Metadata for Corn Growth Stage Model

The corn growth stage model is a heat-unit or growing degree-day (GDD) model in which corn’s growth and development is based on the plant’s physiological response to temperature. The corn stage model is initiated by assuming an average planting date, and accumulated GDD heat units are then calculated and scaled according to corn growth stages as defined by Hanway 1971). In addition, GDD accumulations for the entire growing season are variety specific, with short season varieties requiring less GDD units than long season varieties.

In summary, the corn stage model uses the Hanway Growth Stage (HGS) model as defined below, and four generic corn varieties were then developed with the following respective GDD accumulations in Fahrenheit:

HGS Phenological Stage Var 1 Var 2 Var 3 Var 4
0.0 Emergence 110 140 130 82
1.0 4-Leaves 420 540 500 316
2.0 8-Leaves        
2.5   800 1135 1000 634
3.0 12-Leaves        
4.0 16-Leaves        
4.75   1380 1740 1600 1024
5.0 Silk-tassel        
6.0 Blister Kernel        
6.5   1800 2330 2200 1371
7.0 Dough        
8.0 Begin Dent 2160 2810 2675 1655
9.0 Full Dent        
10.0 Physiological Maturity 2650 3350 3230 2000

The above generic varieties were developed from actual seed varieties, but later used as generic varieties ranging from short (2000 GDD), medium (2650 GDD), and long (>3200 GDD) season varieties. These seed varieties were then matched to the average seasonal GDD potential for different agro-climatic regions, as illustrated in Figure 1 below for the United States. Properly matching the generic seed variety to the average GDD potential for the region allows the growth stage model to approximate the actual phenological stages for different regions.
Figure 1. Average Growing Degree Days (GDD) for the United States (Neild and Newman, 1990)

Additional Growing Degree Day Information

Growing Degree Days (GDD) or heat units is a concept commonly used among seed producers to help growers choose the best seed varieties for a given location and planting date, and with the potential to achieve maximum yields and low moisture content at harvest time. In addition, GDD calculations allow growers to follow crop progress during the growing season and aids in predicting harvest schedules.

The GDD concept is considered more accurate in determining crop maturity, rather than counting calendar days after planting, because plant growth plant is directly related to the accumulation of heat over time. In other words, calendar days do not contribute equally to plant growth because plants grow faster during warm weather than in cold weather.

GDD is calculated each day by averaging minimum and maximum daily temperatures and subtracting a base temperature, as follows:

      GDD = (Tmax + Tmin)/2 – Tbase

where, Tbase = 50 F (10 C) for warm season crops such as corn, sorghum, and millet.

The GDD concept assumes:

  1. There is a base or threshold temperature for which plants do not grow or they grow very slowly.
  2. A base temperature of 50-degree Fahrenheit (10-degree Celsius) is assumed for warm-season crops such as corn, sorghum, and millet; while a lower base temperature of 40-degree Fahrenheit (5-degree Celsius) or 32-degree Fahrenheit (0-degree Celsius) are commonly assumed for cool-season crops such as wheat, oats and barley.
  3. The rate of plant growth increases as temperature increases above the base or threshold temperature.
  4. Length of growing season for crop hybrids is closely related to GDD accumulations from planting to maturity.
  5. Plant growth and development are more closely related to daily mean temperature accumulations above a base value in absence of other limiting factors.

In addition, a modified GDD calculation is commonly used for corn, where minimum and maximum temperatures are modified with the following adjustments:

  • If daily maximum temperature is above 86 F (30 C), it is reset to 86 F (30 C). This modification assumes that plant development slows down as leaf stomates close when temperatures begin to exceed 86 F (30 C).
  • If the minimum temperature is below 50 F (10 C), it is reset to 50 F (10 C). This modification assumes that plant development is limited when temperatures are below 50 F (10 C) and it helps prevent GDD from being negative for minimum temperatures below freezing.

In summary, the modified GDD method is calculated each day as:

GDD = (Tadj-max + Tadj-min)/2 – Tbase

where, Tbase = 50 F (10 C) for warm season crops, and 40 F (5 C) or 32 F (0 C) for cool-season crops.
      Tadj-max is set to 86 F (30 C) when Tmax is above 86 F (30 C)
      Tadj-min is set to 50 F (10 C) when Tmin is below 50 F (10 C).

The above GDD calculation for corn is commonly referred as the "86/50 corn system" or "86/50 cutoff method".

Additional information about GDD calculations are described at:
      http://www.ces.purdue.edu/extmedia/NCH/NCH-40.html
      http://www.ipm.ucdavis.edu/WEATHER/ddconcepts.html

References:

Hanway, J.J. 1971. How a Corn Plant Develops. Agronomy Journal, 55:487-492.

Neild, R.E. and J.E. Newman. 1990. Growing Season Characteristics and Requirements in the Corn Belt. National Corn Handbook, Purdue University, Cooperative Extension Service, West Lafayette, IN, http://www.ces.purdue.edu/extmedia/NCH/NCH-40.html

Ritchie, J.T. 1991. Wheat Phasic Development. In Hanks, R.J. and Ritchie, J.T. (Eds). Modeling plant and soil systems. Agronomy Monograph #31. American Society of Agronomy. Miadison, WI, pp. 34-54.

University of California, 2003. About degree days, Statewide Integrated Pest Management System, Agriculture and Natural Resources, University of California. http://www.ipm.ucdavis.edu/WEATHER/ddconcepts.html