Spring Use of Nitrification Inhibitors

• Facebook
• Twitter
• LinkedIn
• Email

• The addition of nitrification inhibitors is equally important when applying ammonia in the Spring as it is in the Fall  
• Nitrification inhibitors prevent conversion of ammonium-nitrogen to nitrate-nitrogen.
• Nitrification inhibitors, applied in the fall and spring, protect the nitrogen investment from heavy spring rains.

In this article, we will review the mechanisms that drive nitrogen loss (time, temperature, soil moisture), and the best practices for Nitrification inhibitor applications. Additionally, we will look at the performance of Instinct II (a.i. nitrapyrin) from Corteva in MiField trials over a period of three years and look at the National Oceanic and Atmospheric Administration (NOAA) weather outlook for the spring. 

More than 90% of the FS fall-applied nitrogen is done with N-Serve as a nitrification inhibitor.  N-Serve and Instinct from Corteva have the same active ingredient, nitrapyrin.  Nitrapyrin acts on the Nitrosomonas bacteria in the soil and prevents them from starting the nitrification process. Another option for a nitrification inhibitor in the spring is Centuro from Koch. Centuro prevents ammonium from being able to bind to the active site that Nitrosomonas uses to convert ammonium to nitrite, the first step in the nitrification process. In saturated soil conditions, nitrate can be lost through leaching or denitrification.  Best management practices to protect our spring nitrogen investment is to apply a nitrification inhibitor with your nitrogen application.

To understand the value of nitrification inhibitors, let’s look at the spring temperatures from February to May 2019, at a 4” soil depth for Dixon Springs and Freeport (Graph 3 & 4).

Graph 3: Dixon Springs IL, bare soil, 4-inch depth*          
Graph 4: Freeport IL, bare soil, 4-inch depth*
*Source: Water and Atmospheric Resources Monitoring Program. Illinois Climate Network. (2015). Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820-7495. https://dx.doi.org/10.13012/J8MW2F2Q

At both locations, soil temperatures begin to climb steadily above the 50°F point around April 1st.  Note that this climb happens well before corn plants are established to take up nitrogen and put potential loss to an end.  The reality is that nitrification inhibitors provide much of their protection in the timeframe from when the soil temperature surpasses 50°F in early April to the V8 corn growth stage, at which nitrogen uptake increases rapidly. Nearly 70% of the nitrogen is taken up by the corn crop by the time the plant reaches the tassel stage. Nitrogen applied without a nitrification inhibitor during this timeframe is prone to leaching through the soil profile, to tile drains as a water pollutant, or subject to denitrification when soils approach >75% saturation.  Denitrified nitrogen is lost to the atmosphere as a greenhouse gas.  Additionally, keep in mind that today’s hybrids need 30% of their nitrogen in the reproductive stages.  Corn roots will not be able to access any nitrogen that has moved below the top 12” of soil, where 80% of the corn’s root mass is found. 

What does MiField trials tell us about nitrification inhibitors? 
Instinct NextGen contains the same active ingredient as N-Serve (nitrapyrin) only differing in inert ingredients. MiField trials conducted from 2016 to 2018 in 26 locations, evaluated Instinct II in early spring to protect UAN (urea ammonium nitrate solution containing 75% ammonium, 25% nitrate).  In these 26 locations, acres receiving Instinct II yielded 11.8 bu/A more than the grower standard, resulting in a return on investment of $32.05/Acre (Figure 1).  Keep in mind that the 25% nitrate in UAN is a leachable, denitrifiable form of nitrogen making it more difficult to provide a ROI.  

Figure 1: Excerpt from 2018 MiField Yield Trial Results

2023 Spring Midwest Weather Outlook
As we have already mentioned, some of the key factors driving nitrogen loss are soil moisture and temperature. The potential for nitrogen loss may be predicted by looking at the weather outlooks for this spring. Three-month outlooks are available for the United States at the NOAA website. 

Summary 
There is a fairly long period of time between the application of nitrogen in the spring and when the corn plant begins to take up large amounts of N. Corn uptake of nitrogen doesn’t significantly increase until V8, still leaving 30% of its uptake needs for the reproductive stages. This is also the time when we get heavy rains in the spring, so the use of a nitrification inhibitor is very important to ensure that a grower’s nitrogen investment is there when the crop needs it. Our own MiField^® Trial data from 2016-2018 where a nitrification inhibitor was used with spring applied UAN revealed a good return on investment.  This spring’s weather outlook appears to have a high probability of warm and wet conditions, making the use of nitrification inhibitors with spring applied nitrogen a good practice to reduce nitrogen loss.