Farmers aren’t quick to take rain for granted, but the weather this spring has continued to test their patience. As multiple weeks of significant rainfall pushes planting progress far behind last year’s pace, Scott Irwin, professor at the University of Illinois, says these delays may not affect corn yields as much as you think.
Irwin explains corn’s optimal planting window is between April 20 to May 15 in the corn belt, and after that a decrease in yield should be expected.
“I’ve developed some models to estimate that penalty,” he shared on an episode of the Top Producer podcast. “Based on national planting progress statistics, I find that for each percentage of the U.S. corn crop planted after May 20, yield goes down by about 0.35 bushels.”
On average, he says about 20% of corn is planted after the optimal window. However, this year’s USDA planting progress report on May 19 showed 30% had yet to be put in the ground.
“My personal trend yield forecast for the U.S. corn crop this year is 182.1 bushels per acre,” Irwin says. “You’d probably want to drop that by two to three bushels per acre right now because of above-normal late planting.”
While losing that yield isn’t ideal, rain delays during planting likely won’t be the biggest weather event to impact this year’s crop.
“There’s definitely a pecking order in terms of the most important yield influencing factors for corn production here in the U.S.,” Irwin says. “There’s what I call the golden number for Illinois agriculture and that golden number is four – four inches of rain during July. That’s the No. 1 most important factor for corn yields year in and year out.”
Irwin explains his golden number can swing corn yields by 20 to 30 bushels compared to four or five bushels from late planting.
To hear more from Irwin, including his best advice for commodity marketing, listen to this episode of the Top Producer podcast.
