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January 30, 2018

Soybean Pod Shedding in Brazil Explained (maybe)

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

We started reporting two weeks ago that for an unknown reason or reasons, some soybeans in western Parana and southern Mato Grosso do Sul started to shed many of their pods. In the hardest hit areas, the ground was literally covered with pods.

This caught the attention of scientists at Embrapa and after investigating the situation, they have concluded that the problem was a lack of sunshine and excess soil moisture. In southern Mato Grosso do Sul, between December 19th and January 23rd, there was nearly constant cloud cover in the region. During that 36 day period, it rained 30 days. The soybean plants had plenty of water (probably too much in fact), but no sunshine.

The low levels of sunlight resulted in low levels of photosynthesis activity and the plants could not sustain the pod load. In addition, the root zone was saturated resulting in less root respiration and nutrient uptake. When these conditions exist during pod set and pod filling, the plant aborts many of the smaller pods and it reduces the seed size in the pods that were retained. In other words, the plant realizes that it cannot sustain the pod load and it simply aborts many of the pods.

There may also be a variety interaction with the pod shedding. Some varieties may be more susceptible to these conditions than other varieties. I am sure plant breeders probably do not take this into consideration when advancing a new soybean variety. In fact, an important selection criteria is just the opposite - how well does the potential new variety perform under dryer than normal conditions, not under cloudier than normal conditions.

I don't want to make too much of this. Most researchers have never seen this before and we don't know how widespread it is. The extent of yield loss in these fields is unknown. Research has shown that under extreme conditions such as these, yields can be reduced 17% to 26%, but for now, this is just an interesting even, but we don't know the impact on the statewide soybean yield.