Corn Seed Size: Planter Adjustments & Yield Potential

Corn Seed Size and Yield Potential

Commercial seed corn products may produce several seed sizes because of their genetics and seasonal growing conditions. Some corn products are genetically predisposed to produce smaller or larger seeds. Seasonal growing conditions, particularly drought or high heat during pollination and grain fill, can alter seed size. If the ear is well fertilized but poor fill conditions exist after fertilization, seeds may be smaller than normal. Seeds may be larger and rounder when poor embryo fertilization results in fertilized embryos expanding into nearby empty spaces, such as may occur on a commercial grain ear (Figure 1). Under normal growing conditions, large round seeds come from the ear base, flats from the ear center, and small flat and round seeds from the ear tip (Figure 2). Plateless seed usually comes from the ear base or tip. Regardless of seed size or shape, the seed from the same commercial seed product has the same genetic yield potential.^1,2

Though genetic yield potential is not affected by seed size, there may be differences in germination related to seed size when soil conditions become adverse after planting. Because large seeds require more moisture to germinate compared to smaller seeds, they may have slightly decreased emergence rates in dry soil. Small seeds may have slightly decreased emergence in cool or crusted soil because the energy needed for emergence in these environments may be greater than the amount stored in the smaller seed’s endosperm.^{3, 4} The differences noted in early growth related to seed size are usually not apparent after tasseling. Similar silking dates and grain yield potential are expected when emerged plant populations are the same regardless of seed size and shape.³

Corn Yield Potential Based on Seed Size

During the Bayer screening and bagging process, seed is categorized into five sizes and shapes:

• AF – Medium Flat corn seed
• AR – Medium Round corn seed
• AF2 – Large Flat corn seed
• AR2 – Large Round corn seed
• P22 – Small Plateless

As discussed, the genetic yield potential of a corn product is not impacted by seed size. To help address this concern, a study was conducted in 2017 at the Bayer Crop Science Water Utilization Learning Center, Gothenburg, Nebraska to measure the yield potential of five different seed sizes for the same corn product. Yield differences were determined to be insignificant (Table 1).

Table 1. Impact of seed size on potential corn yield and final plant population.

In this trial, the size and weight of the seed did not affect yield potential. Yield potential is determined by genetics, product positioning, proper seed placement in the soil, and other management practices. When purchasing corn seed, it is important to review the seed bag labels and your planter manufacturer’s recommendations. Also talk with your seed brand agronomist or representative for information on dealing with different sizes and weights of seed, planter specifications, adjustments, and proper field placement. When properly managed and properly positioned, corn seed of any size and weight can produce a successful crop.

Corn Seed Size, Count, and Weight

Commercial seed companies, including Bayer, commonly sell seed based on seed count (80,000 seeds per bag) along with seed size and shape instead of selling seed in 50-pound bags. The seed count per unit allows for more accurate purchase of seed for the acreage to be planted. A 50-pound bag could contain a large range of seed counts because of the variation of seed weight per pound. Therefore, more or less seed than needed may have been delivered with 50-pound units. Purchasing seed by count also makes it easier to purchase seed in bulk containers such as the Bayer SeedPak50^®, which contains the equivalent of fifty 80,000 seed count bags. Seed size, unit weight, seeds per pound, seed treatments, and germination information are generally found on a seed tag, printed on a bag, or placed in plastic envelopes on bulk seed containers.

Historically, farmers often purchased specific seed sizes based on planter configuration, personal preference, and the presumed performance of the planter with a certain seed size. However, if different seed sizes were delivered because of supply issues, different seed plates may have been required, which meant each seed box had to be changed to accommodate the delivered seed size. Additionally, the plastic seed plates tended to wear thin and, if they were not changed, the desired planting rate could be altered dramatically.

Today, many planters use one disc (disk) that accommodates multiple seed sizes. Planting rate adjustments are made via increased air or water level pressure and built-in mechanical features that alter hole sizes in the disc. Installed electronic equipment in the tractor can quickly alert the planter operator if adjustments for planting rates are needed.

Lubricants and Corn Seed Treatments

To maintain unobstructed seed delivery from bulk tanks to individual planter rows, seed within the tank should be generously mixed with talc, graphite, or a blend, depending on manufacturer recommendations. Bayer Fluency Agent Advanced Seed Lubricant is a product for consideration. The materials should be added to the tank as seed is poured in to allow for adequate coating. If the lubricants are placed in the middle of the tank after it is filled with seed, they are likely to be funneled down the center instead of adequately covering the remaining seed. Large seed may require additional lubricants, talc in vacuum planters, or graphite in finger pickup planters. Because of the additional lubricants and any seed treatments, air or vacuum pressure adjustments may be required to hold the seed against seed discs and to allow for proper seed flow. Humid conditions, high seed treatment rates, and smaller seed may warrant additional lubricants.

