Biodiversity Loss from Nitrogen Fertilisers

David Bell
17 minutes ago
8 min read

Nitrogen fertilisers are widely used to increase crop yields, but their excessive application is causing major harm to ecosystems. Here's what you need to know:

Impact on ecosystems: Over 80% of nitrogen used in farming escapes into the environment, leading to soil acidification, water pollution, and biodiversity loss.
Biodiversity decline: Nitrogen favours fast-growing species, reducing plant diversity and harming pollinators, herbivores, and aquatic life.
Grasslands and waterways: Long-term studies show nitrogen reduces species richness in grasslands and creates oxygen-deprived "dead zones" in water bodies.
Policy and solutions: Reducing nitrogen use, adopting precision farming, and using diverse grassland mixtures can mitigate these effects. Dietary changes, such as reducing reliance on livestock farming, also play a role.

Tackling nitrogen pollution is essential for protecting ecosystems while maintaining agricultural productivity.

How Nitrogen Fertilisers Cause Biodiversity Decline

Nitrogen fertilisers, while boosting agricultural productivity, have a darker side - they disrupt ecosystems in multiple ways: soil acidification, waterway eutrophication, and shifts in biological communities. These processes don’t act in isolation but instead combine, amplifying their harmful effects on biodiversity in both land and water environments [12][8].

The scale of this issue is staggering. According to the FAO, over 80% of nitrogen applied in farming escapes into the environment through leaching, runoff, gas emissions, and soil build-up, rather than being absorbed by crops [12]. This surplus nitrogen has pushed the global nitrogen cycle beyond a critical threshold, threatening the stability of ecosystems worldwide [2][12].

Soil Acidification and Nutrient Imbalances

Excess nitrogen creates chemical changes in soil that weaken ecosystems over time. When ammonium-based fertilisers break down through nitrification, they release hydrogen ions, which lower the soil’s pH and lead to acidification [8]. Research shows that nitrogen build-up can decrease soil pH by 0.3 to 1.0 units, a shift with significant consequences [8]. Acidic soils lose essential nutrients like calcium, magnesium, and potassium, creating imbalances that affect which plants and microbes can thrive.

These changes favour acid-tolerant species while pushing out sensitive ones. Long-term studies reveal that nitrogen overload alters soil microbial communities, leading to a dominance of fungi over bacteria and a reduction in oligotrophic species [10][8]. This results in a less diverse and less efficient soil ecosystem, which struggles to perform critical tasks such as nutrient recycling and carbon storage. Meanwhile, the nitrogen that escapes from soil causes further damage to nearby waterways.

Eutrophication and Waterway Damage

Nitrogen runoff from fields finds its way into rivers, lakes, and coastal areas, where it causes eutrophication - a process that depletes oxygen levels and disrupts aquatic ecosystems. The European Environment Agency highlights that oxygen-deprived "dead zones" are now common in European waters, making them uninhabitable for many aquatic species [11][2][4]. A study modelling the EU’s "Farm to Fork" nitrogen reduction goals revealed that even with a 43% cut in synthetic fertiliser use and a 4% cut in manure use, nitrogen surpluses would only drop by 30–45%, leaving a significant amount of nitrogen still leaking into ecosystems [11][4]. This underscores how deeply nitrogen pollution is embedded in modern farming practices.

Changes in Plant and Herbivore Populations

Nitrogen enrichment reshapes plant communities by favouring fast-growing species, especially grasses, at the expense of slower-growing native plants, legumes, and specialists. This competitive advantage is driven by increased light competition and the depletion of vital soil nutrients, as demonstrated by the 24-year BioCON experiment [10][8]. A global analysis of nitrogen-fixing plants found that higher nitrogen levels reduce species richness and the evolutionary diversity of nitrogen-fixing lineages, simplifying plant communities and threatening their ability to regulate nitrogen in the long term [9].

These changes don’t just stop at plants - they cascade through entire food webs. For example, the Park Grass experiment at Rothamsted, which has been running since 1856, revealed that increased nitrogen, potassium, and phosphorus fertiliser use reduced flower numbers by five times and cut pollinator populations in half [3][7]. With fewer flowers, herbivores and pollinators lose vital food sources, triggering declines that ripple through ecosystems. This chain reaction illustrates how nitrogen pollution disrupts the delicate balance of biodiversity.

