Most growers know planting corn less than 1.5 inches deep can result in yield loss.
DuPont Pioneer recently funded a study at Iowa State University to take a closer look at yield loss associated with shallow planting. DuPont Pioneer agronomists note deeper planting may be recommended as the season progresses and soils become warmer and drier.
However, planting shallower than 1.5 inches is almost never recommended at any planting date or in any soil type.
Growers who plant at depths less than 1.5 inches expect 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 to complete planting before yield potential begins to decrease after the first week of May. Particularly in soils that crust, speed of emergence is critical to establish plant stands before heavy rainfalls "seal" the soil surface.
When corn is planted 1.5 to 2 inches deep, the nodal roots develop about 0.75 inches below the soil surface. However at planting depths less than 1 inch, the nodal roots develop at or just below the soil surface. Such 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.
Well-documented effects of shallow planting on root development has led to the assumption that planting depth may play a role in managing the drought susceptibility of a hybrid. According to some 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.
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 to provide more 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 study were:
•to evaluate the effect of planting depth on stand establishment of Pioneer brand corn products
•to evaluate the grain yield response of corn products with different drought tolerance ratings to varying planting depths
•to assess if planting depth effects varied across growing environments that differed by soil type
•and planting date.
Locations - This study was conducted by Dr. Peter Thomison in conjunction with the 2011 Ohio State University Ohio Corn Performance Test and established at 10 locations (Hebron, Washington Court House, S. Charleston, Greensville, Van Wert, Hoytville, Upper Sandusky, Bucyrus, Wooster and Beloit).
Plot Design - The experiment was replicated 3 times in a randomized complete block arranged in split-plot layout. The main plot was planting depth and subplot was hybrid. Plot size was (4) 30-inch rows 25 feet in length. Force 3G soil insecticide was applied in a T-band to all plots.
Hybrids and Planting Depth Treatments - 3 Pioneer brand corn products were planted at 3 planting depths (0.5, 1.5, and 2.5 to 3 inches). The drought scores for the 3 products were 8, 7 and 6, respectively. The Pioneer drought rating scale is from 1 to 9 (9 = best).