Well another interesting spring so far. April brought the planters out at a world record pace and May has brought weather similar to March with rain and cool temperatures. So what might we expect in regards to nitrogen losses as we move into the growing season? With the wet conditions we have experienced over a large portion of the corn belt this spring customers will soon be wondering if they have loss substantial amounts of Nitrogen. When soils become saturated from heavy rainfall a major loss of nitrogen can be due to de-nitrification and leaching of nitrates.

Denitrification: Occurs under anaerobic soil conditions and is the conversion of the nitrate to nitrogen as soil microorganisms use the oxygen in the nitrate to survive. Studies have shown that up to 5% nitrate N loss can occur through denitrification each day soils were saturated. As soils remain saturated and the higher the temperature the more N is lost. As an example, studies conducted at University of NE have shown that when soil temperatures are 55-60 degrees the amount of Nitrate-N loss when the soil is saturated for 5 days is approximately 10%, at 10 days saturation the loss can be 25%. Research conducted in Illinois with late May to early June (soil temperatures greater than 65 degrees F) excess application of water on silt loam and clay loam soils indicated approximately 4 to 5 percent loss of nitrate present per day that soils were saturated.

Leaching: The leaching of nitrate through the soil profile is more of a concern in sandier and well drained soils. In lighter textured soils (sandy soils) one inch of rain can move nitrate 6 to 8 inches deeper in the soil profile. Thus, early heavy rains can move the nitrate below the root zone. With heavier soils nitrate can be lost by both leaching and denitrification, although leaching will be less than what occurs in the light textured soils.

Is Supplemental Nitrogen Necessary?

This may be necessary if sufficient N loss has occurred, however it is hard to quantify and it depends on many factors such as soil type, soil temperature, form of N and days of saturation. One method is the pre-sidedress nitrogen test. PSNT soil samples can be collected to a depth of one foot when corn is between 6 and 12 inches tall. Another consideration are general guidelines Purdue University developed which look at recommendations by N form, timing of N application prior to excessive rain and soil type. There are as follows:

Additional N Likely Required:
Consider 60 to 120 pounds of N per acre for fields where urea or 28% UAN was applied more than 2 weeks prior, or anhydrous ammonia applied more than 4 weeks prior, to excessive rain, especially if:

  • Silt loam and poorly drained field areas were saturated long enough to kill the crop and you will be replanting those areas to corn. Also consider starter fertilizer to get the replant corn off to a good start.
  • Sandy fields received more than 8 inches of rainfall that infiltrated the soil.

Additional N May Be Required:
Consider 30 to 60 pounds of N per acre for fields where urea or 28% UAN was applied 1 to 2 weeks prior, or anhydrous ammonia was applied 3 to 4 weeks prior, to excessive rain, especially if:

  • Silt loam field areas were saturated for more than 3 days and the crop survived.
  • Poorly drained field areas were ponded for more than 3 days and the crop survived.
  • Sandy fields received 4 to 8 inches of rainfall that infiltrated the soil.

Additional N Likely NOT Required:
Fields where N loss is estimated to be less than 30 pounds of N per acre and the projected optimum N rate or higher was used initially. For example:

  • Fields where N was applied 2 to 7 days (urea or 28%) or 3 weeks (anhydrous ammonia) before excessive rain.
  • Silt loam field areas that were saturated for less than 3 days.
  • Poorly drained field areas that were ponded for less than 3 days.
  • Sandy fields receiving less than 4 inches of rainfall.

Recommendations:

Some customers may want to consider returning to their corn fields and apply necessary rates of N as a side dress application to replace the lost nitrogen. This can be done with various forms of nitrogen such as anhydrous, UAN, urea, etc. If postemergence applications of UAN are being considered make sure your customers take into consideration the potential for crop injury. The maximum recommended rates of UAN are:

CornGrowthState / Max rate of N from UAN broadcast
V3 to V4 / 90 lbs N
V5 to V7 / 60 lbs N
> V7 / 0 N

Consider the addition of NutriSphere N with the UAN and or Urea applications which will help reduce the loss of nitrogen and improve yield potential.

Another option is to consider the use of SRN28.

  • Apply 1 to 3 gallons of SRN28 at the 3 to 5 leaf stage and again at the 8 to 12 leaf stage. This can be done in combination with a postemergence herbicide application.
  • Follow with another application of 1 to 3 gallons of SRN28 at the 8 to 12 leaf stage. This application can be done in combination with herbicides and or fungicides.
  • SRN28 can also be applied at the VT stage at 1-2 gallons per acre by itself or in combination with most foliar fungicides.

Remember corn will need almost 20-30 % of its total required nitrogen after tasseling. Now is a good time to consider nutrient management practices to insure adequate nitrogen will be available to maximize a corn crops yield potential.