Corn Seed Size and Planter Adjustments

Key Points

  • Corn seed size and shape do not affect genetic yield potential.

  • Corn seed performance can be optimized when growers focus on genetic yield potential, increased plant populations, and planter settings that can more accurately deliver seed.

  • Adjustments to planter settings can help achieve optimal stands by minimizing doubles or skips.

Seed Shape and Size Makes Little Difference in Performance

Seed size is determined by genetics and growing conditions, especially during the pollination and grain fill period, and a variety of sizes and shapes may result from the same product. 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.

Corn seed size and shape are not related to genetic yield potential. All seeds from the same ear, regardless of size or shape, have the same genetic material, and thus the same genetic yield potential. However, seed size can affect germination when conditions are not ideal, which can impact the yield potential of the stand. Large seed may not germinate as well as small seed in dry soil conditions because large seed requires more moisture to germinate. Germination issues may be more pronounced with small seed in cool or crusted soils because the energy needed for emergence may be greater than the amount stored in the seed. After tasseling, differences in germination related to seed size are usually no longer apparent. Regardless of seed size and shape, similar silking dates and yield potential are expected when established stands are the same.

Considerations for Seed Sold by Weight

Farmers are considering seed weight more often lately when purchasing their seed. The decision of what type of seed to purchase is often based on how their planter is configured. More seed companies today are selling their seed based on the weight of the seed as opposed to the size of the seed. As noted above, the size and weight of the seed does not affect yield potential. Yield potential is determined by genetics, product positioning, and management practices. When purchasing corn seed by weight, review the seed bag labels and your planter manufacturer's recommendations, and talk with your seed brand agronomist or representative for information on dealing with different types of seed, planter specifications, and field placement. Corn seed of any size and weight can produce a successful crop when properly managed and properly positioned.

Planter Adjustments for Seed Size and Shape

Planter settings should be set for accurate seed positioning, placement, and seeding rate. When a planter has been adjusted for the appropriate seed size, it can more accurately singulate and deliver the seed. An excessive number of doubles or skips can occur if the planter has not been adjusted properly. This can result in reductions in grain yield potential of 3 to 10 bushels per acre.1

Adjustments for 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. Regardless of disk type, it is important to examine 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.

Use talc, graphite, or a blend of the two to help improve seed flow and drop, especially with high rates of seed treatments and/or humid conditions. It may be necessary to use higher amounts of talc or graphite with small seed because the total surface area is greater with small seed. Talc or graphite should be mixed well throughout the hopper or tank to provide adequate coverage.

Adjustments for Vacuum Planters with Cell Disks. With cell disks, seed is partially held in place by the cell and partially by the vacuum pressure. Different cell sizes and vacuum pressures should be matched to fit a given seed size and shape. Doubles are more likely to occur with disks that have cells on the larger end of the acceptable range for a given seed size, even if the vacuum pressure is adjusted to the lower end of the acceptable range. Skips can occur when low vacuum pressures are used because seed can be more easily shaken off of the disk when planting over rough ground. To help reduce doubles and skips, use disks with cells on the smaller end of the acceptable range while running vacuum pressures on the higher end of the acceptable range.

Adjustments for 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. For ease of use, the eSet and vSet systems use a floating singulator that requires no adjustments 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.

Adjustments for Finger Pickup Planters. Finger pickup planters should be properly maintained 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

Plantability Studies

Plantability tests have been conducted to provide planter setting recommendations for seed lots. Results are represented in terms of percent singulation (the percentage of single seeds released by the seed meter at the proper time). A multiple is when the seed sensor detects two seeds where only one should be; a skip is when the sensor detects nothing where a seed should be. Percent singulation is determined by taking 100% properly timed single seed drops and subtracting the percentage of multiples and skips. Figures 2 and 3 depict singulation data for vacuum or finger pickup planters with various seed sizes and shapes. The finger pickup units were calibrated for larger seed, and data for smaller seed sizes and shapes are not presented. Simulated planter speed was 5.5 miles per hour. Data was collected using seed harvested in 2004 through 2010 for planting seasons in 2005 through 2011, respectively.


1 Nielsen, R. 1996. Seed size, seed quality, and planter adjustments.

Elmore, R. and Abendroth, L. 2005. Do corn kernel size and shape really matter? Crop Watch Newsletter. University of Nebraska-Lincoln.

Shillington, S. Senior Sales and Service Representative for Planters. John Deere Seeding Group. Moline, Illinois. October 22, 2010. Monsanto data. 2010.

Brian Urban, Waterman, IL. Seed Technology Center.

Web sources verified 4/6/16. 


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