U.S. soil scientist warns of glyphosate yield reduction

by BETTER FARMING STAFF

When it comes time to apply glyphosate to his soybean crop, Blake Vince usually adds manganese to the same tank when working on fields deficient in the metal. He does so to save the costs that another run across the field would add, and to avoid damage to the plants.

After hearing a retired U.S. soil scientist discuss his research into the effects of glyphosate on crops at last month’s Innovative Farmers Association of Ontario conference, however, this Merlin-area farmer is rethinking his approach.

The speaker, Don Huber, a professor emeritus from the Indiana-based Purdue University, generated buzz at this conference with his theory that increased glyphosate use, due to the introduction of Roundup Ready crops and widespread adoption of no-till, may actually harm crop yields.

Trish Jordan, a spokesperson for Monsanto Canada, says Huber’s work is often discredited by other academics because it is not indicative of what would happen in a real world situation. “It’s an academic situation,” she says, adding a lot of the research was done on fields predisposed to creating these sorts of issues. “That’s not what growers do,” she says. “Growers use the right herbicide; they use the right fertilizer; generally speaking they take every step they can to ensure they have the right environment to produce a healthy crop.”

Monsanto Canada released a stakeholder update on Feb. 22, raised after Huber’s presentation at the conference, to offer the company’s perspective. “We always update our materials when there’s some sort of public comment because we know we’re going to get calls,” Jordan explains. The update states that Monsanto has analyzed studies that measure the impact of Roundup and Roundup Ready soybeans on manganese uptake and use in the crop. It concludes “there are several information gaps in these studies ranging from the lack of proper soil fertility to the absence of near isogenic lines (conventional and Roundup Ready lines that are otherwise genetically identical).”

Huber says studies he conducted during his final years at Purdue (he retired in 2006), indicate glyphosate ties up manganese, zinc and many other plant nutrients not only within a weed targeted for eradication, but also within the soil.

“Its real impact is on those soil organisms that are responsible for making a lot of our nutrients available,” Huber explains.

Its effects in the soil can in turn end up creating nutrient deficiency in plants. The deficiency is more pronounced on manganese-depleted soils, he says.

Studies are beginning to show the effect is “as damaging to RR (Roundup Ready) crops as to non-RR (Roundup Ready) crops,” he writes in a research paper.

Huber also says research has connected disease in crops following Roundup Ready crops to glyphosate. A 2009 Western Canada study indicates previous glyphosate use was associated with higher levels of fusarium head blight in wheat.

To counter the effects, Huber advises using glyphosate “based on what we need for weed control,” but recognize that a plan is needed to compensate for its more negative effects. That may include applying other nutrients, however he advises waiting eight to 15 days after a glyphosate application before applying these. The glyphosate will affect their effectiveness, he says. “There is enough glyphosate floating around in the plant for eight days that it will essentially zap anything that you put on,” he says.

It’s this word of warning that Vince says affected him the most. “I was in shock a bit.”

It wasn’t as much of a surprise to Allan Spicer, a marketing representative with Can Grow Crop Solutions Inc. His company has been working for three years with Huber “on this whole thing,” he says.

He says many of his clients have switched to identity preserved soybeans over the past year. “It’s been a major swing.” The premiums that come along with growing identity preserved have played a motivating role in the shift, but “yield drag” on Roundup Ready varieties along with the availability of new herbicides are other factors, he says.  

Dale Cowan, a senior agronomist with Southern Co-operative Services, is skeptical of Huber’s claims.

Yields in corn and soybeans remain phenomenal, he points out. He notes there is always the concern about relying on one type of herbicide and the growth of weed resistance. This is one of the reasons why crop rotation is important.

Jordan notes that new technology from the company has resulted in seven to 11 per cent higher yields on average than existing Roundup Ready soybeans “and other competitive products.” But seed technology is not the only factor at play, and therefore farmers will experience a range of yields, she adds.

Horst Bohner, Ontario Ministry of Agriculture, Food and Rural Affairs soybean specialist, notes that other North American researchers have not been able to reproduce Huber’s study results.

“Glyphosate is one of the safest herbicides ever invented,” he says – as long as it is used properly.

Ministry studies that looked at the effectiveness of separating applications of manganese and glyphosate found no yield response compared to combining the two in the same application, he says. But the studies did not include manganese deficient plots. Study is needed to determine if there might be a benefit in separating the applications on manganese-deficient soils.

“To make the general statement that manganese is causing us big, big problems is absolutely incorrect,” Bohner says. “It’s in those fields where there is a true manganese deficiency, yes it can really hold them (soybeans) back.”

He says the average yield gain for soybeans has been “more or less flat” over the last 20 years in Ontario: “We have too many soybeans in the rotation,” he says, pointing out we grow three times as many as we did 30 years ago. There is also more disease, insects and more widespread no-till practice. “There are a number of factors that come into play.”

Mike Cowbrough, the province’s weed management field crops lead, notes a recent Quebec study found no connection between the use of glyphosate and the incidence of fusarium head blight.

However, glyphosate’s impact on crop production systems is receiving more scientific scrutiny, he says.

“Whenever you have a major shift in a production system . . . I think inherently you’re going to look at it more closely and how it impacts the system,” he says. And the impact of glyphosate is undeniable: “If you look back 10 years ago, the use of Roundup Ready corn was pretty low, if not any at that time and soybeans was still relatively modest and now they’re fairly high percentages of use in corn and soybean production.” BF