Research Evidence: Nitrogen's Impact on Ecosystems

2025 Grassland Study Results

A study published in Nature in 2025 revealed that adding nitrogen to ecosystems caused a sharp 53% drop in grasshopper populations [1]. This decline was linked to changes in plant chemistry, where increased nitrogen levels in leaves coincided with a 50% reduction in grasshopper numbers [1]. The altered food quality appears to have a dual effect - proving toxic to some grasshopper species while potentially benefiting others. For instance, species like Euchorthippus unicolor were particularly affected [1].

The absence of grasshoppers, which usually help regulate vegetation, led to significant changes in the ecosystem. Nitrogen addition boosted the biomass of the dominant grass species, Leymus chinensis, by 16%, but at the expense of forb diversity [1]. This shift allowed bottom-up ecological processes to dominate, ultimately reducing overall plant diversity [1]. Furthermore, the study highlighted that increased use of nitrogen, potassium, and phosphorus fertilisers caused a fivefold reduction in flower numbers and halved the population of pollinating insects [3]. These findings underscore how nitrogen's effects on grasslands can ripple through ecosystems, even influencing aquatic environments.

Aquatic Ecosystem Damage from Nitrogen Runoff

Nitrogen's impact doesn’t stop on land - it wreaks havoc in aquatic ecosystems too. Runoff from excess nitrogen fertilisers leads to eutrophication, which causes harmful algal blooms. These blooms deplete oxygen levels in water, often resulting in mass fish die-offs [2][4]. Current models suggest that even with a 43% reduction in synthetic fertiliser use and a modest 4% decrease in manure application, nitrogen surpluses would only drop by 30–45% [11].

The consequences are severe. Persistent nitrogen pollution eliminates sensitive aquatic plants that thrive in nutrient-poor soils. Additionally, the release of nitrous oxide - a greenhouse gas 300 times more potent than CO₂ - further exacerbates global climate challenges [2][4]. These findings not only reinforce earlier concerns but also provide a clearer picture of nitrogen's cascading effects across ecosystems and its contribution to broader environmental crises.

Policy Responses and Mitigation Strategies

EU Farm to Fork Strategy and UK Implications

The European Union's Farm to Fork Strategy, a cornerstone of the Green Deal, requires member states to reduce chemical fertiliser use by 20% by 2030, aiming to cut nutrient losses by 50% [4]. However, modelling suggests this would only lower nitrogen surplus by 10–16% across EU regions [4]. The initiative isn't just about reducing nitrogen levels; it's also designed to protect biodiversity across European and UK farmlands.

A more ambitious scenario outlines a 43% reduction in synthetic fertilisers, coupled with a 4% decrease in manure application and the use of advanced agricultural technologies. This combination could achieve a 30–45% reduction in nitrogen surpluses within the EU [4][11]. Although the UK no longer adheres to EU targets post-Brexit, it faces comparable environmental challenges. Recent agricultural reforms, such as the Environmental Land Management schemes, reflect similar principles and could lead to equivalent reductions in nitrogen surplus with a 20% cut in fertiliser use [3][4]. These policy frameworks provide a foundation for implementing strategies that prioritise nitrogen use efficiency.

Improving Nitrogen Use Efficiency

Beyond policy measures, practical strategies offer tangible and immediate benefits. One effective method is the use of multispecies grasslands, which combine grasses, legumes, and herbs. These diverse mixtures utilise natural grass-legume nitrogen fixation to maintain high yields with reduced nitrogen inputs. A global study across 26 temperate sites found that such grasslands outperformed less diverse fields while requiring lower nitrogen levels [5][6].

Precision fertiliser application is another powerful tool for improving nitrogen use efficiency. Technologies like GPS-guided variable-rate application and soil sensors allow for targeted nitrogen delivery. Trials have shown that this method can cut nitrogen surpluses by 20–30% without compromising yields [4]. For instance, Rothamsted Research’s historic Park Grass experiment, ongoing since 1856, illustrates how reducing fertiliser use in a targeted way can preserve both flower and pollinator diversity. This highlights how precision management not only improves nitrogen efficiency but also strengthens ecosystem resilience and biodiversity [3].

