Thursday, 13 July 2006

Facilitated Transport of Diuron and Glyphosate in High Copper Vineyard Soils.

Sylvie Dousset1, Jean-Baptiste Dessogne2, Astrid Jacobson3, Philippe Baveye3, and Francis Andreux1. (1) Université de Bourgogne - CST - Géosol, 6 Boulevard Gabriel, 21000 DIJON, France, (2) Université de Reims, 9 Boulevard de la Paix, 51100 REIMS, France, (3) Cornell Univ, 1002 Bradfield Hall, ITHACA, NY 14853

Pesticide leaching through soils may occur in a ‘free' form, or in a ‘bound' form. Bound pesticides may result from interactions with endogenic soil components such as organic matter, or exogenic components such as copper from ‘Bordeaux' mixture. Few studies deal with the facilitated transport of ‘bound' pesticides, in particular, pesticides complexed with copper. The objective of this work was to study the influence of soil copper levels on the leaching of diuron and glyphosate through vineyard soils. A calcareous soil from Vosne-Romanée (Bourgogne, France, 21) and an acidic soil from Odenas (Beaujolais, 69) were sampled from 0-10 cm, dried and sieved to 2 mm. The background copper concentrations were 17 and 34 in the calcareous soil and the acidic soil, respectively. Each soil was enriched with copper sulfate to obtain the following total soil copper concentrations: 125, 250, 500 and 1000 For each treatment, the leaching of diuron and glyphosate was studied in sieved soil columns (6 x 6.8 cm) under laboratory conditions. For both soils, glyphosate leaching was influenced by the soil copper level, whereas diuron leaching was not. In the calcareous soil, glyphosate leaching decreased as the copper level increased from 17 to 500 This result may be explained by a formation of soil-copper-glyphosate ternary complexes. On the other hand, in the acidic soil, glyphosate leaching increased as the copper level increased from 34 to 500 In both soils, the shapes of the copper elution curves in presence of glyphosate were similar to those of glyphosate (except for the acidic soil with the copper level of 500 This suggests the formation of Cu-glyphosate complexes leaching through the calcareous and acidic soils. In conclusion, the application of ‘Bordeaux' mixture does not influence diuron leaching in calcareous or acidic soils. However, increasing copper concentrations in soils reduces glyphosate leaching through calcareous soils, and adversely, increases glyphosate leaching through acidic soils. Therefore, in acidic soils with high copper contents, glyphosate should be applied lightly and judiciously.

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