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Corn planting depth, root growth, and yield

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D.R. Hicks
Agronomy and Plant Genetics, University of Minnesota

The intense rains that have occurred since planting have caused the soil surface to settle in some areas resulting in corn seed laying in the ground closer to the surface than the original planting depth. This will not affect grain yield if the desired plant population is achieved and the permanent roots grow normally.

Planting Depth
The original planting depth may have been the intended 2 inches, but seeds are now closer to the soil surface because the rainfall has caused the seedbed to settle. When seedbeds settle the seed usually does not move downward, but the soil surface does. The mesocotyl is the portion of the corn shoot (below ground) between the seed and the crown of the plant. The crown is the base of the corn plant and the position from which the permanent roots grow. As germination occurs, the mesocotyl grows toward the soil surface and stops usually about 3/4 inch below the surface. Under normal situations, the length of the mesocotyl varies as planting depth varies such that seeds with shallow planting depths have very short mesocotyls. If the soil surface settles immediately after planting (or before the mesocotyl begins to grow), there should be no problem with crown placement because the mesocotyl will be very short in length. But, if germination is underway and the mesocotyl has been growing before the soil surface settles, then the crown of the plant may be very close to the soil surface.

Root Development
There is a potential risk of rootless corn with shallow planting depths. Rootless corn is the condition where the secondary or permanent roots do not grow from the crown and the plant falls over as it grows because it does not have roots for support. Plants usually grow 6 to 8 inches in height before they fall over. This is because the initial root growing from the seed is sufficient to nurture and support the plant until plants get to the 6 to 8 inch height. Then this initial root system disintegrates as the mesocotyl roots. If one can predict that rootless corn might occur because the crown is at or very near the soil surface and the soil surface is dry, then a careful cultivation rolling some soil to the base of the plants helps to prevent rootless corn. If the soil surface continues to be relatively moist, the permanent roots usually grow normally even when the crown is close to or very near the soil surface.

Yield
Planting depth will not affect grain yield if the intended plant population is achieved. If the shallow depth causes a reduction in the plant stand, then yield can be reduced because of the lower plant population. An Indiana study (Table 1) shows yields and plant populations resulting from planting depths ranging from 3/4 inch to 3 inches. Neither plant population or grain yield was appreciably affected by planting depth at two planting dates in Indiana.

Table 1. Corn Plant Populations and Grain Yields Resulting From Varying Planting Depths (Beck's Hybrids, Indiana)












































  Planted April 14 Planted May 12
Planting Depth (inches) Yield (bu/a) Population Yield (bu/a) Population
3/4 196 27100 189 26200
1 1/2 196 26100 193 26600
2 1/4 192 25800 192 28000
3 195 25600 191 25800

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