Seed size and planter prep

A conversation with Jeff Rectenwald, DEKALB Asgrow agronomist.

Jeff Rectenwald
Corn seed size and shape can vary significantly based upon where it came from on the ear.

OCJ: Jeff, you get questions every year about seed size and shape and how those factors relate to spring planting and yields. What are some important things growers need to remember about handling different seed sizes in their planters and how it can impact yield?

Jeff: Following manufacturers’ recommendations and considering tools to enhance plantability can help limit the risk of poor plantability. If plantability concerns related to seed size are managed properly, the effect of seed size should not significantly affect yield potential under most conditions.

Corn seed size or shape is not related to genetic yield potential. Research to evaluate the effect of corn seed size on yield potential has been conducted several times finding that seed size does not affect yield potential under normal planting conditions. There are always exceptions to normal conditions. To understand the effect seed size may or may not have on yield potential, it is important to: understand how seed size is determined, examine how it might affect emergence and early growth, understand the importance of proper planter settings, and know management techniques that may be used to help improve plantability of various seed sizes with different types of planters.

Seed sizes from hybrid production will vary field-to-field, and year-to-year due to many factors. These include specific hybrid characteristics, parent pedigrees, and growing conditions, especially during the pollination and seed fill period. Seed from a single ear falls into many size/shape categories. Large rounds usually come from the base of the ear, flats from the center, small flats and small rounds from the tip. Plateless seed usually comes from the base or the tip.


OCJ: How can seed size affect emergence and early growth?

Jeff: There have been minor differences in emergence noted under adverse planting conditions. Large seed can have slightly decreased emergence rates in dry soil conditions as the amount of moisture needed for germination and emergence is relative to the size of the seed. Small seed can have slightly decreased emergence in cool or crusted soils, as the amount of energy needed in those situations may exceed the amount stored in the endosperm. It has also been reported that differences in early growth related to seed size are not apparent by tasseling or soon after. The effect of seed size on yield potential was not significant if harvest populations were similar.

All DEKALB seed sold to our customers goes through cleaning, processing, and quality testing, which include germination and vigor tests. While some seed sizes and shapes may be more susceptible to mechanical damage during cleaning and processing, the sample for germination and vigor tests is taken after all of the cleaning and processing is complete.


OCJ: How should planter settings be adjusted to make the most of planting corn this spring?

Jeff: Planter settings should be adjusted for intended population and accurate singulation. When set properly for the seed size, a planter can more accurately singulate and deliver seed. Planters that are not properly adjusted to seed size can deliver excessive numbers of doubles, triples, or skips, and can reduce grain yield potential by 3 to 10 bushels per acre. Populations that are under the desired stand count increase the risk of not producing maximum yield potential.


OCJ: Getting more specific, what can growers do to maximize yield this fall with different types of planters this spring?

Jeff: For vacuum planters, depending on if the planter is equipped with cell or flat disks, adjustments can be made to the vacuum pressure, cell size, and seed singulation devices that can affect plantability. Additionally, the use of talc or graphite can help improve seed flow and drop. When planting small seed, consider increasing the talc or graphite rate to account for the increased surface area with small seed. The importance of talc or graphite increases with high rates of seed treatments and/or humid conditions. Mixing the talc or graphite well throughout the hopper or tank can help provide adequate coverage. Another component to examine regardless of disk type is the way the disk is adjusted relative to the meter housing. Having the disk rub the housing with light contact can help improve singulation, reduce seed damage, and help load the planter drives, improving their consistency.

Historically, vacuum planters with cell disks were standard with several vacuum planters. Seed is partially held in place by the cell and partially by the vacuum pressure.

To aid plantability, different cell sizes and vacuum pressures can be combined to fit a given seed size and shape. Running a disk with cells that are on the larger end of the acceptable range for a given seed size may increase the potential for doubles, even if the vacuum pressure is on the lower side of the acceptable range. Additionally, running low vacuum pressures increases the risk that seed could be shaken off of the disk when planting over rough ground, resulting in increased skips. A preferred tactic is to use a disk with cells that are on the smaller end of the acceptable range and running vacuum pressures on the higher end of the acceptable range. The latter option helps reduce doubles as well as skips.

Recently, the adoption of the flat disk has increased as they are less sensitive to various seed sizes and shapes, thereby providing more consistent plantability with less need to adjust vacuum pressure. Two examples of flat disks include the John Deere ProMAX 40 Flat and the eSet system from Precision Planting. Generally there is an additional component or two that is needed for singulation when using flat disks. The ProMAX 40 Flat disk requires a double eliminator and a knock-out wheel. The eSet system uses a non-adjustable singulator. While there are differences between the systems, they both greatly reduce the need to adjust vacuum pressure to account for seed size and shape variations, thereby improving the plantability of various seed sizes and shapes versus cell disks4. Please note that flat seed disks may need a slightly different working environment than cell disks. New flat disk users may benefit by visiting their equipment dealer for inspection and testing of their seed meters.


OCJ: What can be done with finger pick-up planters to compensate for different seed sizes?

Jeff: Planter speed is a major component of calibration and accurate seed placement. Planting at speeds faster than recommended in the owner’s manual may result in poor seed singulation and placement, which can adversely affect yield potential. Likewise, planting at speeds lower than the recommended range may result in a lower than intended population. Simulated planter speeds for the plantability studies were 5.5 miles per hour.

Keeping a finger pick-up planter well maintained is a good way to help minimize planting errors. Some items to evaluate and adjust to manufacturer’s specifications include: proper tension on the fingers, meter brushes in good condition, Carrier plate condition, seed delivery belt pliability, seed baffle cleaned, proper lubrication (graphite) rate, good alignment with meter drive and the lugs on the unit 
drive sprocket, and well maintained and lubricated drive chains.


OCJ: What is the take-home message about seed size?

Jeff: Overall, seed size does not affect genetic yield potential. Having a planter set properly can improve the opportunity to achieve an optimal stand by minimizing skips, doubles, and triples. Focusing on genetic yield potential, seed quality, increasing populations, and identifying planter settings that optimize plantability is helpful in increasing yield potential.



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