The report is described as the first comprehensive assessment of the impact of genetically modified crops on American farmers, who have rapidly adopted them since their introduction in 1996. The study was issued by the National Research Council, which is affiliated with the National Academy of Sciences and provides advice to the nation under a Congressional charter.
The report found that the crops allowed farmers to either reduce chemical spraying or to use less harmful chemicals. The crops also offered farmers lower production costs, higher output or extra convenience, benefits that generally outweighed the higher costs of the engineered seeds.
“Many American farmers are enjoying higher profits due to the widespread use of certain genetically engineered crops and are reducing environmental impacts on and off the farm,” David Ervin, the chairman of the committee that wrote the report, said in a statement.
However, added Dr. Ervin, a professor of environmental management and economics at Portland State University in Oregon, “These benefits are not universal for all farmers.”
Nor are they necessarily permanent. The report warned that farmers were jeopardizing the benefits by planting too many so-called Roundup Ready crops. These crops are genetically engineered to be impervious to the herbicide Roundup, allowing farmers to spray the chemical to kill weeds while leaving the crops unscathed.
Overuse of this seductively simple approach to weed control is starting to backfire. Use of Roundup, or its generic equivalent, glyphosate, has skyrocketed to the point that weeds are rapidly becoming resistant to the chemical. That is rendering the technology less useful, requiring farmers to start using additional herbicides, some of them more toxic than glyphosate.
“Farmer practices may be reducing the utility of some G.E. traits as pest-management tools and increasing the likelihood of a return to more environmentally damaging practices,” the report concluded. It said the problem required national attention.
More than 80 percent of the corn, soybean and cotton grown in the United States is genetically engineered. The crops tolerate Roundup, are resistant to insects, or both.
American farmers were the first to widely adopt the technology and still account for about half of all the engineered crops grown. The crops are also being widely grown in Latin America and parts of Asia but still largely shunned in Europe.
The rapid adoption of the crops is evidence that American farmers see the technology as beneficial.
Nevertheless, in the fiercely polarized debate about genetically modified crops, there is little agreement on anything. Critics have issued studies saying that uses of the crops have led to increased pesticide use and has had only a minimal effect on crop yields.
The National Research Council report was prepared by a committee of mainly academic scientists and relied primarily on peer reviewed papers.
Still, the report is not likely to win over critics of the crops.
One critic, Charles Benbrook, who reviewed a draft of the report, said the conclusion that the crops help farmers might no longer be true, or might not be true in the future. That is because the report relies mostly on data from the first few years, before prices of the biotech seeds rose sharply and the glyphosate-resistant weeds proliferated.
“This is a very different future,” said Dr. Benbrook, an agricultural economist who is chief scientist at the Organic Center, which promotes organic food and farming. “The cost is going to be way higher. The environmental impacts are going to go up fairly dramatically.”
As prices of the biotech seeds have risen sharply, even some farmers are now starting to question whether they are worth it. Just last week, Monsanto, the leading agricultural biotechnology company, said it would lower the prices of its newest genetically engineered soybeans and corn seeds because farmers were not buying as many of the seeds as it had expected.
The Department of Justice is now investigating whether Monsanto, which has patents on some of the fundamental technology including the Roundup Ready system, is violating antitrust laws, unduly increasing prices or hindering innovation.
The National Research Council report addresses this issue briefly without mentioning Monsanto. It says that issues of proprietary terms “has not adversely affected the economic welfare of farmers who adopt G.E. crops.” But it said there is some evidence that the availability of non-engineered crops “may be restricted for some farmers.”
The report said that the use of Roundup Ready crops has led to a huge increase in the spraying of glyphosate but a nearly concomitant decrease in the use of other herbicides. That is a net environmental benefit, the report said, because glyphosate is less toxic to animals than many other herbicides and does not last that long in the environment.
The use of herbicide-tolerant crops has also made it easier for farmers to forgo tilling their fields as a way to control weeds. So-called no-till farming helps prevent soil erosion and the runoff of rainwater containing sediments and chemicals.
The improvement in water quality could prove to be the largest benefit of the crops, the report said, though it added that efforts should be made to measure any such effects.
Still the biotech crops are only one factor promoting no-till farming. The report said that about half of soybeans were already being grown with little or no tillage by the time Roundup Ready soybeans were introduced in 1996. That rose to 63 percent in 2008.
The other major class of genetically engineered crops is the so-called BT corn and BT cotton, which contain bacterial genes allowing the plants to produce an insecticide.
The report said that use of chemical insecticides has declined as the BT crops have spread. In areas of with heavy insect pressure, it said, the use of the crops has increased farmer income because of higher yields and reduced expenditures on insecticide.
The report said that when genetically engineered crops were first introduced, some had lower yields than conventional varieties, a finding often cited by critics. But the report said that newer studies show either a modest increase in yield or a neutral effect.