Planting corn too shallow can lead to sidewall compaction
Planting season is here and many fields are very wet. As producers watch the calendar, they'll be headed to fields that may be less than ideal for planting.
Wet soils are easily compacted and sidewall compaction during planting can be a problem, especially if the crop is "mudded in" and a dry spell occurs after planting. Patience is required for waiting for the soil to dry, but if the next rain is coming or the yield penalty for late planting is growing, it's hard to wait.
Many factors contribute to sidewall compaction. While wet soil is often given as the main reason, planting too shallow is the primary problem. In most conditions, corn seed should be planted two to three inches deep for proper root development. Most corn planters were designed for this planting depth, especially those with angled closing wheels. When you properly close the seed-vee, the sidewalls of the furrow should be fractured as the soil closes around the seed, eliminating the sidewalls and providing seed-to-soil contact.
Most sidewall compaction problems on wet soils occur when the press wheels are set with too much downpressure, overpacking the seeds into the soil. When planting shallow, this press wheel compaction is below the seeding depth, making it difficult for the seedling roots to penetrate the soil.
If you look at the angled press wheels from the rear, they intersect at an imaginary point about two inches below the soil surface. This provides seed-to-soil contact at seeding depth while closing the seed-vee. As such, downpressure on the press wheels should be checked at seeding depth, not at the top of the seed-vee.
If the seed-to-soil contact is adequate, don't tighten the downpressure springs trying to close the seed-vee. Make sure that the planter is properly leveled, or even slightly tail down, for the angled closing wheels to have a pinching action to close the seed-vee.
A variety of attachments are available to help close the seed-vee if the standard closing devices can not. Some people use coulters or intermeshing row cleaners to till the soil in front of the planting unit to provide loose soil for closing the seed-vee. However, this loosened soil often sticks to the depth gauge wheels in wet conditions or the tillage dries out the seed zone in dry weather.
A better way to provide loose soil for closing the seed-vee is to do it after the seed has been placed in the furrow. The less aggressive-spoked wheels provide some seed-to-soil contact while closing the seed-vee and reducing air pockets around the seed. The more aggressive-spoked wheels tend to dry the soil more and typically require a seed firmer to provide seed-to-soil contact and a drag chain behind them to level the soil.
As the soils become drier and more seed-to-soil contact is needed, some producers remove the spoked wheels and put the standard closing wheels back on to reduce overdrying the seed zone. If the downpressure is set too high on some of these spoked wheels, they may "till" the seed out of the seed-vee. To reduce the aggressiveness of the tillage and to provide some soil firming and depth control, some producers run one spoked closing wheel and one standard wheel. This combination works well in a wide variety of conditions.