Corn Seed Placement is Critical

Pre-season planter maintenance​ such as checking and replacing worn parts, cleaning seed tubes and monitor sensors, calibration, and other inspections are important tasks to complete before corn planting begins. Another step is to go to a nearby field for a test run to confirm that the desired seed planting depth, seed spacing, and overall population is achieved. If adjustments are needed, always refer to the manufacturer’s manual before performing any maintenance.

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Uniform emergence is critical to maximize yield potential. Uneven emergence can be caused by variable planting depths, open seed trenches, or compacted soil over the seed. Uneven emergence and/or variable plant-to-plant spacing may reduce yield potential by 7 to 15 bu/acre.1

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Planting Depth. After a planting trial run, inspect planting depth in the seed furrow. Shallow planting may be the result of worn double-disc openers, which may be cutting a W-shaped furrow rather than the desired V-shaped furrow. This can interfere with seed placement and firming. The closing wheels may not be able to adequately firm a W-shaped seed furrow.

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Also, down pressure on the coulters affects planting depth and may need to be adjusted for each field’s soil conditions and amounts of residue. Firm soil limits penetration by the seed opener, which may make it difficult for the depth wheels to make solid contact with the ground surface, resulting in shallow planting depth. Excessive down force in firm soils can cause compaction zones and lower the actual seeding depth as well as cause problems later in the growing season as roots attempt to grow into additional soil areas.2 Also, compaction problems can occur if too much pressure is applied when planting in wet soils. It is essential to find the right balance of pressure to provide adequate seed-to-soil contact, but without causing over-compaction.3 If insufficient down force is applied, then the planting depth can be too shallow and seed-to-soil contact may not be adequate.

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Planting depth is critical for nodal root establishment between the seed and the soil surface for corn standability. Seeding deeper than 1.75 inches can help support the development of this permanent root system. Seeding depths of 2 inches or 2.5 inches (in very dry conditions) are generally adequate for corn germination.2 Planting less than 1.25 inches deep can result in poor crown development, rootless corn, or root lodging. Shallow planting can also increase the risk of injury from some soil applied herbicides. Planting deeper than necessary should be avoided; however, if soil is dry, it is generally less risky to plant up to 3 inches deep compared to planting shallow in anticipation of rain.

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Seed Spacing. A properly adjusted planter can better singulate and uniformly space seed. Doubles and large gaps may result in reduced yield potential. Inspect the seed furrow to determine seed spacing. If adjustments are needed. check the operator’s manual. Additional tips to reduce variability in seed-to-seed spacing include:

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  • The planter should be level. An unlevel planter has a seed delivery tube that is at a different angle than designed and the seed is thrown backwards.
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  • Seed tubes should be free of obstructions and kinks, which can hinder seed delivery. Damaged or worn seed tubes may need to be replaced.
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  • Sprocket settings on the planter transmission should be checked.
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  • Gears should be lined up. Worn chains with stiff links may need to be replaced.
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Closing Wheels. Closing wheels should be centered on the seed furrow and have the ability to turn freely. Wheel down pressure on the soil surface should be appropriate for the soil type and/or conditions.

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Under cool, moist planting conditions, farmers may want to examine an alternative to rubber closing wheels. Consider using one spiked wheel (15 inches) and one rubber wheel (13 inches). The spiked wheel can help chop the sidewall, which improves fracturing and sealing in adverse soil conditions.

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Row Cleaners. Increased corn yield results in larger amounts of corn residue, which can be problematic in some corn-after- corn environments. Row cleaners sweep residue away from the row resulting in the seed furrow warming up faster and potentially reducing seedling blight.4

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Row cleaners should be sweeping residue and not moving soil. Observe the row cleaners while planting, as they should not turn constantly, but turn sporadically, especially through heavy residue.4