Ways for botanists to make fertilizers

[Ryumi]

As it stands, important chemical fertilizers like saltpetre and maybe potash are involved and tricky to make via chemistry. Perhaps Hydroponics could get a biomatter recycler that you cram plant matter into to store as biomatter that the machine can convert into a botany item/substance of your choice? It would of course take a lot more plant matter to make the biomatter needed for fertilizers, but it would at least give botanists a much more accessible and renewable source of fertilizer.

That's just one idea though. What other methods could botanists get to renew fertilizers?