Yield potential drops when corn is not planted at the right depth, says University of Missouri Extension corn specialist Greg Luce.
The right planting depth improves the chance of a good stand, Luce says.
“The old rule of thumb—or index finger in this case—is to plant corn at a depth equal to the second knuckle on your index finger,” Luce says. That sounds simple enough, except the length of index fingers varies from farmer to farmer.
Most university extension publications across the Midwest recommend a depth of 1.5 to 2.5 inches. Luce says most agronomists agree that planting corn too shallow leads to more problems than planting too deep. “From my experiences, bad things happen when corn seed is planted shallower than 1.5 inches.” He recommends a depth of 2 inches.
The 2-inch depth allows good seed-to-soil contact for consistent moisture levels throughout the seedbed. Uneven soil moisture in the seed zone is the main cause of uneven emergence and an 8 to 10 percent yield loss, according to a publication by Wisconsin and Illinois agronomists.
Luce says the 2-inch depth helps the plant establish a strong nodal root system, which provides structural support and allows for better water and nutrient intake for the plant. A good nodal root system reduces early-season root lodging and helps the plant perform better under drought stress.
But there are exceptions to the planting depth rules, says Luce.
If soil is dry at planting time, seeds should be planted to moisture to increase chances of uniform emergence. Soil texture also affects suggested planting depth. Plant seeds no more than 2.5 inches in heavy-textured soils and soils with high clay content. Lighter, sandy textured soils accept seeding at 3 inches deep.
Evaluate individual fields for soil types, conditions and tillage practices as you consider proper planting depth, Luce says.
“In summary,” Luce says, “never plant corn less than 1.5 inches deep; 1.75 to 2.25 inches is an ideal target, but, depending on soil type and conditions, seeds may be planted up to 3 inches deep without any effect on stand establishment.”