May 16, 2000
Research Shows Roundup Ready Soybeans Yield Less
CLAY CENTER, Neb. — Soybean plants genetically modified to resist a popular non-selective herbicide yield less than conventional soybeans, University of Nebraska research shows.
Two years of NU Institute of Agriculture and Natural Resources research showed Roundup Ready soybeans yield 6 percent less than their closest relatives and 11 percent less than high-yielding conventional soybeans. This averages to three fewer bushel per acre, or 480 fewer bushels on a 160-acre field.
NU Agronomist Roger Elmore, who headed this study, said the research was initiated after producers began asking yield-related questions about Roundup Ready soybeans in 1997, about the same time early test results from Nebraska and other state universities were released. The questions and early results hinted Roundup Ready soybeans yielded less than conventional beans.
"Preliminary studies indicated something was going on," Elmore said.
Soybeans are broadleaf legumes that grow to about 30 inches, leaving them susceptible to weeds such as velvetleaf, waterhemp and shattercane. Weeds can outgrow soybeans, stealing moisture, sunlight and nutrients, and thus lower yields. Weed management can be tricky because most broadleaf herbicides can wipe out soybeans, along with weeds. Roundup Ready soybeans contain a gene that allows them to be treated with Roundup Ultra, the most popular of the glyphosate-based herbicides.
Going into the research, NU scientists knew one of two things was responsible for the Roundup Ready yield penalty: either spraying with Roundup or the gene insertion process. Their studies showed spraying had no effect. Researchers sprayed 13 Roundup Ready cultivars with three substances: Roundup, ammonium sulfate that enhances herbicide activity and weed control, and water. Roundup Ready yields were consistently 55 bushels per acre, which indicated Roundup didn't affect soybean growth, development or yields. From that, the scientists deduced the gene insertion process was responsible.
Elmore and his colleagues then focused on the effects of the gene insertion process in dryland and irrigated studies at North Platte, Clay Center, Lincoln and Concord. They compared five Roundup Ready cultivars; their closest conventional relatives, called sister lines; and high-yielding conventional cultivars. In this study, weeds in all test plots were controlled with conventional herbicides and by hand; Roundup was not used. This allowed scientists to compare yields without the variable of Roundup application complicating results, Elmore said.
The high-yielding conventional soybean lines yielded 57.7 bushels per acre, their sister lines yielded 55 bushels per acre and the Roundup Ready soybeans yielded 52 bushels per acre. This research showed that Roundup Ready soybeans' lower yields stem from the gene insertion process used to create the glyphosate-resistant seed. This scenario is called yield drag. The types of soybeans into which the gene is inserted account for the rest of the yield penalty. This is called yield lag.
Elmore likened yield drag to the effect an air conditioner has on a new pickup. When the pickup's air conditioner is on, performance is less but it's not the pickup's fault. Yield lag, on the other hand, would be analogous to putting high-octane gas into a 1930's car: the car just doesn't have what it takes to perform by today's standards.
Despite lower yields and more expensive seed, Elmore predicts producers will continue planting Roundup Ready as well as conventional soybeans.
"Farmers are willing to pay some penalty for the better weed control," Elmore said.
This research helps producers still deciding whether to plant conventional or Roundup Ready soybeans weigh the trade-offs, Elmore said. On one hand, Roundup Ready seed costs more and yields less, but fields can be practically weed-free. On the other, conventional seed yields better and is less expensive, but weed control is more complex and perhaps more time-consuming.
Roundup Ready soybeans have become increasingly popular since their introduction in 1996. That year 7 percent of soybeans planted in the United States were Roundup Ready, compared to 57 percent in 1999.
Elmore said some producers would rather pay more for the seed and accept reduced yields in exchange for a clean, weed-free field on their farms, even though that route is more costly.
"If you can control weeds with conventional herbicide, you're probably better off than to go with Roundup Ready," Elmore said. If weed control is a problem, he said planting Roundup Ready soybeans is perhaps the better option.
The Nebraska research provided scientific answers relatively quickly to questions by producers and the Nebraska Soybean Board, which funded the work.
"Two years is awfully fast for this kind of work," Elmore said. This project demonstrates the importance of a land-grant university responding to a pressing local need for research-based information.
This research was conducted by IANR's Agricultural Research Division.
05/16/00-CA
Roger Elmore - Ph.D.
Agronomy & Horticulture
Professor
(402) 762-4433
Cheryl Alberts IANR News and Publications (402) 472-3030
Department: Agronomy & Horticulture
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