Kinda sorta hard to do since P is part of the "complete fertilizer" equation of N-P-K. But I think I get what you're asking. There are phosphate-only ammendments out there. The grow shops carry many varieties. Depending on what your aim is you could use a P-only guano or a triple-phosphate fertilizer (no N or K). There are a couple of manufactuers Bonide being one. Big box retail or farm stores will probably carry it. Grow shops carry liquid P as well. But P is fert. An essential plant need. Hope this helps but if not post back and we'll try to clarify it for ya!
I used bone meal in my soil mix for P, but it's not water soluble so it probably won't do much as a top dressing. High-P bat guano sounds good.
Burned Haze -- That's great to know, thanks! I read a bit of your journal -- sorry about your seed loss, but glad you found some of them! For my next grow I want to get a strain that produces some cannabidiol. I hear they sell seeds with documented percentages at a health center in Cali, but I can't go there anytime soon. The info I've found on the online seedbanks is too vague. Would you happen to have any suggestions? (Sorry for the OT)
Would you consider organic fish bone meal a fertilizer? Or how about using fermented plant extracts? Give me a couple of parameters and I can probably come up with something viable. LD BTW - do you have access to nettle plants?
"P" is for Phospherus. "K" is for potassium...You're suppose to use wood ashes for Potassium (K) problems. Righty righty righty??