The study examined GM crops in rotation with non-GM cereals such as wheat.© Getty Images

Crops that are genetically modified to be resistant to herbicides could make weeds easier to manage without destroying valuable biodiversity. So says the first trial to compare transgenic and conventional crops farmed in rotation.

The four-year study, called Botanical and Rotational Implications of Genetically Modified Herbicide Tolerance (BRIGHT), involved five different agricultural research stations around Britain. The researchers alternated between transgenic sugar beet or winter oilseed rape and conventional wheat or barley on the same plots of land. Farmers use these patterns of crop rotation to preserve nutrients in the soil or disrupt pest life cycles.

The scientists found that the number of weed seeds on the plots, a measure of biodiversity, increased over the four years in all cases. This shows, they argue, that although weed plants themselves can be controlled, transgenic crops do not necessarily damage diversity. This partly echoes the message of the British government's Farm Scale Evaluations, the results of which were published last year, but which gave mixed reports as to whether transgenic crops deplete diversity.

Cheap options

BRIGHT also assessed which farming strategies were best at killing weeds. On 50% of study plots, growing oilseed rape that had been engineered to resist the wide-ranging herbicide glyphosate, also called Roundup, gave the lowest weed numbers throughout the four years. Using such rape could make it easier and cheaper for farmers to keep weeds down, the BRIGHT team said at a press conference in London on 29 November. However, it cautions that in other fields, neither conventional nor transgenic crops were consistently better for battling weeds. Their results have been published online¹.

Transgenic crops could potentially represent a cheap option. Weedkillers for conventional oilseed rape cost £60 (US$113) per hectare, compared with £16 for the Roundup-tolerant crop and £40 for a different transgenic strain that is resistant to the herbicide glufosinate, reports Peter Lutman of Rothamsted Research in Harpenden, UK. Lutman led the oilseed-rape portion of the study. He points out that these figures do not include the costs of seeds: transgenic strains, if approved, are likely to be subject to technology costs set by the manufacturers.

Holistic approach

The results underline the fact that it is the way the crop is farmed, not the crop itself, that determines its effect on biodiversity. "The impact is not due to the crop, it's due to the management of the crop," says Jeremy Sweet, the project's scientific coordinator.

"This asks for a degree of joined-up thinking about how we govern these crops. It's not just picking a genetically modified crop and saying 'this is good, that one's bad'," Lutman adds.

The BRIGHT team does warn that seeds left over from transgenic sugar beet would be impossible to separate from normal sugar beet grown subsequently on the same land. Farmers would therefore struggle to stay under the 0.9% contamination limit required for a crop to be sold in Europe as 'not genetically modified'.

Regulation issues

The team hopes that European governments will take notice of their work when deciding how to regulate transgenic crops. Despite a recent European Union directive calling on member states to impose regulations on the crops, France has declared that it will not draft any legislation until next spring.

Meanwhile, Germany is embroiled in a dispute between opponents of transgenic crops and advocates of the technology. Opponents have welcomed legislation approved by the German parliament on 26 November that will hold GM farmers liable for any contamination of their non-GM neighbours' fields.

But advocates counter that such stringent regulations will foment anti-GM feeling and are unnecessary, citing researchers' claims made at a press conference two days earlier that transgenic corn fields can 'coexist' alongside conventional ones without significant contamination.

Such debates are in danger of missing the point, warns Sweet. Investigators need to take a holistic approach to evaluating biodiversity, he says, rather than simply considering the effect of a single crop strain or weed-killing chemical. "We want people to look at the whole farming system," he says. 

Scientific coordinator, BRIGHT

Broom's Barn research centre

Rothamsted Research

• References

  1. Botanical and rotational implications of genetically modified herbicide tolerance in winter oilseed rape and sugar beet published online (2004).