Growing Degree Days

Growing Degree Days:

It is a very important concept for farmers, farm managers and crop supervisors to understand.

Growing degree days is an indicator to estimate the crop and insect growth stages/rate. It applies when your crop is not facing any shortage of requirements like water (soil moisture) and nutrients(fertilizers). Also not facing any extreme effects of any disease.

What is the growing degree days?

Growing degree days are heat units received by the crop and contributes to crop growth stages by which farmers can analyze current crop growth performance (whether the crop is normal or retard) and can estimate the crop growth stages with the help of future weather forecast of your farm weather station data. (weather data can also be availed from local metrology department or weather websites). Better understanding of growing degree days is also helpful to estimate the insect’s population growth and farmers can plan to minimize the damage to crop yield.

In this blog, we will also perform how to calculate the growing degree days. Before to perform the calculation of the growing degree days, it is important to know some parameters given below:

            Minimum Temperature       (ambient temperature)

            Maximum Temperature       (ambient temperature)

            Base Temperature              (Crop Growth parameter

            High line temperature         (Crop Growth parameter)

Minimum Temperature:    It refers to the minimum value of the temperature dropped in a day.

Maximum temperature:     It refers to the maximum value of the temperature achieved in a day.

Baseline temperature:

It refers to the minimum temperature below that temperature plant stops biological activities (Stop growing).

In case if minimum temperature value dropped below the baseline temperature, then consider baseline temperature value as minimum temperature value. Because drop down in temperature below baseline temperature do not contribute to crop growth. Furthermore, in that case, damage to crop due to chilling/freezing / below freezing point(e.g. when temperature approaches to freezing point or drop more, the water/sap in the plant start freezing and vanes burst continuity of water and nutrients stops then permanent damage occurs) is expected and precautionary measures should be planned.

Detailed Effects of chilling/freezing / below freezing point will be discussed in the future in a separate blog.

High line temperature:       

  

It refers to the maximum temperature above that temperature plant stops biological activities (Stop growing).

In case if maximum temperature value rises above the high line temperature, then consider high line temperature value as the maximum temperature value. Because the rise in temperature above high line temperature does not contribute to crop growth. Furthermore, in that case, damage to crop due to very hot air and rise in soil temperature (hot air persistent for a longer period can damage crop shoots, disturb photosynthesis, growth and pollination while hot soil can burn hair roots) is expected and precautionary measures should be planned,

Moreover, if humidity is also high with very hot temperatures, it encourages the growth of pests and insects within the crop. In this case, farmers must include preventive measures regarding pest and insect attack in their crop production plan.

Detailed Effects of very high temperatures, high humidity, and very high temperature of the soil will be discussed in the future in a separate blog.

Calculation of Growing Degree Days:

To calculate the growing degree days, you have the maximum and minimum temperatures of the day and base

temperature of the crop, by using the below formula you will have the growing degree days.

Growing Degree Days = ((T_max + T_min) / 2) – Base temp of Crop

While using the above formula, you must consider the limitations given below.

If the minimum temperature value will be below the base temperature of the crop, then use base temperature as the minimum temperature value

If the maximum temperature value will be higher than the upper threshold temperature of the crop, then use upper threshold temperature as a maximum temperature value

 Inference of lower threshold temperature.

Based on base temperature, crops can be divided into three categories.

Cold-tolerant plants

Cold-temperate plants

Cold-sensitive plants

Cold-tolerant plants:

The crops with a base temperature of 39o F (3.8C) or lower can be categorized as cold-tolerant crops. Crops at their flowering time are less influenced by lowering the temperature (on an absolute basis) than other crops. For cold-tolerant crops in cold regions, greenhouse temperature settings/requirement suggested 60-65¡ F (15.5 – 18.3 C).

Cold-temperate plants:

The crops with base temperatures between 40F(4.4C) and 45F (7.2C) can be categorized as cold-temperate crops. Flowering of cold-temperate plants is more sensitive to lower temperatures than the cold-tolerant crops category. For cold-temperate crops in cold regions, greenhouse temperature settings/requirement suggested 65-70 F (18.3 – 21.1 C).

Cold-sensitive plants:

The crops with a base temperature of 46F (7.7 C). the flowering of cold-sensitive crops is substantially delayed when the temperature is lowered and thus, plants should generally be grown at warm temperatures. For cold-sensitive crops in cold regions, greenhouse temperature settings/requirement suggested 70-75 F (21.1 – 23.8 C).  

The categories of crops based upon base temperature can help the farmers/farm managers (Specifically farmers in cold region/Greenhouse farmers) to plant their crops in the best way. They can segregate their farm’s crops into categories based on the response to lower threshold temperature. The most important point of focus is that they should not grow cold-tolerant crops with cold-sensitive crops, because crop production parameters contrast with each other.

Some Major Crops Information:

Crops	GDD Units to maturity	Lower Temp. Threshold	Upper Temp. Threshold
Alfalfa	250 to 275	41 oF (5 oC)	86 oF (30 oC)
Corn	2300 to 3000	50 oF (10 oC)	86 oF (30 oC)
Cotton	1700 to 2100	60 oF (15.6 oC)	100 oF (37.8 oC)
Peanut	2000 to 2600	55 oF (12.8 oC)	95 oF (35 oC)
Sorghum	3700 to 4000	55 oF (12.8 oC)	95 oF (35 oC)
Soybean		50 oF (10 oC)	95 oF (35 oC)
Wheat		32 oF (5 oC)	86 oF (30 oC)
Alfalfa Weevil	250 to 300

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