Scott just ask Cody I have bugged him for years with that question. It is very complex thus usually a waste of money for my clients. Orthophosphate in theory might be worth it but usually best to do ortho and total. Yes we have found out the Nitrogen or really the N:P ratio was low in some cases and from this information actually added Nitrogen fertilizer rather than our high P fertilizer. Matt Rayl needs to chime in here and he had a good article in PB about this subject.
