Planting depth recommendations for corn in Ohio are 1.5 to 2 inches deep to ensure adequate moisture uptake and seed-to-soil contact. Deeper planting may be recommended as the season progresses and soils become warmer and drier. Planting shallower than 1.5 inches is generally not recommended at any planting date or in any soil type.
When corn is planted 1.5 to 2 inches deep, the nodal roots develop about 3/4 of an inch below the soil surface. However at planting depths less than 1 inch, the nodal roots develop at or just below the soil surface (Figure 4). Excessively shallow planting can cause slow, uneven emergence due to soil moisture variation, and rootless corn (floppy corn syndrome) later in the season when hot, dry weather inhibits nodal root development (Figure 1). This latter situation has led to the assumption that planting depth may play a role in managing the drought susceptibility of a hybrid.
According to some field agronomists, shallow plantings increase stress and result in less developed roots, smaller stalk diameters, smaller ears and reduced yields. However, data substantiating such claims are limited. Growers have also been encouraged to avoid shallow planting depths because it increases the potential for injury from certain preemergent herbicides, although widespread use of safer herbicides (e.g., glyphosate) has probably decreased this effect.
Ohio growers frequently plant at depths less than 1.5 inches, expecting that seed will emerge more rapidly due to warmer soil temperatures closer to the surface. This is an important consideration, as corn growers across the Corn Belt are planting earlier so they can complete planting before yield potential begins to decrease after the first week of May. Particularly in soils that crust, speed of emergence is critical in order to establish plant stands before heavy rainfalls "seal" the soil surface.
Although previous research has generally documented faster emergence rates with shallower planting depths, the comparisons have often included deeper planting depths than the recommended ranges and results are highly influenced by temperature and rainfall in the given season. Recent studies comparing planting depths that are within the depth ranges commonly used by growers are limited, and none have attempted to compare hybrid differences between planting depths.
DuPont Pioneer has worked to introduce hybrids with improved drought tolerance in order to provide yield stability on variable and droughty soils. Hybrids with higher levels of drought tolerance may provide improved yield stability in shallow-planted situations while also providing improved performance at normal planting depths, though this has not been documented. Improving our understanding of newer hybrid responses to planting depth across planting dates and over different soil types may help improve our understanding of hybrid management and positioning. Incorporation of differing planting dates and soil types will allow a more robust analysis of the impact of temperature, soil water holding capacity and crusting potential over the course of the study.
The objectives of this research study4 were:
Locations: This study was conducted in conjunction with the 2011 Ohio State University Ohio Corn Performance Test (OCPT) and established at 10 locations (Hebron, Washington Court House, S. Charleston, Greensville, Van Wert, Hoytville, Upper Sandusky, Bucyrus, Wooster, and Beloit).
How did planting depth affect corn yields?
2011: Grain yields, averaged across locations and hybrids, were 13% and 15% greater for the 1.5- and 3-inch planting depths, respectively, than the 0.5-inch planting depth (Figure 2).