Hybrid seed corn comes in many shapes, sizes and weights based on ear formation. When planting small corn seed, prepare a proper seedbed, and adjust the planter settings and calibration to maximize the performance of corn hybrids. Small corn seed has a limited energy reserve to manage stress compared with large seed. This bulletin offers guidelines to protect the genetic potential of the seed.
Figure 1. Prepping planters is key to maximizing hybrid performance with small corn seed.
Figure 2. Corn seed size varies depending where it is formed on the ear. Larger seeds form at the base, where silking and pollination occur first. In general, seeds are smaller toward the tip of the ear. Stressful conditions also may contribute to smaller seed size or incomplete ear fill.
• Corn seed comes in different sizes and shapes.
• Seed size does not impact genetic yield potential or quality in favorable conditions.
• Small corn seed needs to be carefully managed under stressful conditions to reach its full potential.
• Optimize soil conditions at planting to promote fast emergence and good early vigor.
• Adjust planters to achieve proper spacing and singulation of small seed.
SEED SIZE VARIABILITY
Corn seed sizes vary by location on the ear. Large, round seed comes from the butt of the ear; flat seed comes from the middle of the ear; small, round seed comes from the ear tip; and medium, round seed can come from either end of the ear (Figure 2).
Under favorable conditions, pollen drop lasts five to eight days. Silk emergence begins slightly before or after pollen drop, depending on temperature and available moisture. Silks are receptive to pollen for about seven days. The silks from the butt of the ear are the first to emerge and become pollinated, followed by silks from the mid ear and finally the tip. Because the tip silks emerge last, they are pollinated last and smaller than other kernels from the butt and middle of the ear. Under stress, kernels at the tip may not be pollinated at all or aborted.
AGRONOMIC CHARACTERISTICS OF SMALL SEEDS
Beginning as early as 1937, researchers have compared yields from varying seed sizes. These studies, along with research in the 1990s, found seeds of various sizes from the same genetics have comparable yield potential and quality.
Note that most seed companies perform cold germination tests on seed lots to simulate how a particular seed lot will perform under stressful planting conditions. It is important to note that cold stress tests are not standardized, and results may differ from one procedure to another. While a cold stress test is an indicator of how a hybrid will perform under stress at planting, it cannot simulate all of the conditions encountered at planting.
Smaller seeds require less moisture for germination, an advantage under dry conditions. However, they have less energy reserve to handle stress related to early planting and adverse conditions. Seed planter adjustments are critical to optimize planter performance to achieve the proper seed spacing and singulation of small seed.
PLANTING CONDITIONS FOR SMALL SEED
After hybrid selection, proper planting is the most important part of corn production. It is important to manage planting conditions to minimize stress. These steps help maximize seed germination and emergence:
• Soil preparation. Prepare a good, firm seedbed to preserve soil temperature and moisture and allow for easier planting.
• Planting depth. Smaller seed may be more sensitive to planting depth. The ideal planting depth is 1.5 to 2 inches deep. Under dry soil conditions, it can be slightly deeper. When planting deeper than 2.5 to 3 inches, wait for adequate moisture availability. Under full irrigation, preirrigate to provide adequate moisture for planting. Seed planted less than 1.5 inches deep may not develop a normal root system and is subject to fluctuations in soil temperature and moisture.
• Soil temperature. Corn begins to germinate slowly at 50 F, taking up to 35 days to emerge. At 55 F, corn will emerge in about 10 days. Protect small seed by planting into warmer soils.
• Soil moisture. Germination requires moisture. Smaller seeds need less moisture for germination.
• Observe weather. Look for seven to 10 days of good, warm weather for uniform emergence.
• Monitor for stress. Optimum emergence occurs about 10 days after planting. Walk fields five to seven days after planting to check soil conditions and the seed germination stage. Look for crusted soils and make sure the coleoptile is straight and not starting to kink. If it is kinking, use mechanical crust breakup or add irrigation to soften or break up the crust.
PLANTER MAINTENANCE AND SETUP
Planter maintenance and setup are essential to proper planting. Understand the strengths and limitations of your planter to increase your chances of success when planting different seed sizes under a variety of conditions.
• Size plate to seed.
• Check cutoff fingers, knocker wheels and floor plate.
• Watch planter speed.
• Check knockoff brushes for wear.
• Check finger pickups and tension; adjust as needed.
• Inspect face plates for wear.
• Check seed conveyor belt and paddles for pliability.
• Proper ground speed is critical — especially high speeds.
• Select the proper disk, especially for cell-type seed disks.
• Adjust all units to the same vacuum pressure.
• Check seals and brushes for wear.
• Clean seed disks and check for wear and warping.
Always follow the manufacturer’s recommendations on wear and replacement of parts. Basic maintenance for all planters is:
1. Start with a clean planter.
2. Adjust disk openers.
3. Monitor row cleaners.
4. Calibrate seed meters.
5. Replace seed tubes and check sensors.
6. Tighten bushings and parallel linkings.
7. Lubricate drive systems.
8. Check for chain and sprocket wear.
9. Level the planter in the field.
10. Adjust closing wheels.
11. Check depth gauge wheels.
Different types of planters require additional adjustments. When checking parts, replace ones that appear to be damaged or worn.
IN-FIELD PLANTER CALIBRATION
Calibrate the planter in the field to ensure it is set up and operating properly. Perform these steps in the field:
• Ensure the planter is level at planting depth.
• Set the planter at its shallowest planting depth and plant 50 to 100 feet at normal planting speed.
• Measure 1/1,000th of an acre based on row spacing (Figure 3).
• Count the number of seeds in that length. Multiply by 1,000 for the plant population per acre.
• Repeat this process for every row to check for uniformity between row units.
• Set the desired planting depth to field conditions.
• Check all row units to make certain all rows are uniform in depth.
• Check planter from field to field, as planting conditions change.
INDIVIDUAL SEED SPACING FOR DIFFERENT PLANT DENSITIES AT VARIOUS ROW SPACING
While corn seed comes in many sizes, shapes and weights, hybrid performance is comparable among hybrids within the same genetics under favorable conditions. Take steps to manage field conditions and configure the planter to optimize the performance of smaller seed.
For more information, contact your local Mycogen Seeds customer agronomist or visit Mycogen.com/Agronomy.
Iowa State University. Do corn kernel size and shape matter?
Dakota Farmer. Why corn kernels come in all sizes.
University of California. Maximizing corn stand establishment and growth.
Agriculture Online. Corn kernel size has little effect on yields.
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