Some of the talk uptown at the Midway Cafe this spring has centered around the issue of seed size in this year's seed corn. There's something about an 80,000 kernel bag weighing 35 pounds that gives a corn grower the heebie-jeebies. Should you be concerned about unusually small hybrid corn seed? What planter adjustments are necessary to accommodate oddball seed sizes?
Genetic Yield Potential. As agronomists and plant breeders have said for years and years and years, the size or shape of the seed has nothing to do with the genetic yield potential of the hybrid. Differences in size and shape are due to the position of the kernel on the cob. Small rounds tend to come from the tip of the cob, large rounds tend to come from the butt of the cob, flats tend to come from the middle of the cob. Genetically, the various sizes and shapes of the kernels coming from an ear are identical.
Seed Quality. In practice, seed size and shape can influence yield of a hybrid due to differences in seed quality, subsequently affecting final plant population. Seed quality differences can occur due to growing conditions of the seed field and quality control during the seed handling and conditioning processes.
Since small rounds come from the ear tip, their seed quality can be suspect if the seed field experienced severe stress during the grain fill period. Severe stress often affects tip kernels more severely because they are often the last to be pollinated and are therefore the youngest kernels on the ear. Large rounds are often difficult to handle without damage during the seed conditioning process because the embryo face of a large round is more exposed than flats.
Problems with seed quality won't always be evident by the warm germination ratings on the seed tag. If you have questions about the quality of large or small rounds, ask your seed dealer for the cold germination ratings. If certain seed lots' cold germination ratings appear suspect, consider planting them last to allow for maximum soil warming to encourage rapid germination.
Plantability Issues. In practice, seed size and shape can also influence yield of a hybrid due to the planter's ability to singulate the seed. Plantability issues occur if planters are not adjusted for the seed size being used. Excessive numbers of double-drops or skips can easily reduce grain yield by 3 to 10 bushels per acre. If you will be planting oddball seed sizes this year, make sure you know what planter adjustments are required to accommodate very small or very large seed.
For air or vacuum planters, adjust the air or vacuum pressure according to the manual's recommendations for the seed size (seeds per pound). Oddball sizes may also require using different seed discs that contain smaller or larger air holes and/or seedcell shapes or using different seed drums (Case-IH).
Planters with finger-pickup mechanisms are less flexible in terms of adjusting for oddball seed sizes. Finger tension can be adjusted somewhat to accommodate different seed sizes, but is difficult to accomplish accurately.
Follow the manufacturer's guidelines for planting speed. Excessive planting speed usually decreases a seed meter's ability to uniformly singulate seed. Remember, also, if you have been increasing your seeding rates in recent years, the optimum planting speed is technically slower due to the faster operation of the seed meter.
Return to the the Chat 'n Chew Cafe.
The Corn Growers Guidebook , a WWW resource for corn management systems in Indiana and the eastern CornBelt.
Purdue University Agronomy Extension WWW Home Page.
Purdue Agronomy On-Line! , Purdue's Agronomy Department WWW Home Page.