Fall Applied NH3 Management

By Cary Skibinski, Agronomy Product Manger:  What happens to NH3 once it leaves the knife?  Sometimes we think of loss of Nitrogen due to the loss of NH3 (Anhydrous Ammonia) from the soil immediately after application, the white puff of smoke.  Several temporary, but dramatic, changes occur to NH3 in a zone about 5 inches right around where the NH3 is applied, such as the following:

  • Increased concentration of NH3 and NH4
  • pH increases to 9 or above
  • Suction of soil solution into the zone
  • Lower populations of microorganisms
  • Organic Matter is solubilized

NH3 can react with Hydrogen gas, water, OH- groups, Calcium, Magnesium and organic matter.  The reaction in the soil needs to happen very rapidly to prevent the NH3 from being lost in the atmosphere.


The point is, many things happen to NH3 depending on soil type, structure, OM and moisture content.  Fields with variable pH will seal differently on different days due to these reactions.

Clay soils with higher CEC can hold more NH3 but tend to be less friable and create air pockets and space that limit these reactions.  Sandy soils have less CEC and limit the amount it can hold.  It is generally not recommended to apply more than 180# N at any one application on coarse soils. Adding N-Serve will not increase the holding capacity of the soil.

The majority of the time, adequate moisture is what is needed. The maximum capacity of NH3 a soil can hold is when soil moisture is at field capacity, but too wet to cause compaction.  The total amount of Nitrogen lost during application is minimal when soil moisture and injection depth is adequate.

The loss of N that I want to focus on happens throughout the growing season and can be much more detrimental.  Plants take up Nitrogen in two forms NH4 (Ammonium) and NO3 (Nitrate).  Both forms are needed in the soil throughout the growing season to maximize yields.  NH3 reacts with water and creates NH4+ (ammonium).   NH4+ is readily available to the plant and does not leach.  However, soil microbe’s like it too.  They will go to work converting it into nitrate NO3- , which is also used by the plant and is held in the soil solution.  It can be leached out of the root zone with excess moisture and time before the crop can use it.

Calendar date or soil temperate?

  • November 1st is the date that the NRD says it’s adequate to apply NH3
  • Generally soil temperatures above 50 degrees have bacteria in the soil that converts ammonium to nitrate.
  • N-serve decreases the population of Nitrate converting bacteria in the soil and slows down the conversion to Nitrate.

Adding N-Serve: Nitrogen in Nitrate form is very mobile in the soil and can move with the water through the soil, so the following are important:

  • Protecting the Nitrogen in the root zone helps maximize the amount of available nitrogen to your corn.
  • N-Serve will slow down N converting bacteria when soil temps are above 50 degrees
  • N-serve residual lasts about 90 days when soil temps are above 40 degrees.  So if there are 30 days in the fall before the temp drops below 40 degrees the N-serve will help protect your nitrogen for another 60 days in the spring once it warms up.
  • N-Serve can be added to the NH3 tank at your UFC location or injection equipment can be added to your toolbar to inject it into the line as you apply.
  • The N-Serve rate is 1qt/ac regardless of the nitrogen rate.  You will need to know how much NH3/Acre you intend to apply so we can mix the right amount of N-Serve into the nurse tank.

Why should you consider N-Serve?  Several variables have changed over the last 10 years, including  yields, Nitrogen rates, fertilizer prices, hybrids and populations. However, if Nitrogen is not the limiting factor on any of your corn acres, a yield increase would not be expected.  N-Serve will help protect your Nitrogen investment, increase your available nitrogen and reduce the amount of Nitrate in your groundwater.

If you have any questions, feel free to contact your FSA for more details!