1. Utilizing Growing Degree Units for Crop Management Decisions
20th Annual National Conservation Systems
Cotton & Rice Conference
Dwayne Beaty, CCA-CPAg

2. Different name same meaning
Growing Degree Units (GDUs)
Growing Degree Days (GDDs)
Heat Units (HUs)

3. GDUs are used to relate plant growth, development and maturity to air temperature
The idea was introduced almost 300 years ago in 1730, by the French scientist Rene A. F. Reaumur (McMaster and Wilhelm, 1997)

4. Growing Degree Units
It has been demonstrated that the amount of time required for corn to pass from one developmental stage to another is contingent on the amount of heat accumulated (Glimore & Rogers, 1958)
GDD has been used as a means to predict the growth stages of many living things (Cross and Zuber, 1972; Klepper et al., 1984; McMaster and Smika, 1988; Russelle et al., 1984

5. Calculating Growing Degree Units Crops
GDU = (Tmin + Tmax)/2 – Tbase
Crop
Tbase
Temp threshold
Corn
50º F
86º F
Rice
Sorghum
100º F
Cotton
60º F
Wheat
32º F

6. Effect of temperature on plant growth with 86º F threshold temperature
Photosynthesis shuts down at temperatures above 86º F
Optimum growth when night temperatures are 10 to 15
degrees cooler than day temperature
Most corn hybrids have fairly specific GDU specifications

7. GDU Calculation Little if any growth below 50º F
Little if any growth above 86º F

8. Management Decisions Weed control (crop growth stage cut-off)
Pest Management
Weed control (crop growth stage cut-off)
Insects (GDU to determine application timing)
Nitrogen timing
Grain drydown

11. Calculating Growing Degree Units Insects
GDU = (Tmin + Tmax)/2 – Tbase
Insect
Tbase
Temp threshold
Armyworm
50º F
84º F
Black cutworm
86º F
Corn earworm
55º F
92º F
Common stalk borer
41º F

13. GDU Accumulation for Grain Drydown
Corn
Grain moisture: 30-25%
30 GDUs to remove 1 point of moisture
Grain moisture: 25-20%
45 GDUs to remove 1 point of moisture
Grain drying rates will vary between hybrids and environments

14. Factors Affecting GDU Accumulation
Tillage (conventional / no-till)
Planting date (mid-March / late May)
Planting depth
Moisture (wet / dry)
Soil temperature (V6)
Solar radiation
Soil GDUs at the seed zone is a dominate factor through emergence
Air temperature / solar radiation is a dominate factor after the growing point rises above the soil surface

15. Formula
=(IF(B5>86,86,B5)+IF(C5<50,50,C5))/2-50

16. Corn Growth Stage by GDU’s Growing-degree day requirements for different phenology stages of a 2700 GDU hybrid
Growth Stage
GDU’s
Radical emergence
65-80
Emergence V2
200 V3
350 V6
475 V8
610
V10
740 R1
1400 R6
2700

18. “The worst place to store Nitrogen is in the soil”
Brewer Blessitt, PhD, CCA - CPAg, DuPont Pioneer Product Agronomist; MS

19. Nitrogen Fertilization
More of an Art
than Science
Applying N by calendar
Precision timing of N applications
Growth Stage
DAE V3
8-10
V6-8
21-36
V12-17
36-60
VT-R1
54-62 R6
DAE: Days after Emergence

20. Bruce Bond: Nitrogen fertilization by GDU’s
#’s N
GDU’s
Growth Stage 80
V2-3
110
V8-10 50
1200
~ 200 GDU’s before silk/tassel emergence
Dan Poston, PhD, DuPont Pioneer Agronomy Research Manager
Brewer Blessitt, PhD, CCA, CPAg, DuPont Pioneer Product Agronomist; MS

21. Bruce Bond Portland, AR
200 GDUs - 80#s N ( ) liquid applicator
GDUs – 110#s N ( w/Agrotain) High Cycle
1200 GDUs - 50#s N ( w/Agrotain) High Cycle

22. 6-750 GDUs V8-10
110#s N
2-300 GDUs V2-3
80#s N

23. 1200 GDUs Pre-Tassel 50# N

24. GDU Accumulation for Grain Drydown
Grain moisture: 30-25%
30 GDUs to remove 1 point of moisture
Grain Moisture: 25-20%
45 GDUs to remove 1 point of moisture
Grain drying rates will vary between hybrids and environments

25. R6 ~ 34-35% moisture
10 days 301 GDUs
~24-25% moisture
7 days GDUs
~ 20% moisture
6 days 170 GDUs
Harvest 17.14%
Grain drying rates will vary between
hybrids and environments

26. GDUs are another tool for management decisions just like these tools