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Predicting Soybean Maturity (R8) (06/16/16)

A model has been developed to predict the maturity date of soybean to be used by eastern North Dakota and northwestern Minnesota growers.

Predicting Soybean Maturity (R8)

A model has been developed to predict the maturity date of soybean to be used by eastern North Dakota and northwestern Minnesota growers. The new tool is part of the North Dakota Agricultural Weather Network (NDAWN) applications and can be found at Soybean Growing Degree Days.

In North Dakota, soybean varieties with a relative maturity (RM) of 00 (double zero) are adapted for production in the most northern parts of the state, while group zero (0) and the early group one (1) are adapted for the southern part of the state. Each variety is classified with a 0 to 9 decimal number following the group number. A variety designated as 0.1 could be grown in the northern part of the 0 (zero) RM zone, while a 0.9 RM variety can be grown in the southern part of the 0 maturity zone.

Soybean growth stages are divided into vegetative and reproductive. The soybean development stage with one pod on the main stem with a mature color is called ‘beginning maturity’ or R7. The R8 stage is defined as 95% of the pods on the plant having reached the mature color and is called full maturity. The new model predicts the maturity at the R8 growth stage and is based on growing degree days (GDD), also called growing degree units. This model was developed to predict the soybean maturity date (R8) based on accumulated GDD from the planting date. Based on 1816 data points, a regression analysis was performed which predicted 1694, 1890, 2058 AGDD to maturity for 00.8, 0.5, and 1.1 RM soybean, respectively.

Northern soybeanplsc.kandel.1 cultivars are limited in growth duration due to the short growing season. Soybean plants may show freeze damage when the air temperatures fall below 32 °F and in North Dakota a killing frost is possible in the second half of September. Therefore it is important that growers select varieties that will be mature before the fall freeze.

For model predictions, agriculturists can select the nearest North Dakota Agricultural Weather Network (NDAWN) station, RM for a variety, and date of planting to predict the maturity date (Figure 1).

The output provides the predicted maturity date, as well as average first day of various frost risks (≤ 36 F, ≤ 32 F, and ≤ 28 F) at the 50% probability level (Figure 2).(Next Page)


In case of dry planting conditions, and the seed is slow to germinate, the selected planting date in the model can be adjusted to another date. For instance, it can be set to a date 5 or 6 days before observed germination date. This will provide a more accurate prediction of the maturity date.

Wet or dry conditions may influence how quickly the crop matures in the fall, and therefore the predicted maturity date for this model may be slightly different depending of the late season weather conditions.

This Soybean model will help growers to evaluate their risks associated with a projected maturity date and frost dates. The model was developed for use by farmers and agriculturist in eastern North Dakota (east of the 100° W longitudinal line in central North Dakota, which runs very close to Highway 83) and northwestern Minnesota.


Hans Kandel

Extension Agronomist Broadleaf Crops


Adnan Akyüz

NDSU State Climatologist


This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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