New Soybean Inoculants Extend Options, but Often Not Necessary

New Soybean Inoculants Extend Options, but Often Not Necessary

May 1, 2009

Research Shows that Only Select Fields Respond to Inoculation

Several new inoculants for enhancement of nitrogen fixation in soybean reportedly have much higher bacteria cell concentration, longer shelf life with improved adherents and anti-desiccants, and/or two or more strains of Bradyrhizobium bacteria. Inoculation rates are around 1,000,000 bacterial cells per seed.

Inoculation materials may be liquid or dry with similar performance although the liquid products typically have a longer shelf life and are easier to use. With new products, viability of untreated seed can be maintained for a month or longer, and for seven days with some fungicide treated seed. Fungicides that are of relatively low toxicity to the inoculum include Apron® XL, Allegiance®, and Maxim® but seed should be planted within seven days of inoculation.

Soybean Response to Inoculants UNL research conducted from 2001 to 2004 did not show a yield increase with inoculation (see UNL NebGuide Soybean Inoculation: Applying the Facts to Your Fields, G1622). From 2005 to 2008 24 trials were conducted in Ohio with 17 to 23 products or product combinations. The average yield increase with inoculation was about 1.2 bu/ac. Several products were tested in Iowa at two locations in 2007 and 2008 with no yield increases in either year.

The trial results indicate that the probability of profitable response to inoculation is low for most fields. NebGuide G1622 provides an excellent guide to identifying fields with a relatively greater probability of response. Response is likely on fields that

  • are coming out of CRP,
  • had not been planted to soybean for three or more years
  • were flooded
  • are sandy
  • had significant sedimentation last year or
  • have a soil pH below 5.8

Charles Wortman
Extension Soils Specialist