There has been a renewed interest in taking samples of soybean leaves for nutrient analysis as a quality control tool to ensure soil and the fertilizer programs are meeting the needs of the plant to eliminate nutrients as a yield limiting factor.

Most soybean fields are at the correct growth stage to take a leaf sample for nutrient analysis as highlighted in the new video, How to take a soybean leaf sample for plant nutrient analysis.

Most soil labs also can conduct plant nutrient analysis. Per sample, the lab cost is about $34 (not including shipping) to run for all 13 plant nutrients or about $26 dollars if chloride and molybdenum are left out (the more common option available).

Once you choose a lab and mail your sample, it should take a week or two to get your results back. Nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), chloride (Cl) will be reported in percent (%) and copper (Cu), iron (Fe), manganese (Mn), zinc (Zn), boron (B), and molybdenum (Mo) reported in parts per million (ppm).

Additional Considerations
About Plant Analysis Interpretation

If any of your nutrient values are below the sufficiency range (Table 1), your next soybean crop may or may not benefit from management changes (drainage, inoculation, fertilization, variety selection, etc.).

Plant nutrient concentrations are sensitive to the environment and vary by variety. Analysis results should be used cautiously or not at all if plant samples were taken under extreme drought conditions, after flooding, or from damaged plants, i.e., herbicide carryover.

However, a properly collected trifoliolate-leaf sample for monitoring soybean nutrition during the growing season is an additional tool besides regular soil testing efforts to assess soil fertility.

The information is mostly useful for making future changes to your fertility program and management, not in-season. Most importantly, soil test are needed to generate fertilizer rate recommendations because plant analysis cannot tell us how much fertilizer to add.