Is the Rain Stealing Nitrogen from Your Corn?

June 23, 2015 07:00 AM
Is the Rain Stealing Nitrogen from Your Corn?

By Ed Lentz and Steve Culman, The Ohio State University

Some parts of the country have recently experienced heavy rains. Producers in these areas may have concerns about nitrogen loss in corn fields. Nitrogen losses occur by two main pathways: denitrification (gaseous loss of N) and leaching of nitrate from soil through water leaving the tile line or into groundwater. There is no tool or test that can tell how much has been lost. An estimate can made on the loss potential, which is based on N source, time of application, soil temperature, and number of days that soils have remained saturated.

Most nitrogen that is lost from a field is in the nitrate form during wet conditions. Time of transformation to nitrate is dependent on the type of N fertilizer applied. Anhydrous ammonia is less susceptible to loss since it converts to nitrate rather slowly. Urea-ammonium nitrate (UAN) solution has about 25% as nitrate at application time has a greater risk for loss than anhydrous.

Soils have been warm enough that some transformation to nitrate may have already occurred this year depending on application date. However, the nitrate N will not be lost by denitrification unless soils have remained saturated long enough. Risk of loss is minimal for soils that remain saturated for one day, moderate risk for two days of saturation, and a substantial risk for three or more days of saturated conditions. Standing water is evidence of saturated soils, but even soils without standing water are considered saturated if an individual cannot walk across without making footprints.

Since there are no absolute tests that can tell the N status a point system developed years ago by the University of Minnesota and modified to Ohio conditions has been useful. This system asks a series of questions and assigns a point value depending upon the answer. The probability of a response to additional N increases with more points. The questions and points are given below:


FACTOR 1: What N product was used?

  • Anhydrous ammonia with N-Serv    2 points
  • Anhydrous Ammonia                            3 points
  • Other fertilizer banded                         4 points
  • Other fertilizer broadcasted               5 points


FACTOR 2: When was the majority of the fertilizer N applied?

  • After April 20                    3 points
  • Before April 20                 5 points


FACTOR 3: What has been the field soil moisture status the past month?

  • Normal soil conditions                   1 point
  • Wet soils                                              3 points
  • Standing water/saturated soils   4 points


FACTOR 4: What is the crop's current condition?

  • Green plants > 12" tall             1 point
  • Green plants < 12" tall             2 points
  • Chlorotic plants < 12" tall       3 points
  • Chlorotic plants > 12" tall       5 points


Total the score for the four factors and use the following guidelines:

  • Less than 11       No supplemental N recommended
  • 11‑16                    Evaluate again in 4-7 days
  • 17 or more          Add an additional 40 or more lbs. N/acre


The "re‑evaluation" option is only viable until you no longer have side dressing options.  Illinois research from the 1990’s found that 50 lb. N/acre as a supplemental N rate was satisfactory for a wide range of conditions.  While a total score of 17‑18 would merit a 40 lb./acre N recommendation.  A total score of more than 18 may require a higher N rate. Losing 100% of the N fertilizer applied via denitrification or leaching is extremely unlikely and so a reapplication of the total amount of N for the season is not recommended.

How are fields looking in your area? See what other farmers are saying and share your own photos on AgWeb's Crop Comments section.

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Spell Check

nyc, NY
6/23/2015 05:48 PM


Rudy Hiebert
Abbotsford, BC Canada, WA
6/23/2015 05:37 PM

  Too many crop producers use chemical fertilizers which leach out of the soil. When quality organic concentrate from sea kelp and fish extract is used it would prepare the crop for stress and facilitate the plant to get access to nitrogen and other nutrients that have been become part of the seed bed.

DeLancey, NY
6/23/2015 09:01 AM

  For replishment of Nitrogen, investigate the restorative properties of industrial hemp -