Brad Wehr enjoys seeing how much corn he can grow per acre. It’s why he participates in the National Corn Growers Association corn yield contest. He took the top prize nationally in 2020 in the strip till/ no-till non-irrigated division, with a recorded yield of 347.4597 bushels per acre.

Perhaps more important than winning is what he’s learning, Wehr says. Wehr and his family farm both in Dubois and Pike counties in southwest Indiana.

“We’ve got some good creek bottom ground where we usually place the contest entry, and it works well with strip till,” he says. “We hire someone to make strips and apply fertilizer at the same time, usually near planting. Using RTK guidance, we plant on those strips. Residue is cleared off, and the corn usually gets a good start. We still conventional-till some fields, and no-till our most rolling fields.”

In 2020, the contest field wasn’t planted until May 25. “It was cool and wet early, and although we planted other corn before then, our later-planted corn generally yielded better,” he adds.

They planted 41,500 seeds per acre with Dekalb 65-95RIB on the contest field. Typically, he plants at 34,000 to 36,000.

Late, healthy corn

Wehr says the biggest thing he’s learned is the importance of keeping corn healthy as long as possible. “We combined at around 21% with dry husks, but stalks were still green,” he says. “We believe we’re picking up extra bushels on all our corn when we keep plants healthy longer.

“The extra yield is coming through more weight in those kernels. Corn needs to be healthy as long as possible to keep filling kernels.”

Wehr sometimes sprays fungicides at V10, then again right before or right after tasseling. “If we think there is good yield potential on our best ground, we might spray three times, but normally it’s less 9than that. We want plants filling kernels as long as possible.”

Bob Nielsen, Purdue University Extension corn specialist, agrees that keeping corn healthy as long as possible is critical for optimum yield.

“The grain-filling period determines kernel weight,” Nielsen says. He points to data indicating that more than half of total kernel dry weight is added during the final 30 days before corn reaches black layer. “Basically, that’s after early dent stage,” he explains. “Some used to say that if you got corn to early dent, you had the crop made. Obviously, that’s not the case. The final 30 days is still a key period.”

How much difference can kernel weight make on final yield? Nielsen offers this example. Suppose you estimate yield using the traditional method, and find 32,000 plants per acre, with 16 rows of kernels and 35 kernels per row per ear. Which “fudge factor” you choose to represent kernel weight makes a huge difference.

At 90, the yield would be 199 bushels per acre. At 80, more common with today’s hybrids, it’s 224. If you have very large kernels and use 65, it’s 276. If it’s a stress year with light kernels, at 100, it’s 179.

“You can vary your yield estimate almost 100 bushels per acre simply by changing the factor for kernel weight,” Nielsen says. “It’s a critical component.”

Nielsen outlines other important factors for yield in a three-part video, “High corn yields: Strategies and Philosophies,” posted at Purdue’s Chat’n Chew Café, bit.ly/highyieldforcorn.