Adjusting Planters for Corn 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 (drop one seed at a time) and deliver seed into the seed furrow. When improperly adjusted for seed size, planters can deliver excessive numbers of doubles (when two seeds are attached to a cell as it rotates during planting) or skips (when there is no seed attached to the cell as it is rotating). Consequently, grain yield potential can be reduced by three to 10 bushels per acre when a mis-adjusted planter does not accurately meter the seed.¹ Table 2 provides initial guidelines for vacuum and water vacuum settings on corn planters and Table 3 provides guidelines for plate type planters. Equipment operating manuals should also be reviewed

Table 2. Initial planter settings based on seed weight.

Table 3. Planter plate suggestions for corn.

High Speed Planting Technology for Vacuum Planters

John Deere ExactEmerge^®, Kinze^® True Speed^® Metering system, and Case IH Advanced Seed Delivery™ with Precision Planting^® SpeedTube^® are designed, depending on manufacturer, to plant at speeds up to 10 to 12 miles per hour. Instead of a gravity-based open seed tube, high-speed planters use a belt in the seed tube to deliver seed to the furrow. There are also high-speed planters that use air pressure to deliver the seed to the seed slice. High speed planters require increased row unit downforce and closing wheel force to maintain seed depth and slice closing as soil conditions change and speed increases. Often a hydraulic downforce system is preferred over an air downforce system due to the improved response time of a hydraulic system.⁵ The exact settings for each system are dependent on field conditions and spring tillage practices. In general, expect 20 to 40 pounds of increased downforce and one additional notch in the closing wheel pressure when planting at speeds over eight miles per hour.⁶ When possible, it is a good idea to annually run all planter units on a test stand to document the meter system’s performance and to check for any misadjustment or excessive meter wear that can negatively affect performance.

Vacuum Planters

Singulation adjustments can be made to vacuum planters by several methods including vacuum pressure and changing disk and/or cell size. Most often, fine adjustments are made after the disk is selected by using changes to the vacuum setting. Depending on the disk used, 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 the appropriate light contact can help improve singulation, reduce seed damage, and help load the planter drives.

Vacuum Planters with Cell Disks

Vacuum pressure is used to help hold the seed in place by the cell, which is matched to the seed size and shape. Plantability is aided by matching different cell sizes 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 the disk when planting over rough ground or at higher planting speeds, 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. Flat disks usually require 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 require a slightly higher vacuum level than is used on a cell disc, because there is no cell to hold the seed on the disk. Users may benefit by visiting their equipment dealer for inspection and testing of their seed meters. Always make sure to set your vacuum planter monitor to the correct number of cells for each disk used as they can change depending on the style of disk used.

Sources

¹Nielsen, R.L. 1996. Seed size, seed quality, and planter adjustments Purdue University, Purdue Pest Management & Crop Production Newsletter or Corny News Compendium. https://www.agry.purdue.edu/ext/corn/news/index.html
²Elmore, R., Russell, K., and Abendroth, L. 2005. Corn kernel size depends on order of pollination. University of Nebraska Extension, CropWatch. https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1290&context=cropwatch
³Elmore, R. and Abendroth, L. 2005. Do corn kernel size and shape really matter? CropWatch. University of Nebraska Extension. https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1290&context=cropwatch
⁴Kimmelshue, C.L., Goggi, A.S., and Moore, K.J. 2022. Seed size, planting depth, and a perennial ground groundcover system effect on corn emergence and grain yield. MDPI. Agronomy. 12(2): 437. https://doi.org/10.3390/agronomy12020437
⁵Brooks, R. 2021. High-speed planting keeps promise. AG WEB, Farm Journal. https://www.agweb.com/news/crops/farm-journal-test-plots/high-speed-planting-keeps-promise
⁶Darr, M. and Bergman, R.W. 2020. High speed planting technology. Integrated Crop Management. Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/cropnews/2020/03/high-speed-planting-technology

Additional Resources
Kinze. https://www.kinze.com/
Case IH. https://www.caseih.com/en-us/unitedstates
John Deere. https://www.deere.com/en/
Bayer Historic Seed Size Planting Information
Web sources verified 05/04/26. 1214_74416