Given a choice, most farmers would rather plant corn sooner than later, especially now. Yet Bob Nielsen, Purdue University Extension corn specialist, says planting date plays a limited role in determining final corn yields. He points to Indiana and USDA data to back him up.

It’s what Nielsen calls a “conundrum.” Webster’s dictionary defines a conundrum as “a difficult and confusing problem or question.” In this case, how can it be that everyone understands corn yield tends to decline after a certain planting date, yet statewide averages for corn yields and planting dates are not strongly related?

“Early planting date favors higher yields for corn, but planting early doesn’t guarantee higher yields,” Nielsen says. “Planting date is just one of many yield-determining factors.”

Here’s a closer look at the conundrum:

Planting date window. The window for ideal planting without potential yield loss typically closes about May 10 in all but northern Indiana, where it closes a week later, Nielsen says. Agronomists have calculated potential yield loss per each day of delay. You can find the information in the Purdue Corn and Soybean Field Guide.

What USDA-NASS data says. Nielsen looked back at crop planting progress reports versus final yields over the past 25 years in Indiana. He mapped the comparisons and made an interesting discovery.

“There isn’t a strong relationship between planting date and absolute corn yield or departure from trend yield for that year in Indiana,” he says. Trend lines related to planting date only account for about 12% to 16% of the departure from trend yield in any one year, he adds.

“A number of other factors besides planting date affect yield in any one year,” he explains. Find his full report with the graphs he constructed online.

“Possible yield” concept. Several researchers have verified that relative yield potential of corn begins to decline after about May 1, with the decline increasing later in the calendar. However, actual yield response in any one year is relative to the maximum possible yield in that year, Nielsen emphasizes.

He explains with this example: Suppose the optimum yield for a crop planted April 30 is 220 bushels per acre. With a 10-day delay, the new possible yield is 213 bushels per acre. “However, suppose all the other factors which influence yield conspire to make the actual possible yield that year only 150 bushels per acre,” he says. “Then using the percentage delay per day, the 10-day delayed planting should yield 146 bushels per acre.”

Year-to-year comparisons. “It’s possible for early-planted corn one year to yield more than, less than or equal to later-planted corn in another year, depending on the exact combination of yield-influencing factors for each year,” Nielsen says.

Bottom line. There is no reason to panic about planting date, especially in early to mid-May, Nielsen says. He sees no reason to change crop inputs such as hybrid choices at this time. However, you might consider some management tweaks.

“Mudding in corn early to avoid planting late is almost always a bad decision,” he says. He adds that you may want to consider skipping unnecessary tillage trips, and perhaps opting to plant now and sidedress nitrogen later versus applying preplant nitrogen now.

If you’re planting when temperatures are warmer, you may also be able to cut back seeding rate slightly, because stand establishment should be more successful.