Corteva™ Soil Health

How is Nitrogen Lost?

How is Nitrogen Lost? 

Volatilization is the loss of ammonia gas (NH3) to the atmosphere that occurs when urea fertilizer is hydrolized at the soil surface by urease enzymes.

  • Urea hydrolysis converts urea to ammonium (soil stable)
  • Urea hydrolysis increases soil pH which can increase ammonium conversion to volatile ammonia
  • Ammonia gas at the soil surface can volatize into the atmosphere

 

Factors Affecting Hydrolysis Loss

  • Soil texture and organic matter - higher organic matter increases urease enzymes that cause urea hydrolysis
  • Temperature - high temperatures increase the rate of hydrolysis
  • Moisture - hydrolysis slows in dry soils and speeds up in warm, moist soils
  • Tillage type - higher urease activity is usually found in no-till and minimum till systems
  • Soil pH - conversion of ammonium to volatile ammonia increases with increasing pH
  • Soil organic matter - Volatilization risk increases on low organic matter soils that absorb less ammonium and are more susceptible to pH increases caused by urea hydrolysis
  • Weather - high temperature, wind, sunlight increase rates of volatilization
  • Incorporation - quickly (within 24-36 hrs) incorporating urea is an effective way to reduce volatilization
  • Mechanical incorporation - urea should be incorporated to a depth of 3-4 inches
  • Water - 0.25 inches of rain or irritagation is sufficient to blend urea into the soil

 

While incorporation of urea is the best management practice for increasing nitrogen use efficiency, it is not always practical or possible. Difficulties with incorporation of urea include :

  • Perennial crops
  • No-till operations
  • Time constraints
  • Weather constraints
  • No access to irrigation
  • Thick residues

 

Areas of low rainfall

After nitrogen fertilizer application, naturally occuring soil bacteria quickly convert ammonium into nitrate in a two-step process called nitrification. This process is impacted by many factors including soil temperature, soil moisture, and soil pH. However, once converted to nitrates, nitrogen is subject to loss. Nitrate is prone to leaching with precipitation or irrigation. It can also be lost through denitrification or volatilization. Nitrogen losses commonly approach 25% of the applied nitrogen and can reach as high as 50-60% in some situations (Cassman, 2002). These losses are significant since the global market for nitrogen fertilizer is estimated at 113 million MT (IFA, 2014). It means that costly nitrogen fertilizer inputs are lost to the environment and not utilized by the crops.