How do I determine how much nitrogen my wheat crop needs for the topdress application?

Sandra Wick, Crop Production Agent

You might think it is too early to think about fertility management for your wheat, but now is a good time to start planning for your topdressing nitrogen (N) application on your winter wheat crop.   The first task is to access or evaluate your wheat stand to determine the potential of your crop.  This might be a rather challenging decision as some of the wheat in many fields is small due to late planting and the unusual wet conditions this fall and winter.  So there are some key elements that need to be considered when deciding on exactly what to do.  These include timing, N source, application method or placement and N rate.

“Timing is the key for your topdress application as the N in your topdress application needs to be into the root zone, with precipitation, by rapid plant growth and nitrogen uptake well before jointing begins in order to be most efficiently utilized by wheat,” according to Dr. Dorivar Ruiz Diaz, K-State Research and Extension Nutrient Management specialist. With some of the wheat out there with fairly limited growth, having adequate N available to support spring tillering when it breaks dormancy will be important. The following will discuss some of the issues to consider when making topdressing decisions. 

While some producers often wait until spring just prior to jointing, this can be too late in some years, especially when little or no N was applied in the fall. For the well-drained medium-to fine-textured soils that dominate our wheat acres, the odds of losing much of the N that is topdress-applied in the winter is low since we typically don’t get enough precipitation over the winter to cause significant denitrification or leaching. For these soils, topdressing can begin anytime now, and usually the earlier the better.  However, remember there are conditions when it is NOT recommended to apply nitrogen such as frozen ground or snow covered where runoff can occur and interfere with the distribution of the nitrogen.

The next factor that can affect the efficiency of the topdress application is the application method or placement.  Most topdressing is broadcast applied. In high-residue situations, this can result in some immobilization or “tie-up” of N, especially where liquid UAN is used. “If no herbicides are applied with the N, producers can get some benefit from applying the N in a dribble band on 15- to 18-inch centers,” added Ruiz Diaz.  This can minimize immobilization and may provide for a little more consistent crop response.

Source is another important factor in nitrogen utilization.  The typical sources of N used for topdressing wheat are UAN solution and dry urea. Numerous trials by K-State over the years have shown that both are equally effective. In no-till situations, there may be some slight advantage to applying dry urea since some of it will fall to the soil surface and be less affected by immobilization than broadcast liquid UAN, which tends to get hung up on surface residue.

Lastly, but certainly not the least is the rate.  As discussed earlier, the rate would depend on the potential of the crop or more ideally, based on soil tests, specifically a profile N test, that was collected on your fields.  It is not too late to use the profile N soil test if taken in late winter/very early spring before the wheat greens up. While it won’t be as accurate as when sampled in the fall, it can still point out fields or areas in fields with high levels of available nitrate N.  Remember, topdressing should complement or supplement the N applied in the fall and the residual soil N present in the soil. The total N application, at planting and topdressing, should equal the target recommended rate.

To address the nutrient management topic, our Post Rock Extension District will be hosting a “Nutrient Management Update” meeting on Thursday, February 14 in Jewell at the Community Center.  The meeting will start at 10:00 a.m. and include at 12:30 p.m.   Lunch will be served following the program.  CCA and CEU credits available.  10 registered participants are needed to hold the meeting.   RSVP is requested by Monday, February 11 either ONLINE at www.postrock.ksu.edu or to any of our Post Rock District Offices in Beloit, Lincoln, Mankato, Osborne or Smith Center.  NO COST, thanks to our sponsor Randall Farmers Coop Union. 

For further questions on nitrogen management in your wheat, contact me at any Post Rock Extension District Offices in Beloit, Lincoln, Mankato, Osborne or Smith Center.

Post Rock Extension District of K-State Research and Extension serves Jewell, Lincoln, Mitchell, Osborne, and Smith counties. Sandra may be contacted at swick@ksu.edu or by calling Smith Center, 282-6823, Beloit 738-3597, Lincoln 524-4432, Mankato 378-3174, or Osborne 346-2521.  Join us on Facebook at “Post Rock Extension” along with our blog site at postrockextension.blogspot.com.  Also remember our website is www.postrock.ksu.edu and my twitter account is @PRDcrops.