Sequential extraction and availability of copper in Cu fungicide-amended vineyard soils from Southern Brazil

The continuous use of cupric fungicides in vineyards, mainly copper sulfate (as a component of the bordeaux mixture), has increased Cu concentration in soils to levels near or even above the maximum established by the Commission of Soil Chemistry and Fertility of the States of Santa Catarina and Rio Grande do Sul, Brazil. Besides the total content, the fractions of the element along the soil profile must be known, because the total content of Cu in the soil is not sufficient to express its environmental impact. The objective of this study was to evaluate the variation of Cu contentes along the soil profile and its speciation and partitioning in 29 soil samples from vineyards in the state of Rio Grande do Sul, Brazil. Samples were collected in areas cropped with vineyards older than 15 years that had been frequently treated with the bordeaux mixture. These samples were from Nitosols, Acrisols, Cambisols and Leptosols and were analysed by sequential extractions and several chemical extractors. Soils had diverse chemical and physical attributes: clay content in the plowed layer (0-0.2 m) ranged from 120 to 610 g kg(-1), pH ranged from 5.3 to 7.3 and organic carbon contents varied from 2.9 to 51 g dm(-3). Among the 29 samples, 16 had the total Cu above the maximum limit allowed by the European Community regulations (140 mg kg(-1)). The average amount of Cu bonded to the oxide fraction accounted for 49.5% of the total Cu.