CORN Newsletter: 2009-10, April 21, 2009

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C.O.R.N Newsletter 2009-10
April 21, 2009 - April 28, 2009

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Heat Units Required for Corn Emergence
by Peter Thomison


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Cool wet conditions have thus far limited corn planting in April. A few fields were planted as early as late March and early April. Now there are questions as to when this corn will emerge. According to USDA-NASS http://www.nass.usda.gov/oh/ as of April 12, we were behind in heat unit (growing degrees day, GDD) accumulation compared to the long term norm - with GDD accumulation since April 1 averaging about 42 across the state

Corn requires about 100 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. Dry soil conditions can cause uneven emergence in some fields that may impact yield if emergence delays exceed 1.5 to 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.

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C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868


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