ProCrop

Growing Degree Days and Corn Maturity 

"Growing-degree days" (GDD) or heat units has been developed to more accurately rate corn maturity. It is based on the number of growing degree days between emergence date and physiologic maturity of a hybrid (Table 1). Growing degree days vary in North Dakota from 2400 GDDs in southeastern areas to 1900 GDDs in the northern areas (Table 2).

In calculating growing degree days (GDD), temperatures from a lower limit of 50F and an upper limit of 86F are accumulated for the growing season by applying the following formula to each day's maximum and minimum temperatures.

GDD=(Max. Temp. + Min. Temp.) - 50
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                2

Maximum temperatures higher than 86F are entered as 86 and temperatures below 50 F are entered as 50 in the formula. GDDs are accumulated from seedling emergence until physiological maturity. Kernel moisture content at physiological maturity generally averages about 34 percent. At physiological maturity a "black layer" will form under the outer layer of the kernel tip. When this forms it signals that kernel dry matter accumulation has reached the maximum level. Corn will not be hurt by frost after that point. Hybrids may vary up to 10 percent in kernel moisture at physiological maturity.

Table 1. Approximate GDD Heat Units and Relative Maturity for Corn in the Northern Growing Regions (North Dakota and Minnesota).

Table 2. Growing Degree Day Accumulations at Various North Dakota Locations (1970-96)
(For calculating GDD go to http://www.ndawn.ndsu.nodak.edu/application/corn-degree-days-form.html)

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