ILSOYADVISOR POST

Understanding the Road Map of Soybean Reproduction

Planting soybeans can sometimes be simple, however growing soybeans can be challenging, and growing 100 bu soybeans consistently can be very challenging. Over the last 10 years, there have been major leaps forward in improving soybean genetics and agronomic practices. I always challenge growers to be a student of their fields and that if they are listening, their fields are telling them what’s wrong, but only if we’re willing to listen. As a soybean producer, it’s important to evaluate what you’re seeing or not seeing in a particular field and start asking the question of why.

 

As most know, the reproductive stages of a soybean plant includes many different stages and depending how well a plant survives will determine the outcome. Below is a short roadmap of how the reproductive stages work and notes on the areas you can influence the most to improve yields. 

 

1. Understand soybean reproduction.

A soybean plant will produce a cluster of blooms at nodes on the main stem and on the branches. Unlike a corn plant, a soybean has both male and female parts located in the blooms. Plants self-pollinate, and pollination will occur within the flower. Once a pod grows to R6, the plant has made a commitment to supporting it. Therefore, stress during R2-R5 will have a strong influence on final pod counts.

            -Minimize weed pressure

            -Minimize nutritional deficiencies

            -Minimize herbicide application

 

2. Build blooms and pods.

Photosynthates are carbon-based compounds produced during photosynthesis that are used to produce starch, oil and protein in the seed, and produce the weight that growers harvest. The plant will make necessary adjustments along the way based on the demands of growth for energy. However, if a plant aborts blooms and pods and then growing season conditions improve during the R4-R6 stages, the plant can either remobilize and/or produce more photosynthates to make the bean seeds bigger or support new pod growth at the top of the plant. In the 2012 drought, growth and pod set was limited. However, when the rain returned in August, plants came back to life, filled a new crop of pods near their tops and the resulting seeds were larger than average. These top pod clusters are sometimes called the “August Bonus.”

 

3. Minimize stress.

Single stress events typically don’t have a large impact on bloom/pod retention or even yield, however compounding stress can have a major impact. Therefore, when implementing modern agronomic practices, adopt strategies to either prevent or reduce as much stress as possible. By doing so, when a singular or compounding, non-controllable stress appears, the soybean is better equipped to fight through the stress. 

 

4. Ask yourself—how and why is yield at risk?

A soybean seed is comprised of a high concentration of proteins, which are compounds of carbon, hydrogen, oxygen and nitrogen that form amino acids.

  • Amino acids are rich in nitrogen; therefore, a soybean plant will have a high demand for nitrogen, about five to six pounds per bushel.
  • A soybean plant is a C3 crop (corn is C4), which indicates how carbon is metabolized during photosynthesis. C3 plants are often considered carbon limiting because they are not as efficient at capturing carbon dioxide from the atmosphere. And stresses will further compromise their ability to capture carbon dioxide and produce the metabolites necessary to build oil and protein.
  • During R1-R6, compounding stresses can make an already less efficient process worse. A plant will realize it’s been compromised and will adjust accordingly: bloom abortion, pod abortion, reduced seed count or reduced seed weight.
  • Hot and dry conditions can make this process even less efficient because of photorespiration and carbon losses, requiring more energy to metabolize carbon.
  • Research has shown this process can reduce photosynthesis output by nearly 25 percent. This directly correlates to a plant’s ability to retain blooms, pods and yield. 

Todd Steinacher
Steinacher is an ISA CCA Soy Envoy alum and currently supports ISA on agronomic content as well as serving as an Illinois CCA board member. He was recently awarded the 2020 IL CCA of the Year & the 2021 International CCA of the Year. He has over 15 years agronomic experience, currently working with AgriGold and GROWMARK previously. Steinacher has an associate degree from Lincoln Land Community College, a B.S. in agronomy and business from Western Illinois University and a master’s degree in crop science from the University of Illinois at Urbana-Champaign. If you have any questions for him about this article, he can be reached at steinacher@ilsoy.org.


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