Ok, how about this?
Off the top of my head I'd guess that the order things would disolve would be K, N, P; but I'd be completely unwilling to wager any of my own money on that.
I say that because most potassium salts are highly soluble (then there are a few that are completely insoluble), you could engineer something that is slow release for it but off the top of my head I can't think of a good one.
Some common forms of nitrogent are ammonium nitrate and urea, both highly soluble.
"super phosphate" I have often found is moderately soluble in water and takes a while to disolve.