I'm not sure if this is a mod conflict or how it's supposed to be.

On Gleba to make overgrowth soils I need liquid fertilizer, but I can't make liquid fertilizer anywhere but Certys or Muluna.

Is this how it's supposed to be or should there be some way to make fertilizer on Gleba?

You can (or at least should be able to) craft liquid fertilizer in space. If that's not the case, then another mod is interfering and causing issues for this mod. Either way, the intended way to produce liquid fertilizer for overgrowth soil is to make it in space and ship it down.