Fabián Fernández, University of Illinois Extension specialist in soil fertility and plant nutrition, ranked his choices for N application based on availability, crop protection, nitrogen loss reduction and cost minimization. His rankings follow.
First choice: Injected anhydrous ammonia or urea ammonium nitrate (UAN) solution between rows
Anhydrous ammonia converts quickly to ammonium in the soil and is less prone to loss compared to other sources if weather conditions become too wet after the application.
Between-row applications keep N at a safe distance from the crop to avoid injury and also puts N where the roots will be growing. Applications between rows have become even easier than in the past with RTK guidance systems. There is no advantage to applying N close to the row since roots will grow into the row-middles by around the fourth-leaf stage, Fernández says.
“Another option to increase speed, reduce horsepower or both, is to apply N in every other row instead of every row,” Fernández says. “Research has shown that there will not be a negative impact on yield by doing this placement because every row will have N applied on one side or the other.”
Second and third choices: Broadcast application of solid ammonium-containing fertilizers or broadcast urea with Agrotain
Surface application of ammonium-containing fertilizers is recommended because these fertilizers are not subject to volatilization, Fernández says.
On the other hand, if urea is used, include Agrotain to protect it from volatilization. Since farmers won’t be able to incorporate these broadcast applications with tillage after the crop is planted, apply before it rains at least half an inch so the fertilizer gets incorporated into the root zone. To avoid volatilization losses, the sooner it rains the better. Normally little is lost if it rains within 10 days or so from the time of urea application
Fernández says, “Broadcast urea applications work fine until the crop is knee-high. However, the sooner it is done, the better. Earlier applications can help reduce canopy injury and increase the chance of a good rain to work the urea into the ground. While you would likely see some leaf burn with urea applications at the early stages of corn growth, the damage is aesthetic and likely will not result in yield reduction.”
Fourth choice:Dribble UAN solution between rows
Dribbling UAN solution is slow, Fernández says. Part of the N is subject to volatilization, and just like with dry N fertilizers, it needs a good rain to be incorporated into the root zone.
Fifth choice: Broadcast UAN solution
As a last resort, broadcast UAN application could be used. However, he says it’s the least desirable practice because in addition to some of the same concerns mentioned for dribble UAN solution applications, it can cause severe leaf burn.
For more information, check out The Bulletin, an online publication written by U of I Extension specialists in crop science.