Urea phosphate is a 1:1 combination of urea and phosphoric acid that is used as a fertilizer. It has an NPK formula of 17-44-0,[1] and is soluble in water, producing a strongly acidic solution.
Urea phosphate is available in fertilizer vendor bags that carry a UP signet on the packaging. It is sometimes added to blends which contain calcium nitrate, magnesium nitrate and potassium nitrate to produce water-soluble formulas such as 15-5-15 and 13-2-20. The acidity of urea phosphate allows Ca, Mg and P to co-exist in solution. Under less acidic conditions, there would be precipitation of Ca–Mg phosphates. Urea phosphate is often used in drip irrigation to clean pipe systems.[2][3]
The phosphoric acid and urea molecules in the urea phosphate crystal structure form a complex hydrogen-bonding network,[4] with the hydrogen atoms bonding more strongly to urea molecules.[5] It freely dissociates when dissolved in water.
Urea phosphate is produced as a non-ionic adduct of urea and phosphoric acid,[6] with the typical 17-44-0 grade of fertilizer produced using wet process phosphoric acid at concentrations that vary from 54%[1] to 90%:[7]
^Stroehlein, J. L.; Rubeiz, I. G.; Oebker, N. F. (April 1986). "Urea Phosphate Applied by Subsurface Drip Irrigation Increases Availability of Soil Nitrogen and Phosphorus". Vegetable Report. hdl:10150/214135.