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

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

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)

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

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

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

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

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

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

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

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

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

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 100-120 V2 200 V3 350 V6 475 V8 610 V10 740 R1 1400 R6 2700

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

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 105-120 DAE: Days after Emergence

Bruce Bond: Nitrogen fertilization by GDU’s #’s N GDU’s Growth Stage 80 200-300 V2-3 110 600-750 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

Bruce Bond Portland, AR 200 GDUs - 80#s N (28-0-0-5) liquid applicator 600-700 GDUs – 110#s N (28-0-0-5w/Agrotain) High Cycle 1200 GDUs - 50#s N (28-0-0-5w/Agrotain) High Cycle

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

1200 GDUs Pre-Tassel 50# N

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

R6 ~ 34-35% moisture 10 days 301 GDUs ~24-25% moisture 7 days 226.5 GDUs ~ 20% moisture 6 days 170 GDUs Harvest 17.14% Grain drying rates will vary between hybrids and environments

GDUs are another tool for management decisions just like these tools