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Studies on weed-attacking soil microbes ongoing

A soils scientist at the University of Missouri is studying naturally occurring soil microorganisms that appear to attack and suppress weed seeds and weed seedlings in crop fields.

Robert Kremer, MU adjunct professor with the USDA Agricultural Research Service, said the weed-suppressing microbes “are not going to replace herbicides any time soon,” but they could have immediate practical applications for sustainable agriculture and organic farmers in particular.

Kremer said his interest in the microbial benefits began when he was investigating biological control of weeds. Although the presence of microbes that attack weed seeds and seedlings had already been established, “technically, it's a very complex process to isolate and assay these microbes for weed-suppressive activity.”

“We can culture no more than 10 percent of bacteria out of the soil,” he said. “We might be missing a large majority of them.” Although he can pinpoint specific organisms by extracting and analyzing DNA directly from soil, “you can't culture all of them in order to obtain the bug you want. They might be of the same genus or even the same species, but their characteristics vary from site to site.

“We're not going to be able to market a ‘Bugs-in-a-Jug’ product for simple field application.”

Accordingly, “we decided on an approach that conserves these natural biological control agents by linking them with beneficial soil characteristics,” Kremer said.

In plots at MU Bradford Farm and at Sanborn Field on the MU campus, Kremer and his research team are using “practices that maintain soil organic matter and a high diversity of soil microorganisms.” Those techniques include the addition of compost, manure or organic mulch to the soil, crop rotation and the introduction of cover crops.

“Unfortunately, a lot of those practices aren't done much on a large scale anymore,” he said. “Once a cropping system becomes chemically dependent, your soil bio-diversity decreases, and certain organisms dominate and overwhelm others that are responsible for beneficial natural processes.”

In soil samples from the plots, Kremer assays for several properties that indicate the presence of beneficial microbes. “Two important properties are certain enzyme activities and good soil structure, which reflects optimum microbial activity. We found a high correlation between those factors and the presence of beneficial microorganisms.”

Weed-suppressing organisms “make up a very small percentage of the soil microbe population,” he said. “We believe that we can manipulate the soil so more of them can express that trait, but to be successful we need to re-examine traditional agricultural practices.”

Those practices survive mainly on small farms using sustainable agriculture, Kremer said. “We have a several small farms and family farms that are really interested in this. They're letting us assay their fields to examine the link between improved soil quality with these practices and potential weed-suppressive microorganisms in the soil.”

Forrest Rose is an Extension and ag information specialist with the University of Missouri.

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