The connection between nitrogen fertilizer and corn yields is old news. But today’s new vocabulary for fertilizer management — nitrogen use efficiency, or NUE; average optimum nitrogen rate, or AONR; and economic optimum nitrogen rate, or EONR, to name a few — reflects the industry’s efforts to hone N management into a finely tuned instrument. That’s going to have a big impact on your pocketbook as well as on the environment.

Changes in the corn plant itself have made a massive difference in nitrogen use efficiency, notes Tony Vyn, cropping systems Extension agronomist at Purdue University. Purdue researchers reviewed decades of corn studies and determined that 1 pound of N produces 22% more grain today than it did in 1940. That’s one of the benefits of modern genetics.

Crop guides applications

The reality of nitrogen management is that the vast bulk of the corn crop’s N is applied in the fall or early spring based on price and workflow considerations. However, a growing set of tools is emerging to encourage more targeted, environmentally friendly in-season applications.

Ideally, says Fabian Fernandez, University of Illinois Extension soil fertility specialist, split applications would be the way to go, as 40% of corn’s N use occurs after flowering.

“Just a small amount of N is needed in the spring to get the corn plant growing early on,” Fernandez says. “Plus, people who split-apply their N don’t have to compensate as much for lost N as those who apply everything in the fall.”

Grower Ed Winkle of Martinsville, Ohio, takes this approach. Winkle says planting-time applications provide enough N for early “workhorse” hybrids, while doses of 28% UAN, along with his postemergence herbicide pass, and a later sidedress application push “racehorse” hybrids on their path toward 200-bushel-
per-acre yields.