“We had a very, very wet fall and rhizobial bacteria do not survive wet conditions well at all,” says Jim Beuerlein, retired Ohio State University extension agronomist and technical advisor to inoculant manufacturer Becker Underwood. “And, I’ve already seen some long-range forecasts for a wetter-than-normal spring planting season.
“Those factors lead me to believe there will be a good response to the use of soybean inoculants, or enhanced soybean treatments that contain a rhizobial component, this year,” Beuerlein says. “We always expect a positive response to inoculants, but these abnormally wet conditions across the Corn Belt will likely result in a greater response than usual.”
The process of inoculation is the application of commercially available rhizobia bacteria to the seed or into soil where a legume, such as soybeans, will be planted. Rhizobia are the key active ingredient in most legume inoculant products.
The presence of rhizobia is necessary for a legume to be able to convert atmospheric nitrogen into a form usable by the plant. This process is referred to as nitrogen fixation.
Beuerlein has evaluated rhizobial inoculants in hundreds of field trials over many years and reports an average yield increase of 1.94 bushels per acre for inoculated seed. “Of course, we saw premium quality products which did much better than this average, and some questionable products that showed little or no advantage,” Beuerlein says.
“Most evaluations are performed in fields that essentially offer optimum growing conditions for soybeans – fields planted to a corn/soybean rotation – and we’ve still seen an average yield advantage of nearly two bushels per acre,” Beuerlein says. “In many instances, I believe soybean growers could see even better results in their own fields, especially when using a quality product that provides high rhizobia counts.”
Beuerlein offers the following tips for soybean growers considering the use of a soybean inoculant, or enhanced soybean treatments containing a rhizobial component, in 2010. “Give the product a try in a side-by-side comparison and be sure to keep the evaluation honest,” he says. “Have a professional apply the product so the beans are uniformly treated at the correct rate. It’s very easy to either over-apply or under-apply which can create planting problems or failure to achieve the expected response.”
A second important step, Beuerlein says, is to plant the beans soon after treatment. Viability of the rhizobia on the seed will vary by product used and any other chemical treatments applied to the seed. “Planting within 35 or 40 days of treatment is usually fine,” he says, “but growers need to follow the recommendations provided by the inoculant manufacturer or seed treater, and the seed should always be stored in a cool, dry place until ready to plant.”
Scott McKee, a soybean grower from Hawarden, Iowa, was a first-time soybean inoculant user in 2009. He participated in an inoculant yield challenge program sponsored by Becker Underwood. The experiment, he says, proved very worthwhile.
“We like to try different things to see how they impact yield. We always need to be experimenting and I think the Vault LVL soybean inoculant we used did make a difference.”
McKee planted four trials covering a variety of soil types and topography. The Vault LVL soybean inoculant-treated plots yielded an average 4 bushels-per-acre more than the untreated. Each field had been in corn in 2008.
“The treated beans were greener, looked healthier and seemed to have more vigor at emergence,” McKee says. “I’d never used an inoculant before, but it seems like more people now are. It was definitely worthwhile to do and I know we’ll use an inoculant again this year.”
Ken Koenig, Sandborn, Indiana, also participated in the Vault LVL Yield Challenge in 2009 and reported a 6 bushel-per-acre advantage for the inoculant-treated plot compared to the untreated.
“We had an awfully wet spring,” Koenig says. “We planted the untreated beans first, then got delayed by rain and didn’t plant the inoculant-treated beans until a week later.”
Koenig says his seed dealer treated the beans and ran the harvest check through a weigh wagon. He calls the yield boost impressive as the trial location was “certainly not our prime ground. And, with soybeans at $10 a bushel, that extra yield really makes a difference.”
“Return on investment for inoculation is excellent,” Beuerlein says. “At current soybean prices, it only takes about a third of a bushel to break even.”
“Our evaluations have shown that, over time, inoculants deliver a 300 percent to 500 percent return on investment, and they do this over a wide range of soil types and production systems,” Beuerlein says. “To me, soybean inoculants, or enhanced soybean treatments that contain a rhizobial component, like the new Vault HP system from Becker Underwood, are one of the most consistently profitable inputs growers can use in their operations.”