Purdue University Department of Agronomy

Corny News Network

Originally published May 2000, Updated May 2008
URL: http://www.kingcorn.org/news/timeless/Emergence.html

The Emergence Process in Corn

R.L. (Bob) Nielsen
Agronomy Dept., Purdue Univ.
West Lafayette, IN 47907-2054
Email address: rnielsen at purdue.edu
 

uccessful germination alone does not guarantee successful emergence of a corn crop.  The coleoptile must reach the soil surface before its internal leaves emerge from the protective tissue of the coleoptile.  Growth stage VE refers to emergence of the coleoptile or first leaves through the soil surface (Ritchie et al., 1993). 

As with all of corn growth and development, germination and emergence are dependent on temperature, especially soil temperature. Corn typically requires from 100 to 120 GDD (growing degree days) to emerge (Nielsen, 2008b; Nielsen, 2008c). Under warm soil conditions, the calendar time from planting to emergence can be as little as 5 to 7 days. Under cold soil conditions, emergence can easily take up to four weeks.

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Elongation of the mesocotyl elevates the coleoptile towards the soil surface.  The mesocotyl is the tubular, white, stemlike tissue connecting the seed and the base of the coleoptile.  Technically, the mesocotyl is the first internode of the stem.

Useful Tip: Physiologically, mesocotyls have the capability to lengthen from at least a 6-inch planting depth.  Realistically, corn can be planted at least three inches deep if necessary to reach adequate moisture.

As the coleoptile nears the soil surface, exposure of the mesocotyl to the red light portion of the solar radiation spectrum halts mesocotyl elongation. Continued expansion of the leaves inside the coleoptile ruptures the coleoptile tip, allowing the first true leaf to emerge above the soil surface.  Since the depth at which the mesocotyl senses red light is fairly constant, the resulting depth of the crown (base) of the coleoptile is nearly the same (1/2 to 3/4  inch) at seeding depths of one-inch or greater. 

Useful Tip: When corn is seeded very shallow (less than about 1/2 inch), the crown of the coleoptile will naturally be closer to the soil surface if not right at the surface.  Subsequent development of the nodal root system can be restricted by exposure to high temperatures and dry surface soils.

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Troubleshooting Considerations

Several factors can cause the coleoptile to split prematurely, allowing the leaves to emerge underground.  Usually, more than one of the following factors are present when this problem occurs, making it difficult to place the blame on any one factor. 

Exposure to light at deeper soil depths than usual due to cloddy seedbeds, dry seedbeds, sandy soils, or open slots in no-till. 

Injury from certain herbicides, particularly under stressful environmental conditions.  Symptoms include corkscrewed coleoptile, swollen mesocotyl and true leaves emerged from side of coleoptile. 

Surface crusting, cloddy seedbeds, rocky seedbeds, planter furrow compaction, or otherwise dense surface soil that physically restrict mesocotyl elongation and coleoptile penetration. The pressure of the expanding leaves within the coleoptile eventually ruptures the side of the coleoptile. Symptoms include corkscrewed coleoptile, swollen mesocotyl and true leaves emerged from side of coleoptile.  Note the similarity to those symptoms from herbicide injury.

Cold temperature injury, either from exposure to long periods of soil temperatures around 50F or from exposure to wide daily swings (25 to 30F) in soil temperatures.  Symptoms include absence of emerged coleoptile, corkscrewed mesocotyl or coleoptile and true leaves emerged from side of coleoptile. Note the similarity to those symptoms from herbicide injury.

Useful Tip: The mesocotyl should remain firm, white and healthy through at least the 6-leaf stage, if not longer. If it is mushy, discolored, or damaged prior to this stage, then it is likely part of the crop problem being investigated.

Related References

Nielsen, RL (Bob). 2004. Corkscrewed Corn Seedlings. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/articles.04/Corkscrew-0501.html. (URL accessed 5/7/08).

Nielsen, RL (Bob). 2008a. Germination Events in Corn. Corny News Network, Purdue Univ. [On-Line]. Available at  http://www.kingcorn.org/news/timeless/GerminationEvents.html.  (URL accessed 5/7/08).

Nielsen, RL (Bob). 2008b. Heat Unit Concepts Related to Corn Development. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/timeless/HeatUnits.html. (URL accessed 5/7/08).

Nielsen, RL (Bob). 2008c. Requirements for Uniform Germination and Emergence of Corn. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/timeless/GermEmergReq.html. (URL accessed 5/7/08).

Ritchie, S.W., J.J. Hanway, and G.O. Benson. 1993. How a Corn Plant Develops (SP-48). Iowa State Univ. [On-Line]. Available at http://www.extension.iastate.edu/hancock/info/corn.htm. (URL accessed 5/7/08).