Madison, Wisconsin
April 22, 2008
Source:
The American Society of
Agronomy (ASA)
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 (Roundup), which is currently the most widely used
herbicide in the world.
In a four-year study, researchers at the USDA-ARS’s North
Appalachian Experimental Watershed near Coshocton, OH 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, published in the
March-April issue of the Journal of Environmental Quality, 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.
More importantly, 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”. Concentrations of atrazine in runoff were up
to 240 times greater than its drinking water standard while
alachlor concentrations were up to 700 times greater than its
standard. Conversely, the maximum glyphosate concentration noted
was nearly four times less than its standard. Glufosinate
currently has no established standard, but was only detected at
low concentrations and was below its detection limit 80 days
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.
The full article is available for no charge for 30 days
following the date of this summary. View the abstract at
http://jeq.scijournals.org/cgi/content/abstract/37/2/401.
The Journal of
Environmental Quality is a peer-reviewed, international
journal of environmental quality in natural and agricultural
ecosystems published six times a year by the American Society of
Agronomy (ASA), Crop Science Society of America (CSSA), and the
Soil Science Society of America (SSSA). The Journal of
Environmental Quality covers various aspects of anthropogenic
impacts on the environment, including terrestrial, atmospheric,
and aquatic systems.
The American Society of
Agronomy (ASA) is a scientific society helping its 8,000+
members advance the disciplines and practices of agronomy by
supporting professional growth and science policy initiatives,
and by providing quality, research-based publications and a
variety of member services.
|
|
