Seed corn genetics are better than ever today, but even science has not outwitted old Mother Nature. In a fit of fury, she can deliver her wrath on a field of seed corn planted too soon and make you utter the five words every farmer hates to say: “I wish I had waited.”
What’s happened is easily explained and often easily ignored in the rush to plant.
“Seed corn is very sensitive to soil and soil water temperatures that are below 50°F at planting and during the first 48 hours afterwards,” says Ken Ferrie, Farm Journal Field Agronomist.
He says soil water temperatures above 50°F gives seed cell membranes elasticity, allowing them to stretch and expand appropriately as they take on moisture.
The opposite extreme occurs when temperatures are below 50°F. Cold seed cells have little elasticity, so as they take on moisture instead of swelling, they tear.
“This is what we call seed chilling, and it can take 7% to 10% out of your corn stand,” Ferrie says.
That Sick Feeling In Your Stomach
Seed chilling can be a big deal, because you now likely have some damaged seed corn sitting out there in the field, says Greg Kruger, University of Nebraska Extension cropping systems specialist, in an online article.
“In the plant (chilling) may somewhat disrupt the embryo/endosperm enzymatic conversion to energy, but mostly it results in leakage of cell solutes and sugars,” Kruger explains. “This, in turn, is likely to reduce growth rate and interfere with normal regulation and growth of the emerging seedling.”
Ferrie says the signs of seed chilling show up in different ways.
“Sometimes the seed doesn’t fire at all,” he says. “Sometimes it’ll throw a root but no shoots. Sometimes it’ll throw a shoot but no roots. The most common form of chilling farmers see is corkscrewing at the mesocotyl, and the spike doesn’t reach the surface.”
While seed chilling can happen at 50°F degrees or at a lesser temperature, the risk decreases significantly above that temperature.
“Temperatures can drop into the 40s but all that happens is the plant is going to be slower to emerge. The longer the plant spends in the ground, of course, the higher the risk of seedling diseases and insect damage,” Ferrie adds.
Go Get The Shovel
Seed chilling is not something you can observe driving by in your pickup or just walking out into the field. You have to dig up some of the seed corn and eyeball it, says Bob Nielsen, Purdue University Extension emeritus agronomist.
“The most common symptom of imbibitional chilling damage is often simply swollen seed with little to no evidence of sustained germination progress,” he says, in this article.
If swollen kernels of seed corn are what you find, all you can do for now is wait and see if and how they emerge and then do stand counts to determine next steps.
Check Soil Temperatures
If you haven’t started planting corn yet -- or even if you’re in the process -- Kruger says to do the following before taking off in the field:
1. Check the average soil temperatures for the last seven days.
2. Check the air temperature predicted for your area for the next 48 hours after planting. Note that soil temperatures, particularly in wet soils, change more slowly than air temperatures.
3. Test the soil temperatures in your field. Get a thermometer with a probe (for example, a meat thermometer that’s kept for soil tests).
On the day you’d like to plant, Kruger says to take a reading just after dawn — this is the coldest period during a 24-hour timeframe — to determine today’s soil temperature.
“If the results of these tests indicate soil tests are currently below 50°F or are expected to drop for much of the 48-hour imbibition period, consider delaying planting,” he says.
In other words -- just don’t do it. Save yourself from having to utter the dreaded words, “I wish I would have waited.”
More ears at harvest is the key to higher yields. Follow these 9 Steps to a Perfect Corn Stand.
