Yield-killing sidewall compaction

Wet springs and sidewall compaction go together like toast and jelly … except sidewall compaction is not a sweet treat but, instead, a bitter yield-killing pill. 

Compacted sidewalls cut germination, cause uneven seed emergence, restrict root growth and stunt seedlings. 

As if those affects weren’t bad enough, if the weather turns dry, corn in compacted sidewalls will be challenged to thrive in a rapidly drying out seedbed made worse by the development of telltale cracks.

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“Sidewall compaction refers to soil compaction and soil smearing in and around the seed furrow, which can result in restricted root growth, poor emergence, and lost yield potential,” explains Dan Quinn, Purdue University Extension corn specialist.

Beyond early-season scouting for disease, pests, and nutrient deficiencies, it is also important to scout fields for potential compaction issues, Quinn advises. Dig out corn plants in problem areas to examine their roots. 

“A healthy root system should have adequate and uniform vertical and horizontal root growth all around,” he points out. “However, if the majority of the corn roots exhibit only vertical growth and poor horizontal growth [see photo, above], this can be an indicator that roots could not penetrate the sides of the seed furrow due to compaction. In addition, it is also important to examine the seed furrow following planting and look for smooth or shiny surfaces within the furrow — these can indicate that smearing and compaction occurred.” 

The image at the left shows corn roots that have grown down the length of the row. The image at the right shows corn roots that grew across the row. Notice how roots exhibit poor and nonuniform growth due to sidewall compaction at planting, says Dan Quinn with Purdue University.

Many factors contribute to sidewall compaction. Opening a seed-vee in wet soil is often given as the main reason. Yet planting too shallow is the primary problem, says Paul Jasa, University of Nebraska. “In most conditions, seed should be planted 2 to 3 inches deep for proper root development. Most planters were designed for this planting depth, especially those with angled closing wheels. When the seed-vee is properly closed, the sidewalls of the furrow will be fractured as the soil closes around the seed, eliminating the sidewall compaction and providing seed-to-soil contact.” 

Jasa adds that often sidewall compaction problems occur when the press wheels are set with too much down pressure. This overpacks seeds into the wet soil.

Shallow Setting Woes

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 2 inches below the soil surface,” Jasa explains. “This provides seed-to-soil contact at seeding depth while closing the seed-vee. Down pressure 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 increase down pressure springs trying to close the top of the seed-vee. Make sure 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.

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Changing Closing Wheels

Another option for eliminating sidewall compaction is to replace one of the planter’s solid closing wheels with a spiked version. Spiked wheels fracture the sidewall and provide loose soil in the future. The remaining solid closing wheel provides seed firming and depth control. 

“If the closing wheels can be staggered, mount the spiked one in front,” Jasa adds. 

Some producers use coulters or intermeshing row cleaners to till the soil in front of the row 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,” Jasa warns. 

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. 

“There are several brands of spiked closing wheels available to replace the standard press wheels with ones that till in the sidewall around the seed,” Jasa says. 

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 spiked wheels and attach the standard solid closing wheels to reduce overdrying the seed zone.

Too Much Down Pressure

Closing devices should fracture the sidewall when closing the seed-vee. Otherwise, the smeared soil may harden when it dries, making root penetration difficult. Disk openers may create some sidewall smearing while pushing the soil outward to form the seed-vee. 

Too much down pressure on the depth gauge wheels will pack the soil downward at the same time, causing compaction that may be too dense for the closing devices to fracture, Jasa adds. “When this occurs, producers typically put more pressure on the press wheels trying to close the seed-vee, making the compaction around the seed worse yet,” he notes. “Down pressure on both the row unit [depth gauge wheels] and the press wheels should be reduced in wet soil conditions.”

Seed-Vee Cracking

Another challenge of planting when it is too wet occurs when the seed-vee cracks open during dry conditions after planting, particularly with heavy clay soils. “Staggering the closing wheels, one in front of the other if possible, will help reduce the seed-vee from opening back up,” Jasa advises. 

Another contributor to sidewall compaction is the lack of soil structure in many tilled fields. Without soil structure, the standard closing wheels pinch the sidewalls closed over the seed, particularly in heavier soils. However, as the soil dries, it shrinks and the seed-vee may open back up, exposing the seeds. 

This is less of a problem in higher organic matter soils and in continuous no-till soils with improved soil structure. 

If there is a dry layer on top of the soil at planting time and good soil moisture at planting depth, don’t use residue movers to remove the dry soil because it has already shrunk, Jasa points out. “Also, when possible, leave residue over the row to reduce drying of the soil and to protect the seed zone from raindrop impact,” he says.