Brian Klubek's twist on an old crop management technique is capable of boosting soybean yields an astonishing 15 to 29 percent in a good year, but he's not satisfied.

Now the SIUC soil microbiologist is trying another twist, hoping to make those yields more reliable while fighting fungal disease in soybeans as well.

The management technique, called inoculation, involves coating soybean seed with bacteria that churn out nitrogen, a mineral the plants need to be highly productive.

Inoculation works well in fields that have not been planted to soybeans for a long time. But fields where farmers grow beans year after year host native populations of nitrogen-producing bacteria that often reach the roots first.

These native strains are more aggressive, crowding out the laboratory-inoculated strains, but they aren't as effective at providing the soybean plants with nitrogen.

In order to give his nitrogen-producing bacteria an edge, Klubek turned to another soil bacterium, Streptomyces kanamyceticus, that makes its own antibiotic.

"The antibiotic doesn't kill the native bacteria--it just slows them down a little," he says.

After developing strains of nitrogen-producing bacteria that tolerate exposure to the antibiotic, Klubek and former master's student Amelia Gregor began inoculating soybean seed with both the nitrogen-producing bacteria and the antibiotic-producing bacteria.

The microbe combo turned out to be a dynamic duo. In field tests a few years back, Klubek and Gregor achieved soybean yield increases of 15 to 29 percent with it.

In 2002, Greg Kurwicki, a Nashville, Ill., farmer who had read about Klubek's work, asked if he could use the combination in a demonstration plot on his land. "The inoculated soybeans out-yielded the other varieties he was testing, even though Ma Nature was not very good to us in 2002," Klubek says.

"He got a 17 percent increase in yield. While most of his [soybean] varieties were averaging 21 to 22 bushels per acre--that's how dry it was that year (typical yields for Southern Illinois are 40-45 bushels per acre)--the ones he inoculated with my bugs produced 28 bushels per acre."

Still, Klubek's inoculant mix does not always perform better than standard soybeans when environmental conditions are less than ideal. SIUC test plots didn't produce yield increases in 2002 and 2003, which were very dry years.

"We have shown good root nodule occupancy [by his strain of nitrogen-producing bacteria], and an increase in leaf nitrogen content," says Klubek. "But we don't yet have the consistency we're looking for."

So he and current master's student Chad LaMontagne have begun experimenting with adding a third inoculant to the mix: another type of root-dwelling bacterium with a number of helpful habits.

"They are reported to enhance or stimulate more rapid seed germination and root development, and they're also reported to be antagonistic to fungal pathogens like SDS (Sudden Death Syndrome), which offers an additional advantage," Klubek says of these microbes.

The two researchers are testing various combinations of two of the nitrogen-producing bacterial strains Klubek developed, the antibiotic-producing bacteria, and the growth-promoting bacteria.

"As far as I know, we're the only ones using three different organisms in inoculation," Klubek says. "It's a first."

They're also adding some ingredients to the inoculant mix--sucrose, glutamic acid, and an organic complex that keeps iron soluble--all aimed at helping the microbes thrive. And they're adding a second soybean variety to the testing, to see if results obtained with the one hold true for the other.

If all goes well, the souped-up soybeans will eventually be patented and licensed for commercial sales.

--by K.C. Jaehnig, Media & Communication Resources