Considering a sidedress nitrogen application this spring? Fabián Fernández, University of Minnesota Department of Soil, Water and Climate assistant professor, addresses some key questions for supplemental nitrogen management decisions.

I applied all my nitrogen preplant. Do I need to apply additional nitrogen?
Typically, when there is excess rain and the soil is wetter than normal, additional nitrogen will be needed. If growers have fields that have had standing water for a long period of time, these conditions are ideal for needing additional nitrogen.

If a field has lost nitrogen, and the crop can benefit from additional nitrogen application to help the plant reach its full yield potential, it’s recommended to apply. However, in the event the soil has lost nitrogen, but the crop is not going to benefit from an additional application because yield potential is already severely impacted, it is not recommended.

How do I determine if I should make a sidedress application?
One of the first things to consider is the time of year and the condition of the soil. If it’s later in the season and the plants already have nitrogen deficiency — or if plants have been severely damaged by standing water or other factors — growers will not have the same yield potential that they would with a crop that was planted, started growing and is well-established. A full rate of application is not recommended if the full yield potential is not present.

Another way to determine if additional nitrogen is needed is if there are areas of the field where the crop looks healthy and very green, and other areas where deficiencies are observed. This is an indication that nitrogen is most likely needed. Additionally, if growers suspect that nitrogen is lost, but are not able to see that in the field, they should consider applying nitrogen in a strip. They should then wait seven to 10 days to see if there are any major differences between the plants in the strip and those in the field.

What source of nitrogen should I use?
The nitrogen source is key when considering a sidedress application. Growers should use a source of nitrogen that is readily available to the plant, so a slow-release or controlled-release fertilizer is not recommended. Another source to consider is urea. When broadcasting urea on the soil surface, for instance, growers should add NBPT, a urease inhibitor. Without the inhibitor, urea can start to volatilize as it transforms to ammonia (NH₃), and be lost to the atmosphere.

Another application method is through injection of urea-ammonium nitrate (UAN). If injected between the rows while the plants are at the early development stage, this method works very well.

Typically, if growers are going to inject fertilizers, the ideal window of time to do so is before V6. After V6, the roots of the crops start to grow into the center of the rows, and by injecting fertilizer, you may cut through those roots. If injection is not a good option for a particular farmer, dribbling UAN on the soil surface works well.

How can I maximize my nitrogen use during low-trending corn prices?
When considering what rates to apply, it is recommended to use the Nitrogen Rate Calculator found at cnrc.agron.iastate.edu. This calculator helps growers calculate economic return to nitrogen application with different nitrogen and corn prices, and find profitable nitrogen rates directly from recent nitrogen rate research data.

Growers should also consider downloading the U-M Crop Nutrient Calculator app on their mobile device. The Crop Nutrient Calculator app features the In-Season Corn Nitrogen Calculator. While a simple tool, it’s very beneficial for growers. By asking three questions about the conditions of their fields, the tool determines if supplemental, or extra, nitrogen is needed midseason.

The Minnesota Agricultural Fertilizer Research and Education Council funds various soil fertility and plant nutrient research projects that explore tools to sustain crop production and reduce potential environmental effects from crop nutrients. To learn more about the results of the council’s research, visit mnsoilfertility.com.

Source: Minnesota Agricultural Fertilizer Research and Education Council