Jan 07, 2009
Warmer Temperatures Cause Early Soybean Flowering In Brazil
Author: Michael Cordonnier/Soybean & Corn Advisor, Inc.
Soybean producers in three southern Brazilian states, Parana, Sao Paulo, and Mato Grosso do Sul, have noted that some of their soybeans are very short in height and they summoned researchers from Embrapa to find out why. The scientists determined that the problem was caused by warmer than normal temperatures during the crop's vegetative development and that certain varieties were more sensitive to the warmer temperatures than others.
The types of soybeans that are grown in Brazil are called determinant soybeans. These types of soybeans generally grow to nearly their full height before they start to flower. After flowering begins, there is little further growth of the plant. This is in contrast to the soybeans grown in the northern latitudes of the United States, which are indeterminate soybeans. These soybeans start to flower based on the amount of daylight they receive and they continue to grow taller and flower at the same time throughout the plant's life cycle.
In northern Parana for example, early-maturing and semi-early-maturing soybeans that are planted at the end of October usually start to flower 45 to 50 days after emergence when the plants are generally taller than 60 centimeters (25 inches). This year though, the soybeans started to flower 25 to 30 days after emergence when the plants were approximately 30 centimeters tall (12-13 inches). It turns out that the temperatures in northern Parana during the month of November were approximately 10% warmer than normal. During the month of November, there were 18 days where the nighttime temperature exceeded 19 degrees C and there were 12 daytime temperatures that exceeded 30 degrees C, both of which are approximately 10% warmer than normal.
Short stature soybeans were also observed in Mato Grosso do Sul and the scientists found a similar temperature profile in that state as well. In the city of Dourados, which is the main soybean growing region of Mato Grosso do Sul, between October 16 and November 25 the daily maximum temperature surpassed 33 degrees C on 23 days and the nighttime temperature surpassed 22 degrees C on 26 days. Both of these temperatures are approximately 10% warmer than normal.
For soybeans, there is not a direct correlation between the height of the plant and the final yield. Soybeans that are tall in stature may have a low number of pods and the eventual yields may be disappointing. On the other hand, some short stature soybeans may have a heavy pod set and end up having an excellent yield. The yield of soybeans is determined by the number of pods, the number of seeds per pod, and the size of the seeds. The growing conditions have been very good in the areas where the short stature soybeans have been observed and farmers in the region are still expecting average to above average yields even though the soybeans are shorter than normal.