Nitrogen Confusion

As the spring season starts off and you are planning your fertility programs a question may arise as to what is the best way to handle nitrogen? When we used to talk about nitrogen management it was largely based on your method of application, were you going to put the nitrogen in the ground or apply it on top. After that we would recommend different fertilizers due to their properties to minimize loss. These approaches still work, however the focus has now been turned to nitrogen stabilization products to help keep nitrogen in the field and crop available.

Before we get too deep into these products we first need a basic understanding nitrogen and the major ways we can lose it. For plants there are two forms of nitrogen they can utilize, ammonium and nitrate. Each of these have their own losses associated with them. It is also important to note that these forms are not static in the soil, for instance ammonium can change forms to nitrate.

The most common form of loss is volatilization. This occurs when ammonium (NH₄⁺) looses a hydrogen ion to form ammonia (NH₃). The ammonia ion is what we associate with some of the manure smell on broadcast applications. This ammonia is a gas and it is lost to the atmosphere. This only happens in our soils with products containing urea such as UAN and manures. The 'old' way to control this loss was to incorporate these products into the soil by either injection or tillage.

The other loss mechanism is leaching. If we think back to basic soils we may remember that our soil has a negative charge. This allows it to hold positively charged ions such as ammonium, potassium, calcium and others. However the negative to this is that our other plant available form of nitrogen, nitrate, is negatively charged. As we all know like charges repel. This means that the nitrate molecules are not held to the soil and can be washed out of the root zone during wet conditions.

Now how do you choose between the products on the market such as Agrotain, Agrotain Plus, N-Serve, Twin N, Instinct; just to name a few. Although there are a many products the answer still lies in what you are applying and how you will be applying it. It is very important to ask your sales representative what form(s) of nitrogen loss their product inhibits. For instance, if you are applying UAN (an ammonium product) with a sprayer or broadcasting dry urea your largest worry is volatilization. This means you want a product that inhibits volatilization. These products are broadly known as urease inhibitors. This actually stops the reaction that changes ammonium to ammonia. So if you are broadcasting nitrogen that is subject to volatilization (UAN, Urea, etc.) you want to use a urease inhibitor. Agrotain is an example of a urease inhibitor.

If you are injecting your nitrogen you are already limiting the losses due to volatilization so you are more likely to be worried about losing nitrate nitrogen. For this situation you will need to use the product broadly called a nitrification inhibitor. It is important to note that these products to not stop the leaching of nitrate already in the soil they simply do not allow the ammonium ion to convert to nitrate. Products such as N-Serve , Instinct, and Guardian are nitrification inhibitors. Nitrification inhibitors have the most value when N is applied long before expected crop uptake and especially on soils at the extreme of soil drainage ie. excessively well drained or very poorly drained soils. For example, a lot of N is fall applied in the midwest and a nitrification inhibitor is essential but that is not a common practice in our area. The last class of nitrogen stabilization products are nothing new but actually a mix of the two previous. Products such as Agrotain Plus and Twin N are actually a mixture that will mitigate volatilization and nitrate leaching.

The important point on all of this is pay for what you need, not what you don't need. For instance, if you are injecting it makes little sense to use a urease inhibitor, but a nitrification inhibitor may be a good option depending on your soil conditions and timing of N application. For those who are broadcasting you have the choice of using just a urease inhibitor to stop volatilization or both urease and nitrification inhibitors. This will largely depend on your rate of application and how long you are depending on that nitrogen. If you are putting everything on up front well before crop uptake you may want to use both inhibitors, if not maybe only a urease inhibitor.

A final note is that the products mentioned are only a few of the total products out there. For products not listed, simply ask what the specific mode of action is for the product. If you have any other questions please contact me or your local extension agent.

Additives	Mode of Action	Example Products
Urease Inhibitors	Inhibit volatilization from surface applied urea containing fertilizers	Agrotain
Nitrification Inhibitors	Inhibits conversion of ammonium N (NH4+) to nitrate N (NO3-). Can reduce loss of N by leaching in well drained soils or denitrification in poorly drained soils	N Serve Instinct Guardian
Combination Products	Both urease inhibitor and nitrification inhibitor	Agrotain Plus