Corn requires about 100 growing degrees days (GDDs) to emerge (but emergence requirements can vary from 90 to150 GDDs).

To determine daily GDD accumulation, calculate the average daily temperature (high + low)/2 and subtract the base temperature which is 50 degrees F for corn. If the daily low temperature is above 50 degrees, and the high is 86 or less, then this calculation is performed using actual temperatures, but if the low temperature is less than 50 degrees, use 50 degrees as the low in the formula. Similarly, if the high is above 86 degrees, use 86 degrees in the formula.

If it takes a corn hybrid 100 GDDs to emerge, and daily high and low temperatures average 70 and 50 degrees following planting, 10 GDDs accumulate per day, and corn should emerge in about 10 days (100 GDDs to emerge/10 GDDs per day = 10 days).

However, if daily high and low temperatures are cooler, averaging 60 and 45 degrees after planting, 5 GDDs accumulate per day, and it may take nearly 3 weeks (100 GDDs to emerge/5 GDDs per day = 20 days) for corn to emerge. In 2005, corn planted in mid- April took as long as 3 to 4 weeks to emerge in many fields.

Seedling emergence is dependent on soil temperature and air temperature. Also, keep in mind that estimates of emergence based on GDDs are approximate and can be influenced by various factors including residue cover, tillage, and soil organic matter (soil “color”) and moisture content.

Corn emergence can be slowed by inadequate soil moisture. Moreover dry soil conditions can cause uneven emergence in some fields that may impact yield if emergence delays exceed 1.5 – 2 weeks. We observed this problem in some corn fields in 2007 when weather turned dry after a wet April.

Crops vary widely with regard to the minimum moisture content required for emergence. For corn, the minimum moisture content at which the radicle emerges is 30% of the seed dry weight. In contrast, for soybean, the reported minimum moisture content required for germination is 50%. However since a soybean seed generally weighs only 2/3 or less the weight of a corn seed, a soybean seed requires less water to germinate.

For more detailed information on heat units, germination and emergence in corn, I’d encourage you to check out a series of excellent articles (noted below) which Dr. Bob Nielsen, my counterpart at Purdue University has recently written. These articles include great photos and figures that will assist your understanding of these growth and development processes.

• Nielsen, RL (Bob). 2007. Germination Events in Corn
• Nielsen, RL (Bob). 2007. The Emergence Process in Corn
• Nielsen, RL (Bob). 2007. Heat Unit Concepts Related to Corn Development

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