GM crops increase yield potential
GM crops do not increase yield potential – and in many cases decrease it
GM crops are often claimed to give higher yields than naturally bred varieties. But the data do not support this claim. At best, GM crops have performed no better than their non-GM counterparts, with GM soybeans giving consistently lower yields.3
Controlled field trials comparing GM and non-GM soy production suggested that 50% of the drop in yield is due to the disruption in genes caused by the GM transformation process.4 Similarly, field tests of Bt maize hybrids showed that they took longer to reach maturity and produced up to 12% lower yields than their non-GM counterparts.5
A US Department of Agriculture report confirmed the poor yield performance of GM crops, saying, “GE [genetically engineered] crops available for commercial use do not increase the yield potential of a variety. In fact, yield may even decrease.... Perhaps the biggest issue raised by these results is how to explain the rapid adoption of GE crops when farm financial impacts appear to be mixed or even negative.”6
The definitive study to date on GM crops and yield is Failure to Yield,2 by Dr Doug Gurian-Sherman, senior scientist at the Union of Concerned Scientists and former biotech adviser to the US Environmental Protection Agency. The study, which is based on peer-reviewed research and official US Department of Agriculture (USDA) data, was the first to tease out the contribution of genetic engineering to yield performance from the gains made through conventional breeding. It is important to bear in mind when evaluating the yield performance of GM crops that biotech companies insert their proprietary GM genes into the best-performing conventionally bred varieties.
The study also differentiated between intrinsic and operational yield. Intrinsic or potential yield, the highest that can be achieved, is obtained when crops are grown under ideal conditions. In contrast, operational yield is obtained under field conditions, when environmental factors such as pests and stress result in yields that are considerably less than ideal. Genes that improve operational yield reduce losses from such factors.
The study found that GM technology has not raised the intrinsic yield of any crop. The intrinsic yields of corn and soybeans did rise during the twentieth century, but this was not as a result of GM traits, but due to improvements brought about through traditional breeding.
The study found that GM soybeans did not increase operational yields, either. GM maize increased operational yields only slightly, mostly in cases of heavy infestation with European corn borer. Bt maize offered little or no advantage when infestation with European corn borer was low to moderate, even when compared with conventional maize that was not treated with insecticides.
The study concluded, “Commercial GE crops have made no inroads so far into raising the intrinsic or potential yield of any crop. By contrast, traditional breeding has been spectacularly successful in this regard; it can be solely credited with the intrinsic yield increases in the United States and other parts of the world that characterized the agriculture of the twentieth century.”2
In 2009, in an apparent attempt to counter criticisms of low yields from its GM soy, GM seed producer Monsanto released its new generation of supposedly high-yielding GM soybeans, RR2 Yield. But a study carried out in five US states involving 20 farm managers who planted RR2 soybeans in 2009 concluded that the new varieties “didn’t meet their [yield] expectations”.7 In June 2010 the state of West Virginia launched an investigation of Monsanto for false advertising claims that RR2 soybeans gave higher yields8
If GM cannot increase yields even in the United States, where high-input, irrigated, heavily subsidised commodity farming is the norm, it is irresponsible to assume that it would improve yields in the Global South, where farmers may literally bet their farms and livelihoods on a crop.
We agree with the conclusion of Failure to Yield that the funding and research that are currently poured into trying to produce high-yield GM crops should be redirected toward approaches that are proven effective in improving crop yields, including conventional plant breeding as well as use of agroecological practices. These are by far the most efficient, affordable, and widely practised methods of improving yield.