"Soil testing has proven to be a reliable tool to guide fertilizer recommendations. However, growers are looking for additional ways to confirm that soil and fertilizer applications are meeting the nutritional needs of the soybean plant to maximize yield," said Nathan Mueller, an assistant professor and SDSU Extension Agronomist in SDSU's Plant Science Department.

Mueller and his colleagues are working to help soybean growers find those answers. Through a partnership with the South Dakota Soybean Research and Promotion Council, SDSU researchers are focused on improving our understanding of plant nutrient analysis, commonly called tissue testing, as a tool to monitor soybean plant nutritional health.

Mueller explains that soybean plant nutrient analysis research in Ohio and Illinois back in the 1960's generated guidelines for the amount of a particular nutrient a healthy plant should have, called a sufficiency range. These sufficiency ranges were determined from a specific plant part, called a trifoliolate or leaf, during flowering prior to pod set.

Mueller says this is similar to human health screenings that determine if someone has a normal or sufficient range of iron and glucose in their blood.

What's surprising - and concerning - is that the same nutrient sufficiency ranges for soybean have been used without much alteration over the last five decades.

Thus, Nathan Mueller and fellow researchers Ron Gelderman, Peter Sexton, Anthony Bly, and Jixiang Wu have initiated a three-year project to analyze nutrient sufficiency ranges for South Dakota soybeans.

The 2013 field season marked the first year of the project. Eleven small-plot trials and six field length strip-trials were established with farmer cooperators and AES research station managers across eastern South Dakota.

The SDSU researchers are particularly interested in soybean phosphorus nutrition, one of the most limiting nutrients for soybean yield in South Dakota, says Mueller. An additional trial will assess 12 varieties on a weekly basis throughout the growing season to determine nutrient concentration changes in leaves and leaf stems.  

Mueller concludes, "Crop consultants and farmers compare the lab values or concentrations to these nutrient sufficiency ranges to determine if the plant is deficient or sufficient, so it is important to collect the proper plant part at the right growth stage to allow us to compare apples-to-apples. Educational materials being developed from this research will ensure growers have good guidelines for determining soybean nutritional health for the future."