Humans have been working to increase crop yields since agriculture began, and major advances were made during the “green revolution” that began in the 1940s. Genetic engineering has been portrayed as the latest step in this process.  The majority of approved engineered seeds are aimed at decreasing losses due to pests and weeds; a primary example is Bt corn, produces a bacteria that kills the European corn borer and other insects.

A 2009 report by the Union of Concerned Scientists, “Failure to Yield: Evaluating the Performance of Genetically Engineered Crops,” is a good source of information on the potential of both genetically engineered seeds and traditional breeding methods in increasing crop yields.

The report, by the Union of Concerned Scientists, analyzes more than a decade of peer-reviewed research, and determines that:

• Corn yields have increased 28% since Bt corn was commercialized in 1996. Of this increase, only 14% can be attributed to Bt varieties. The majority of the increase, 86%, is attributable to other technologies or methods such as traditional breeding.
• When the infestation of pests that Bt corn targets is low to moderate, the genetically modified crop provides little or no yield advantage.
• The most widely commercialized form of genetically engineered soybeans is associated with a yield decrease of approximately 5%. While this crop makes up some 90% of the U.S. harvest, the author attributes its adoption to factors other than yield, such as simplified pesticide application. A new variety has been developed, but its productivity is improved only because it avoids the earlier version’s “yield drag.”
• Genetically engineered crops can confer some advantages, including a reduced need to apply insecticides, but these benefits diminish with time.
• Between 1987 and 2008 more than 3,000 field trials of crops having traits associated with increased yield were conducted. Of these, only five have resulted in genes that have been used commercially, and none is used in any significant degree.

The author stresses the importance of understanding the difference between intrinsic and operational yield — in the lab versus in the field, essentially. He also cautions readers, when examining claims of yield increases, against those that draw broad conclusions based on limited trials and field experiments. Yields are subject to a number of variables, including weather, pest species and amounts, and the effects of crop rotation.

Tags: agriculture, food, technology, organic, nutrition

By Leighton W. Klein | September 18, 2009