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| Fig. 1: Yara Belle Plaine Nitrate Based Fertilizer manufacture in Regina Canada. (Source: Wikimedia Commons) - This figure dangles. - RBL |
Nitrogen, the most abundant element in the Earth's atmosphere, is a key building block for the survivability of life on Earth, as it is an essential component in proteins, which are vital for cell structure and enzymes, among other functions. Though abundant, its standard form, Dinitrogen, is chemically inert and unusable by plants without modifications (or "fixation"). [1] One common, highly reactive form of fixed nitrogen is Ammonia. Ammonia is the primary ingredient in nitrogen fertilizers, making it critical for sustaining modern crop yields and global food production.
The Haber-Bosch process, which produces the ammonia used in the nitrogen fertilizers that feed approximately 3.8 billion people globally. [2] However, this process presents a critical sustainability challenge due to its immense environmental and economic footprint. This conventional, centralized method is extremely energy-intensive, consuming over 2% (8.6 exajoules per year) of global energy and 3 - 5% of the world's natural gas. [3,4] Not only is this process energy intensive it is extremely carbon intensive on average 2.6 - 2.9 tCO2/tNH3 equating to 475.8 - 530.7 million tCO2 directly emitted. [3] To exacerbate this issue, ammonia production is concentrated in the global north (Fig. 1). Because these products must then be distributed globally, this distribution results in approximately 0.5 million tCO2 of indirect emissions. [5,6] Moreover, this geographical concentration of these large plants in the global north creates issues of equity and access where developing nations and lower-income communities must pay significantly higher prices for fertilizers than the global average. Most fertilizer is also used in the global north. The exception to this is Brazil, where they are the 4th largest consumer of ammonia while also importing 14% of global imports. [5]
The compounding issues of sustainability and equity stemming from the Haber-Bosch process have made the decarbonization of the food supply hinge on finding viable, low-carbon alternatives. The compelling solution involves adopting low-carbon production methods that offer a more sustainable and equitable model than the current centralized infrastructure. The two primary pathways for achieving this sustainable shift fall into two categories: 1) Small-Scale, Electrified Production (Green Ammonia) which uses renewable energy such as solar or wind for on-site or near-site ammonia synthesis. This approach drastically minimizes the need for long distance transport, both of energy and the final fertilizer, thereby optimizing energy consumption and lowering fertilizer prices for local communities. 2) Decentralized and Circular Pathways where innovative methods that utilize nitrogen from non-traditional, often local, sources. For instance, processes exploring the recovery of nitrogen from waste streams, such as human urine, can serve as a nitrogen source for fertilizer production. Interestingly, there has been studies aiming to combine both ideas. For example, recent studies such as Coombs et al. explores proof of concept a solar-powered process to recover ammonia fertilizer directly from urine. [7]
While these decentralized and circular pathways are scientifically promising, most remain at the proof-of-concept stage. Scaling laboratory or pilot scale recovery technologies to a level that meaningfully displaces Haber-Bosch ammonia will require major advancements in engineering, logistics, and policy. Despite this challenging endeavor, the raw materials are abundant; for example, urine contains enough nitrogen to meet 14% of fertilizer demand, little of which is being recovered for fertilizer use. [8] Capturing and converting even a fraction of this waste-stream nitrogen would demand widespread infrastructure redesign and robust economic models that currently do not exist at scale. Without credible pathways to industrial implementation, these concepts risk remaining niche sustainability projects rather than becoming the global endeavors necessary to secure a more sustainable and equitable future.
© Larry Marshall. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] J. W. Erisman et al., "How a Century of Ammonia Synthesis Changed the World.", Nat, Geosci. 1, 636 (2008).
[2] L. Rosa and P. Gabrielli, "Energy and Food Security Implications of Transitioning Synthetic Nitrogen Fertilizers to Net-Zero Emissions", Environ. Res. Lett. 18, 014008 (2022).
[3] "Innovation Outlook: Renewable Ammonia," International Renewable Energy Agnecy, 11 Oct 21.
[4] Y. Schueler et al., "How Are Decarbonization Policies in the US and Canada Shaping Low-Carbon Ammonia Production Strategies?" Environ. Res. Lett. 19, 114064 (2024).
[5] S. Mingolla and L. Rosa, "Low-Carbon Ammonia Production Is Essential For Resilient and Sustainable Agriculture," Nat. Food 6, 610 (2025).
[6] "Towards Hydrogen Definitions Based on Their Emissions Intensity," International Energy Agency, April 2023.
[7] O. Z. Coombs et al., "Prototyping and Modelling a Photovoltaic-Thermal Electrochemical Stripping System For Distributed Urine Nitrogen Recovery," Nat. Water 3, 913 (2025).
[8] C. Wald, "The Urine Revolution: How Recycling Pee Could Help to Save the World," Nature 602, 202 (2022).
