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Sidewall compaction can occur when planter furrow openers smear wet soil on the sidewall of the furrow as they travel through the field. The smearing essentially seals the soil from root penetration. Additional compaction can occur from press wheels that have too much down pressure, particularly in overly moist soils. If seed placement is too shallow within the furrow relative to the positioning of the press wheel, compaction can occur below the seed and result in reduced or poor root penetration through the compacted layer.
Medium and fine textured soils typically have a greater moisture holding capacity, are slower to dry, and are more vulnerable to compaction. Coarse textured soils and those with high levels of organic matter are less prone to compaction. Soils are generally considered fit for field operations when soil taken from a 3- to 4-inch depth is formed into a ball that will fracture easily when dropped, or will not form a ball at all. Another technique is to press soil between your thumb and fingers in an attempt to form a soil ribbon. Fit soil will crumble and will not form a ribbon of any significant length.
To confirm possible sidewall compaction, use a spade to carefully remove one side of the seed slot to a depth of about 3 to 4 inches.Corn roots will be found following the seed furrow down the row (Figure 1). Signs of sidewall compaction are flattened roots with a proliferation of secondary roots growing horizontally along the planter trench. Also, there may be evidence of the furrow opener smearing and sealing the soil of the sidewall.
Soil conditions that can cause sidewall compaction often result in poor seed-to-soil contact, shallow seed placement, and open seed furrows. Consequences can include reduced germination and poor stands, uneven emergence and growth, restricted root growth, and stunted seedlings. Plants with restricted root growth often show symptoms of phosphorus (P) deficiency, a purpling of seedling leaves, even in soils with adequate P soil test values because the roots are unable to reach the non-mobile P. If dry conditions develop after planting, the germinating seedling and its early roots may suffer from inadequate amounts of moisture. Longer-term effects on yield potential may be possible in corn plants subjected to sidewall compaction.
Corn plants affected by sidewall compaction may appear stunted, show less vigor, and will lag behind normal development.1 Unexpected nutrient deficiency symptoms may also be observed. This may become most pronounced around the V3 growth stage as the nutrient reserves in the kernel are depleted and the plant must rely on its root system to sustain development. Rootless or floppy corn syndrome is often associated with sidewall compaction and shallow planting because the roots are unable to grow deep enough to anchor the plant.2
Tips for reducing sidewall compaction
1 OMAFRA. 2009. Compaction - soil diagnostics. http://www.omafra.gov.on.ca
2 Nielsen, R.L. 2013. Root development in young corn. Corny News Network Articles. Purdue University. http://www.agry.purdue.edu
3 Jasa, P. 2010. Tips to reduce sidewall compaction. University of Nebraska-Lincoln CropWatch. http://cropwatch.unl.edu
Web sources verified 3/29/17; 170330171008