A proposal to standardize soil/solution herbicide distribution coefficients

Authors:
  • JWJerome B. Weber
    Jerome B. Weber
  • GWGail G. Wilkerson
    Gail G. Wilkerson
  • HLH. Michael Linker
    H. Michael Linker
  • JWJohn W. Wilcut
    John W. Wilcut
  • RLRoss B. Leidy
    Ross B. Leidy
  • WWWilliam W. Witt
    William W. Witt
  • MBMichael Barrett
    Michael Barrett
  • WVWilliam K. Vencill
    William K. Vencill
  • DSDavid R. Shaw
    David R. Shaw
  • TMThomas C. Mueller
    Thomas C. Mueller
  • DMDonnie K. Miller
    Donnie K. Miller
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Abstract
Herbicide soil/solution distribution coefficients (Kd) are used in mathematical models to predict the movement of herbicides in soil and groundwater. Herbicides bind to various soil constituents to differing degrees. The universal soil colloid that binds most herbicides is organic matter (OM), however clay minerals (CM) and metallic hydrous oxides are more retentive for cationic, phosphoric, and arsenic acid compounds. Weakly basic herbicides bind to both organic and inorganic soil colloids. The soil organic carbon (OC) affinity coefficient (Koc) has become a common parameter for comparing herbicide binding in soil; however, because OM and OC determinations vary greatly between methods and laboratories, Koc values may vary greatly. This proposal discusses this issue and offers suggestions for obtaining the most accurate Kd, Freundlich constant (Kf), and Koc values for herbicides listed in the WSSA Herbicide Handbook and Supplement.

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