Many factors affect early corn growth and development. A common question is “how many Growing Degree Days (GDD) does it take for my corn to emerge?” Since corn emergence is directly related to soil temperature and soil moisture, the days to emergence vary especially when one compares early planting dates to later planting dates. It is assumed that it takes 120 GDD for corn to emerge under favorable conditions. However, we know that some planting practices and environmental conditions can decrease or increase the amount of GDD needed for corn to emerge.
We use the GDD calculation for air temperature to estimate how long it will take corn to emerge even though soil temperature is the driving factor. Growing Degree Days (GDD) or Growing Degree Units (GDU) calculation is determined from air temperature. The corn equation for GDD or GDU = (Daily Maximum Air Temperature + Daily Minimum Temperature)/2 – 50. When the maximum air temperature is greater than 86 degrees, we set the value at 86 in the equation, as the growth rate of corn does not increase much beyond 86. Likewise, when minimum air temperature is less than 50 degrees, we set the value equal to 50 in the equation. The sum of daily GDD or cumulative GDD for corn emergence is approximately 90 to 120 under favorable conditions based on research in Iowa.
Additional research shows more adjustments are needed to help fine tune expected emergence dates based on GDD determined from air temperature. Planting practices that change the amount of GDD for corn to emerge include planting date, depth, and residue cover. A table of these variables and adjustments can be viewed online at cropwatch.unl.edu/growing-degree-units-and-corn-emergence. For example, it takes about 10-25 more accumulated GDD for emergence with early planting dates. Planting deeper than 2 inches will increase the number of GDD to emergence by about 15. More than 75% residue cover increases the accumulated GDD needed for emergence, ranging from 30 to 60 GDD more. Dry seedbed conditions will require more GDD. Crusted or cloddy soils can increase GDD by 30 more. Heavy textured soils require more GDD than coarse textured soils. Corn genetics also can affect GDD needed for emergence. Therefore, the amount of accumulated GDD from planting to corn emergence can range easily range from 90 to 200 GDD.
In Nebraska, the U2U online tool at mygeohub.org/groups/u2u/purdue_gdd can be used to determine local accumulated GDD based on your planting date. For example, at the tri-county corner of Saline, Jefferson, and Gage counties from April 10 to May 1, we accumulated 177 GDD and the 30-year normal from 1981-2010 was 180 GDD for the same time frame. In summary, remember that numerous factors drive corn emergence and assuming a standard 120 GDD for corn to emerge will not always hold true. For more agronomic information from Nebraska Extension, contact me at or 402-821-1722. Know your crop, know your tech, know your bottom line at croptechcafe.org.