Conclusion: Managing Nitrogen for Biodiversity Protection

Excess nitrogen is a major driver of biodiversity loss worldwide. It disrupts ecosystems like grasslands, rivers, lakes, and coastal waters through processes such as eutrophication and soil acidification [11]. Addressing this issue is crucial to achieving goals related to climate, air quality, and biodiversity, all while maintaining agricultural productivity [4].

The solution lies in practical, science-backed strategies. The FAO highlights the importance of improving nitrogen use efficiency - essentially producing more yield per unit of nitrogen. This approach can reduce pollution, curb biodiversity loss, and lower greenhouse gas emissions without sacrificing crop output [12]. Techniques like advanced farming practices, diverse cropping systems, and buffer zones to intercept runoff can help maintain productivity while reducing the strain on ecosystems [5].

However, tackling this issue requires more than just farm-level changes. A significant portion of nitrogen usage supports livestock feed production, making dietary shifts another critical factor. Advocacy groups like The Cultivarian Society promote alternatives such as cultivated meat, which offers the potential to produce real meat without relying on resource-intensive feed crops or excessive nitrogen inputs. These broader, systemic changes complement on-the-ground efforts to minimise nitrogen leakage and restore ecological balance.

Ultimately, protecting biodiversity and ensuring food security demands collaboration across all sectors [11]. Sharing data, monitoring key indicators like pollinator populations and water quality, and adapting policies based on outcomes are essential steps. Whether it’s farmers adopting precision methods, consumers choosing lower-impact diets, or citizens advocating for stricter nutrient management policies, everyone has a role to play in creating a more sustainable approach to nitrogen use. Together, these efforts can pave the way for a healthier planet.

FAQs

How does using nitrogen fertilisers harm biodiversity?

Nitrogen fertilisers can have a damaging effect on biodiversity, primarily through a process called eutrophication. When excess nutrients from these fertilisers enter nearby ecosystems, they trigger an overgrowth of algae in aquatic environments. This algae bloom consumes large amounts of oxygen, leaving little for other organisms. The result? Oxygen-deprived waters that disrupt the delicate balance of these habitats, making it difficult for many plant and animal species to survive. Over time, this significantly reduces the biodiversity of the area.

On land, the impact is just as concerning. Nitrogen fertilisers can alter soil composition, promoting the growth of certain plant species at the expense of others. This imbalance reduces the variety of plants in the area, which can ripple through the ecosystem, affecting insects, animals, and other organisms that rely on a diverse plant community. These changes weaken the ecosystem's ability to adapt to environmental shifts, leaving it more vulnerable in the long run.

How does nitrogen from fertilisers affect aquatic ecosystems over time?

Nitrogen from fertilisers can have damaging effects on aquatic ecosystems over time. When excess nitrogen washes into rivers, lakes, or coastal waters, it triggers a process called eutrophication. This creates conditions for algal blooms - rapid algae growth that blocks sunlight from reaching underwater plants and depletes oxygen levels in the water. With less oxygen available, aquatic species face serious challenges, often leading to biodiversity loss and disrupted food chains.

These changes don’t just affect the environment; they also take a toll on industries like fishing that depend on healthy aquatic ecosystems. Protecting these waters from nitrogen pollution is essential to maintaining their balance and preserving both natural habitats and livelihoods.

How can nitrogen pollution be reduced without compromising crop yields?

Reducing nitrogen pollution while keeping crop yields steady requires embracing farming methods that are both productive and environmentally mindful. One key approach is precision fertilisation, which focuses on applying the right amount of fertiliser exactly when and where it’s needed. Another is crop rotation, a technique that enhances soil health and reduces dependence on synthetic fertilisers.

Farmers can also benefit from adding organic materials like compost or manure to naturally boost soil quality. Additionally, adopting integrated pest management helps manage pests effectively without overusing chemical inputs. By combining these strategies, it’s possible to achieve a balance between high yields and protecting the environment.