Urea is the most widely used form of N fertilizer, and can be formulated as dry granules or as a fluid, ammonium nitrate (UAN). Urea is also present in animal manures. All these forms of urea have the disadvantage of undergoing considerable losses as ammonia gas if not incorporated into soil soon after application.
Factors conducive to N loss as ammonia from urea:
- Surface application
- Less than 10 mm (0.4 in.) of rainfall and/or irrigation in the first few days after application
- Presence of crop residues
- Open crop canopies
- High temperatures
- High soil pH
- Low cation exchange capacity soils
- Urease inhibitors are used to temporarily reduce the activity of the enzyme and slow the rate at which urea is hydrolyzed. The most widely used urease inhibitor is N-(n-Butyl) thiophosphoric triamide (NBPT). (This paragraph could be deleted).
Urease inhibitors are potentially useful tools for controlling or reducing gaseous losses of ammonia following fertilization with urea. They can restrict urea hydrolysis for up to 7 to 14 days, after which rain, irrigation, or soil mixing would be required to further restrict ammonia losses. Research suggests NBPT-treated urea use can reduce ammonia loss by 50% to 90% when compared to untreated urea. The preserved N will boost yields by keeping the applied N in the root zone.