Growing Degree Days (GDD): A tool to track a crop’s growth and development
Growing Degree Days (GDD) is a weather-based indicator used to estimate the growth and development of plants during the growing season. The basic concept of GDD is that crop growth will only occur if the microclimatic temperature exceeds a minimum development threshold, also known as base temperature or TBASE. TBASE is determined experimentally and is unique for each organism. In simple words, GDD is a calculation used by crop producers to measure heat accumulation and predict plant development rates such as the date that a crop reaches maturity.
In the absence of extreme conditions such as drought or disease, plants grow in a cumulative stepwise manner which is strongly influenced by the ambient temperature. The GDD calculation allows producers to predict the plant’s pace towards maturity. Daily GDD values are added together from the beginning of the season, indicating the energy available for plant growth. GDD totals are used for comparing the progress of a growing season to the long-term average and are useful for estimating crop development stages and maturity dates.
GDD calculation:
GDD is typically measured from the start of growth or the start of the season depending on the crop. GDD is calculated each day as the maximum temperature plus the minimum temperature divided by 2 (or the mean temperature), minus the base temperature. GDD is accumulated by adding each day’s GDD contribution as the season progresses. If the average temperature is below the base temperature, the growing degree day value for that day becomes zero.
The maximum temperature is usually capped at 30°C since most plants do not grow any faster above this temperature. However, some warm temperate and tropical plants do have significant requirements for days above 30 °C to mature fruits or seeds. Negative values are treated as zeros and ignored.
Example: For tracking grape development — Imagine a day with a recorded maximum temperature of 30°C and minimum temperature of 20°C. The GDD calculation for that particular day is as follows:
Recorded maximum temperature: 30°C
Recorded minimum temperature: 20°C
Grape’s base temperature: 10°C
Mean temperature = (30°C + 20°C)/ 2 = 25°C
GDD = 25°C — 10°C = 15
So, 15 is the GDD for that particular day for the grape crop. A grape crop will require approximately 1897.8 cumulative GDD to reach maturity as shown in the table below.
Benefits of Using the GDD Calculator Tool:
Different crops require different exposure amounts of GDD or heat units to complete their lifecycle. For some crops, like corn and soybeans, one can actually use GDD to determine at what stage the crop is in its development cycle. This information can be helpful in calculating their growth stage and also in determining the optimum time for crop scouting.
In addition, GDD can be used for a variety of other things including:
- Assessing the suitability of a region for the production of a particular crop.
- Estimating the growth stages of crops, weeds, or even life stages of insects.
- Predicting maturity and cutting dates of forage crops.
- Predicting the best time to apply fertilizers or pesticides.
- Estimating the heat stress on crops.
- Planning the spacing of planting dates to produce separate harvest dates.
How Fasal utilizes GDD?
People often utilize the calendar method to predict plant development for management decisions. However, calendar days are often misleading, especially during early growth stages. Research has shown that utilizing GDD provides a more accurate physiological estimate than calendar days alone. The ability to predict a crop’s growth stage facilitates better crop management. It may be worth mentioning that only slight deviations in development can be expected if the crop becomes limited by mechanisms other than heat, such as moisture.
At Fasal, we provide stage-specific irrigation, insect pest, and disease prediction advisories, in accordance with the crop growth stages. We utilize GDD to track the stage-wise growth and development of the crops. Farmers can utilize this to predict their harvest dates and sell their produce through Fasal Fresh*.
*Fasal Fresh is a new initiative by Fasal, where Fasal customers can sell their produce for a better price and maximize their income.
