Maximizing soybean yields starts with understanding how nutrients move within the plant. While soybeans are known to remobilize nutrients from lower leaves to developing nodes, researchers are still uncovering the specifics of how, when, and which nutrients are available to these new nodes. An Illinois Soybean checkoff-funded study is tackling this challenge by using tissue testing to better inform nutrient recommendations during the growing season. 

Dr. Fred Below shared an update on the first year of the study: “Our tissue test data clearly show that different nutrients behave differently within the plant. Nitrogen concentrations consistently decrease over time, while phosphorus levels drop faster before stabilizing. Sulfur, on the other hand, decreases in the lower canopy, maintains a steady state in the middle canopy, and then decreases again later in the season, while accumulating in the upper canopy.”

Dr. Fred Below and Dr. Connor Sible (Photo provided by Illinois Soybean Association)

Another important finding was related to boron. “Boron doesn’t move from leaf tissues,” Dr. Below explained. “This explains why some growers apply boron, see their tissue tests improve, but may not actually see a yield benefit.” The data suggests that these applications may not be improving yield as much as they’re just influencing tissue test results. 

One key takeaway from the first year of research is the identification of the most “mature” trifoliate—the third to fourth nodes below the terminal bud. This is different from the commonly tested second to third nodes, which may not provide the most accurate nutrient information. 

Looking ahead to the 2025 growing season, researchers will include labeled nitrogen and sulfur to track how these nutrients are utilized by the plant. This will help answer important questions: Does the plant use fertilizer nutrients before those from the soil? And how do these nutrients move within the plant—do they travel from the older canopy to the newer canopy or directly to the developing pods? 

These findings have the potential to help farmers make more accurate in-season nutrient decisions, ultimately leading to better yields and more efficient nutrient use. 

As this study progresses, more valuable information will be gathered that could directly impact your soybean management practices. To stay up-to-date on the latest findings and learn more about how tissue testing can maximize your soybean yields, visit the Field Advisor Research Hub. 

For those interested in participating or sharing field data, don’t hesitate to reach out. Your involvement could help shape future recommendations and optimize nutrient management across Illinois soybean fields.