Failure to Yield

Frequently Asked Questions

What is new about the Failure to Yield report?

This is the first report to analyze nearly two decades worth of peer-reviewed research on the yield of genetically engineered food/feed crops in the United States and to arrive at new yield values for those crops. The report reveals that only one major GE food/feed crop—Bt corn, a variety engineered with a gene from the bacterium Bacillus thuringiensis, which produces toxins to protect the plant from several insects—has achieved any significant yield increase in the United States. The 3–4 percent yield increase achieved by Bt corn over the 13 years that it has been grown commercially is much less than what has been achieved over that time by other methods, including conventional breeding. Over the past several decades, corn yields have increased about one percent per year, or about 14 percent (due to the compounding property of yield gain) over the 13 years since Bt was first commercialized. Therefore, by this rough calculation, Bt has contributed only 21–28 percent of yield gain in corn, with other approaches contributing 72–79 percent.

The report contrasts this small yield increase achieved by engineered Bt corn with the yield of a suite of alternatives including organic, low-external-input methods, conventional breeding, and modern breeding methods that use technological advances to speed up the selection process for desired traits without actually inserting new genes. Collectively, such methods are capable of increasing crop yields far more than GE has yet managed to do (see Failure to Yield, Chapter 4). However, the public funding deck has been stacked against these other methods to date, as resources have been channeled toward GE research and development.

What is the difference between intrinsic yield and operational yield, and why does it matter?

Failure to Yield distinguishes between two kinds of crop yield—intrinsic yield and operational yield. Intrinsic yield, which may also be thought of as potential yield, is the amount of food that crops can produce under ideal circumstances. Operational yield is the amount achieved after pests and other environmental stresses reduce the potential yield. Both are important, and GE has had limited success in enhancing operational yield by reducing losses caused by insect pests. But crop breeders must find ways to increase intrinsic yield if they are to boost the maximum production that may be obtained from a crop. Conventional breeding has been successful at increasing intrinsic yields; no GE crop has yet achieved such an increase. 

Biotech has been around for 20 years. Why hasn’t it increased crop yields significantly in all that time?

Failure to Yield documents an extensive effort by the industry to increase yields through GE, with several thousand experimental field trials of GE traits associated with yield carried out in the United States over a period of 20 years (see Failure to Yield, Chapter 3). Still, only Bt corn has increased yield, and that small gain is for operational rather than intrinsic yield. One likely reason is that new yield genes often have much more complex genetic interactions with the plant genetic material than the few currently successful transgenes, and therefore cause more genetic side-effects that often lead to undesirable agricultural properties. Because of this, many of these new genes may not be successful, or may come with undesirable properties in addition to increased yield (see Failure to Yield, Chapter 5).

If GE crops haven’t significantly increased yields, why have so many farmers adopted them?

GE crops have provided other benefits important to U.S. farmers.  Bt corn provides protection against insect pests, and the GE traits are often available in varieties producing higher yields as a result of traditional breeding. GE soybeans provide increased convenience and save time. Herbicide-tolerant (HT) soybeans are engineered with genes from bacteria or other organisms that are not affected by a particular herbicide, such as glyphosate (also known as Roundup). Prior to the introduction of HT soybeans, conventional farmers often used three or four different herbicides applied several times a year, and these usually had to be applied when the crop was not growing to avoid damage. With HT soybeans, farmers found that they had flexibility to apply glyphosate herbicide directly onto the crop during the growing season, and to do so only once or twice. Recently, however, this time-saving benefit has begun to diminish with the advent of weeds that have developed resistance to glyphosate and a shift to weeds naturally more tolerant of glyphosate and the conditions under which it is used. Several million acres of GE soybeans and cotton are now infested with glyphosate-resistant and tolerant weeds. According to data from the U.S. Department of Agriculture (USDA), the number of glyphosate applications by farmers has risen considerably, and the amount of herbicide used on HT soybeans now appears to be considerably higher than it was prior to the introduction of this HT crop.

Have any other crop production methods had success in increasing yields?

Conventional plant and animal breeding have been spectacular performers, accounting along with synthetic fertilizers, for most of the increase in the yields of food and fiber crops throughout the 20th century. Corn yields have increased about six fold since 1930. It is believed that improvements through breeding account for about half of these yield increases. Yield increases from traditional breeding of major grain crops have continued over the last few decades at a somewhat slower pace. New methods such as the use of genomic information (e.g. marker assisted selection), other sophisticated trait selection methods, and use of an expanded range of crop varieties and wild crop relatives as breeding material may enhance crop breeding (research is needed to better understand and develop the potential of these newer methods). Recent studies also suggest that organic and other sophisticated low-external-input methods can produce yields that are largely equivalent to those of conventional agriculture, even though limited investment has been made in these agro-ecological methods.

Why is it important to evaluate yields in the United States, which currently produces food in abundance?

Farmers in the United States have grown more GE crops over a longer period of time than farmers in most other countries, offering more—and more reliable–data on their yields. U.S. agriculture also illustrates how GE stacks up against other advanced production technologies. By contrast, in resource-poor developing countries, addition of most types of resources, such as fertilizer or organic methods, can increase yields–so whether GE can increase yields in those countries is a less critical test of the technology. More data on yield are needed from developing countries, because data that are relevant in the United States are often not applicable to these countries. 

