The Corn Watch ’21 field is like many other fields in the eastern Corn Belt. Despite the challenges of the 2021 growing season, the potential for good yields is still there. Ear counts are adequate, and number of kernels per row appears to be hitting the upper end allowed by the genetics of each hybrid, in many cases. Where plants didn’t run short on nitrogen due to earlier losses, long ears with 40 to 42 kernels per row are common.

“The deciding factor will be what happens to kernel size during grain fill,” says Dave Nanda, director of genetics for Seed Genetics Direct, the company that sponsors Corn Watch ’21. “We need adequate moisture and good environmental conditions during grain fill so that ears don’t abort any tip kernels, and fill out all kernels as much as possible.”

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Although rain was plentiful during most of July where the Corn Watch ’21 field is located, Mother Nature turned off the spicket in late July. The field received only a couple of 0.1 to 0.2 rains during the following month and beyond.

“Plants were hanging in there in mid-August, but a good rain would certainly have upped the chances for plumper kernels and higher yields,” Nanda says. Grain fill typically continues for nearly two months. He expects the Corn Watch field to reach black layer around mid- to late September.

Why grain fill matters

Here’s an example from an area Nanda checked in the field that shows how much impact kernel size can have on final yield. Using the standard yield formula outlined in the Purdue University Corn & Soybean Field Guide, he picked a spot at random and counted ears in 1/1,000 of an acre, which is 17 feet, 5 inches in 30-inch rows. He counted 30 ears on each side of his measuring rope.

To determine kernels per ear, he decided on checking ears 5, 10 and 18, numbers picked at random to avoid bias. Those five ears averaged 17.33 rows per ear with 41 kernels per row, which is 709 kernels per ear, or 21,279 kernels per 1/1,000 acre.

Here’s where kernel size becomes huge, Nanda says. Twenty years ago, people tended to divide by 90, a factor representing number of kernels per bushel. With modern hybrids, people often divide by 80. But environment can either increase or decrease kernel size, despite what genetic potential was built into the plant. Here’s how the calculation looks using different factors:

That’s a 70-bushel swing based on kernel size. If the field didn’t receive additional rain, the 90 figure might be in play. One meaningful rain before black layer could keep 85 or maybe even 80 in play.

Nanda adds another caveat. The entire field isn’t at this level. Some places suffered more nitrogen loss due to poor drainage last spring after application. To get an accurate picture, do yield estimates at various locations within the field.