Recent research and new formulations suggest you ought to take another look at soybean inoculation.

In fact, if you live in some Northern states, you might want to forget about the old rule-of-thumb on inoculation and start inoculating soybeans every year you grow them in the rotation.

Previously, inoculation wasn't recommended if inoculated soybeans had been grown in the past three to five years.

Secondly, you can forget the old hassle involved in inoculation with old formulations. The hot, new way to do it is with recently introduced liquid formulations.

"Speed of application is a must, and there are a lot of farmers who don't do it because it's a hassle with the old formulations," says Jim Beuerlein, Ohio State University extension soybean specialist. "Almost nobody wants to put some seed in the drill, scatter some black powder inoculant on it, stir it up with a hoe or something, then put in more seed and repeat the process.

"As far as I'm concerned, the best thing we've got going for us today is the new liquid formulations," says Beuerlein. "They can be applied mechanically in either on-seed or in-furrow applications, and it's quick and easy - and more effective."

Ed Oplinger, University of Wisconsin extension soybean specialist, agrees. "The development of new strains of rhizobia and new formulations of superior inoculants has changed the picture. The biggest challenge we have in the Upper Midwest is convincing a grower who is getting 55-bu/acre soybeans that there's an advantage to adding inoculation.

"In looking at our research studies, even using the old standard formulations there was an advantage - a substantial advantage," he adds. "And with the new liquid products, the yield and profit advantages were substantially greater. It's clear from our research data why these newer products are on the way to becoming a popular way to inoculate soybeans."

The change of thinking on inoculation frequency is based on a three-year no-till study. It doesn't apply in all areas of the Corn Belt - only in the states farthest north.

In the study, soybean inoculants were evaluated in 44 trials across seven states: Illinois, Indiana, Michigan, Minnesota, Ohio, South Dakota and Wisconsin. When grain yields and cost of production were compared in 18 tests in the three farthest-south states (Illinois, Indiana and Ohio), there was little difference due to inoculation.

However, in 26 tests in the other four states, inoculated soybeans yielded 3.8 bu/acre (8.6%) more than non-inoculated soybeans. And cost of production was reduced from $4.80 to $4.18/bu (13% decrease).

"Thus, under the cooler soils of the Northern states, using inoculation was more profitable than using uninoculated seed in this study," notes Oplinger. "In recent Wisconsin studies conducted over four years, when averaged across all inoculants tested, yields were increased an average of 4.6 bu/acre (8%). The newer, sterile-seed-treatment liquid materials increased yields as much as 7 bu/acre over the untreated control."

The bottom line: "In Wisconsin, we recommend that growers inoculate soybeans with an effective product every year beans are planted," he says.