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This article in JEQ

  1. Vol. 24 No. 1, p. 68-79
    Received: Aug 23, 1993

    * Corresponding author(s): deeweed@iastate.edu
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Dissipation and Distribution of Herbicides in the Soil Profile

  1. D. A. J. Weed *,
  2. R. S. Kanwar,
  3. D. E. Stoltenberg and
  4. R. L. Pfeiffer
  1. Dep. of Agronomy, Univ. of Wisconsin, Madison, WI 53706;
    USDA-ARS, National Soil Tilth Lab., Ames, IA 50011.



The distribution and dissipation of alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl) acetanilide], atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5 triazine), and metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] in soil were studied in 1990, 1991, and 1992. Crop management practices included four tillage methods—chisel plow, moldboard plow, no-till, and ridge-till—and two crop rotations—continuous corn (Zea mays L.) and a corn-soybean [Glycine max (L.) Merr.] rotation. All herbicides were broadcast-spray applied with no incorporation. No-till plots had the smallest amounts of alachlor and metribuzin, whereas ridge-till plots had the smallest amounts of atrazine. Moldboard-plow plots usually contained the highest amounts of all three herbicides, although ridge-till plots had the highest metribuzin levels in 1992. These differences were seldom significant at the 0.05 level of probability, however. Throughout the growing season, 50 to 84% of the alachlor and metribuzin were retained in the top 10-cm layer of soil, and at least 68% of the atrazine was retained in the top 20 cm. From 84 to 98% of the herbicide applied was lost each year, probably by microbial degradation and, for alachlor, by volatilization after application. First-order half-lives were 36 d for alachlor, 55 d for atrazine, and 32 d for metribuzin. A two-compartment model better fitting the alachlor data returned a half-life of 24 d for that herbicide.

Journal Paper no. J-15481 of the Iowa Agric. and Home Economics Exp. Stn., Ames, IA 50011. Project no. 3003. This research was funded by the Leopold Center for Sustainable Agric., Ames, IA, and the CSRS-USDA Project on Management Systems Evaluation Areas (MSEA). Work was done at Iowa State Univ., Ames, IA.

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