Unlock the Secrets of How Herbicides Interact With Soil and Subsoil
August 16, 2001
Predicting how herbicides move in
soil requires accurate estimates of how these chemicals bind to soils and
geologic materials--vital information thats often lacking for materials
below the soils surface.
Now, Agricultural Research Service
microbiologist Thomas B. Moorman at the National
Soil Tilth Laboratory in Ames, Iowa, working with researchers at
University-Miami and Iowa State
University-Ames, has measured how one important herbicide, atrazine, binds
to and lets go of particles in different soil types. Unlike previous research,
this project measured atrazines binding deep into Iowa soil.
Atrazine is an organic compound, widely used as a herbicide for control of
broadleaf and grassy weeds. During the 1980s, atrazine was estimated to be the
most widely used herbicide in the United States. Today, because of its low
cost, it is still applied to millions of acres of U.S. croplands, especially
corn and sorghum fields.
The scientists used a variety of simulation models to predict the risk of
this herbicides movement into groundwater. For accurate prediction, these
models integrated information about rainfall, waterflow, soil types and
The team found that the soils were low in organic carbon. But they retained
more herbicide than would have been predicted, based on past research. The
researchers also found that certain glacial till materials--geologic sediment
of sand, silt and clay in the saturated zone beneath the groundwater
surface--were able to retain atrazine quite strongly, greatly limiting its
leaching. This geologic sediment was deposited as glaciers retreated from Iowa
about 15,000 years ago.
The researchers believe this knowledge should increase scientists and
farmers ability to predict herbicide contamination of groundwater and aid
in developing practices that protect water resources from contamination. This
will help producers manage herbicides more carefully and assure better water
quality for the general public.
ARS is the U.S. Department of
Agricultures chief scientific research agency.