Features

• Urea contains carbon, oxygen, hydrogen, and two atoms of nitrogen; the molecular formula is CO (NH2)2. According to the University of Minnesota Extension, urea's nitrogen content is high compared with other fertilizers; moreover, it's neither flammable nor explosive and poses few environmental hazards. These features make it a popular choice as an agricultural fertilizer.
  
  

Function

• Urea is water-soluble and when added to soil is broken down into ammonium and carbon dioxide. This process occurs more rapidly in alkaline soils. According to the University of Minnesota Extension, high temperatures or highly alkaline soils can increase the rate of urea loss and thereby make urea application less efficient.
  
  

Effects

• Initially, urea breakdown increases ammonia concentration, which makes soil immediately surrounding urea particles more alkaline. This zone can be somewhat toxic to seedlings until the ammonia is neutralized, although this process takes place rather quickly. It's usually a few days before nitrogen from the urea becomes available to the plants. Despite its initial effects, urea ultimately makes soil more acidic.