Decarbonising the Fertiliser Industry

How to Tackle Soil and Production Emissions at Once

Nitrogen is an essential element for plant growth. Together with potassium and phosphorus, it makes up 78% of the atmosphere in the form of nitrogen gas (N2). However, N2 is a very stable molecule and needs to be activated first for plants to use it and incorporate it in amino acids and other compounds. The underlying mechanism making this possible is called nitrogen fixation.This occurs either via reduction or oxidation of atmospheric nitrogen, yielding (H)NOx or NH3, which are more easily absorbed by plants from the soil.

In nature, most nitrogen fixation occurs via biological pathways powered by nitrogen-fixing bacteria thanks to a specific enzyme called nitrogenase. As discussed before, given the growing population and rising demand for food, we can’t rely on natural processes alone. The Haber Bosch (HB) process has been the main contributor to artificial nitrogen fixation since its commercialisation in 1913. Today, it is estimated that synthetic nitrogen fertilisers sustain half of the world’s population. This process breaks the triple bond of the chemically inert nitrogen molecule, which is one of the main reasons why it is so energy intensive.

Contrary to popular belief, it’s not the production process, such as the Haber-Bosch method, that is the biggest climate culprit. That accounts for “only” 38.8% of emissions. Soil emissions are actually the main drivers of emissions in the fertiliser industry, followed by production-related emissions.

Now to the billion dollar question: How can we tackle both emission drivers — field and production — at once?

To start with, we’ll compare the current Haber Bosch process with two selected synthetic processes of nitrogen fixation — electrified Haber-Bosch and non-thermal plasma — and one natural pathway: nitrogen fixing bacteria. When comparing the energy requirements of these four processes, it becomes clear that the electrified HB is the most energy intensive option, even more so than the conventional HB process. This is because it relies on electricity to produce green hydrogen (via water electrolysis) and to power the conversion of H2 and N2 into ammonia (NH3). Green hydrogen is currently too expensive to make the electrified Haber-Bosch process economically viable. This technology was discussed further in the technology overview, but it will not be the focus here since producing green ammonia doesn’t reduce the soil emissions which occur after the fertiliser is applied in the fields.

Now let’s have a look at non thermal plasma and N fixing bacteria approaches to understand if these processes could address both emission drivers:

Non thermal plasma

This process uses air (N2 and O2) to fix nitrogen into NOx, which can be reacted further to calcium nitrate (with a calcium source) or to ammonium nitrate (by adding water). These compounds are commonly used in the fertiliser industry. In simple terms , this pathway produces fertilisers that are fully compatible with existing agricultural infrastructure and practices, making them 100% drop-in alternatives to conventional, grey nitrogen products. The theoretical energy requirement is as low as 3.37 MWh/t N, which is less than half of the Haber Bosch process’ energy requirements (8.1 MWh/t N). If achieved at scale and depending on electricity prices and factors such as energy efficiency, this is a key reason why this approach can compete on cost with grey alternatives — while being substantially greener.

How the process addresses production emissions

Since hydrogen is not fed directly into the process, this approach is completely independent from volatile fossil resources, such as . natural gas for hydrogen production, and of expensive and scarce green hydrogen . This provides advantages in supply chain stability and cost. . Additionally, with its lower energy requirements and mild conditions, this process integrates with intermittent renewable energy sources.

How the process addresses field emissions

A broader adoption of nitrates, promoted by lower production cost, could reduce soil emissions.Studies (1, 2) have demonstrated that nitrate-based fertilisers generate less N₂O emissions under certain soil conditions and for specific crops compared to currently cheaper urea and NH3 (conventionally used for lower margin large volume crops)

Challenges

- Further R&D and process optimisation efforts: energetics are promising but there is still a long way to go in terms of R&D, reactor design and process optimisation to improve energy efficiency. Efficiency stands currently around 20–40% at lab scale vs 60% thermal efficiency for HB at scale. Energy inefficiencies are due to the generation of heat and side products.

- Scale up from lab scale (kW) to industrial scale (MW): Managing uniform plasma and heat removal, and maintaining plasma stability at scale are issues that yet need to be addressed.

- Equipment degradation: Plasma environments include high energy ions and electrons and reactive species such as radicals which can affect the reactor walls, electrodes and other components.

Startups to watch: NitroCapt, PlasmaLeap, Nitricity, N2 Applied, plasNifix

Nitrogen fixing bacteria

Biological nitrogen fixation on crops can be done using either engineered microbes, designed through synthetic biology to improve nitrogen delivery, or naturally selected bacteria, which avoid genetic modification. Both methods aim to reduce the use of synthetic nitrogen fertilisers, cutting emissions and environmental impact. The chart above shows an energy need of 6.15 MWh/t N. This is the theoretical energy that the bacteria use in their metabolic process rather than an external energy source that powers the process.

How the process addresses production emissions

If the bacteria are integrated effectively into crops, fertiliser manufacturing can be bypassed completely, eliminating the associated energy input. Nitrogen would be fixed at the roots and made available directly to the plant, with the bacteria requiring only basic nutrients to function.

How the process addresses field emissions

The bacteria associate directly with the plant, producing nitrogen on demand and where it’s needed, thereby avoiding excess nitrogen in the soil that is typically converted to more volatile compounds and generates the soil emissions.

Challenges:

- Crop and soil specificity: bacteria are usually specific to certain crops and soil conditions so that developing a solution that has a broad applicability and works with little to no adaptation for each application is likely not possible

- Unknown fit with current farming practices: farmers may need to adjust practices, such as reducing fertiliser use, avoiding certain pesticides, or changing how seeds are planted or coated, potentially adding steps that may not yet be common in the industry to prevent impacting the effectiveness or survival of the bacteria

- Only < 50% replacement of synthetic nitrogen fertilisers: Due to the low effectiveness of biological solutions, some synthetic fertiliser application is still necessary.

- Long term plant root colonisation: Bacteria need to effectively associate with root surfaces to persist throughout the growing season; however, colonisation is often not long-term, as it depends on various factors such as adhesion to or penetration of root tissues, environmental changes like nutrient availability and pH, and competition from other microorganisms.

- Unit economics: Further field trials are needed to validate cost reduction compared to conventional fertilisers, which is a crucial aspect for farmers given the low-margin nature of their business.

Startups to watch: NetZeroNitrogen, Enthela, Pivot Bio, Algaenite, Kula Bio

Over the last year, we have looked in depth into the space — there is a real need for innovative solutions that can support the growing population and at the same time be more climate friendly. On top of that, we need products that are independent from volatile feedstocks and that can compete with current fertilisers on price, given the small margins for farmers. Generally, there’s still a long way to go in making the fertiliser industry truly resilient and sustainable.

If you’re working on a solution to address these challenges, we’d love to hear from you! Please reach out.

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