GDD Accumulations
Under Various Freeze Risks

Figure 1. Growing degree day (GDD) accumulations under high freeze risks, based on 30 years of average GDD accumulations in Nebraska.

 

Figure 2. Growing degree day (GDD) accumulations under medium freeze risks, based on 30 years of average GDD accumulations in Nebraska.

Figure 3. Growing degree day (GDD) accumulations under low freeze risks, based on 30 years of average GDD accumulations in Nebraska.

---

Sources for Figures 1-3: Freeze risk data for this analysis was obtained from the High Plains Regional Climate Center. GDD information for this analysis was collected from www.agclimate4u.org, which originally obtained data from Regional Climate Centers - Applied Climate Information System (www.rcc-acis.org).

---

Growing Degree Days (GDD) are a measure of accumulated heat units that correspond with the growth and development of any given crop. GDD for corn is calculated based on minimum (50oF) and maximum (86oF) temperature thresholds. (Corn generally does not grow when temperatures are outside this range.)

It is important to keep track of GDD accumulations because length of a crop's growing season is often measured as accumulated GDDs. For example, if a particular corn hybrid is rated as reaching maturity at 2700 GDD, that means the corn requires 2700 GDDs from planting to physiological maturity, irrespective of the "days to maturity" estimated for each growth stage. Most corn seed companies rate hybrid maturity on the basis of growing degree days.

By understanding the potential for accumulating GDDs during the growing season, you can determine whether to plant a shorter season, mid-season, or longer season corn variety.Figures 1-3 correspond with the GDD accumulations for corn across Nebraska under low, medium, and high freeze risks. These maps can help you determine how much GDD accumulation can be obtained given you take certain freeze risks. For example, there would be enough accumulated GDD in a season to grow longer season hybrids (> 3200 GDDs) for the medium and high risk levels in southeast Nebraska, given average conditions. However, the GDD accumulation potential for northeast Nebraska is between 2200 and 2600 GDD for the low-risk scenario.

Please note that these calculations were done using 30 years of data. Since, year-to-year variations can significantly change GDD accumulations, this information is intended to be used for long-term planning.

Once the growing season progresses, I will provide periodic updates in CropWatch for GDD accumulations for this year. These can be compared with the long-term averages and help provide a basis for tracking crop development expected maturity. 

Figures 1-3 summarize GDD accumulations under three spring and fall freeze risks scenarios — low, medium, and high.

• Low freeze risk corresponds to a 10% chance of freeze impacting corn in spring/fall.
• Medium freeze risk corresponds to a 50% chance of freeze impacting corn in spring/fall.
• High freeze risk corresponds to a 90% chance of freeze impacting corn in spring/fall.

Tapan Pathak
Extension Educator for Climate Variability

How are Growing Degree Days (86/50) Calculated for Corn?

GDD = [(Maximum Temperature + Minimum Temperature) / 2] – 50

Conditions

1. If daily minimum temperature is below 50°F, it is set as 50°F in the formula

2. If daily maximum temperature is above 86°F, it is set as 86°F in the formula

Example 1

Given daily maximum and minimum temperatures of 65°F and 40°F, calculate GDD units by:

GDD = [(65 + 50)/2] – 50

GDD = 7.5

April 4, 2014 Release