By EMMA HOPKINS-O’BRIEN

Indiana Correspondent

LEBANON, Ind. — At a recent field day presented by the Indiana Agriculture Nutrient Alliance, Purdue University professor of agronomy Tony Vyn shared research and tips on late-split nitrogen application – when it is most beneficial, and when it will not benefit crops at all.

He described late-split application as the intentional application of a portion of the total nitrogen to be applied on a crop after the V10 stage (the corn vegetative growth stage).

“I’ve used V10 as a sort of cutoff,” Vyn explained. “If you’re after V10, you’re talking about a late-season nitrogen application. That’s the first thing, is the timing.”

Different placements with coulters, Y-drops, or urea applicators that are broadcast are also key options involved with the timing constraint, which he said is somewhere between the V10 and V14 stages in corn’s production cycle. He does not have a straightforward recommendation that applies all the time involving late-split application, but he can offer explanations of why late-split works sometimes, while it has no response other times.

Vyn explained late-split application is almost always going to be of more benefit when the majority of nitrogen is applied earlier. “The later you apply the majority of the nitrogen, the less benefit there is in terms of yield in holding the last 20 percent of application after V10,” he said.

“In a number of the studies, we are getting the optimal in terms of timing, and the majority of the nitrogen was applied in an early sidedress application – let’s say, V4 or something close to that.”

Consideration of late-split application is warranted because corn hybrids have changed significantly in terms of how much nitrogen they take up after flowering. In his recent research, Vyn and his associates found that on average, the corn hybrids experiments done around the world took up 64 pounds of nitrogen after flowering, compared to about 40 pounds years ago.

“When you begin to think of that amount of nitrogen going in after flowering, you begin to think, ‘surely we would have more benefit from a late-split application today than when our fathers and mothers did years ago.’”

In this situation, nitrogen continues to go up after flowering in V5, V10, V15, and R1. At the same time, phosphorus, zinc, and other nutrients are taken up in the post-flowering period.

Vyn said his first experience with late-split nitrogen was an initial investment with Pioneer Hybrids in 2014, a study in which he looked at hybrids ranging from 20 years old to current hybrids, using a whole range of nitrogen timings and rates.

“The focus of this was ‘how do these hybrids respond to a V12 application of Y-drops, when we’re putting on – intentionally – 40 pounds in that late V12 application?’ and this research was coordinated with the assistance of Sara Mueller, a PhD student at the time, and was later also supported by the Indiana Corn Marketing Council (ICMC),” he noted.

Vyn described an actual situation where 180 pounds of nitrogen was applied at V3 – an early sidedress – and then split-applied, putting 140 pounds at B3 and 40 at V3 and another 40 at V12. In this case, the test plot gained about 20 bushels per acre, more than could be yielded out of a single-time application of 220 pounds applied at that same sidedress time as 180.

“The impression I want you to gain from this is: The opportunity gained from a late-split is going to be less automatic in a sidedress-application program,” Vyn said. “It’s fair to say that it probably is hybrid- and weather-dependent because to some extent, it depends on how much loss occurred and the nitrogen that was applied at that sidedress time.”

The conclusion of the research, sponsored by the ICMC, was that essentially there was little, if any, yield gain associated with a late-split nitrogen application when the producer sidedress-applies their nitrogen. However, there was an opportunity with the late-split, if a producer has technology in terms of sensor equipment and leaf analysis, to skip the late-split application, and end up with the same yields with less nitrogen.

“So, one of the benefits of an intentional late-split nitrogen approach is if we can accurately decide in what condition the corn needs to be so that it would not respond anymore to further nitrogen,” Vyn said. “Then there is an opportunity to variable rate-apply less total nitrogen. so that’s what we learned in those studies, and those are continuing this year.”