How Deep Should You Plant Corn?

How Deep Should You Plant Corn?

Aim for a planting depth of 2 inches, but be willing to adjust to conditions, say ISU Extension agronomists.

Can you plant corn a little shallower, say 1.5 inches deep or only 1 inch deep, rather than 2 inches deep or 2.5 inches, to try to get corn up and growing and out of the ground faster in these cooler than preferred soils?

That's a question some farmers are asking Clarke McGrath and other Iowa State University Extension field agronomists this week. McGrath, who writes the "Corn/Soybean Insight" column each month in Wallaces Farmer magazine, says "Based on my experience of years of checking fields and digging up corn that was planted anywhere from 1 inch to 5 inches deep, targeting 1.5 inches as the best planting depth is not my preference."

SOIL MOISTURE: Planting corn at a target depth of 2 inches is ideal. But you may want to adjust it a little to accommodate for soil moisture variance. This may mean planting a quarter of an inch deeper or shallower. To get more even germination and emergence, it's best to plant corn at a depth of uniform soil moisture.

So how deep should you plant corn? Some agronomists say "2 to 3 inches" and some say "1.5 to 2 inches," notes McGrath. "I say you should target your planting depth to 2 inches."

Target corn planting depth according to conditions
As you get out of the tractor and walk behind the planter to check seed spacing and depth, take a good look at where that corn seed is at and make sure it is at least 1.75 inches deep, he advises. And remember that rain may and probably will settle the soil around the seed zone and shallow up the depth a little, so plan your depth accordingly. "This is especially relevant if you happen to run your trash whippers more aggressively. Disc openers tend to work better around the 2-inch target in my experience, too."

McGrath recommends farmers aim for a 2.5 inch seed depth if the soils get dry. Planting 'too deep' such as 2.5 to 3 inches usually isn't nearly as problematic as too shallow, "but I have seen some loss of stand, loss of vigor and uneven emergence from 3-inch planted corn in cool, wet soils—occasionally. I see many more season long issues with shallow planted corn than deep planted corn, though."

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What happens if you plant too shallow? That can result in big problems, he notes. Such as rootless corn, sidewall compaction, poor root development, increased seed/root system mass in the herbicide zone, poor seed zone closing, the shallow seed zone can dry out, and other problems. I would rather err on the side of planting corn a little 'too deep' rather than too shallow."

Aim for planting depth of 2-inches, but be willing to adjust
Mark Licht, another ISU Extension field agronomist, agrees that planting at a target depth of 2 inches would be ideal. "But I'd also like to leave the door open for slight adjustments to accommodate soil moisture variance," adds Licht. "To get more even germination and emergence, it's best to plant corn at a depth of uniform soil moisture. This may mean planting a quarter inch deeper or shallower. Obviously this is more critical when rainfall is sparse."

Corn plants compete with neighboring plants for nutrients, water and sunlight. This competition is minimal early in the season when plants are smaller or when lower seeding rates are being used, says Licht. It is for this very reason that 'uniformity' is often mentioned when it comes to corn stands and planting recommendations. "To me, this uniformity needs to be not only in seed-to-seed spacing or singulation but should also be considered for seed depth, soil moisture, soil temperature and crop residue management," he says. "Some would even include nutrient management."

Planting tips to help get uniform corn stands
ISU agronomist Mark Licht offers several other corn planting tips to help ensure uniform plant stands.

1) Make sure crop residue is uniform across the field. Uneven residue distribution can be caused by the combine at time of harvest or with each tillage pass. Soils may be slightly wetter and slightly cooler under areas with more residue compared to areas with less residue. This unevenness of soil moisture and temperature, especially early in the planting season, can lead to more variable germination and emergence of corn stands.

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2) Have the seed units tuned-up for perfect singulation. The closer plants are to each other the more competition they will have for water, nutrients and sunlight. Granted, higher seeding rates mean plants are closer together but the problem of having a non-uniform distribution within the row can be minimized by eliminating skips, double and triple seed drops. Reducing seed bounce in the furrow is also important.

3) Plant into soil that's 50 degrees F and rising. Planting into soils warm enough results in a higher percentage of seeds germinating and emerging, compared to planting in cooler soils. Planting 24 to 48 hours ahead of a cold front that brings rain can be problematic for seeds that imbibe this cold water. The cold water itself may have little effect on the time needed for imbibition but growth of the radicle root is directly tied to soil temperature.

The radicle root will grow at soil temperatures as low as 46 degrees F but the mesocotyl and coleoptile require 60 degrees F for growth. Large soil temperature swings associated with early corn planting can hurt emergence or stunt growth of affected plants. Planting when soil temperatures are above 50 degrees F and expected to stay above is ideal for a more uniform stand.

4) Don't plant into marginal or wet conditions. Planting into wet or marginal soils results in sidewall compaction, which often leads to "mohawked" roots. If the furrow dries out and breaks open, this could lead to rootless corn. Either scenario results in poor root development and adversely affects corn growth.

TAGS: USDA Extension
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