Applying seed inoculants was routine when soybeans first were grown in the Midwest and there weren't native bacteria in the soil to provide sufficient nodulation growth and development. Today, however, most times there is enough Rhizobium bacteria present, unless the field hasn't been in soybeans for many years.
Mark Lawson, a farmer and technical agronomist with Syngenta, based at Danville, says that there is still evidence that seed inoculants for soybeans could pay for themselves and in some cases show a nice return. University studies over the past three decades often show at least a one bushel per acre increase. If that's $12 per acre, it should more than cover cost of the inoculant. There are also better inoculants available today.
Just because you're applying treated seed doesn't mean you have an inoculant going out with it. Ask your seedsman exactly what is in the seed treatment on your beans. It's more than likely an insecticide and one or more fungicides blended together.
While he doesn't have proof, Lawson says common logic says this might be a good year to apply some of the newer, potent inoculants, even if you haven't done so for a while.
"When we used to handle inoculants years ago, the package always said "don't let the contents get too hot" Those selling inoculants always advised farmers not to leave the package in the front window on the dashboard of the pickup, for example.
"The explanation was that if the bacteria got too hot, it could affect their survival, which would affect whether or not the product worked well," Lawson says.
It doesn't take much to extrapolate from last year's conditions into why that might be a factor this year. Soil temperature in the top couple of inches reached up to 140 degrees F, according to agronomists, in some fields last summer, especially if the corn was short and didn't canopy over correctly. Was that enough to affect some of the bacteria and cut back on populations of the bacteria that form nodules on the roots of soybeans?
"While I have no data to go on, it makes sense to me that it isn't worth taking a chance. Besides, past data says that the inoculant should pay for itself in increased yield anyway, whether bacteria were bothered by the heat or not. It just seem like it makes sense for this year," Lawson concludes.