Terrestrial ag fertilizers don't have to be produced by fossil fuels.
The Haber–Bosch process used to make ammonium nitrate can be solar powered instead of using methane.
Phosphate rock processing could greenified for a green "green" phosphoric acid wet process.
Potassium from potash is mostly a passive solar evap process.
For seaweed aquaculture, iron sulfate is used because iron availability is the most frequent limiting factor. It's frequently a byproduct of steel production, in much need of greening itself, and produced in large quantities. Volcanic ash is another abundant source.
Terrestrial ag fertilizers don't have to be produced by fossil fuels.
The Haber–Bosch process used to make ammonium nitrate can be solar powered instead of using methane.
Phosphate rock processing could greenified for a green "green" phosphoric acid wet process.
Potassium from potash is mostly a passive solar evap process.
For seaweed aquaculture, iron sulfate is used because iron availability is the most frequent limiting factor. It's frequently a byproduct of steel production, in much need of greening itself, and produced in large quantities. Volcanic ash is another abundant source.