Now is a good time for producers to start planning topdress nitrogen (N) applications to winter wheat. Given the dry conditions in a large part of the state and some fairly small wheat in many fields due to delayed fall planting, there are some key elements to consider when deciding on the exact N fertilizer program for your crop. These include: timing, N source, application method and N rate.
Ideally, the N in topdress applications will be moved into the root zone with precipitation well before jointing begins in order to be most efficiently utilized by wheat. With some of the small wheat out there with limited fall tillers, having adequate N available to support spring tillering when it breaks dormancy will be important. Also, the potential number of meshes per head is determined after spring green-up and prior to jointing; thus, having available N in the root zone can help ensure good yield potential. Some combination of fall preplant or at-seeding N, and/or early topdressed N, is also normally needed to supply adequate N to support head differentiation. The following will discuss some of the issues to consider when making topdressing decisions.
Timing of N application
The most important factor in getting a good return on topdress N is usually timing. It is critical to get the N on early enough to have the maximum potential impact on yield. While waiting until spring, just prior to jointing, can be done with success, 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 during the winter to cause significant denitrification or leaching. For these soils, topdressing can begin anytime, and usually the earlier the better.
For wheat grown on sandier soils, earlier is not necessarily better for N applications. On these soils, there is a greater chance that N applied in the fall or early winter could leach completely out of the root zone if precipitation is unusually heavy during the winter. Waiting until closer to spring green-up to make topdress N applications on sandier soils will help manage this risk.
On poorly drained or shallow claypan soils, especially in south-central or southeast Kansas, N applied in the fall or early winter would have a significant risk of denitrification N loss. Waiting until closer to spring green-up to make topdress N applications on these soils will help minimize the potential for this type of N loss.
Also keep in mind that N should not be applied to the soil surface when the ground is deeply frozen and especially when snow covered. This will help prevent runoff losses with snow melt or heavy precipitation.
On sandy soils subject to leaching and poorly drained soils prone to denitrification, split applications might be a strategy to consider. This would involve applying enough N in the fall at or prior to planting to give good support for fall growth and tillering — generally 20 to 30 pounds of N. Follow up with an additional application of approximately 20 to 30 pounds of N in late winter or early spring to support spring tillering, possibly applied with herbicides. This late-winter/early-spring application becomes especially important when stands are thin due to poor emergence, as many fields are this year. Finally, come back around jointing or a few days later with a final application to support heading and grain fill. This strategy also can provide flexibility in a year like this with uncertainty due to dry conditions and poor fall growth allowing to hold back part of the N for later in the spring as we have a better idea of soil moisture and weather conditions for the season.
Most topdressing is broadcast applied. In high-residue situations, this can result in some immobilization of N, especially where liquid urea ammonium nitrate (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. This can minimize immobilization and may provide for a more consistent crop response.
Next week’s article will address nitrogen source and rate. Mentioning next week on Wednesday, there will be a Spring Crops Update from 11 a.m. to 2:30 p.m. at the Cottonwood Extension Office meeting room, 601 Main, Hays. Topics of discussion include production practices for corn and sorghum, seeding rates, row spacing, hybrid selection, production problems, and a question-and-answer period. RSVP requested for meal count by noon on Tuesday by calling (785) 628-9430 or emailing Theresa firstname.lastname@example.org.
Stacy Campbell is a Kansas State Research and Extension agent in Hays for the Cottonwood Extension District Office.