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This article in JEQ

  1. Vol. 30 No. 5, p. 1631-1635
    Received: Oct 30, 2000

    * Corresponding author(s): ohno@maine.edu
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Oxidation of Phenolic Acid Derivatives by Soil and Its Relevance to Allelopathic Activity

  1. Tsutomu Ohno *
  1. Department of Plant, Soil and Environmental Sciences, Univ. of Maine, 5722 Deering Hall, Orono, ME 04469-5722


Previous studies have suggested that phenolic acids from legume green manures may contribute to weed control through allelopathy. The objectives of this study were to investigate the oxidation reactions of phenolic acids in soil and to determine the subsequent effects of oxidation upon phytotoxicity. Soils were reacted for 18 h with 0.25 mmol L−1 benzoic and cinnamic acid derivative solutions and Mn release from the suspension was used as a marker for phenolic acid oxidation. The extent of oxidation in soil suspensions was in the order of 3,4-dihydroxy- > 4-hydroxy-3-methoxy- > 4-hydroxy- ≅ 2-hydroxy–substituted benzoic and cinnamic acids. The same ranking was observed for cyclic voltammetry peak currents of the cinnamic acid derivatives. This suggests that the oxidation of phenolic acids is controlled by the electron transfer step from the sorbed phenolic acid to the metal oxide. A bioassay experiment showed that the 4-hydroxy-, 4-hydroxy-3-methoxy-, and 3,4-dihydroxy–substituted cinnamic acids were bioactive at 0.25 mmol L−1 concentration. Reaction with soil for 18 h resulted in the elimination of bioactivity of these three cinnamic acids at the 5% significance level. The oxidative reactivity of phenolic acids may limit the potential of allelopathy as a component of an integrated weed management system. However, the initial phytotoxicity after soil incorporation may coincide with the early, critical stage of weed emergence and establishment, so that allelopathic phenolic acids may still play a role in weed management despite their reactivity in soil systems.

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Copyright © 2001. American Society of Agronomy, Crop Science Society of America, Soil Science SocietyPublished in J. Environ. Qual.30:1631–1635.