Cold, dry conditions are less cause for concern for corn seed than cool, wet soils, an agronomist said
By Jackie Clark
As we roll through planting season, some farmers in Ontario may be noticing that their April-planted corn is emerging more slowly than they’d expect. This is likely not cause for concern, just a product of a cooler-than-average spring, Greg Stewart, agronomy lead at Maizex, told Farms.com.
“Generally, the minimum threshold for the seed to have some activity is 10 C (50 F) … When you have soil temperatures that are below 10 C (50 F), clearly the seed goes into stagnation,” Stewart said.
“If you look at the history of the last four weeks here in Ontario, we’ve had more days than normal where the soil temperature wouldn’t have gone to 10 C (50 F), and so that sort of puts a pause on the germination emergence process,” he explained.
Farmers and agronomists calculate crop heat units (CHU) using daily maximum and nighttime minimum air temperatures. When daytime temperatures are less than 10 C (50 F) and nighttime temperatures fall below 4.4 C (40 F), zero CHUs are counted for the day. Daily CHU values accumulate to estimate crop stages.
“You’ve got to have in the neighborhood of 150-180 CHU before the corn crop would emerge,” Stewart said. “Given the number of cool days we’ve had this planting season, the CHUs aren’t adding up as quickly.”
In a typical year, corn tends to emerge 10-15 days after planting. In some locations this year, Stewart is predicting corn seeded in late April will emerge 24-25 days after planting.
“We’re in a window now where temperatures are better and so some of the corn is going to move along, especially once we get soil temperatures that don’t drop below 10 C (50 F) every day,” he added.
Factors like soil texture, moisture and residue cover can impact the soil temperature and, therefore, time to corn emergence.
“If your soils are wetter because of rainfall, or if your soils have more clay content in them, they hold more water. Soils that have more water or hold more water are slower to warm up. So, in a given day, if you have a lighter-textured soil, a sandy soil that’s dryer, it’ll warm up quicker,” Stewart explained. Sandy soils may also cool off more at nighttime, but generally dryer soils are warmer.
“One of the good things about the past four weeks is that, up until this past weekend, we have been fairly dry,” Steward added. Cold and wet is the worst-case scenario for corn seed.
“Many of our soils have been cold, but not necessarily terribly wet. … That has boded well for the seed to be able to sit there and move slowly through the germination process,” he said.
Fields with residue cover may take longer to warm up, whereas “a field that is absolutely free of crop residue generally will warm up a little faster,” Stewart explained.
Finally, planting depth will affect corn emergence.
Some research suggests that planting deeper “is a good thing in terms of uniformity,” said Stewart, but planting deeper in a cool year can further delay emergence.
“I think, for the most part, there’s no reason to worry. We just simply haven’t had enough heat to germinate and emerge most fields,” he added.
If farmers are concerned, they can dig up a few individual seeds from their fields.
“There should be some root growth,” said Stewart. Plants further along will have evidence of a shoot emerging as well.
“The problem signs are if the seed is soft, if it has a bit of a mush feel to it, then you might get concerned that something has happened to the seed. Those would be situations where generally the seed sat in really wet conditions,” Stewart explained. Saturated, cold conditions are more likely to cause seeds to deteriorate.
“The seed is most sensitive to cold shock when it’s imbibing the first water that it gets,” Stewart said. “Sometimes those seeds will look slightly abnormal. The shoot that grows out of it that should normally grow quite straight, towards the soil surface, can have some funny twisting or distorted growth.”
Twisted young shoots are a sign of cold shock during imbibing. Because of this spring’s field conditions, Steward doesn’t expect to see too much of that in Ontario, but if a farmer sees that shoot characteristic, it would be a field to keep an eye on, he said.
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