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Soil Temps Below 50 Degrees? Don't Put Off Corn Planting Too Long

While corn planting is rolling hard in much of the Corn Belt this week, a look at the soil temperature map shows there's still a lot of dirt out there not quite at that 50-degree mark of optimal growing conditions for newly planted corn seeds.

Morning soil temperatures at the 4-inch depth are above 50 degrees in Kansas, Nebraska, parts of South Dakota, and Missouri and much of the mid-South, but remain in the 40s through much of the heart of the Corn Belt. While corn planting is running hard and nearing completion in some parts of the region, those soil temperatures may make rain delays coming this weekend and into next week a good thing for the young crop, one expert says.

"For each individual field, we still need to try to plant as early as conditions allow. Even if planting a week or two later would have little effect on yield in that field that year, we need to start so we can finish -- getting all fields planted by early May is a goal as we try to maximize yield potential," says University of Illinois Extension corn agronomist Emerson Nafziger. "But might this year be an exception, with potential for harm from planting into cool soils in the last week of April, with the weather forecast indicating that temperatures may stay low for the next week?"

In general, moisture is more important at this point in the year than temperature when it's close to the 50-degree mark; though it's not perfect, soils at temps below 50 degrees won't inflict damage on germinating seeds, they'll just slow the process. The real danger comes when trying to plant seeds in those soils when it's too wet, Nafziger says, making it important to ensure you don't rush after weekend and early-week rain before you get back to planting.

"Our first question should be whether or not the soil is dry enough; if the answer is no, then we wait. Cool soils dry slowly, and wet soils warm slowly, so waiting might take an extra measure of patience, especially if a neighbor brings out the planter. There is some comfort in the fact that germination and emergence are slow in cool soils, so planting a few days earlier when it’s cool makes very little difference in how far along the crop will be on a given date later in the season," he says. "The chances of getting good emergence when planting into cool soils are higher if there is little or no rain between planting and emergence. Cool soils bring slow germination and emergence, but they may lower the chance of emergence problems due to soil crusting or to saturated soil. Crusting problems usually develop after intense rainfall followed by warm, dry conditions that help 'bake' the crust. Warm soils mean more rapid growth of seedlings, which can mean running out of oxygen sooner if soils become saturated. So while we would prefer warmer and relatively dry soils, next best is having cool and dry soils. Most stand problems occur when soils are warmer, simply because that’s when the plants are trying to grow faster. Still, warm soils help bring the crop up, and we hope that they start to warm soon."

Generally, though you want to pay close attention to your specific soil conditions, don't let lingering sub-50-degree soil temperatures discourage you too much from staying on your normal planting schedule, weather permitting.

"Taking the longer view, temperatures in May will inevitably start to rise at some point in time, and this will speed up emergence. Taking all the factors together, I would suggest that planting proceed as long as soil conditions are good, even if the germination process will be slow due to cool soils in the near term," Nafziger adds.

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