Artificial Fertilizers: Disrupting Ancient Cycles & Sustainable Solutions

At the beginning of the 20th century, a groundbreaking process now known as the Haber-Bosch process was discovered. This process enables the creation of ammonia, a fundamental building block of fertilizer, from atmospheric nitrogen and hydrogen. The widespread adoption of artificial fertilizers that followed dramatically increased crop yields and played a crucial role in feeding a rapidly growing global population.

For millennia, humans have utilized fertilizers to enhance agricultural productivity. Initially, these were exclusively organic in origin. Over time, however, artificially produced fertilizers largely replaced their organic counterparts.

How Artificial Fertilization Works

Fertilizers supply plants with essential nutrients – nitrogen (N), phosphorus (P), and potassium (K) – that are vital for photosynthesis and growth. These nutrients support plant development and contribute to increased crop production.

However, improper or excessive fertilization can have negative environmental consequences. The side effects of artificial fertilizer use include groundwater pollution, over-fertilization of oceans, loss of biodiversity, and an acceleration of climate change. Critically, the hydrogen used in the Haber-Bosch process has historically been derived from fossil fuels.

Disrupting the Natural Nitrogen Cycle

The addition of artificial fertilizers to the soil disrupts the natural nitrogen cycle, a finely balanced process that has evolved over millions of years, with microorganisms playing a central role. These microorganisms bind molecular nitrogen from the air and convert it into ammonium, making it available to other microbes, plants, and the broader food chain.

Unabsorbed nitrogen undergoes a series of chemical transformations – into nitrite, nitrate, and nitrous oxide – before ultimately returning to the atmosphere as molecular nitrogen. While the basic principles of these processes are well understood, the immense diversity of soils and the microorganisms within them make a complete understanding of the dynamics challenging.

Towards More Sustainable Agriculture

Research conducted at the Center for Microbiology and Environmental Systems Science (CeMESS) at the University of Vienna is shedding new light on the natural nitrogen cycle and informing efforts to develop more environmentally friendly agricultural practices. This research is part of the Cluster of Excellence “Microbiomes drive Planetary Health” of the FWF Science Fund, coordinated by Michael Wagner, founding director of CeMESS.

A key discovery, published in 2015, challenged the long-held understanding of nitrification – the process of converting ammonia into nitrite and then into nitrate. Researchers found that certain microorganisms, termed “Comammox” (complete ammonia oxidizer), are capable of carrying out both steps of the process independently. This finding overturned the previous belief that two distinct groups of microorganisms were responsible for these sequential conversions.

The implications of this discovery are significant. Researchers now hypothesize that Comammox bacteria are more efficient at utilizing nutrients, particularly when nitrogen input is slow and limited.

The current situation is characterized by a substantial influx of nitrogen into the environment through human activities – from fertilizers to wastewater and fuels – effectively doubling the natural nitrogen input. This excess nitrogen can lead to several problems.

Nitrate, the end product of nitrification, is easily washed out of soils and can contaminate groundwater. It can also contribute to the over-fertilization of waterways. Nitrate is thought to potentially increase the risk of certain health issues, including cancer, due to the formation of nitrosamines in the body.

As explained by a microbiologist, the rapid conversion processes triggered by large amounts of artificial fertilizer often outpace the plants’ ability to absorb the nitrogen.

One fertilization strategy to mitigate these issues involves slowing down the production of greenhouse gases. Utilizing organic fertilizers, which support microorganisms with low nitrous oxide emissions, could help cushion the climate-damaging effects. Comammox bacteria may also play a role in this process.

Alternatives to Synthetic Fertilizers

Researchers are also exploring ways to naturally prevent nitrogen loss from the soil. One goal is to identify alternatives to industrial nitrification inhibitors. The potential health risks associated with synthetic substances accumulating in plant and animal foods remain a concern.

The team at the University of Vienna is investigating plant-derived substances that can reduce fertilizer conversion and loss. Initial findings suggest that some promising substances have been identified and are undergoing further investigation.

The ultimate aim is to develop a natural additive for fertilizers that can prolong the availability of plant-accessible nitrogen in the soil. This could represent a significant step towards a more sustainable approach to soil management and the preservation of microbial diversity.

The large input of artificial fertilizer overwhelms the finely balanced microbial ecosystem in the soil. This leads to a situation where the conversion processes occur so rapidly that plants cannot effectively absorb the nitrogen, resulting in significant losses to the environment and contributing to climate change through the release of nitrous oxide.