Perhaps no single practice has been studied more closely recently than the split application of nitrogen. The idea is simple: Save some nitrogen for a late-season trip before tasseling. On the surface it makes sense. Agronomists report that newer genetics tend to need more nitrogen later in the season. And the equipment to make effective late-season applications is available today.

Go beneath the surface and the situation becomes murkier. Some trials show a yield and/or economic response in some seasons, while others don’t. Here’s a closer look at a trial that does both. It shows a significant response at one location, but not at a second location, all in 2016.

“Our split-nitrogen application trials in corn were part of our protocol trials for our Agronomy in Motion program,” notes Trevor Perkins, an agronomist for Stewart Seeds. Perkins is part of a team of Stewart Seeds agronomists that conducts trials in Indiana, Ohio and Kentucky. Other members of the team include Brian Denning and Justin Petrosino.

Sidedress vs. split
The goal of this study in 2016 was to compare a traditional sidedress application to a sidedress plus pretassel application with a high-clearance rig. About 180 pounds of actual N per acre were applied in all the trials.

Perkins notes that the trial was repeated twice — in Clay County, Ind., and Wood County, Ohio, near Perrysburg. Trials were replicated either three or four times at each location.

The results turned out to be quite different, Perkins notes. In the Indiana trial, there was no significant difference in yield between the sidedress application by itself and the combination sidedress and pretassel application. There was also no significant difference in revenue. In other words, if this trial were run again at Clay County, there’s no reason to expect that there would be any significant difference between 180 pounds of N applied sidedress and 180 pounds of N split between sidedress and pretassel applications.   

However, Perkins notes that there was a significant difference favoring split-application in the Ohio test. When averaged across both locations, there was a 7.7-bushel increase, amounting to increased revenue of $19.95 per acre for split vs. sidedress.

Differences
Why did the results vary by location? There aren’t answers, but there are questions. Application method, form of nitrogen and soil type were different at each location, Perkins observes.

In Indiana, N was applied as urea with Agrotain, broadcast from a high-clearance spinner-spreader. In Ohio, 28% N was applied with Y-Drops.

The yield level was higher in Indiana, averaging more than 200 bushels per acre, compared to yields in the 150-to-170-bushel-per-acre range at the Ohio site. The agronomists collected rainfall information, and it also varied site to site, Perkins notes. Total rainfall during the growing season was 13.4 inches in Ohio and 28.1 inches in Indiana.

Do form, application method, soil type and environment matter? These questions remain. For now, these agronomists recommend looking at split applications first on sandier, low organic-matter soils or in fields with excessive rainfall.