Soybean inoculants increase nodulation and fix nitrogen
Weather extremes at planting, such as too little or too much moisture, are a sign your soybean crop might benefit from a commercial inoculant, a biological product made of living microorganisms called rhizobia.
Rhizobia help soybeans boost nodulation and fix nitrogen, says Russ Berndt, legumes and northern crops product manager with Becker Underwood, now part of BASF. "This leads to a more robust root structure, better nitrogen fixation and more yield potential," Berndt explains.
He estimates 50% of soybean seed in the U.S. is treated with a commercial inoculant, and that’s trending up.
Arthur, Ill., farmer Cory Green saw a return on investment from seed inoculant in 2012, despite the historic drought that plagued the Midwest.
"We saw a 1-bu.- to 2-bu.-per-acre yield increase," says Cory, who owns Heritage Family Farms with his brother, Justin, and dad, Mike.
The Greens have used an inoculant on seed beans the past three years. Their strategy is to use one on early planted soybeans and in soybeans after continuous corn. "That’s when we see the best yield results," Cory reports.
A yield increase of 2 bu. to 3 bu. per acre from an inoculant is common under either of those scenarios, he says, based on side-by-side comparisons of treated versus untreated seed.
The Greens do not use an inoculant for soybeans strictly planted in a corn–soybean rotation. "That’s not to say you shouldn’t, but we haven’t seen enough yield to justify it," Cory says.
Vince Davis, University of Wisconsin cropping systems Extension specialist, says a 1-bu.-per-acre yield increase from inoculant use is common. "With beans at $13 per bushel and a $2 to $4 per acre cost [for the inoculant], it takes very little yield benefit to pay for itself," he says.
Nodes for nitrogen. Inoculants also offer benefits beyond yield, Berndt notes. Well-nodulated soybeans produce an average nitrogen credit of 40 lb. per acre. This nitrogen is in the soil, in a highly stable form, and available for use by the next year’s crop.
The potential payoff from a soybean inoculant increases in one or more of these five scenarios,
according to Iowa State University Extension research:
- Seed Guide 2013