Nitrification & Urease Inhibition

Advanced Nutrition

Nitrification inhibition

Nitrification is a natural biological process of oxidation of ammonia (NH3) or ammoniacal forms (NH4 +) of nitrogen in nitrite (NO2-) by means of bacteria Nitrosomonas and then to nitrate (NO3-) by bacteria of the Nitrobacter family. The nitrification inhibitors are substances which retard the production of nitrate form of nitrogen (NO3-) in soil solution acting up and preventing the activity of bacteria Nitrosomonas.

NH4 + (Nitrosomonas) => NO2 - (Nitrobacter ) => NO3 –

The duration of inhibiting the production of nitrate form of nitrogen may be increased -in case of using fertilizers enriched with nitrification inhibitors- up to 10 weeks. This is of great importance because by this way losses of nitrogen can be minimized in order for the plant to have the time to absorb nitrogen before it is washed or denitrificated.

Urease inhibition

Urea into the soil through the mechanism of hydrolysis and the presence of urease enzyme is being converted to ammonium form (NH4 +) and is held by the colloids in the soil cation exchange sites. However, part of the urea nitrogen can suffer losses as ammonia gas (NH3) according to the equation:

 (NH2)2CO + 2H2O (urease)=> 2 NH4HCO3 => 2 NH3 + H2O + CO2

These losses of nitrogen can be enormous especially when the following conditions occur or their combination:

  • Not adequate incorporation of urea
  • High temperatures
  • High pH
  • Crop residues
  • Soils of low cation exchange capacity

Urease inhibitors are substances used to temporarily reduce the activity of the urease enzyme and slow hydrolysis rate of urea. There are many substances that can inhibit the action of urease, but only a few (e.g. NBPT) are non-toxic, effective at low concentrations, chemically stable and able to be mixed or coated with fertilizers containing urea. In case of using fertilizers enriched with urease inhibitor it has been observed that the urea breakdown (due to the hydrolytic action of urease enzyme) can be delayed up to 3 weeks. Thus, protecting urea  is of great importance because otherwise nitrogen losses from volatilization can reach or exceed 40%.