Harvest is over and many producers were not satisfied with soybean yields. As we begin planning what we might do for next year, some producers are thinking the answer may be in adding a biological inoculant.  Before committing to a product, producers should consider the following studies.

This is reprinted from a Dakota Dirt article from 2010.  Many of these products have never been tested by an unbiased source. SDSU tested a number of products marketed for soybean in 2009, (the source and components / contents of the products tested are given in Table 1).   The study was partially supported by the South Dakota Soybean Research and Promotion Council.  The details of this study are provided in the footnotes of Table 2. 

Grain yield was not significantly influenced by any of the products tested (Table 2).  In addition, any additive effect of using all the products together was not significantly different from the check.  Of course we need rhizobium inoculant to fix N for our soybeans. So why didn’t we see a response to the Rootastic product? The sites were in a corn soybean rotation so soil rhizobium would be abundant. Some studies show viable rhizobium up to 12 years after the inoculant was applied.  However, most producers will use rhizobium with every soybean crop planted because of the low cost and the “insurance” factor.

Table 1. Product list for soybean studies at SE Research farm (Beresford) and Brookings SD in 2009.

Table 2.  Influence of several biological inoculants and other products for soybeans on soybean grain yield at SE Research farm and Brookings in 2009.