Compacted soils are largely the result of heavy equipment passing over soils that contain too much moisture. The degree of compaction can vary depending on soil texture. Coarse textured soils and high organic soils are less prone to compaction compared to medium and fine textured soils that can hold more moisture.
There are a couple of methods to determine the operational fitness of a field. The methods involve removing a small amount of soil from a 3- to 4-inch depth. If the sample can be formed into a ball that breaks apart easily when dropped, it is generally considered to be fit for field operations. For the other method, press the soil sample between thumb and fingers in an attempt to form a soil ribbon; a crumbling soil rather than the formation of a ribbon indicates fitness.
Sidewall compaction can occur when planter furrow openers smear wet soil on the sidewall of the furrow as they travel through the field (Figure 1).1 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.
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 deficiency, a purpling of seedling leaves, even in soils with adequate phosphorus soil test values because the roots are unable to reach the non-mobile phosphorus (Figure 2). 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.2 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 (Figure 3).3
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 (Figure 4). Sidewall compaction symptoms include corn roots restricted to the seed furrow, flattened roots, and a proliferation of secondary roots growing horizontally along the planter trench. Sidewall smearing may also be evident from the furrow opener. Figure 3. Rootless or floppy corn syndrome. Figure 4. Use a spade to determine if sidewall compaction exists.
Planting when too wet is the main cause for sidewall compaction; however, other causes can include planting too shallow, too much down-pressure on depth gauge wheels, and too much down-pressure on seed furrow closers. Down-pressure on both the row unit's depth gauge wheels and the press wheels should be reduced if planting into wet soil conditions. If the seed has good seed-to-soil contact and the seed slot remains open, there are other devices that can be used aside from the standard closing devices or press wheels. In heavy, wet soils, seed slot "pinch" from angled closing wheels can also be a problem. This happens when the soil in the seed slot dries, shrinks, and opens up the slot to expose the seed. A suggestion is to remount the wheels one ahead of the other, which causes the second wheel to move soil over the first wheels path.
1 Thelen, K. 2007. Exercise patience in deciding when to resume field operations. Michigan State University Extension. http://msue.anr.msu.edu/news/exercise_patience_in_deciding_when_to_resume_field_operations.
2 OMAFRA. 2009. Compaction - soil diagnostics. http://www.omafra.gov.on.ca/IPM/english/soildiagnostics/ compaction.html.
3 Nielsen, R.L. 2013. Root development in young corn. Corny News Network Articles. Purdue University. https://www.agry.purdue.edu/ext/corn/news/timeless/roots.html.
4 Jasa, P. 2010. Recommendations for avoiding sidewall compaction at planting. CropWatch. University of Nebraska-Lincoln. http://cropwatch.unl.edu/unl-cropwatch-april-16-2010-recommendations-avoiding-sidewallcompaction- planting.
5 Jasa, P. 2010. Tips to reduce sidewall compaction. CropWatch. University of Nebraska-Lincoln. http://cropwatch.unl.edu/unl-cropwatch-april-16-2010-tips-reduce-sidewall-compaction. Web sources verified 3/03/2016 Doc ID #: 140519060655