Soil temperatures are dropping and moving toward the 50 degree threshold for fall nitrogen applications. If you’re thinking about fall applications, should you use an inhibitor? Our research shows that nitrification inhibitors can protect fall nitrogen against loss and increase the amount of nitrogen present in the ammonium form the following spring, as long as best practices are followed.
Nitrification Inhibitors vs. Urease Inhibitors
The two main types of inhibitors are nitrification inhibitors (NI) and urease inhibitors (UI). UIs, like NBPT, NPPT, Agrotain Ultra, Factor and Limus, protect fertilizers from ammonia volatilization. Generally, they are not needed with fall applications due to cool temperatures and incorporation.
NIs, which include Nitrapyrin, N-Serve, Instinct and DCD, stop or slow the nitrification process. This keeps fertilizer N in the NH4+ form longer, which protects it from leaching and denitirification losses.
The greatest potential for a return on investment with NIs is with fall anhydrous ammonia on medium and fine textured soils in South Central, Southwest and West Central Minnesota. Apply ammonia after soil temperatures at six inches is less than 50 degrees F. There is also potential for a return on investment with NIs on fall applied liquid swine manure, especially when manure is applied in early October, when soil temperatures are above 50 degrees F.
Long- and Short-Term Inhibitor Research
A 15-year study at Waseca showed addition of N-Serve to fall-applied ammonia increased corn grain yields 9 bu/ac. It also increased nitrogen use efficiency and decreased NO3 losses in tile drainage. However, in seven of the 15 years spring applied ammonia without N-Serve had 12 bu/ac greater corn yields than fall-applied with N-Serve.
In recent years, adding N-Serve to fall-applied AA has increased yield about 50 percent of the time and the average yield increase is about eight bu/ac.
A four year study at Waseca found adding Instinct to liquid swine manure applied in early October increased corn yields 7-10 bu/ac; however, delaying manure application until early November produced equal yields.
Be sure to discuss the value of inhibitors for your farming operation with an independent crop consultant or University of Minnesota soil scientist. Always remember to choose a proven NI, one with years of unbiased research data. Inject your nitrogen source and NI whenever possible to maximize effectiveness.
Support for this project was provided in part by the Agricultural Fertilizer Research & Education Council (AFREC).