Most of the need for increased crop yield is in developing countries. Has GE increased food crop yields in those parts of the world?

There are few peer-reviewed papers evaluating the yield contribution of GE crops in developing countries—not enough to draw clear and reliable conclusions. However, the most widely grown food/feed crop in developing countries, herbicide-tolerant soybeans, offer some hints. Data from Argentina, which has grown more GE soybeans than any other developing country, suggest that yields for GE varieties are the same or lower than for conventional non-GE soybeans.[1]

What are GE’s prospects for increasing future crop yields in developing countries?

The record so far suggests that GE is unlikely to play a major role in increasing yields in developing countries—especially those with limited public infrastructure—in the foreseeable future. Overall, GE has not had a major impact on yields in developing countries. As with developed countries, there are only a few GE crops, with herbicide-tolerant soybeans being most widely grown (in South America), followed by Bt cotton, primarily in India and China. There are small amounts of Bt maize (corn) in South Africa and a few other countries. 

Are GE crops and industrial style-agriculture the only alternatives available to the developing world?

No, but much more political will and investment of resources is needed to develop and promote these other methods as aggressively as GE has been promoted. The recent International Assessment of Agricultural Knowledge, Science and Technology for Development (IAASTD)—supported by the World Bank, several United Nations (UN) agencies and numerous governments, and several hundred scientists and others—suggested that GE should play a secondary role to other investments deemed more productive. The IAASTD specifically cited farming methods based on agro-ecology (such as organic), as well as infrastructure improvements such as the building of new roads for market access. Another UN study summarized 114 organic and low-input agriculture projects underway for several years across Africa, which showed average yield increases of 116 percent, along with increased income and other benefits. A recent peer-reviewed summary of world-wide organic production found that organic and near-organic methods in developing countries increased yields more than industrial production methods.     

How will agriculture change in the face of global warming?

As the global climate warms, crop yields are likely to decrease in many parts of the world due to higher temperatures, more frequent and severe droughts, flooding and coastal inundation, and severe weather. In addition, warming will likely increase the range of some crop pests. Operational yield traits such as drought and heat tolerance, as well as intrinsic yield, must therefore be improved. At the same time, industrial agriculture is now a major contributor to global warming, producing by some estimates 20 percent of the world’s emissions of heat-trapping gases, and some methods of increasing yield can exacerbate this negative impact. For example, crops that achieve higher intrinsic yield often require more fossil fuel-based nitrogen fertilizer, some of which is converted by soil microbes into nitrous oxide, a heat-trapping gas nearly 300 times more potent than carbon dioxide. Minimizing global agriculture’s future climate impact will require investment in drought-tolerant and other crops adapted to changing environments and systems of agriculture less dependent on industrial fertilizers, and agro-ecological methods that improving soil water-holding capacity and resilience. UCS is currently analyzing the contribution that GE and other breeding technologies might make to the development of such crops and will release our results in a future report 

What are genetic side-effects (pleiotropy) and why are they important?

Genes do not function in isolation in any organism. Rather, they interact with and influence each other. When genes are manipulated by GE or conventional breeding, these interactions can lead to unintended side-effects that alter traits other than the intended one and lead to unintended changes in the crop. Genetic side-effects associated with GE have been widely observed (see Failure to Yield, Chapter 5). But while the two types of widely commercialized genes for insect resistance and herbicide tolerance in crops have relatively limited interactions with other genes, many genes under consideration for increasing yield typically have much more complex interactions in the plant, and many side-effects are associated with them. Specific side-effects can’t reliably be predicted by current science, often because they occur only in specific plant tissues, at certain stages of development, or under particular environmental influences.

Although many genetic side-effects may be harmless, some can impair important agricultural properties of the crop (such as its ability to fend off pests or withstand stress), alter its nutritional properties, or result in the production of harmful substances. So while these complex genes may have success increasing yields in the future, their side-effects may end up decreasing other valuable crop properties at the same time.   

Is a technological breakthrough likely soon that would increase GE crop yields?

The prospects for such a breakthrough are unclear. Improved methods of gene discovery are making many more genes available; identification of more of the genetic elements that control gene expression (called promoters) allows fine-tuning of transgene function that can limit side-effects; and new methods of monitoring gene, protein, and metabolic expression for the entire plant genome make looking for harmful side-effects increasingly feasible. The ability to engineer multiple genes simultaneously is also progressing. But none of this changes the fundamental challenge of the integrated nature of the genome that leads to side-effects (even if they can be somewhat reduced), the limitations of an incremental rather than systematic approach to yield, and the many other challenges of agriculture.

How many GE crops are currently in use in the United States, and who makes them?

The main U.S. GE crops are herbicide-tolerant soybeans and corn and Bt insect-resistant corn and cotton. In addition, virus-resistant GE papaya is grown in Hawaii, and very small amounts of virus-resistant summer squash have been grown. GE plums resistant to the plum pox virus have been approved and some may have been produced. In 2008, herbicide-tolerant sugar beets began to be planted commercially in the United States.  Monsanto Company is by far the largest maker and seller of GE seeds. Other important GE seed companies include Dow Agrosciences, Syngenta, and DuPont. A handful of companies dominate the U.S. and international GE seed markets.

[1] Qaim, M. and G. Traxler. 2005. Roundup ready Soybeans in Argentina: farm level and aggregate welfare effects. Agricultural Economics 32: 73–86.

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