce fertilizer demand.
4. What practical levers can enable more sustainable agriculture?
To reduce the environmental impact of fertilizers while maintaining adequate food production, several strategies can be implemented in parallel. Technically, fertilizer management can be improved by refining application rates, timing, and better utilizing organic fertilizers such as manure and slurry, which are often undervalued—leading farmers to overapply synthetic inputs. Expanding the use of legumes such as peas, lentils, and beans is also critical, as these plants fix atmospheric nitrogen through root-associated bacteria, reducing the need for mineral fertilizers.
At a broader scale, the territorial organization of agricultural production is key. Today, regional specialization—livestock farming concentrated in Brittany, cereal production in the Paris Basin—prevents effective nutrient recycling. “In Brittany, there is too much nitrogen and phosphorus; in the Paris Basin, synthetic fertilizers are required,” Pellerin explains.
Reconnecting crop and livestock systems would help close nutrient loops and correct both surpluses and deficits. Finally, dietary change plays a fundamental role. Eating less meat and more plant-based protein reduces pressure on agricultural land. “At present, two-thirds of our protein intake is animal-based. Reversing that ratio would be beneficial for the planet,” he affirms.
5. How does this issue relate to the concept of planetary boundaries?
The disruption of nitrogen and phosphorus cycles is one of the nine planetary boundaries defined by science—and among the most critical, given the scale of overshoot. As Pellerin explains, what was once perceived as a local agricultural concern is now a global challenge: widespread fertilizer use, transboundary marine pollution, and nitrous oxide emissions all signal a systemic planetary problem. This justifies global reflection on thresholds that must not be crossed.
Yet this boundary cannot be viewed in isolation. The planetary boundaries are interconnected. Reducing fertilizer use produces co-benefits for air quality, biodiversity, climate, and human health. But rebound effects are also possible.
For example, reducing fertilizer inputs without changing diets would lower yields and increase pressure for cropland expansion—potentially driving deforestation and additional CO₂ emissions. “If yields drop but diets remain unchanged, more land will be needed. Clearing land means more CO₂ emissions and greater harm to biodiversity,” Pellerin warns.
Current scientific research is therefore focused on modeling large-scale scenarios that integrate agricultural, dietary, and climate dimensions. “That’s where much of the research effort lies now: developing scenarios to inform public policy,” he concludes. It is precisely this alignment of science, policy action, and individual behavior that will allow us to safeguard planetary balances while ensuring global food security.
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Sylvain Pellerin is Research Director at INRAE (National Research Institute for Agriculture, Food and the Environment), based at the Nouvelle-Aquitaine–Bordeaux center, and a member of the mixed research unit ISPA (Soil–Plant–Atmosphere Interactions). An agronomist and ecologist by training, he has spent more than 30 years studying the major biogeochemical cycles—particularly those of nitrogen, phosphorus, and carbon—and their disruption under intensive agriculture.
A recognized authority on agricultural sustainability, he has contributed to several scientific assessments for French ministries, the European Commission, and international organizations. He also co-directed the Climae program, a pioneering national initiative on the interactions between climate change and agriculture.
