The calendar may say it’s time to topdress winter wheat, but Mother Nature disagrees says Dave Mengel, fertility specialist for Kansas State University Research and Extension. Damp soils have kept many farmers from applying nitrogen (N) fertilizer to the young wheat crop. However, Mengel says there is plenty of time to perform the spring ritual across Kansas and many other production areas.
"Don't panic. There is still opportunity for a good response to topdress application for quite some time. There are some areas where it is just now starting to green up," he says. "Physiologically, the wheat is not very far along, particularly in some of the late-planted fields, which didn't have a lot of fall growth."
Mengel recommends that as the weather warms up and the wheat crop begins to grow more quickly, farmers begin thinking about shifting from a liquid-N-solutions topdress program to urea.
"As the wheat grows, farmers using liquid fertilizer while topdressing expose the wheat crop to leaf tissue burn. In many cases, the wheat isn't far enough along that it can easily withstand any leaf burn back," he says. "Right now, liquid fertilizer applications won't hurt anything. But soon it will be getting warmer, the wheat will begin growing in earnest and I would be cautious about using liquid-N solutions."
One caveat, notes Mengel, is that farmers can use "streamer bars," which can be installed on sprayer nozzles. These devices allow a stream of liquid fertilizer to be dribbled onto the crop about every 5-6 in. "We've used streamer bars clear up to boot stage and have seen very little damage," Mengel adds.
Ideally, the N in topdress applications will be moved into the root zone with precipitation well before jointing begins to be most efficiently utilized by wheat, Mengel says.
"With some of the small wheat out there this spring, having adequate N available to support spring tillering when it breaks dormancy will be important," he says. "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. This is the stage when head size is being determined and can begin about two weeks before jointing."
Producers should have started the season with a certain N recommendation in hand, ideally based on a profile N soil test done before the crop is planted and before any N has been applied.
"If some N has already been applied to the wheat crop, it's too late to use the profile N soil test since it's not reliable in measuring recently applied N," says Mengel. "Topdressing should complement or supplement the N applied in the fall, with the total application amount equaling that targeted rate."
Mengel adds that if the wheat was grazed through the fall and winter, producers should add an additional 30-40 lbs. N/acre for every 100 lbs. of beef weight gain removed from the field. If conditions were favorable for heavy grazing, additional N may be necessary.