At this point of the season, reminder of planting depth based on soil and weather conditions is still appropriate for talking about with farmers in some northern regions. David Karki, Ph.D.,SDSU Extension agronomy field specialist, explains that planting depth is one of many factors growers need to consider when planting a corn crop.
"A common principle of planting depth is to place a seed deep enough in the soil to reach adequate moisture for germination and emergence," Karki said.
According to Karki, the most common corn planting depth is 1.5 to 2 inches. "The depth can be slightly increased if the soil is abnormally dry and warm, however, it is not generally advised to place seed deeper than three inches," he said.
He explained that planting deeper than normal results in slower emergence with the increased likelihood of problems such as crust formation after rainfall before the plant has emerged from the ground.
Today, due to advancements in planting equipment, growers have much better control on planting depths and are equipped with better closing systems than older machinery. This, Karki said, makes it appealing for growers to try shallower planting depths.
However, he said corn fields planted at shallower depth usually result in poor and uneven emergence which can have potential negative effects on grain yield.
Additionally, surface residue can impact seeding depth. "If the field has good residue cover, the depth can be shallower than normal, as the soil warms up slower in high residue and no till systems," Karki said.
Karki does not recommend a seeding depth less than 1.25-inches. "Seeds that are planted shallower than recommended form nodal roots that are very close to the surface and may not develop proper root growth later in the season causing severe stress on the growing plant," he said.
Now, growers who find earlier planting conditions favorable, and plan to plant early, may consider a shallower than normal seed depth due to soil temperatures—but again, Karki does not recommend planting any less than 1.25-inches deep.
Even though optimal seeding depth can be somewhat dependent on soil type, available soil moisture and rain forecast, Karki said planting at 2-inches deep will facilitate germination and allow plants to develop proper root system.
Karki is reminding growers be aware of natural field-to-field variability and check their seeding depth at each field.