Welcome to the United States Growing Degree Days Information
About the website
This website will display the annual accumulated GDD for corn for all ASOS stations in the continental United States. The home page displays the map of United States from where the user can navigate to various states and get the
annual accumulated GDD for corn for different ASOS stations in the state. Directly the search drop down list can help to have a direct access to each state. Data sets of annual accumulated GDD in form of excel sheets can also be
downloaded for all ASOS stations in each state.
Purpose
The purpose of this site is to be able to provide information about the annual accumulated Growing Degree Days for corn for over a century (ending year 2009) in various states of continental United States.
Corn Growing Degree Days (GDD)
For most plants, phonological development is strongly related to the accumulation of heat or
temperature units above a threshold or base temperature below which little growth occurs.
This lower threshold temperature varies with plant species. Scientists have determined the
lower base temperature for corn is 50 �F (10 �C). In some plants there is also an upper
threshold temperature, above which conditions are stressful to the plants. The upper
limit for corn is 86 �F (30 �C). Although temperature is the most important factor
controlling the rate of plant development, other factors such as water and light availability
and daylight length may modify its effects.
The most common temperature index used to estimate plant development is growing degree days (GDD)
which are calculated from the daily maximum and minimum air temperature. Growing degree days
have proven useful for crop consultants, producers, and scientists who use them to predict
plant development rate and growth stage.
As an equation:
Tbase varies for different plants and is the lowest temperature where metabolic processes result in a net substance gain in aboveground biomass.
Tbase for corn is 500 F or 100 C.
Corn Growing Degree Day Calculation
Corn growing degree days (GDD) are calculated by subtracting the plant's lower base or threshold
temperature of 50 �F (10 �C) from the average daily air temperature in �F or �C. Average daily
air temperature is calculated by averaging the daily maximum and minimum air temperatures measured
in any 24-hour period.
In Formula Form
The Daily Average Temp (�F) = (Daily Max Temp �F + Daily Min Temp �F) / 2
Daily Corn GDD (�F) = Daily Average Temperature �F - 50 �F
Constraints on maximum and minimum temperatures are used to eliminate the effect of low or high temperatures that prevent or retard growth. For corn these constraints are:
If the daily Max and/or Min Temp < 50 �F (10 �C), it's set equal to 50 �F (10 �C)
If the daily Max Temperature > 86 �F (30 �C), its set equal to 86 �F (30 �C)
