Urea (46-0-0), first introduced in 1935, is now the primary source of dry nitrogen (N) fertilizer in the U.S. due to its relatively high N content, ease of handling, and price. Although ammonium nitrate (34-0-0) may be superior in some situations to urea, due to liability concerns it is no longer available in many regions of the U.S. Fortunately, decades of experience and research suggest that urea and fluids containing urea are effective substitutes for ammonium nitrate when managed appropriately.
Widespread acceptance of urea was delayed in part due to its greater potential for N loss via ammonia volatilization (conversion from dissolved ammonia to ammonia gas). While all topdressed ammonia- and ammonium-based N fertilizers can volatilize, the potential is greatest with urea and fluids containing urea such as urea-ammonium nitrate (UAN; 28-0-0 or 32-0-0). While urea volatilization losses under worst-case conditions can be substantial, with proper management losses can be negligible.
With reduced availability of ammonium nitrate and increased reliance on urea, recent increases in N prices, and increasing environmental concern over atmospheric ammonia emissions, it should prove helpful to review conditions that affect ammonia volatilization and recommend ways to use urea effectively.
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