Graph 3: Dixon Springs IL, bare soil, 4-inch depth*
- The addition of nitrification inhibitors is equally important when applying ammonia and urea containing fertilizers in both the Spring and 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.
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 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 nitrogen investment is to apply a nitrification inhibitor with your nitrogen application in both the fall and the spring.
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 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 prior to 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 Nitrous Oxide, one of the most potent greenhouse gasses. 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.
Summary
There is a long period of time between the application of nitrogen in the fall and 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.