We often talk about evaluating the components of yield from plant population to pod number per plant to seed number per pod and seed size. However, the number of pods a plant can set, retain and grow to maturity appears to be the most promising factor to influence with good management practices. Seeds per pod and seed weight have a much smaller impact on final yield.
There are three facts we should acknowledge:
  1. Dr. Fred Below’s Six Secrets of Soybean Success research has proven that each additional pod added on a soybean plants adds two bushels per acre.
  2. Early planting increases the time before R1 (flowering) and adds more nodes to each plant and more nodes mean more pods.
  3. And we have very little control over how many pods a soybean plan sets by the end of the season; it is almost uncontrollable.
Final pod count is so crucial to final yield that it can’t be overestimated. And unfortunately, it’s also very difficult to track pod numbers in the field because it is so variable across plants. Plant spacing is also quite variable, which leads to variable pod numbers per plant. Earlier in my career I went on the ProFarmer Crop Tour seven years in a row. Scouts on the tour counted soybean pods on 3 plants taken from a row. ProFarmer staff then took those pod counts and miraculously turned them into yield estimates. I can say from experience I would count anywhere from 20 to 100 pods on a plant—so variable that it’s hard to get a true average value of pod count in field.
Back in 2013 the Illinois Soybean Association funded a white paper titled “Improving Soybean Yield: Research into Increasing Soybean Pod Number” authored by freelance agricultural writer Steve Werblow. Werblow highlighted the following points:
  • “Pod number per plant as the yield component was most influenced by change in cultural and environmental conditions.
  • Pod number increased significantly between 1992 and 2006, according to USDA’s National Agricultural Statistics Service … but it is a highly variable attribute.
  • Setting, maintaining and ultimately filling soybean pods is a complex affair, susceptible to disruption at nearly any moment. It is well accepted that soybean plants produce far more flowers and pods than they will ever fill.
  • The plant’s reaction to stress—or, as we’ll soon see, to hormonal shifts that could hint that stressful conditions are afoot—is to jettison pods to lower demands on its threatened resources.  The soybean plant is constantly reacting to its environment by adjusting its pod count, and thus the number of seeds it must fill by the end of the season.
  • Identifying crucial genes and teasing apart the complex, multi-gene traits that enable plants to better endure stress could produce varieties that set and maintain more pods in the face of adversity.
  • Early planting delivers two key benefits to the crop—the opportunity to put more nodes on the plant and the chance to capture more light during the growing season.
  • The role of nutrients and biological agents in the formation of nodes and the stimulation of both vegetative and reproductive growth is an avenue worth exploring.
  • More research needs to be done on the details of proper ratios among the hormones—and the timing of those ideal levels—as well as the best ways to deliver        products that influence hormone levels.
  • Protect the plant and its foliage, adopting the proper strategies to protect against disease and insects that stress a plant and alleviate stress in general.”
At the time Werblow’s article was written (and primarily reviewed my me), it was cutting edge information and provided us with new directions. And six years later, as apparent from the above highlights, we have come to accept and adopt many of these facts in today’s soybean production systems, as evidenced by 80-, 90- and 100-bushel soybeans being produced. Nevertheless, there is still a lot we do not know about what triggers flower and pod abortion and how to abate it in a routine, systematic and predictable manner. Yet early planting, foliar protection and alleviating stress are obvious tools today.
Several more recent articles on soybean pod set have been posted on ILSoyAdvisor (see below).

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About the Author: Dan Davidson

Soybean agronomist Daniel Davidson, Ph.D., posts blogs on topics related to soybean agronomy. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.