Under ideal conditions, corn will emerge in 10 days or less after planting. But, the cool, wet weather throughout much of the Corn Belt during April has been anything but ideal. Given these cooler soil conditions, germination could take three weeks or more once corn is planted if temperatures remain lower than normal.

Corn's germination process involves several steps which are driven by temperature. The corn seed must first absorb 30 percent of its weight in water, note Pioneer agronomists. Seeds can absorb water below 50º F; however, growth will not occur until soil temperatures are above 50º F. As temperatures rise, the processes required for germination occur at a faster rate, leading to more rapid emergence.

Typically, about 125 accumulated Growing Degree Units (GDU) are required between planting and emergence. To calculate GDUs in your area, take the daily high temperature plus the daily low temperature and divide by two. Take that high-low average and subtract 50. For example, if the day's high is 70º and low is 42º, six GDUs would be accumulated in the given day.

Numerous environmental and management factors influence the number of GDUs needed for corn's emergence, the University of Wisconsin's Joe Lauer points out. For example, when conservation tillage leaves more that 75 percent residue, an additional 30 to 60 GDUs are needed for corn emergence. Other factors include:
• Fine soil texture, add 30 to 60 GDUs
• Coarse soil texture, subtract 30 to 60 GDUs
• Seed-zone soil moisture (below optimum), add 30 GDUs
• Seedbed condition (soil crusting or massive clods), add 30 GDUs
• Seeding depth (for each inch below 2 inches), add 15 GDUs

For more on the subject, go to http://corn.agronomy.wisc.edu/WCM/W039.aspx