Top Crop Manager

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Sponsored: Helping farmers calculate growing degree days

October 17, 2019  By Top Crop Manager

For many farmers, 2019 has had its fair share of varying weather. From the floods in the Midwest to drought in the Canadian Prairies and everywhere in between, farmers have dealt with the challenges of uncooperative weather. The downpour of rain in the Midwest caused thousands of farmers headaches and heartaches wondering when or even if they could get a corn or soybean crop in the ground this growing season.

Those who were able to plant their corn now realize how important growing day accumulation is. Farmers can look to eKonomics for our easy-to-use Growing Degree Days calculator to help determine what growth stage or development level their crop is at based on daily temperature.

How does it work?

Each crop has a specific “base temperature” or the minimal temperature threshold that has to be exceeded for the crop to develop (see table below).


Once the farmer enters their location and crop, the eKonomics calculator uses a modified GDD equation for determining the mean daily temperature based on previous weather data (up to the past six months).

Specifically, for corn, if the high temperature was above 86°F, then the maximum temperature for that day is adjusted to 86°F. If the low temperature was below 50°F, then the minimal temperature for that day is adjusted to 50°F. By doing so, we are assuming that crop development is limited when temperatures exceed 86°F or fall below 50°F.

After the minimal and maximum temperatures are adjusted accordingly, the mean temperature is calculated:

The GDD or heat units are then calculated by subtracting the base temperature (in the table above) from the mean temperature.

According to an article by Emerson Nafziger, “A 90-day hybrid (needing 2,159 GDD) planted on July 5 in central Illinois is predicted to pollinate on August 24 and to accumulate only 2,000 GDD by October 23; it is not expected to reach black layer by the end of December.” The same corn hybrid planted in other weather patterns may mature earlier due to higher GDD, and a farmer can track the progress using the eKonomics calculator.

Unfortunately, the eKonomics GDD calculator is not set up to determine future potential growing degree days based on previous years’ weather data. However, a farmer can track where their crop is to-date with development and potentially help make decisions like whether to cut corn for silage as opposed to trying to finish grain if late planting did occur.

For more information, visit Nutrien-eKonomics.


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