Polyphosphoric acid contg. 70-84% P2O5, polycondensation deg. (K-p) 45.8-87.7%, was treated with aq. 25% NH3 at 30-50 degrees C to yield various ammonium ortho/polyphosphates (APP) solutions contg. 30-38% P2O5. Soly. (g. metal/100 g P2O5) was detd. for blvalent Zn, Cu, Fe, and Mn micronutrients (hydrous sulfate added) In the APP soins. of pH 4-7 at 18-20 degrees C and multiply regressed on pH and K-p. The solns., pH 6.0-6.5, gave NPK fertilizers (10-11)-(34-57)-0 contg. max micronutrient concns., durable for min. 4 weeks, e.g., the 11-37-0 soln. contained about 2% of the micronutrients. Fe(II) and Mn(II) were least sot. No phosphate form was favorable. Total potyphosphate content appeared to be the crit. factor for the soly.