Editing Urea (section)

=== Finishing ===

Urea can be produced in solid forms ([[prill]]s, [[:wikt:granule|granules]], pellets or crystals) or as solutions.

==== Solid forms ====

For its main use as a fertilizer urea is mostly marketed in solid form, either as prills or granules. Prills are solidified droplets, whose production predates satisfactory urea granulation processes. Prills can be produced more cheaply than granules, but the limited size of prills (up to about 2.1&nbsp;mm in diameter), their low crushing strength, and the caking or crushing of prills during bulk storage and handling make them inferior to granules. Granules are produced by acretion onto urea seed particles by spraying liquid urea in a succession of layers. [[Formaldehyde]] is added during the production of both prills and granules in order to increase crushing strength and suppress caking. Other shaping techniques such as pastillization (depositing uniform-sized liquid droplets onto a cooling conveyor belt) are also used.<ref name="Meessen 2012"/>

==== Liquid forms ====

Solutions of [[UAN|urea and ammonium nitrate]] in water (UAN) are commonly used as a liquid fertilizer. In admixture, the combined solubility of ammonium nitrate and urea is so much higher than that of either component alone that it gives a stable solution with a total nitrogen content (32%) approaching that of solid ammonium nitrate (33.5%), though not, of course, that of urea itself (46%). UAN allows use of ammonium nitrate without the explosion hazard.<ref name="Meessen 2012"/> UAN accounts for 80% of the liquid fertilizers in the US.<ref name="Ren 2021">{{cite journal | last1=Ren | first1=Baizhao | last2=Guo | first2=Yanqing | last3=Liu | first3=Peng | last4=Zhao | first4=Bin | last5=Zhang | first5=Jiwang | title=Effects of Urea-Ammonium Nitrate Solution on Yield, N2O Emission, and Nitrogen Efficiency of Summer Maize Under Integration of Water and Fertilizer | journal=Frontiers in Plant Science | volume=12 | date=2021-08-03 | page=700331 | issn=1664-462X | doi=10.3389/fpls.2021.700331 | pmid=34413867 | pmc=8369924 | doi-access=free }}</ref>