Relationships between extractable copper, soil properties and copper uptake by wild plants in vineyard soils

The repeated use of Cu fungicides to control vine downy mildew has been responsible for the heavy increase of total Cu content in vineyard soils. In a French Mediterranean region (Département de lʹHérault), the total Cu content observed in the upper layer of vineyard soils ranged from 31 to 250 mg kg−1, versus 14 to 29 mg kg−1 in woodland plots. Cu distribution with soil depth showed that Cu input from Cu treatment was essentially concentrated in the upper layers, except for two soil profiles which presented Cu enrichments in deep horizons. EDTA, DTPA and ammonium acetate-extractable Cu were highly correlated with soil total Cu, and were weakly correlated with Cu content in wild plants grown in the plots. These observations suggested that these extraction methods are of limited interest for predicting the availability of Cu to plants in Cu-contaminated soils. In comparison, CaCl2 extractable Cu was not correlated to total Cu and depended mainly on soil pH. When the soil pH increased the quantities of extractable Cu decreased. For soil with neutral to acid pH, CaCl2 extractable Cu was correlated with the contents observed in wild plants. It thus appeared as the best way of predicting plant-available Cu in vineyard soils.