To calculate GDD, add the daily maximum and minimum temperatures together and divide by 2, producing a mean daily temperature. If the minimum temperature for the day is below a crop's minimum base temperature, the crop's base temperature is used. If the high temperature for the day is above 86 degrees Fahrenheit, 86 degrees is used because growth activity of most crops will peak at that temperature. The crop's minimum base temperature is then subtracted from the mean temperature to give the daily GDD.
If the mean daily temperature is lower than the base temperature then no GDD are accumulated.
Minimum base temperatures for selected crops(degrees Fahrenheit):
|Example for Corn:|
|High temperature: 72|
|Low temperature: 48|
|72+50/2 = 61 - 50 = 11 GDD|