Producing food for the world has an environmental cost. Not just from water and energy use, but also the carbon footprint of fertilizer. Producing ammonia, the key ingredient of fertilizer, results today in 2% of global carbon emissions.
Researchers now propose an unusual idea to make ammonia that does not require high heat and pressure. Their idea is to use the Earth itself as a reactor. Using the rocks, heat and pressure naturally found under the Earth’s surface, the MIT team says it should be possible to make ammonia without emissions.
“We can use the Earth as a factory to produce clean flows of hydrogen,” said MIT materials science and engineering professor Iwnetim Abate in a press release. The study appears in the journal Joule.
This work is part of a growing effort to reduce the climate impact of fertilizers. There has been an interest in extracting nutrients such as phosphorus and nitrogen from urine as well as solid waste. And many researchers are targeting ammonia, which is the base material for fertilizers. It is produced today using an energy-intensive process.
The MIT team proposes injecting water into iron-rich rock formations underground. They would first lace the water with nitrogen and a metal catalyst. At the temperature found in those subsurface rocks, nitrogen in the water reacts with the iron to release clean hydrogen. The hydrogen then combines with nitrogen to form ammonia.
The researchers tested the idea in a model system in their laboratory. They used olivine, a natural iron-rich rock, and simulated underground temperatures of 300°C. The process yielded 1.8 kg of ammonia per ton of olivine. The researchers plan to test the process out in the real world at an underground site in the next year or two.
Source: Yifan Gao et al. Geological ammonia: Stimulated NH3 production from rocks. Joule, 2025.
Photo by Nurhadi Cahyono on Unsplash
