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Journal of Environmental Quality Abstract - Surface Water Quality

Comparative Losses of Glyphosate and Selected Residual Herbicides in Surface Runoff from Conservation-tilled Watersheds Planted with Corn or Soybean


This article in JEQ

  1. Vol. 40 No. 4, p. 1281-1289
    Received: Oct 15, 2011

    * Corresponding author(s): martin.shipitalo@ars.usda.gov
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  1. Martin J. Shipitalo *a and
  2. Lloyd B. Owensa
  1. a USDA–ARS, North Appalachian Experimental Watershed, P.O. Box 488, Coshocton, OH 43812-0488. Names are necessary to report factually on available data. However, USDA neither guarantees nor warrants the standard of the product and the use of the name by USDA implies no approval of the product or the exclusion of others that may also be suitable. Assigned to Associate Editor Robert Malone


Residual herbicides regularly used in conjunction with conservation tillage to produce corn (Zea mays L.) and soybean [Glycine max (L.) Merr] are often detected in surface water at concentrations that exceed their U.S. maximum contaminant levels (MCL) and ecological standards. These risks might be reduced by planting glyphosate-tolerant varieties of these crops and totally or partially replacing the residual herbicides alachlor, atrazine, linuron, and metribuzin with glyphosate, a contact herbicide that has a short half-life and is strongly sorbed to soil. Therefore, we applied both herbicide types at typical rates and times to two chisel-plowed and two no-till watersheds in a 2-yr corn/soybean rotation and at half rates to three disked watersheds in a 3-yr corn/soybean/wheat–red clover (Triticum aestivum L.–Trifolium pratense L.) rotation and monitored herbicide losses in surface runoff for three crop years. Average dissolved glyphosate loss for all tillage practices, as a percentage of the amount applied, was significantly less (P ≤ 0.05) than the losses of atrazine (21.4x), alachlor (3.5x), and linuron (8.7x) in corn-crop years. Annual, flow-weighted, concentration of atrazine was as high as 41.3 μg L−1, much greater than its 3 μg L−1 MCL. Likewise, annual, flow-weighted alachlor concentration (MCL = 2 μg L−1) was as high as 11.2 and 4.9 μg L−1 in corn- and soybean-crop years, respectively. In only one runoff event during the 18 watershed-years it was applied did glyphosate concentration exceed its 700 μg L−1 MCL and the highest, annual, flow-weighted concentration was 3.9 μg L−1. Planting glyphosate-tolerant corn and soybean and using glyphosate in lieu of some residual herbicides should reduce the impact of the production of these crops on surface water quality.

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Copyright © 2011. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.