Degradation of Isouron in Soils

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  • OZAKI Mamoru
    Aburahi Laboratories, Shionogi Research Laboratories, Shionogi & Co., Ltd.
  • TANAKA Yoshimi
    Aburahi Laboratories, Shionogi Research Laboratories, Shionogi & Co., Ltd.
  • KUWATSUKA Shozo
    Faculty of Agriculture, Nagoya University

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Other Title
  • 土壌中におけるイソウロンの分解
  • 土壌中におけるイソウロンの分解〔英文〕
  • ドジョウチュウ ニ オケル イソウロン ノ ブンカイ エイブン

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Abstract

The degradation of the urea herbicide isouron [3-(5-tert-butyl-3-isoxazolyl)-1, 1-dimethylurea] was studied using 6 kinds of soils under upland conditions. Isouron was stable in soils in general, but in volcanic ash Kanuma and Nasu soils the rapid degradation of isouron occurred after 3 and 6 months of incubation, respectively. Isouron was hardly degraded in loamy sand Toyohama and light clay Kohnan soils during 7 months of incubation. In sandy clay Ryuoh and sandy loam Aburahi soils isouron was easily degraded at the initial stage of incubation with the half-life of 2.1 and 2.5 months, respectively. The populations of bacteria and actinomycetes were larger in Ryuoh and Aburahi soils than in the others, but isourondegrading organisms could not be detected in any of these soils by the most probable numbers method. No correlation was found between the degradation rate and the absorption of isouron. When Kanuma or Toyohama soil was adjusted to neutral pH, isouron was rapidly degraded. Particularly in Kanuma soil adjusted to pH 7.0, the half-life of isouron shortened to 1 month. The degradation product of isouron in the soils was identified as 3-(5-tert-butyl-3-isoxazolyl)-1-methylurea formed through demethylation of the dimethylurea side chain.

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