Posted: May, 2016
Impact of Genetic Engineering on Crop Yields Not Obvious,
NAS Panel Concludes
A major new review of the research on genetically engineered crops concludes
that there is no significant evidence that genetic engineering technology by
itself has increased the rate of yields for the three most frequently planted
genetically engineered crops in the U.S. – maize, soybeans, and cotton. Such
yields have been increasing, but it’s not possible to determine how much the
increases are due to GE technology, versus other factors, despite the
review’s effort to tease out such a positive effect. The report,
Genetically Engineered Crops: Experiences and Prospects, was produced
by a committee of the prestigious U.S. National Academies of Sciences,
Engineering, and Medicine.
The committee added: “There is disagreement among researchers about how much
GE traits can increase yields compared with conventional breeding. In addition
to assessing detailed surveys and experiments comparing GE with non-GE crop
yields, the committee examined changes over time in overall yield per hectare
of maize, soybean, and cotton reported by the U.S. Department of Agriculture
(USDA) before, during, and after the switch from conventional to GE varieties
of these crops. No significant change in the rate at which crop yields
increase could be discerned from the data. Although the sum of experimental
evidence indicates that GE traits are contributing to actual yield increases,
there is no evidence from USDA data that they have substantially increased the
rate at which U.S. agriculture is increasing yields.”
Fred Gould, the committee’s chair, wrote in the report’s preface that
comparing “the merits of technology-intensive agriculture compared with more
agroecological approaches” was beyond the scope of his committee’s work. He
added, however, that such a comparison would be an “important” one to conduct.
The committee called for research to “isolate effects of the diverse
environmental and genetic factors that contribute to yield.” GE crops already
on the market “do not have greater potential yield than non-GE counterparts,”
the report states, and genetic engineering technologies alone cannot be
expected to increase food security, because of the “wide variety of complex
challenges” facing small farmers. Whether growing GE crops will benefit
farmers depends on the particular social and economic context in which genetic
engineering technology is developed and distributed, it adds.
But the committee also stated that it had “found no substantiated evidence
that foods from GE crops were less safe than foods from non-GE crops.”
The report noted that earlier national committees have called since 2000 for
U.S. data to be collected to make it possible to trace the impact of GE crops
on measures of environmental sustainability, including biodiversity. But it
concluded that such databases remained “inadequate” in 2015, when this
committee was conducting its own review. So the lack of data limits “the
ability to assess effects on abundance of monarchs and many other species.”
As for how genetically engineering plants to be herbicide resistant (HR) has
affected pesticide use, the committee concluded: “The use of HR crops
sometimes initially correlated with decreases in total amount of herbicide
applied per hectare of crop per year, but the decreases have not generally
been sustained.” It added, however, that merely measuring in kilograms how
much total herbicide use per hectare per year has risen or fallen “is not
useful for assessing changes in human or environmental risks,” as the mix and
relative hazards per kilogram of different herbicides also matters. The report
noted that weed resistance to glyphosate “is a problem,” and that in areas
where GE crops have led to a heavy reliance on that herbicide, such resistance
is now “a major agronomic problem.”
To slow evolution of weed resistance to it and other herbicides, the report
calls for “integrated weed-management practices beyond simply spraying
mixtures of herbicides” for HR crops engineered to resist multiple herbicides.
In addition to its wide-ranging examination of the effects of genetic
engineering, the report provides a wealth of data and a very readable account
of the history, the technical aspects, and the current status of GMOs. As of
2015, it states, 12 percent of the world’s croplands were planted in GMOs.
That includes nine food crops, three non-food crops (cotton, alfalfa, and
poplar), and two types of flowers (carnations and roses). GE maize and soybean
were the most widely grown GE crops. GE varieties now account for about 80 per
cent of all the soybeans grown worldwide, and GE maize accounts for a third of
all the maize planted. The other GE food crops are: apple, canola, sugar beet,
papaya, potato, squash, and eggplant. But many other GE food crops are now in
development. About 39 per cent of all GE crops in 2015 were grown in the U.S.
About half of all cropland in the U.S. was planted in GE crops in 2014 –
mainly maize, soybeans, and cotton.
The report also calls for research on such possible unintended effects of
genetic engineering technologies as:
Whether they are contributing to “farmer de-skilling,” and if so, to what
Whether varieties engineered with more than one new trait are leading to
more expensive seeds than farmers need.
Whether seed market concentration is affecting the price of GE seeds and if
so, is that helping or harming farmers.
Download a chart showing the studies discussed in the report, including their
funding sources where that was available,
here. Read or download a copy of the
full report, Genetically Engineered Crops: Experiences and Prospects,
National Academies of Sciences, Engineering, and Medicine (2016).
Genetically Engineered Crops: Experiences and Prospects.
Washington, DC: The National Academies Press.