Fertilizer recommendations without a soil test are guesswork. Say so.
Well established · suboptimal if ignored → advise
How it works
N-P-K sufficiency is site-specific and unknowable a priori.
What to do about it
We will not invent an NPK number. Your county extension office will test this soil for about $15. Until then, feed heavy feeders, do not feed root crops, and add compost.
The evidence
Evidence: settled without a trial - epistemics.