Denitrification: A Key Nitrogen Loss Mechanism

When it rains, it pours.  And when it pours, we should be thinking about the nitrogen we’ve already applied to our fields.  While we haven’t received a uniform dose of rain across the major corn growing regions this spring, some areas received more than their typical share.

Especially in moderate to heavier soils (think silt loams to silty clays), saturated soils during the early growing season can cause a lot of issues.  It delays necessary field operations like tillage, planting and spraying, and even if the soils start to dry out, we risk soil compaction on ground that isn’t quite fit to go.  But silently, we can have large amounts of expensive nitrogen loss due to denitrification while the soil is soaking wet.

A natural process, denitrification converts nitrate and nitrite (NO3 and NO2), first to nitric oxide (NO), then to nitrous oxide (N2O), and then to atmospheric nitrogen (N2).  This occurs when the soil is saturated with water and without oxygen.  Certain species of bacteria, including Pseudomonas aeruginosa, Paracoccus denitrificans, and Thiobacillus denitrificans, rely on organic matter and operate in limited oxygen environments.  These bacteria “breath” the oxygen found in the nitrate and nitrite ions (NO3 and NO2) instead of atmospheric oxygen (O2) to reduce these ions.  Only nitrate is considered plant-available, so any reduction from nitrate to other forms of nitrogen removes it from crop usage.

Of course, high precipitation is a key driver for denitrification to occur in soils – you have to have the water to saturate the soil.  But the soil’s properties play a major role as well.  The speed at which a soil can drain by gravity under saturated conditions is called hydraulic conductivity, or KSat in scientific terms.  Often in units of millimeters per second or inches per hour, a soil’s hydraulic conductivity is often determined in a lab with specialized equipment.  In general, soils with more clay content will have lower hydraulic conductivity due to clay’s smaller particle sizes – it’s more difficult for water to flow through it than larger particles like silt or sand.

There’s not much you can do about your soil’s texture and thus hydraulic conductivity, but knowing this is key to proper nitrogen management and outsmarting denitrification.

By reducing the amount of applied nitrogen in the soil prior to potential wet periods (think fall or spring anhydrous ammonia before May rains), you reduce the chances of loss due to denitrification.  Another strategy is to use nitrification inhibitors with any applied ammonium fertilizer products, like N-Serve or Centuro.  This will keep the nitrogen in the ammonium form longer.  Ammonium nitrogen is not subject to loss through denitrification.

If possible, install tile drainage.  While some may argue that this leads to nitrate losses through tile lines, reducing the time the soil is saturated will reduce the environment and effects of denitrification.

After a period of saturated conditions, it is reasonable to ask “How much of my nitrogen do I have left?”  A great way to measure this is through mid-depth soil sampling.  Assuming nitrogen was applied on 30” centers with a UAN or NH3 applicator, and further that tillage may have been performed to wipe of any sign of where the application bands were, one can take a series of soil samples perpendicular to the path of travel with 11 cores taken 3” apart from each other.  These samples can be taken at 0-12" depth to capture the typical depth of the placement band.  Composite these cores together, mix thoroughly, and send in a soil sample to your favorite laboratory.  Make sure to have both nitrate and ammonium (NO3 and NH4) tested in the analysis.  If the results are in parts per million, multiple them by 4 and add together to get a rough idea of how many pounds of nitrogen you have in the top foot at the sample point.

Weather is going to happen, and we can’t easily change the soils we’re given.  But we can be smart about a major loss mechanism of nitrogen, both by avoiding or reducing its risk and quantifying the potential losses.  Tools like Sentinel’s All-N can also help estimate the losses through modeling and remote sensing.  Paired with soil sampling above, the smart farmer can both determine what was lost and what to do about it next with Sentinel.

Prime Denitrification scenario in South-Central Iowa fields, May 2026