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February 19, 2021

Pod Abortion in Parana Soy Attributed to Reduced Solar Radiation

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

There have been two strange occurrences with the 2020/21 soybean crop in Brazil. One is a still as yet unidentified disease in Mato Grosso that seems to cause individual seeds to rot inside of what looks like an ordinary pod. The other is the high amount of pod abortion in soybean fields in the state of Parana.

Scientists at Embrapa Soja (Embrapa Soybeans) released a communication this week addressing the pod abortion situation in western, northern, and northeastern Parana. A similar event of pod abortions was also noted in Parana during the 2017/18 growing season.

Normally, a soybean plant sets excessive amounts of flowers with many of the flowers aborted before turning into a pod. The amount of flowers and pods that are aborted depends on a complex interaction between environment factors and the genetics of the individual soybean variety.

When pods are aborted, it is generally in response to some adverse factor in the environment. Those adverse factors could include: weather conditions such as precipitation, temperature, cloud cover, relative humidity, and the amount of solar radiation as well as cultural practices such as date of planting, weed control, diseases, soil fertility, chemical use, and physical and biological factors in the soil, etc. As you can see, the potential interactions are very complex.

There does appear to be one overriding factor that is the most important and that is a prolonged period of excessive rainfall, overcast conditions, and a lack of solar radiation. In the case of soybeans in Parana, the regions that exhibited the most pod abortion registered 20-25 days of rainfall during January with rainfall amounts of 12 to 16 inches during the month, which was up to twice the normal amount. The heavy rainfall resulted in saturated soils which restricted root respiration resulting in reduced uptake of macro and micro nutrients.

The other major factor was reduced solar radiation due to the constant heavy overcast. The reduced solar radiation resulted in reduced photosynthesis and the production of photosynthate (generally sugars that are broken down to create energy for use by the plant) needed to maintain vegetative and reproductive metabolism. In other words, the plant could not conduct enough photosynthesis to maintain both the vegetative part of the plant and the developing pods, so the plant aborted pods in proportion to the amount of photosynthate available.

In the case of the most drastic pod abortion, yield losses could be in the range of 50% to 100%. In addition, the pods that were retained generally contained seed that were small and under developed. The pod abortion in Parana appears to be a complex interaction between climate, management practices, genetics and it varies by location, soybean variety, and date of planting.