It's easy to see what happens when you spray glyphosate herbicide on a field of Roundup Ready soybeans—the weeds curl up and die. Still, there's more going on in that field than meets the eye, says Robert Kremer, a USDA Ag Research Service scientist based at the University of Missouri. He is a microbiologist who has studied the fate of glyphosate in the soil for a number of years.
Kremer will explain his findings when he gives a talk at Iowa State University in Ames April 14 at 4 p.m. at Kildee Hall Auditorium. He is guest speaker at the 2011 Staniforth Memorial Lecture. The title of Kremer's talk is "Glyphosate Interactions Beyond Weed Control—Current State of Knowledge." The public is invited to attend.
The 2011 Staniforth Lecture is the 22nd in the annual series honoring professor David W. Staniforth, a long-time ISU weed scientist. Staniforth helped develop many of the popular herbicides used to manage weeds in corn and soybeans and he promoted the early preplant herbicide application and no-till crop production systems.
For over 10 years this scientist has studied the fate of glyphosate
Kremer says glyphosate has an effect on the mysterious world of the rhizosphere, which is the narrow sliver of soil influenced by root secretions and soil microorganisms. Changes in numbers and types of microbes living in that underground world can have a significant effect on how nutrients are cycled, and whether they are available to the plant.
Over the past decade Kremer has focused on finding where glyphosate goes in the plant and what effects it has. His work has shown glyphosate is released from Roundup Ready soybeans into the root zone, and there are consequences to the microbes that surround these roots.
Another finding is that colonization of roots with the fungal disease pathogen Fusarium was typically two to five times higher on RR soybeans treated with glyphosate, as compared with soybeans receiving a conventional herbicide or no herbicide. "We've continued to evaluate Round Ready soybeans and glyphosate treatments and we've found consistently high Fusarium root colonization on those plants," he says.
Questions raised about effect on availability of micronutrients
There's also a question of whether shifts in the rhizosphere can have an effect on the availability of micronutrients such as manganese. Recent studies, including research by Kremer and colleagues in cooperation with Brazilian researchers, have found there is a link. Kremer has documented that glyphosate "leaks" from RR soybean roots, along with high concentrations of soluble carbohydrates and nitrogen-containing compounds. "This strongly suggests an influence on the rhizosphere microbial communities," he says.
The hard part is figuring out how to manage the system differently so that these potential negatives in glyphosate tolerant crops can be reduced or eliminated. It all starts with the basics, Kremer points out, suggesting growers test soil and make sure to correct any nutrients (including micronutrients) that fall short.