Soybean Research

Assessing new soybean “biostacked” inoculant technology
Horst Bohner, OMAFRA; Dr. Hugh Earl, University of Guelph

Soybeans require a significant amount of nitrogen to produce a high yielding crop. A 50 bushel per acre crop requires 210 pounds per acre of nitrogen. About 75 percent of that nitrogen comes from nitrogen fixation. Once the nitrogen fixing bacteria are established in the soil they will survive in the ground for many years. At present about 60 percent of Ontario soybeans receive an annual application of inoculants. Research conducted with older inoculant formulations confirmed that yield gains were inconsistent and very small if the field had successfully grown soybeans in the past.

Advances in inoculant technology have provided new soybean inoculant technology called “pre-inoculants”. These products contain highly efficient strains of bacteria and “extenders” that prolong the viability of inoculants. Seed can be treated before it is delivered to the farm. Reduced inoculation procedures at planting time and excellent coverage are significant advantages to the grower, compared to traditional drill box application. These high quality inoculants provide between 800,000 and 1,400,000 bacterial cells per seed, much higher concentrations than were previously available.

Researchers from Ohio State found yield gains to be common in productive fields with a history of soybeans. The average yield response from 64 Ohio trials was 1.9 bushels per acre from all inoculants tested. At a cost of $3.00 to $4.00 per acre (depending on the seeding rate) a ½ bushels per acre yield increase could be considered “break even”. Researchers from Ohio suggest a profit of 300 percent compared to the investment when using an inoculant. Some states such as Michigan, Indiana, and North Dakota have also found average gains ranging from 1.0 to 2.7 bushels per acre in fields with a history of soybeans. Other regions have found much lower gains.

In Ontario, 16 field trials were established in 2007 to assess the efficacy of two pre-inoculants in fields with a history of soybeans. Another 12 sites were conducted in 2008. A variety of soil types, yield potentials, crop rotations, and environments were chosen.

Statistically significant yield differences were found between the untreated and the inoculant treatments. No statistical difference was found between the two inoculants. The average statistical yield gain of the inoculants compared to the untreated control was one bushel per acre across the two years. At a selling price of $10.00 per bushel and a yield gain of one bushel per acre a return of $6.67 per acre would be realized when using an inoculant. (Assuming a cost of $3.33 per acre for the inoculant)