The Chilling Effect

Cool Weather in the Midwest Endangers Corn, Soybean Seedlings

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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Check soil temperatures in your field, as well as the 5-day forecast, before planting corn or soybeans. (DTN photo by Pamela Smith).

ROCKVILLE, Md. (DTN) -- April is drawing to a close and farmers are itching to get planters rolling.

However, a cool, wet trend moving across the Midwest this week puts corn and soybean seeds at a high risk of imbibitional chilling, agronomists warn.

Imbibitional chilling occurs when corn or soybean seeds first take in water (imbibition) after planting. If that water is below 50 degrees, it can damage or even kill the seeds.

A lot of corn acreage is at risk of this phenomenon this week if growers plant now, said DTN Senior Ag Meteorologist Bryce Anderson.

"It looks like about 40% of the intended corn acreage will be affected by the cold and wet pattern," namely Iowa, Minnesota, Wisconsin, North Dakota, South Dakota and Michigan, Anderson said.

Together, those states account for roughly 36 million corn acres out of the 90 million predicted by USDA's March 31 Prospective Plantings report. Based on weekly crop progress reports, up to 34.5 million acres of that remains unplanted -- or 38% of the U.S.'s potential corn acreage, Anderson said.

CORN SEEDS

In northwest Iowa, farmer and agronomist Jay Magnussen has watched warily as corn seed was planted, despite forecasts for cool temperatures and rain.

"We just had rain and it's only 40 degrees out," he told DTN. "Pretty tough conditions for corn seedlings."

Corn seeds take in water in the first 24 to 48 hours after planting, which kick-starts germination, explained Mark Licht, an Iowa State Extension cropping systems specialist.

Water below 39 degrees can damage the cell membranes within the corn seed, which will hamper growth and emergence and -- in severe cases -- prevent germination altogether.

In Magnussen's neck of the woods, up to 25% to 30% of corn is in the ground, he estimated. A lot of that went in over the weekend, but even those growers aren't necessarily safe, Licht noted.

"You're not quite out of the woods even if you planted corn seven days ago," he said. After germination, the plant's first root (the radicale root) elongates, the mesocotyl pushes up toward the surface, and secondary roots (seminal roots) start to stretch out, as well.

This is a vulnerable time for the corn seedling.

"There is some loss of vigor for seedlings planted a week ago and now facing cold weather," Licht said. "They are still losing some vigor and at greater risk for pathogenic infections of the radicale, the seminal roots and the mesocotyl."

SOYBEAN SEEDS

Soybean seeds take in water a little faster than corn seeds, a group of five University of Nebraska scientists noted in a Crop Watch article on imbibitional chilling. After the first 24 hours, the seed's water uptake slows and then it can better withstand cool soils.

However, soybeans are slightly more cold sensitive than corn.

"Chilling injury occurs with temperatures of less than 50°F within 24 hours of planting," the Nebraska scientists wrote. "Germination failure and seedling death occur at soil temperatures around 40°F. The longer the seed is in the ground at warm soil temperatures before cold temperatures occur, the less chance there is for chilling injury."

WHAT TO DO NOW

If you haven't planted yet, check your soil temperatures daily and watch the 5-to 7-day forecast, Licht said.

"It may not be perfect but it will tell you the direction things are going," he said.

Aim for soil temperatures above 50 degrees. Many land grant universities post state soil temperatures online (see Nebraska's here: http://bit.ly/…), but be sure to check your field individually on the day of planting.

Take a look at the label of your hybrid or soybean seed, as well, the Nebraska scientists added. They may have varying levels of cold tolerance.

Finally, if you already planted and fear for your seeds, scout during and after emergence, Licht said.

Swollen seeds with no germination or spotty germination are evidence of imbibitional chilling, according to Purdue University's corn agronomist Bob Nielsen. Twisted or "corkscrewed" seedlings mean germination occurred but cold temperatures or compacted soil restricted the mesocotyl's growth later on.

See the University of Nebraska CropWatch article here: http://bit.ly/….

See information on poor corn emergence from Nielsen, here: http://bit.ly/….

Emily Unglesbee can be reached at Emily.unglesbee@dtn.com

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(PS/CZ)

Emily Unglesbee