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Original link is just PR. I prefer the company paper: https://www.nitricity.co/_files/ugd/142f34_bc5fa8b90ac647dab...

"For the past century, nitrogen fertilizer has been produced as ammonia (NH3) in Haber-Bosch facilities often situated very far from farmers who need and use fertilizer. State-of-the-art Haber-Bosch factories require hydrogen production via coal or methane reforming and use high-pressure and temperature reactors to transform hydrogen and nitrogen gas into ammonia. "

"The distributed production and fertilization with nitric acid is relatively underexplored. Known nitric acid production methods require about 3 times more energy per pound of nitrogen than ammonia processes."

"In the current study, we focus on a plasma-based production process that fixes nitrogen as nitric acid on-site for a plot of irrigated processing tomatoes."

This work is interesting in that it may decentralize nitrogen fixation. Traditional Haber-Bosch plants can also decarbonize ammonia production if they use electrolytic hydrogen produced with clean electricity. Some 20th century Haber-Bosch plants operated that way with electrolytic hydrogen made via hydroelectric power.
This type of process has already been developed industrially: https://en.wikipedia.org/wiki/Birkeland%E2%80%93Eyde_process

The trouble is that it is inefficient and will ultimately release some NOx compounds into the atmosphere since the conversion rate is not 100% to HNO3. I'm surprised there is not a single mention of this process in their paper.

The process you mention is for a "hot plasma" formed by electric sparks. Presumably this companies technology uses "cold plasma" aka non-thermal plasma which is significantly more efficient and more selective toward HNO3. Heres a good review paper: https://link.springer.com/article/10.1007/s42768-021-00074-z

Here's another interesting one: https://pubs.acs.org/doi/10.1021/acssuschemeng.9b04997

There is still some NOx production, but likely low enough enough concentrations to be filtered.

I'm sure there are some optimizations that can be done on the process but yeah, it isn't new. I don't think the NOx issue is significant because you can sequester them, but it does add to the expense and lower the efficiency(unless you have a source of animal urine and can use the urea maybe?).

Is the efficiency difference between it and the Haber-Bosch process small enough to be made up by the lack of transportation?

I wonder if the nitric acid is a benefit in places with alkaline soil and water chemistries?

I’m curious why we can’t just seed something nitrogen-fixing like clover alongside our normal crops? Clover is pretty short, so taller crops will not be confused and accidentally harvested. Does anyone know why this isn’t done?
I've seen clover grown in the off season. It'll need some light though, so the shade of something over it might be a problem.

There are lots of good combinations of plants to grow together, like the three sisters: https://gardening.cals.cornell.edu/lessons/curricula/the-thr...

Can we not run the normal Haber-Bosch process on renewable energy or is it somehow tied to coal/natural gas as this article seems to insinuate?
You can, but then you have to transport the product to the farm to use it.

And, of course, practically all the Haber-Bosch equipment is not on renewables, and will not be for a long time. It is better for now to displace it until carbon taxes can be used to force conversion.

Solar power gathering above cropland also increases yield by reducing water and heat stress. So even after they convert, you will still be better off with this.

It appears that fossil fuels are used as a hydrogen source for the reaction. I wonder if you could split water and use that as a hydrogen source? It is probably a much less efficient process to source hydrogen.
You can, and it is done. Just not much yet.
Great to see that making ammonia production more environmentally friendly is actively being worked on from different angles. There was another process announced recently that produced ammonia from supplied nitrogen (which would still be separated from air as I understood) in an electrolysis cell. These are links for this other approach:

Paper: https://www.science.org/doi/10.1126/science.abg2371

Article on the paper: https://newatlas.com/energy/green-ammonia-phosphonium-produc...

Submission here: https://news.ycombinator.com/item?id=29427914

The company's website is here [0] but I could not find any detailed information on their process there. A search term that seems to be more useful for that, even though it does not give details on their process exactly, seems to be "ammonia fixation non-equilibrium plasma"

[0] https://www.nitricity.co/

Edit: an article on the Stanford website:

https://suncat.stanford.edu/news/boots-ground-stanford-team-...

Edit2: removed name and information about research of someone who seems to be involved with the company because they were not mentioned by name on the company website and might appreciate their privacy.

Here in the Netherlands we have the opposite problem: too much nitrogen is produced. So much that now the government want to buy out farmers in order to be allowed to build more houses. Being the second food exporting country may be related to this.