The difference in the size and shape of corn seeds depends on the position of the kernel on the cob. Large, round seeds grow on the butt of the cob; flat seeds grow in the middle; small, round seeds grow on the tip of the cob. All seeds on a cob are genetically identical. The size of seed kernels has little or no effect.
Agronomists at Iowa State University say that research in the American corn belt and the European Union in the 1990s found that corn yields were usually the same regardless of the shape or size of the seed planted.
Research by Dr. Theodore H. Kiesselbach of the University of Nebraska published in 1937 indicated that the size or shape of seed corn had nothing to do with yield.
Small Seed Growth
Iowa State researchers believe believe that if a field experiences drought or stress during the period that small seeds are filling then their quality may suffer. Agronomists at Purdue University agree, saying that small, round kernels on the tip of the cob are often last to be pollinated so they are more easily damaged by stress.
In laboratory stress tests reported by Iowa State agronomists, larger seeds germinated better than small seeds. Small seeds that were planted early in cool soils or encrusted soils produced smaller yields than larger seeds.If small seeds are planted early in cool soil, more seeds should be planted.
Small seeds also produce shorter plants, less leaf area and less dry weight of shoots through the eighth stage of leaf development. Shortly after plants begin to produce tassels those differences disappear.
Mechanical handling can more easily damage large, round seeds because they have more of the face of the embryo exposed than the flat seeds in the middle of the cob. As the result of these differences, Purdue agronomists say, planters need to adjust their equipment to handle both flat seeds and large, round seeds.
If the planting equipment is not adjusted to handle seeds of different size and shapes then the seed can be planted twice in some spots and no seeds at all in other places. This can result in a 3 to 10-bushel per acre drop in corn yield.
Dr. Theodore Kiesselbach noted in his research that small seeds produced smaller yields if they are sowed deeper than normal.
Purdue agronomists say growers should check the cold germination ratings of seeds before they buy them. If the cold germination rating of a seed lot appears suspect, those seeds should be planted last to give the soil more time to get warm.
Tom Doerge, a research Pioneer Hi-Bred International (See Reference 3), a subsidiary of the DuPont corporation, says "Extensive field research by Pioneer and university scientists has found that kernel size has minimal effect on seed vigor, field emergence or final yield." He says corn yield is impacted most by the genetics of the crop, insect resistance and the treatment of the seed.