Seed Size and Yield Potential

Since the 1930s, research has been conducted to evaluate the effect of corn seed size on yield potential. Conclusions from these studies have been consistent; under normal conditions, corn seed size or shape is not related to genetic yield potential. When plant stands were similar, yields were usually the same, regardless of seed size or shape.
Varying environmental conditions may result in a variety of seed sizes and shapes from the same corn product. Seed size is also affected by corn product genetics and growing conditions, especially during the pollination and grain fill period. Typically, large rounds come from the base of the ear, flats from the center, and small flats and small rounds from the tip (Figure 1). Plateless seed usually comes from the base or the tip.

Effect on Germination

Under adverse planting conditions, seed size can have an effect on germination. Large seed can have slightly decreased emergence rates in dry soil conditions because large seed requires more moisture to initiate germination compared to small seed. Small seed can have slightly decreased emergence in cool or crusted soils because the energy needed for emergence in these environments may be greater than the amount stored in the endosperm. The differences noted in early growth related to seed size are usually not apparent after tasseling. Similar silking dates and grain yield are expected when emerged plant populations are the same regardless of seed size and shape.

Planter Adjustments for Seed Size and Shape

Planter settings should be adjusted for accurate seed positioning, placement, and seeding rate. When adjusted for seed size, a planter can more accurately singulate and deliver seed. Planters can deliver excessive numbers of doubles or skips when improperly adjusted for seed size. Consequently, grain yield potential can be reduced by 3 to 10 bushels per acre.1

Vacuum Planters. Adjustments can be made to the vacuum pressure, disk and/or cell size, and seed singulation devices that can affect plantability. Planters equipped with cell or flat disks have different requirements for adjustment. Another component to examine, regardless of disk type, is the way the disk is adjusted relative to the meter housing. Having the disk rub the housing with light contact can help improve singulation, reduce seed damage, and help load the planter drives, improving their consistency.
Using talc, graphite, or a blend of the two can help improve seed flow and drop, especially with high rates of seed treatments and/or humid conditions. Higher amounts of talc or graphite may be necessary for the increased surface area with small seed. Talc or graphite should be mixed well throughout the hopper or tank to provide adequate coverage.

Vacuum Planters with Cell Disks. With cell disks, seed is partially held in place by the cell and partially by the vacuum pressure. Plantability is aided by matching different cell sizes and vacuum pressures to fit a given seed size and shape. Disks with cells that are on the larger end of the acceptable range for a given seed size could lead to doubles, even if the vacuum pressure is adjusted to the lower end of the acceptable range. Low vacuum pressures can increase the chance of seed being shaken off of the disk when planting over rough ground, resulting in increased skips. To help reduce doubles and skips, disks with cells on the smaller end of the acceptable range can be used while running vacuum pressures on the higher end of the acceptable range.

Vacuum Planters with Flat Disks. Flat disks are less sensitive to different seed sizes and shapes and can provide more consistent plantability while reducing the need to adjust vacuum pressure. Examples are the Precision Planting® eSet® and vSet® systems and the John Deere® ProMAX 40 Flat Disk. Use of flat disks usually requires an additional component or two for singulation. The eSet and vSet systems utilize a floating singulator that requires no adjustments for ease of use while the ProMAX 40 Flat Disk uses a double eliminator and a knock-out wheel. Flat seed disks may need a slightly different environment than cell disks and users may benefit by visiting their equipment dealer for inspection and testing of their seed meters.

Finger Pick-up Planters. To help minimize planting errors, the following items can be evaluated and adjusted to operator manual specifications:

• Proper tension on the fingers
• Condition of meter brushes and carrier plate
• Pliability of seed delivery belt
• Seed baffle cleanliness
• Proper lubrication (graphite) rate
• Good alignment with meter drive and the lugs on the unit drive sprocket
• Well-maintained and lubricated drive chains