Planting soybeans early is increasingly a norm for farmers in the Midwest, but research from Iowa State suggests there’s a fine line between early and too early.
According to Iowa State University Extension cropping systems specialist Mark Licht, the decision on when to start planting isn’t found on a calendar.
“When we think about planting, we really should be thinking about soil conditions,” Licht says. “Are the soils fit? What’s the moisture of those soils? We don’t want them too wet, because that causes compaction.”
Know Your Conditions And The Forecast
Licht urges growers to watch for soil temperatures of about 50°F and rising, before heading to fields. The focus should be on “fit” soils –not too wet to avoid compaction from wheel traffic and down pressure. He also advises checking the weather outlook for three or four days after planting.
“Really, the first 12 to 24 hours are the most important, because that’s when the seed is imbibing water… if it’s kind of a cold water, the shock can disrupt cell membranes and cause germination issues down the road,” he warns.
Planting into cold, moisture-saturated ground doesn’t just slow things down—it also invites seedling diseases and the potential for a costly replant, which carries an automatic yield penalty.
Finding the Planting Sweet Spot
While an “ultra-early” trend of planting soybeans in March has gained traction in some farming circles, Licht’s data suggests it’s not worth the gamble. In Iowa field trials, mid-March planting showed farmers saw a reduction in final stands, gained only a meager three days in emergence and had no yield increase.
“Planting early is good, but not too early… April 15 to May 20 [in Iowa] is probably about the sweet spot,” he says.
Beyond that timing, though, yield penalties usually start to mount. Survey data from Iowa farmers show losses “anywhere from a .2 to a .5 bushel per acre per day” as planting is delayed after May 20, Licht reports.
The Corn Pivot: When to Switch Gears?
As planting season progresses, your strategy should shift from “when to start” to “what to prioritize.” The calendar does come into play.
Licht notes that if farmers in Iowa can wrap up both corn and soybeans by mid-May, the planting order for the two crops is flexible.
“But if we can’t get everything planted timely, then we should prioritize planting corn timely, because it has a much steeper penalty for being planted late, compared to soybeans,” Licht says.
Ken Ferrie, Farm Journal Field Agronomist, adds some perspective for those farmers who might feel behind by the time May arrives if they aren’t in the field. In central Illinois, May-planted corn has actually outperformed April plantings for the past three consecutive years due to better moisture availability.
Still, Ferrie says: “My advice for farmers here in central Illinois is if the ground is fit in April, plant some corn.”
But he also cautions against forcing the issue, as May can provide benefits.
“We never know how the rest of the year will play out,” Ferrie says. “Breaking the planting window up is a good way to mitigate risk and take the jam out of the fall of having everything ready at the same time.”
Osler Ortez, Ohio State Extension corn specialist, agrees that flexibility is key especially for those farmers with a single planter. “Focus on corn then [when conditions are right]. Once you get it planted, you can go back to finish up soybeans,” he says.
Hear more of Mark Licht’s perspective at YouTube on the Do’s and Dont’s of Early Soybean Planting here.