Tissue testing has been a tool for detecting nutrient deficiencies in soybeans, but new research funded by the Illinois Soybean Association checkoff program suggests it may be time to revisit how those samples are taken. 

Dr. Below and Dr. Sible tissue testing in a field near Champaign. Photo provided by Illinois Soybean Association

Dr. Fred Below and Dr. Connor Sible of the University of Illinois are leading a study to evaluate whether current tissue sampling guidelines still hold up under modern soybean production systems. Their work explores how nutrients move through the soybean canopy and whether current sampling methods are truly capturing the full picture. 

Traditional recommendations advise sampling the “most recently mature trifoliate” at the top of the plant. However, because soybeans display indeterminate growth, producing new leaves even as pods develop, this approach may miss early deficiencies in the lower canopy. 

To test this, the research team conducted detailed tissue sampling every 10–14 days between the V7 and R6 growth stages. By analyzing both leaf and pod nutrient levels, the study aims to offer a more complete view of nutrient remobilization throughout the plant. 

Early Findings Show Seasonal Shifts 

Initial results suggest: 

• In early vegetative stages, the 3rd or 4th trifoliate below the terminal bud is the most mature and reliable leaf tissue to sample. 

• During later reproductive stages (R4–R6), upper trifoliates continue growing while lower leaves begin to drop, potentially skewing nutrient readings. 

This means leaf maturity, and the accuracy of tissue testing, may shift as the plant develops, especially after the R3 growth stage. 

While the research is ongoing, current tissue testing practices remain valid: sampling the 3rd or 4th trifoliate below the terminal bud through R3 still offers the most consistent results. 

As the study progresses, findings may lead to more precise sampling recommendations—especially for farmers using in-season application tools like undercover nozzles. This information could improve nutrient management decisions and ultimately contribute to better yield and input efficiency. 

This project represents another example of how Illinois Soybean Checkoff investments are delivering data-driven solutions to support Illinois growers in the field. For the latest update on this project, visit Field Advisor’s Research Hub.