By Dick Hagen
The Land Staff Writer
August 01, 2008 02:30 pm
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Critics of biotechnology apparently are still trying to “punch holes” in this continually expanding resource that drives crop production to increasing levels of yield, often improved quality, generally lesser levels of pesticide inputs and often with a net reduction in costs per unit of production.
Currently in the bull’s eye of some protagonists are Roundup Ready soybeans. Their claim is that RR soybeans are more suspect to micronutrient deficiencies (particularly manganese) and subsequent disease pressure.
University research comparing the yield response of conventional to glyphosate-tolerant soybean varieties, or glyphosate-tolerant varieties to manganese applications, found the following.
• University of Minnesota research showed no yield response to manganese with either conventional or glyphosate-tolerant varieties regardless of the herbicide program (John Lamb, 2007).
• University of Illinois data indicated no yield response to manganese applications when comparing three glyphosate-tolerant soybean varieties.
So are the critics barking up the wrong tree? Very likely. The Illinois research from six experiment station locations and eight on-farm locations from 2004 to 2006 evaluated yield response comparing both foliar- and soil-applied manganese applications. It reported no effect on soybean yield or trifoliate leaf manganese composition on any of the three glyphosate-tolerant soybean varieties. Also glyphosate rate had no effect on leaf manganese level.
For more than a decade, farmers’ experience with Roundup Ready soybeans has been extremely positive, including excellent weed control and increased profits. RR soybeans were introduced in 1996 and today are grown on 93 percent of U.S. soybean acres.
The weight of evidence from Roundup Ready cropping systems where manganese is present at sufficient levels in the soil indicate there is no yield effect either from Roundup applications or the RR trait.
Here’s a run-down of some of the common questions out there.
Q: Does glyphosate negatively affect soil microorganisms?
A: Long-term studies show that repeated applications of Roundup has no impact on soil microorganism.
Q: Does application of glyphosate cause manganese deficiency in RR soybean?
A: Where soils contain adequate levels of manganese, tests showed no yield effects attributable to glyphosate or the RR trait. Any nutrient deficiency can reduce yields regardless of the use of RR soybeans or the Roundup product.
Q: Does the application of glyphosate cause manganese to be unavailable either within the plant or soil?
A: Studies checking the level of manganese in plant tissue across several crops (corn, alfalfa, wheat, soybeans) have shown no difference between crops with or without the Roundup Ready trait.
Extension entomologist Bruce Potter, with the University of Minnesota’s Southwest Research and Outreach Center near Lamberton, puts it this way: “Here in Minnesota, we don’t have any evidence of glyphosate impacting soil microorganisms or manganese uptake on Roundup Ready soybeans or, for that matter, conventional soybeans.”
Dick Hagen is staff writer of The Land. He may be reached at dickhagen@rswb.coop.
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