Copper Accumulation, Availability and Adsorption Capacity in Sandy Soils of Vineyards with Different Cultivation Duration

Abstract:

Bordeaux mixture is a copper-based (Cu) fungicide and bactericide applied in vineyards to control plant diseases. Since it is applied several times per year, it accumulates in large quantities on plants and in soil. This study evaluates the Cu accumulation in, and desorption kinetics and adsorption capability of a sandy Ultisol in a natural field and in 3 vineyards for 5 (V1), 11 (V2), and 31 (V3) years in South of Brazil. Soil samples were collected in 8 depths (0-60 cm) of all four soil profiles, which all displayed similar soil properties. The following soil properties were measured: pH, organic matter (OM), soil bulk density, Cu total concentration, and Cu desorption and adsorption curves. A two first-order reactions model and the Langmuir isotherm were fitted to the desorption and adsorption curves, respectively. An increase in the total mass of Cu in the vineyards followed a linear regression curve, with an average annual increase of 7.15 kg ha^-1. Cu accumulated down to a depth of 5, 20, and 30 cm in V1, V2 and V3, respectively, with the highest Cu content reaching 138.4 mg kg^-1 in the 0-5 cm soil layer of V3. Cu desorption parameters showed a high correlation with its total concentration. Approximately 57 and 19% of total Cu were immediately and slowly available, respectively, indicating a high potential for plant absorption and/or downward movement. Cu concentrations extracted by EDTA from soil layers not affected by anthropogenic Cu inputs were very low. The maximum Cu adsorption capacity of the 0-5 and 5-10 cm soil layers increased with the vineyard age, reaching concentrations higher than 900 mg kg^-1. This increase was highly related to OM and pH, which both increased with cultivation duration. Despite of low clay content of these soils, there is low risk of groundwater Cu contamination for actual conditions. However, high Cu concentrations in the surface layer of the long-term vineyards could cause toxicity problems for this and for companion crops.