[gardeners] FW: New Clues: How Herbicides and Soil Interact

Lon J. Rombough (gardeners@globalgarden.com)
Thu, 16 Aug 2001 06:59:53 -0700

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From: "ARS News Service" <isjd@ars-grin.gov>
To: "ARS News List" <ars-news@ars-grin.gov>
Subject: New Clues: How Herbicides and Soil Interact
Date: Thu, Aug 16, 2001, 3:20 AM

Researchers Unlock the Secrets of How Herbicides Interact With Soil and


ARS News Service
Agricultural Research Service, USDA
August 16, 2001
Jennifer Arnold, (301) 504-1624, jaarnold@ars.usda.gov

Predicting how herbicides move in soil requires accurate estimates of how
these chemicals bind to soils and geologic materials--vital information
that's often lacking for materials below the soil's surface.

Now, Agricultural Research Service microbiologist Thomas B. Moorman at the
National Soil Tilth Laboratory in Ames, Iowa, working with researchers at
Florida International 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 atrazine's 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 herbicide's movement into groundwater. For accurate prediction, these
models integrated information about rainfall, waterflow, soil types and
atrazine use.

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 Agriculture's chief scientific research
agency. The ARS National Soil Tilth Laboratory is on the web at