7 MIN READ

The Impact of Corn Seed Size and Shape

September 29, 2025

  • The size and shape of a corn seed does not affect its genetic yield potential as all the seeds on the ear have the same genetic yield potential.
  • Corn yield potential is determined by the product’s genetics and can be dramatically affected by management practices and environmental conditions during the growing season.

Does Corn Seed Size and Shape Affect Yield Potential?

A corn ear produces a variety of seed sizes and shapes. Large rounds typically come from the base of the ear, flats from the center, and small flats and small rounds from the tip (Figure 1). All seeds from the same ear, regardless of size or shape, have the same genetic material and yield potential. Corn yield potential is determined by genetics but can be dramatically affected by management practices, such as planting conditions, fertilizer program, weed and insect management, and environmental conditions throughout the season.

Figure 1. Seed size and shape on a corn ear varies from large rounds (left, cob base), flats (middle of cob), to small rounds (cob tip).
Figure 1. Seed size and shape on a corn ear varies from large rounds (left, cob base), flats (middle of cob), to small rounds (cob tip).

Extensive research has evaluated the effect of corn seed size on yield potential. Conclusions from these studies have been consistent: corn seed size or shape is not related to genetic yield potential under normal growing conditions.1 One study conducted in three locations in Illinois tested the effect of seed size and of mixtures of seed sizes on the grain yield of two corn products. Seed size had no effect on the yield of either corn product, regardless of whether the plantings were of uniform seed size or were mixtures of sizes.2 A study in 2017 completed at the Bayer Water Utilization Learning Center in Gothenburg, NE measured the yield potential of five different seed sizes of the same corn product and yield differences were determined to be not significant (Table 1).3

The size and shape of a corn seed does not affect its genetic yield potential.


Table 1. Impact of seed size on yield and final stand count, Bayer Water Utilization Center, 2017.

Table 1. Impact of seed size on yield and final stand count.

Does Seed Size and Shape Affect Corn Emergence and Early Growth?

Although seed size doesn’t have an impact on corn yield potential, it may impact seedling vigor. In laboratory tests that modeled stressful planting conditions, small seeds had reduced stands (5 to 15% in one study) as compared to larger seed.4 Such stress at early planting can be associated with cool soil crusting. It has been suggested that the poorer performance of small seed in these environments is related to increased mechanical damage to smaller, round seed during handling, compared to larger, flat seeds.4 However, small seed germinate faster than larger seed in dry soils.4 Larger seeds require more moisture to germinate compared to smaller seeds.

After tasseling, differences in the rate of growth 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 uniform.4 In the same study completed in 2017 by the Bayer Water Utilization Learning Center, data indicated that the rate of germination can be different for five different evaluation dates for the five different seed sizes (Figure 2).


Figure 2. Average number of plants per acre counted on five different evaluation dates. Medium flat, AF 34.5 lb/80,000 kernels, Medium flat, AF 40.0 lb unit/80,000 kernels, Medium round, AR 43.0 lb unit/80,000 kernels, Large flats, AF2 48.5 lb unit/80,000 kernels, Large rounds, AR2 59.0 lb unit/80,000 kernels.
Figure 2. Average number of plants per acre counted on five different evaluation dates. Medium flat, AF 34.5 lb/80,000 kernels, Medium flat, AF 40.0 lb unit/80,000 kernels, Medium round, AR 43.0 lb unit/80,000 kernels, Large flats, AF2 48.5 lb unit/80,000 kernels, Large rounds, AR2 59.0 lb unit/80,000 kernels.

Management of Different Seed Sizes

Seed companies typically sell corn seed based on shape and size and list the bag weight for that seed size grade and lot. The weight of a bag of seed is what that bag will weigh when filled with 80,000 (80K) kernels, which is currently the industry standard. Farmers have historically purchased specific seed shapes, sizes and weights based on how the plates in their planters were configured. With a shift toward vacuum or pressure delivery systems, it is now often more common for producers to request seed lots that are close to the same bag weight to help reduce planter adjustments necessary from one seed lot or type to another. When properly managed and properly positioned, corn seed of any size and weight can produce a successful crop.

  • Planter settings should be adjusted for accurate seed positioning, placement, and seeding rate based on the size and shape of the seed. 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.
  • Plant seed according to soil temperature and moisture conditions. If there are concerns about seed size and germination, consider waiting to plant until conditions are conducive to rapid germination, emergence and early growth.
  • Understand how different soil types and conditions in your field can affect seedling emergence and early growth.


Sources

1Nielsen, R.L. 1996. Seed size, seed quality, and planter adjustments. Purdue University. Purdue Pest Management and Crop Production Newsletter. https://www.agry.purdue.edu/ext/corn/news/articles.96/p&c9606.htm#:~:text=In%20practice%2C%20seed%20size%20and%20shape%20can%20also%20influence%20yield,to%2010%20bushels%20per%20acre
2Nafziger, E. 1992. Seed size effects on yields of two corn hybrids. Journal of Production Agriculture 5: 538-540. https://acsess.onlinelibrary.wiley.com/doi/abs/10.2134/jpa1992.0538/
3Impact of corn seed size and shape on yield potential. 2017 Regional Report. Bayer Learning Center at Gothenburg, NE.
4Kernel size and shape. 2005. Iowa State University. Integrated Crop Management. https://crops.extension.iastate.edu/encyclopedia/kernel-size-and-shape.


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