Urea is an organic N compound that is manufactured in large quantities. It is used as a fertilizer,
including controlled-release fertilizers, and in many industrial processes. The U.S. production of urea
was 9,330,000 tons in 1999 (Anon. 2000). Urea is the soluble form of N that is excreted by mammals.
Therefore, large amounts of urea are added to the surface soils of feedlots and dairies. However, urea
is rapidly hydrolyzed to NH3 and CO2, so it is not expected to make up a significant part of organic N
in water bodies, soils, or sediments.
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