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This article in AJ

  1. Vol. 69 No. 5, p. 820-824
    Received: July 24, 1976

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Influence of Soil pH on the Phytotoxicity of Three s-Triazine Herbicides1

  1. R. S. Adams and
  2. D. J. Pritchard2



The bioactivity of s-triazine herbicides is known to vary with soil pH. The purpose of this study was, on one soil type and under similar climatic conditions, to determine the influence of soil pH on the phytotoxicity of atrazine (2 - chloro - 4 - (ethylamino) - 6 - (isopropylamino) - s - triazine), prometryn (2, 4 - bis (isopropylamino) - 6 - (methylthio) - s - triazine and secbumeton (N - ethyl - 6 - methoxy - N - (1-methylpropyl) - 1, 3, 5 - triazine - 2, 4 - diamine). Greenhouse and field bioassays were used with chemicals applied at four rates ranging from 0 to 4.5 ppm. Soybeans (Glycine max L.) was the bioassay plant in the greenhouse and maize (Zea mays L.) in the field. The soil was Port Byron sil (Typic Hapludolls) and had been in a long term lime study (five rates) for 19 years prior to these studies. Soil pH varied from pH 5.4 to pH 7.4. Soil pH demonstrated the dominant influence on the phytotoxicity of prometryn and secbumeton, but demonstrated much less influence on atrazine toxicity. Organic carbon variation did not effect the phytotoxicity of prometryn or secbumeton, but was the principle factor influencing atrazine phytotoxicity. In the field studies maize was injured severely by high rates of prometryn and secbumeton in the calcareous soil samples, but not in the acid treatments. Maize was not affected by any rate of atrazine or at any pH examined. The influence of pH on s-triazine toxicity appeared due to differential adsorption or differential hydrolysis by the soil.

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