Planned, late-season nitrogen applications are more common today than they used to be. Seed company representatives and agronomists believe modern corn hybrids use a bigger percentage of nitrogen later in the season compared to top hybrids of the 1970s or 1980s.
Tony Vyn, a Purdue University Extension agronomist, says it’s true that modern hybrids use more N later. And while it’s logical to assume that means the later you apply, the better, he hasn’t proved this in his research trials.
Vyn looks for ways to improve nitrogen use efficiency, both to reduce nitrogen losses into the environment and to improve yields. He presented what he’s learned at a field day sponsored by the Indiana Agriculture Nutrient Alliance.
Vyn and his team saw a response for applying up to 40 pounds of N per acre at V12 one season, but then saw no response in another year. In fact, in 2015, their highest yield came from 140 pounds of N per acre applied at planting. The hallmark of what he’s seen for planned, late-season N applications is inconsistency. That matches up with findings by Purdue agronomists Bob Nielsen and Jim Camberato. After several years of comparisons, they report a benefit in some years, but no benefit in other years.
You would expect efficiency for N applications to line up this way: sidedressing more efficient than at-planting applications, at-planting more efficient than early-spring N, and early-spring more efficient than fall-applied N.
That holds up in his work, Vyn notes. What he has difficulty saying with confidence, however, is that you will see another yield bump if you hold the last 30 or more pounds of nitrogen for application at the V10 to V12 stage.
“If you sidedress correctly and have all your nitrogen applied by V4, you may or may not see any benefit from applying more nitrogen later,” Vyn says. “Whether you will see a yield advantage for sidedressing versus planting applications or midseason versus sidedressing applications may be somewhat hybrid-dependent. But it’s also dependent on weather and the potential for N loss. Generally, you expect less loss after sidedressing than after earlier applications. If there isn’t much loss after sidedressing, you may not see much, if any, yield response for a later application.”
That doesn’t mean Vyn isn’t still looking at various N application options. He’s still evaluating different timings and various methods of UAN application, especially for late-season N applications. You can add UAN with coulters or by dribbling. Several people use Y-drop applicators to place nitrogen near the row.
Vyn and his team are comparing Y-drops on both sides of the row versus dribbling N in the middle of the row. They’re also looking to see if there’s an edge for broadcast-applying urea with potash after the V8 stage in on-farm trials.
“We continue to look for ways to make applications most efficient,” he concludes. “But as of now, the consistency isn’t there to say we can expect a yield bump for a partial late-season N application versus sidedressing.
“However, if canopy sensors were reliable at the V12 stage, there may be an opportunity to save on nitrogen costs by only applying supplemental N in areas within the field which don’t have enough N to reach optimum yields.”