Today’s soil temperature might not be as important to corn seeds as tomorrow’s soil temperature
At one time, many farmers thought corn seeds had the ability to lay dormant after planting until soil temperature and soil moisture were right for germination and emergence.
Corn seeds are miraculous things, but they aren’t patient or wise. Unless planted into drought conditions, seeds absorb moisture within hours after planting and begin the germination process
almost immediately. That’s when significant problems can develop in early planted corn if soil temperatures fall and stay below 50°F.
Cold chill inhibition, also known as cold shock, occurs when corn seeds absorb water colder than 50°F. Absorbing cold water causes the cell membranes to rupture and release fluids that provide food sources for soil pathogens. These can invade developing seedlings and dramatically harm the germination and early season vigor of young corn plants.
Cold shock was a problem in some parts of the Corn Belt in 2011, when corn planted into relatively warm soil received a cold rain that severely chilled the soil for a week or more.
"Cold shock is a unique occurrence," says John Swalwell, a territory agronomist for Monsanto Company. "The exact circumstances don’t happen very often. But it can clobber germination and emergence if you get caught."
Double whammy. Symptoms of cold shock are abnormal-looking, corkscrew twisted, whitish-yellow sprouts that have difficulty emerging from the soil. In severe cases, when poor vigor is combined with the crusted soils that are common after pounding rains, cold shock can reduce final stands by 10,000 plants per acre.
Cold shock has the potential to slam corn with a double whammy because it not only damages sprout development but also diminishes the vigor of any seedlings that do manage to emerge.
Chris Doud, an area agronomist with Pioneer Hi-Bred, says bad-looking stands of corn stay bad even after they start looking good. "Farmers have good reason to be concerned when they have a thin or uneven-looking stand of corn after emergence," he says.
"Tough-looking early season corn stands are often forgotten once they hit a growth spurt.
Many of these fields experience disappointing yields at harvest due to early season stresses that reduced initial stands and decreased seedling vigor," he adds.
That’s because research indicates corn seedlings need energy stored in their kernel even after emergence. Seedlings that struggle for a week or more to emerge from cool, wet soil drain their kernel’s energy reserves. Erratic emergence is then exaggerated by uneven growth and elongation.
Doud says the full toll of a cold snap isn’t evident until harvest.
"If you have a final corn stand that’s reduced by 4,000 to 6,000 plants per acre, and also have a significant number of the remaining plants more than one leaf behind their neighbors, those delayed plants are basically weeds," he says. "You’re going to see significant yield losses even though that field ‘came around’ and ‘looked better’ later in the summer."
Greg Peters, area agronomist for LG Seeds, says the best way to minimize damage from cold shock when planting early is to select corn hybrids that are tolerant of cool soil temperatures and to closely monitor weather forecasts.
"Genetics and seed treatments help some hybrids withstand cold shock better than others," Peters says. "But no hybrid is completely resistant to cold shock. If you start planting a couple weeks ahead of the optimum for your area, keep a close eye on the three- to five-day forecast.
"Last year, we saw a major cold front setting up to move across the Midwest in mid-April," he says. "We warned our farmers who were already planting to stop planting three to four days ahead of that front. The ones who stopped planting came out with some of their best yields from their early planted fields because early planted corn has shown strong yield advantages when conditions are right.
"The ones who raced that cold front," Peters adds, "who only quit planting when sleet was hitting their windshields, had some significant yield reductions."