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August 28, 2019

Cool Temperatures slow U.S. Soybean Crop Development

Author: Michael Cordonnier/Soybean & Corn Advisor, Inc.

The weather has improved over the last several weeks in general, although not everyone has received the rains they needed. There has not been any excessive heat and in fact, there is a definite "fall like" feeling to the weather.

Recent temperatures have turned cool and pleasant, which is good for humans, but not the best type of weather for late developing soybeans. Warmer temperatures would be better for the soybeans as long as it is not excessive. Ever since the soybean planting was so delayed last spring, I thought the soybeans would run a greater risk of a disappointing yields this year than the corn. Results from last week's Pro Farmer Crop Tour illustrated the sub-par performance of the soybeans, at least up to this point in the growing season.

The Pro Farmer 2019 U.S. soybean yield was 46.1 buy/ac +/- 2% (47.0 - 45.2 buy/ac) with a total production of 3.49 billion bushels. For the seven states they surveyed, the pod counts were down about 15% from their 3-year average.

It is always very difficult to judge soybean yields because it is a "work in progress" until the crop matures. Under the right conditions, the plant can keep adding pods and the seed size can also be influenced by the weather late in the season. Additionally, frosts can also influence the final yield.

One of the questions concerning the soybeans is how soon will the soybeans in the Corn Belt start turning yellow? Once the leaves start to turn yellow, there is no more yield gain and the soybeans seeds start to lose water. Last year on August 27, 2018, 7% of the soybeans were dropping leaves compared to 5% in 2017 and 4% for the 5-year average. So, some of the earliest soybeans in the Corn Belt could start turning color this week.

The relationship between day length and the soybeans turning yellow is not a straight line. Generally, for every week that planting is delayed, the soybean maturity is delayed one day. Additionally, the amount of rainfall and the temperatures can also impact the rate of maturity. If the weather is very wet, the soybeans stay green a little longer. Conversely, if the weather is very dry, the soybeans generally mature a little early. If the temperatures are cool, it may take a little longer to mature.

The soybeans are 94% blooming compared to 100% last year and 99% for the 5-year average. The soybeans are 79% setting pods compared to 94% last year and 91% for the 5-year average.

It is normal for double crop soybeans to start blooming late in August. What is not normal is for full season soybeans to not start blooming by the end of August. In Indiana, Ohio, and Michigan, there is still 10-11% of the soybeans that have not started to bloom much less set pods.