Washington, April 23 : A new study has suggested that planting herbicide-tolerant crop varieties can reduce herbicide loss and concentrations in water bodies where they are grown.
The residual herbicides commonly used in the production of corn and soybean are frequently detected in rivers, streams, and reservoirs at concentrations that exceed drinking water standards in areas where these crops are extensively grown.
When these bodies of water are used as sources of drinking water, this contamination can lead to increased treatment costs or a need to seek alternative sources of supply.
Additionally, these herbicides can have negative effects on aquatic ecosystems at concentrations well below their drinking water standards.
When genetically modified, herbicide-tolerant, corn and soybean became commercially available in the 1990s; it became possible to replace some of the problematic residual herbicides with strongly sorbed, short half-life, contact herbicides that may be more environmentally benign.
By 2004, almost 90% of the soybean grown in the US was genetically modified for tolerance to the contact herbicide glyphosate, which is currently the most widely used herbicide in the world.
In a four-year study, researchers at the USDA (United States Department of Agriculture) compared relative losses of both herbicide types when applied at normal rates to seven small watersheds planted with Liberty-Linked corn or Roundup Ready soybean.
In their report, soil scientists Martin Shipitalo and Lloyd Owens, and agricultural engineer Rob Malone, noted that losses of contact herbicides in surface runoff were usually much less than those for the residual herbicides, as a percentage of the amount of herbicide applied.
Averaged for all soybean crop years, glyphosate loss was about one-seventh that of metribuzin and one half that of alachlor, residual herbicides it can replace. Similarly, average loss of the contact herbicide glufosinate (Liberty) was one-fourth that of atrazine, a residual corn herbicide it can replace.
According to project leader Martin Shipitalo, "The concentrations of the contact herbicides in the runoff never exceeded their established or proposed drinking water standards, while the residual herbicides frequently exceeded their standards, particularly in the first few runoff events after application."
In light of increased economic incentives to grow more corn and soybean for biofuel production, these results suggest to farmers and the regulatory community that herbicide losses and concentrations in runoff can be reduced by planting herbicide-tolerant varieties of these crops and replacing some of the residual herbicides with the contact herbicides compared in this study.