Incorporate urea within 24 to 36 hours to avoid nitrogen loss from volatilization. Mechanical incorporation by plowing down, disking in, cultivating in as a sidedress, and timing the application just before a rainfall all are effective methods. One-half inch of rain is sufficient. Broadcasting urea on corn plants causes some leaf injury, and although this is not a widespread practice, it has been used by some farmers and in research trials with satisfactory results. Sidedressing that is incorporated is preferred over topdressing.
UAN solutions are approximately one-half urea.
Therefore, observe the above application methods for urea, but do not apply UAN as a topdress, because such application would cause severe leaf injury. Incorporating or knifing-in the UAN improves efficiency slightly over dribble applications. Ammonium nitrate, ammonium sulfate, and the ammoniated phosphates can be surface applied without significant volatilization losses. It has long been known that the efficiency of recovering applied nitrogen is improved by sidedressing. Sidedressing also shortens the time during which the nitrogen is subject to possible field losses from leaching or denitrification.