Ammonium nitrate is an important fertilizer with the NPK rating 34-0-0 (34% nitrogen). It is less concentrated than urea (46-0-0), giving ammonium nitrate a slight transportation disadvantage. Ammonium nitrate's advantage over urea is that it is more stable and does not rapidly lose nitrogen to the atmosphere. During warm weather it is best to apply urea soon before rain is expected or to cover it with soil to minimize nitrogen loss.