UAN is a solution of urea and ammonium nitrate in water used as a fertilizer.
The combination of urea and ammonium nitrate has an extremely low critical relative humidity (18% at 30 °C) and can therefore only be used in liquid fertilizers.
The most commonly used grade of these fertilizer solutions is UAN 32.0.0 (32%N) known as UN32 or UN-32, which consists of 45% ammonium nitrate, 35% urea and only 20% water.
The solutions are quite corrosive towards mild steel (up to 0.5 inches (1.3 cm) per year on C1010 steel) and are therefore generally equipped with a corrosion inhibitor to protect tanks, pipelines, nozzles, etc.
A thick, milky-white insoluble precipitate forms that may plug nozzles.