How to track growing degree-days, precipitation and phenophases

5 min readJun 7, 2019

We added charts of growing degree-days and accumulated precipitation to the free OneSoil web platform for precision farming. From now on, you can check the amount of heat and precipitation your fields receive and evaluate the change of these indicators. And (hooray!), you are able to leave notes and mark the phenophases right on the chart! All the data about your crop development is now available in one place.

Growing degree-days

What it is

For growth and development, the plant needs heat. To enter the new stage of the development, or phenophase, every plant requires a specific amount of heat. Growing degree-day (GDD) is a measure of heat the plant has accumulated to date. For instance, in Belarus, for alfalfa to bloom it needs 400–475 degree-days, and for spring wheat to emerge 67 degree-days are needed. During the colder-than-usual years, the plant will need more time to accumulate the required amount of growing degree-days; during the warmer-than-usual years — less time.

How we calculate it

We build a chart from the sowing date which OneSoil web-platform users have to record themselves. We use the following formula:

– Add each day’s maximum and minimum temperature

– Divide the sum by two to get the average temperature

– Subtract the base temperature for the plant

The base temperature is the minimum threshold below which the plant development stops. For instance, for wheat it is +5 С° — only above this temperature does the vegetation begin. For different crops in different countries, base temperatures may vary. Our agronomist Philip Kondratenko collected information from a bunch of sources and created a pivot table for the base temperatures; we use it when building charts of growing degree-days in the OneSoil web-platform.

I relied mostly on the research of American universities. In particular, Montana State University and The University of Georgia. Also, I used USDA data along with data from several weather networks like NDAWN. I looked for publications of research institutions on crops that are specific to certain regions. For instance, papers from Australia and Brazil helped us to determine the base temperature for cotton. All the discoveries make up the pivot table which holds info on 100+ crops; mainly the base temperature equals to +5 С° or +10 С°.

Philip Kondratenko

Where we get weather data from

We have two sources of information. We use historical data collected by the NOAA, and the actual weather forecast for 5 days is provided by the DarkSkycompany. The historical data is available up to the year 2000. This information helps to understand how the weather contributed to crop development in the past and how it may affect plants in the future.

If you want to know the precise weather forecast, it is better to use local weather sensors; it will significantly increase the forecast’s accuracy. We have developed and assembled affordable weather sensors that measure air humidity and soil moisture, the temperature of both soil and air, and light intensity for a part of the field. The first hundred of these sensors are being tested in the fields of Belarus, Ukraine, Germany and the USA. If you want to order a sensor, please fill out this Google Form.

Notes and phenophases

Growing degree-days allow us to predict plant phenophases. This info is crucial for planning field works such as fertilizer and pesticide application, as well as harvesting. Using our GDD chart, you can easily add notes and track phenophases, which is really cool.

How to use notes

11 Save all the info in one place
The crop, the season, sowing date, harvest date, precipitation, growing degree-days, weather forecast, field operations, phenophases — you can keep all the records on plant development in one place. This data will never be washed away with the rain or eaten by your dog (as it so often happens to paper notes).

22 Analyze the weather impact on crops
You can analyze how the weather affected plant development. When determining the required amount of degree-days for a crop, we usually rely on books and research. Keeping your own records will allow you to rely on your own experience.

33 Predict phenophases
If you have data on phenophases for several years, you can better understand when a particular stage will begin. When using our charts, you can easily switch between years.

To describe the phenophases, we use the BBCH international scale. It was developed in 1992 by several German state institutions. It is a kind of universal language for farmers and agronomists around the world. The BBCH scale has several important advantages over other similar scales. First, it is very detailed — for the main crops, the scale describes 70–100 stages of development. Secondly, it is international — there are official translations in English, French and Spanish languages. It is also used by large producers of seeds, fertilizers and pesticides in their product descriptions; thus helping to spread the BBCH scale in the world.

On the OneSoil web platform, farmers can make notes on the phenophases for eight groups of crops (cereals, canola, grapes, corn, beets, cotton, soybean and sunflower) in seven languages (English, German, French, Italian, Spanish, Portuguese and Russian). The list of crops and languages will be expanded in the course of time.

The chart of accumulated precipitation

For building the charts, we once again use weather data from NOAA and DarkSky. The charts of accumulated precipitation allow us to evaluate the soil’s moisture reserve. Using this information, you can predict the yield and calculate fertilizer rates more accurately.

The chart of vegetation change

There is also a chart that shows the change of the NDVI index for each day (if there was a clear satellite image). The purple line stands for the average value of the NDVI for a field. The upper and the lower points of the light-purple range indicate the maximum and the minimum NDVI values for the day. If you want to see the visual representation of the NDVI index, simply choose the day and click on the chart. In a separate browser window, the field photo with the NDVI visualization will open.

If you have any questions regarding the charts, the OneSoil web platform or the meaning of life — post a comment or reach out to us at




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