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Research Highlights
Where’s the Protein?

Photo: United Soybean Board

By Lisa M. Balbes, Ph.D.

Have you ever wondered if seeds from different parts of the soybean plant had different compositions of protein and oil? Well, maybe you should, because they do.

Genetics, environment and management practices can affect overall soybean yield, as well as changing the concentration of protein and oil, by up to as much as 20 percent.  In addition, these factors affect how many branches the plant produces, how many pods are on those branches, and many other (often related) characteristics. For example, low plant density encourages more branching, but the seed pods on those branches often flower and set later than seed pods on the main stem. 

Given these differences, is it somewhat surprising that few scientific studies have looked at the relationship between plant branching and the distribution of protein, oil, and other components at different canopy portions (main stem vs. branches). Back in 1956, Collins and Cartter found that the oil content of soybeans changed depending on the position of the pod on the plant, and the position of the seed in the pod. However, very little work has been done in this field since then, more than half a century later.

Until now, that is. 

Researchers at Kansas State University led by Dr. Ignacio Ciampitti and his lab recently conducted an investigation of how the amount of yield, protein, oil, amino acids and fatty acid varies throughout the soybean plant (Rosso, Reis and Ciampitti 2021).

The researchers looked at four different soybean varieties, planted over two growing seasons, and treated according to current best agronomic practices. At maturity, seeds were collected separately from the upper, middle, and lower stem, and from the branches, making four sampling regions per plant.

Detailed statistical analysis revealed some interesting patterns in the distribution of oil, protein, and other components throughout the soybean plant. 

  • Unsurprisingly, greater branching of the soybean plant led to higher yields, as the seeds from the pods on the branches added to the overall quantity.
  • Within the main stem, seed number remained fairly constant, but seed size decreased from top to bottom of the plant.
  • Seeds from the upper main stem contained 25 percent more protein and 15 percent more oil than seeds from the lower main stem.
  • Oil concentration was 3 percent greater in the lower main stem then in the upper main stem, while protein concentration was 9 percent lower in the lower main stem.
  • Seeds from branches had lower oil concentration, lower levels of limiting amino acids, and lower fatty acid ratio (oleic over linoleic plus linolenic) than the main stem.
  • Higher quality protein (abundance of limiting amino acids) was found in the lower stem.
  • Higher oil quality (better fatty acid ratio) was found in the upper main stem.

It remains to be seen how these variations play out in other soybean varieties, and under different environmental and management conditions, and highlights the fact that there is a lot to learn about the contribution of different canopy sections to soybean quantity and quality. 

“Because separating upper and lower canopy with the current harvesting machinery is impossible, growers should look at canopy architecture, especially branching, as important factor of soybean quality. Management practices such as variety selection, planting date, density, and arrangement are critical for defining soybean architecture, but future research has the challenge of exploring changes on architecture at similar yield levels,” Ciampitti says.

“This work is critical to understand the main opportunities for potential improvements to both yield and seed quality simultaneously, emphasizing the need to increase the market value of our U.S. soybean production.”

References

Vertical Canopy Profile and the Impact of Branches on Soybean Seed Composition.
Luiz Henrique Moro Rosso, André Froes de Borja Reis and Ignacio Antonio Ciampitti
Frontiers in Plant Science, September 2021, Volume 12, Article 725767
https://www.frontiersin.org/articles/10.3389/fpls.2021.725767/full

Variability in Chemical Composition of Seed From Different Portions of the Soybean Plant.
F. I. Collins, J. L. Cartter
Agronomy Journal, Volume 48, Issue 5, May 1956, Pages 216-219
https://doi.org/10.2134/agronj1956.00021962004800050006x

This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.