What happens to soybeans when frost occurs at the R6 stage?

April 14, 2021

Frost can affect soybean crops, depending on their stage of growth. The extent of the damage—either major or minor—will also vary with the length of time at which they are exposed to frost.

In this article, our team briefly explains the effect of frost on soybeans at a specific growth stage: R6. 

The impact of frost on soybeans: an overview

Lower temperatures damage soybean plants by causing ice to form between and inside the cells. The water surrounding the cells is first to freeze, followed by that inside the plant’s cells.

Soybeans, whose reproductive development growth stage is divided into 8 phases, is easily damaged by frost before it reaches the R7 growth stage. In addition to directly affecting the seed’s germination energy, frost is also likely to significantly reduce yield.

The impact of frost on soybean yield

The soybean yield is reduced when frost occurs at or before the R6 stage. Studies have shown that earlier maturing varieties are subject to greater losses in yield due to frost occurring at later growth stages than it would with later maturing varieties.

Frost at or before the R6 stage reduces the number of soybeans per plant, as well as the plants’ height. These consequences inevitably result in a reduced yield overall. 

The impact of frost on soybean germination

The impacts of frost on soybean germination has no impact on the percentage of seeds that germinate for plants affected by frost, regardless of whether the frost is before or after growth stage R6, despite their water content at the time of freezing. The higher their water content, in combination with less advanced growth stages, the greater the damage frost will cause. The seeds that are still green and have not reached physiological maturity will not germinate. A large number of these seeds in a seed lot will affect its germination percentage. 

However, soybean seeds from plants affected by frost have shown low seedling emergence scores. These plants’ seeds are also more susceptible to fungal attacks. 

The impact of frost on soybean protein

The effect of frost on the soybean’s protein is a cause for concern. It has been shown, however, that frost does not affect the protein content of mature seeds at stages R6 to R8. That said, a significant reduction in protein content has been observed in soybean seeds that froze before and around growth stage R6. 

How to adjust the combine harvester to harvest soybeans damaged by frost

Soybeans that have been damaged by frost contain more moisture than normal. Consequently, seed pods containing these seeds are a lot more difficult to thresh with a combine harvester and there are certain handling rules to follow.

To ensure an optimal harvest, the combine harvester should be adjusted to suit the situation. The first step is to lower the clearance of the tractor’s rotary combine.

After this step, if adequate threshing has still not been achieved, it is recommended to increase the speed of the combine or rotor and to make these adjustments progressively.

Frost doesn’t necessarily mean game over for your soybeans

Frost damages soybeans when it occurs at or before the R6 growth stage. However, the damage caused by frost is limited in plants that have reached growth stages R7 or R8.

There are a number of recommendations soybean producers can follow to reduce the adverse impacts of untimely frost. To learn about these recommendations, we invite you to contact us. You can also visit the Blog section of our website to learn more about the world of soybeans 

Have a great harvest!