Kernel Size and Shape

Encyclopedia Article

Producers and researchers alike have concerned themselves with the possibility that seed size and shape may affect corn yield. As early as 1937, Dr. Kiesselbach (University of Nebraska) compared across several years, large (29.2 g or 1.03 oz/100 seed) and small (15.8 g or 0.56 oz/100 seed) seed of open-pollinated corn. He concluded, "There may be considerable difference in seed size without greatly affecting the yield of corn under ordinary planting conditions."

In the 1990's scientists across the U.S. Corn Belt and in Europe compared corn with different seed sizes and shapes. They found that when plant population was similar across different seed sizes, the yields were usually the same no matter the size or shape of seed planted, just as Kiesselbach had concluded. However, Kiesselbach also noted that small seed would be at a disadvantage with greater than normal planting depths.

Although recent research seems to answer the yield question conclusively, there are some advantages and disadvantages of small seed to consider in selecting and planting corn. Small seed does not germinate well in laboratory stress tests relative to larger seeds. It is not surprising then in the field that small seed subjected to various stresses at planting, had reduced stands (5-15% in one study) as compared to larger seed. These stresses are sometimes associated with: early planting, cool soil temperatures, and soil crusting. The poorer performance of small seed in these environments is perhaps related to increased mechanical damage to smaller, round seed during handling, especially relative to larger, flat seeds. Small seed, on the other hand, germinate faster than larger seed in dry soils.

Small seed also produce smaller and less vigorous plants in the vegetative period before tasseling. These differences, reported by different researchers, include: less shoot dry weight through the 8th leaf stage, shorter plants, less leaf area, and slower development. By tasseling, or soon thereafter, these differences disappear.

Thus during the critical seed-fill stages there are no differences among plants coming from seed of different sizes and shapes. This helps us understand why there are no reports of yield reduction associated with planting different seed sizes and shapes. However, we can speculate that because of the less vigorous plants during vegetative stages, plants from small seed may suffer more from vegetative stresses (weed pressure, drought, etc.) than plants from large seed during that time period.

Based on these research reports, there is no need for concern over the productivity of seed of various sizes and shapes with normal planting and vegetative period conditions. What is important is obtaining the optimum plant population. If small seed are planted in cool wet conditions early in the planting season, consider increasing planting rates. If emerged plant populations are the same, silking dates and grain yield likely will be similar among all sizes and shapes of seed planted. Instead of focusing on seed size and shape, the main focus should be on selecting hybrids with the best package for yield and genetic traits, seed quality, and seed price.


Graven, L.M. and P.R. Carter. 1990. Seed size, shape, and tillage system effect on corn growth and grain yield. Journal of Production Agriculture. 3: 445-452.

Nafziger, E.D. 1992. Seed size effects on yields of two corn hybrids. Journal of Production Agriculture. 5:538-540.

This text, written by Roger Elmore and Lori Abendroth, is taken from a Crop Watch article (University of Nebraska extension newsletter) written April 8, 2005.