How Planting Depth Affects Your Corn's
Potential from Germination to Harvest
by Don "Moe" Moeller, Sales Agronomist

You might think that planting depth is only a concern in the spring. In reality, it can be a problem that continues through harvest. In order to comprehend the full-season ramifications of shallow planting depth, we must first understand the early growth of the corn plant's root development.

As a kernel germinates, the extension that grows from the seed to the soil surface is called the mesocotyl. This is where the main root system of the corn plant develops. In most cases, the main or nodal root system of the young corn plant begins growing on the mesocotyl about 1-1/2 inches from the kernel. Consequently, seed planted less than 1-1/2 inches deep will most likely be developing its main root system at or above the soil surface. This makes the fragile roots vulnerable to many stresses including weather, insects, herbicides, lack of early fertility, plant health and development. In extreme cases, this phenomenon in young plants is called rootless corn syndrome.

Incorrect planting depth usually affects the corn's health and yield potential from early establishment all the way through harvest. For example:

• Shallow planting can reduce the total effectiveness of technology (such as seed treatments like Poncho®) by slowing down or limiting the amount of the chemical the plant will absorb. This occurs because root development is slowed down and not up to its potential development and size.

• Shallow planted plants may not be protected as long or as well if an early freeze occurs.

• Proper planting depth can also help provide a better final stand and more even plant height throughout the field and year.

• Field tillage practices have changed. Many operators do very little cultivation and rely on chemicals to control weeds instead. Shallow planted corn is more likely to be damaged by herbicides, fertilizer or other chemicals sprayed directly on the exposed developing roots. This can put the plant under stress at a time when yield potential is being determined.

• The plant's ability to handle dry periods will be reduced because root mass is generally smaller or may be more concentrated in the upper soil surface.

• Plants with root masses concentrated in the upper soil surface will be more vulnerable to insect damage, season-long fertility intake limitations, drought stress, standability
problems and storm damage.

• Plants with smaller root systems are easily pulled out of the ground by the combine at harvest, and other late season harvestability and standability problems are more probable.

• Stalk size is usually smaller when seed is planted shallow, creating a greater risk of goose necking or stalk breakage, which can cause slowdowns and delays at harvest time.

It still takes good judgment, and there are other factors (such as speed, planter maintenance and environment) that are very important considerations when planting. However, depth can and does play a major role in the final yield. Recently, engineers from one of the major equipment manufacturers were here at Hooper and commented that, in their opinion, there are areas this year where corn planted 1/2-inch too shallow probably cost a farmer up to 50 bushels per acre. What is the ideal depth to plant corn? At least 1-1/2 inches deep, but preferably 2 inches.

Seed Depth Example
These samples are of 2661 Poncho® 250 dry land roots taken in August 2005 from a field at Hooper, Nebraska. The only difference between these roots is that the seeds were planted at different depths. All other factors (hybrid, field and treatment) were the same. Planting depths from left to right are:

(A: 2") (B: 1" to 1-1/2") (C: 1/2" to 1") (D: 1/4" to 1/2")

Note the difference in both root size and stalk size. The smaller root size shows the effects of the plant's ability to handle dry weather.