By analyzing two decades worth of corn yield data from Wisconsin, a team of University of Wisconsin-Madison researchers has quantified the impact that various popular transgenes have on grain yield and production risk compared to conventional corn. Their analysis, published online in a Nature Biotechnology correspondence article, confirms the general understanding that the major benefit of genetically modified corn doesn't come from increasing yields in average or good years, but from reducing losses during bad ones.
"For the first time we have an estimate of what genetically modified hybrids mean as far as value for the farmer," says UW-Madison and UW-Extension corn agronomist Joe Lauer, who led the study.
Lauer, who is also a UW-Extension corn agronomist, has been gathering corn yield and other data for the past 20 years as part of the Wisconsin Corn Hybrid Performance Trials, a project he directs. Each year, his team tests about 500 different hybrid corn varieties at more than a dozen sites around the state with the goal of providing unbiased performance comparisons of hybrid seed corn for the state's farmers. When GM hybrids became available in 1996, Lauer started including them in the trials.
"It's a long-term data set that documents one of the most dramatic revolutions in agriculture: the introduction of transgenic crops," says Lauer, who collaborated with UW-Madison agricultural economists Guanming Shi and Jean-Paul Chavas to conduct the statistical analysis, which considered grain yield and production risk separately.
Grain yield varied quite a bit among GM hybrids. While most transgenes boosted yields, a few significantly reduced production. At the positive end of the spectrum was the Bt for European Corn Borer trait. Corn plants with this added transgene, which comes from the bacterium Bacillus thuringiensis, are protected from a damaging caterpillar. When the researchers combined the yield data from all of the ECB hybrids grown in the trials over the years, they found that the ECB plants out-yielded conventional hybrids by an average of more than six bushels per acre per year. GM hybrids with "stacked traits," or multiple transgenes, tended to have slightly improved yields — an extra two or three bushels per acre. On the other hand, grain yields from hybrids with the Bt for Corn Rootworm transgene trailed those of regular hybrids by a whopping 12 bushels per acre.