Interesting idea.
So, farms are definitely setup already to accomplish this. Most farms have moved to central pivots for irrigation, and they already inject fertilizer into the pivot [1]. If fertilization could be generated onsite, then you could theoretically have everything plumbed together to "just work" without much intervention or shipping of chemicals.
[1] https://www.farmprogress.com/farming-equipment/chemical-fert...
> I would guess nitrogen is not one.
It's the main fertilizer applied.
Here's another site talking about common problems with this technique (from a farmer's perspective). [1]
[1] https://www.valleyirrigation.com/blog/valley-blog/2022/06/13...
Farmers use anhydrous ammonia that bounds with water in the soil and then bonds to the soil.
I don't know that farmers wear anything special when applying it, but there are safety procedures. I work with a farmer and he was telling me about one time he forgot to switch one of the valves off and when he disconnected a hose, the fumes knocked him out. Luckily it was just the fumes from the hose and not the whole tank or he likely would have died instead of just being knocked out.
Farmers already do keep an eye when it will rain before applying fertilisers. So, this is already part of their calculation. Although, yes , this means they will not apply it everyday. Depending on their location this means that a lot of weeks are out of the picture.
Rain will wash nitrogen away (down to streams, rivers, and then the ocean creating lots of problems) so you want to apply nitrogen with an eye on when it will rain so your fertilizer stays on the field where you want it. Your link doesn't specify what fertilizer is being applied, I would guess nitrogen is not one.
Ammonia should be applied to the soil - in the air it is a hazard that can kill people and harm the plants (farmers wear lots of protective gear when working with ammonia, with more other things they don't bother).
As such I'm not convinced that is the right answer. You want a system that will apply nitrogen