The relationship between copper accumulated in vineyard calcareous soils and soil organic matter and iron
Résumé
The intensive use for over 100 yr of copper sulfate (Bordeaux mixt.) to fight mildew in vineyards has led to a substantial accumulation of copper (Cu) in surface soils. To assess the effects of such large concns., the surface soils of 10 Burgundy vineyards were sampled and analyzed for total org. matter (carbon and nitrogen) and metal (copper and iron) contents. Phys. (i.e. size fractionation) and chem. (sequential extn.) methods were used to det. the distribution of these elements. The most Cu-contaminated plots showed the largest accumulation of org. carbon and Cu in the coarse sand and fine sand fractions. Copper was strongly correlated with org. carbon and org. nitrogen in the coarse sand fraction and with org. nitrogen in the fine sand fraction. Copper was also highly correlated with both Fe and org. nitrogen in the clay fraction but not significantly with org. carbon. The sequential extn. showed that Cu was bound mainly to the Fe oxides. However, in the most Cu-contaminated plots, a part of added Cu was bound to org. matter. Apparently, Cu protected indirectly the org. matter present in the coarse fractions against biodegrdn., and therefore modified the distribution of org. carbon among the particle-size fractions. Iron appeared as the main factor responsible for Cu accumulation in the clay fraction, mainly through inclusion of Cu in Fe oxyhydroxides and possibly in clay-humus complexes.