The Nitrogen Cycle
The Nitrogen Cycle

Nitrous oxide (N2O) is produced naturally in soils through denitrification processes. These natural emissions can be increased by a variety of agricultural practices and activities including:

Direct addition of nitrogen to soils:

  • use of synthetic and organic fertilizers
  • production of nitrogen-fixing crops
  • cultivation of high organic content soils
  • application of livestock manure to croplands and pasture

Indirect addition of nitrogen to soils:

  • surface runoff and leaching of applied nitrogen into ground water and surface waters
  • denitrification of the organic nitrogen in livestock manure and urine

Denitrification and the generation of nitrous oxide is a natural process in which the nitrate molecule is stripped of oxygen under anoxic or anaerobic conditions. In the process the nitrogen molecule is reduced through a series of intermediate gaseous nitrogen oxide products and may ultimately end up as molecular nitrogen (N2).

Denitrification can be biological or chemical. The biological process is a respiratory process in which the microbes reduce oxidized forms of nitrogen in response to the oxidation of a carbon source such as organic matter at low oxygen levels (anoxic conditions) in the soil. The process starts with nitrate (NO3–). Once the nitrate is reduced to nitrite (NO2–) then both biological and chemical denitrification takes place with the generation of nitrous (N2O) and nitric (NO) oxides.

Where Do Nitrification Stabilizers, Inhibitors and Controlled Release Fertilizers Fit?

By definition:

  • Nitrogen Stabilizer: substance added to a fertilizer which extends the time the nitrogen component of the fertilizer remains in the soil in the ammoniacal form
  • Nitrification inhibitor: substance that inhibits the biological oxidation of ammoniacal nitrogen to nitrate nitrogen
  • Urease inhibitor: substance which inhibits, blocks or delays the hydrolytic action on the urea molecule by the urease enzyme
  • Slow or Controlled Release Fertilizer: chemical binding with urea or ammonia in a form which delays its availability for plant uptake and use after application, or which extends its availability to the plant.

Each has the ability to inhibit nitrification by a chemical or physical process. Nitrification inhibitors are used to decrease the possibility that large losses of nitrate will occur between the time a nitrogen fertilizer is applied and the time it is taken up by plants.

Where Nitrification Inhibitors Should be Used?

Nitrification inhibitors should be used in areas with high rainfall, finer-textured soils and cold soil temperatures during the winter. However, overall only about 50 percent and 70 percent of the trials with spring- and fall-applied nitrogen have shown yield response from nitrification inhibitors. There is a good probability of reducing nitrogen loss from fall-applied nitrogen fertilizers with the application of nitrification inhibitors to ammoniacal fertilizers, countering the potential for nitrogen loss through ammonia volatization.

The use of nitrification inhibitors will allow producers to apply nitrogen fertilizers somewhat earlier than generally considered feasible; otherwise, 50°F is the maximum soil temperature for application of ammoniacal fertilizers in the fall without a nitrification inhibitor. Heavy fall application of nitrogen is not recommended for low-cation-exchange-capacity (CEC), coarse-textured soils because of the possibility of urea, ammonium and, for certain, nitrate leaching.

Tillage Matters When Using Nitrification Inhibitors

More consistent yield responses have been obtained with no-till grown crops than with conventional tillage systems fertilized in the spring. This finding results from greater infiltration rates, higher water content, a higher population of denitrifying bacteria in no-till soils and, thus, increased nitrogen losses from leaching or denitrification.