Evaluation of Soybean Yield Response to Existing Rhizobia Populations and the Use of Inoculant Products.

Evaluation of Soybean Yield Response to Existing Rhizobia Populations and the Use of Inoculant Products

Rhizobial inoculants are used to encourage biological nitrogen fixation (BNF) during production of soybean [Glycine max (L.) Merr.].  Given the variability of inoculant efficiency, development of a rhizobia soil test could assist producers in the decision making process surrounding inoculant use and allow for further research opportunities.  The objectives of this research were 1) to evaluate soybean yield response to residual soil rhizobia populations and 2) to evaluate the performance of seed applied rhizobia inoculants in various production environments.  Field trials were established at nine locations throughout Wisconsin in 2009 and 2010, and additionally on three sites (2009) which had been flooded (standing water) for greater than three weeks during the 2008 growing season.  At each trial location soil samples were collected at the time of planting and rhizobia populations were quantified using quantitative (real-time) polymerase chain reaction (qPCR).  Across all flooded sites, seed yield and protein and oil content did not respond to seed treatment.  Seed yield and protein content were negatively correlated to the initial rhizobia population, and seed oil content was positively correlated to the initial rhizobia population.  Preliminary results from the wide area testing indicated a yield advantage to using rhizobia inoculants, but no seed protein or oil content response.