Solid-phase speciation and phytoavailability of copper in representative soils of Italy

A study was conducted to determine the solid phase distribution of copper in representative soils of Italy with wide differences in the chemical and physicochemical properties. Sites selected varied in location as well in current vegetation and land use. Samples with a high load of Cu, 133.2-252.9 mg kg(-1) from a vineyard cultivation area were also included to study the effect of contamination on the distribution of Cu amongst solid-phases. The solid-phase fractionation of Cu in the soils was determined using a nine-step selective sequential extraction method. The results indicated that copper was dominantly associated with organic binding sites, 62.6-74.8%. The relative importance of the solid-phase fractions in assessing the Cu phytoavailability by durum wheat in a greenhouse setting and the effectiveness of two soil tests, the DTPA-TEA and NH4Cl extraction methods, for predicting the phytoavailable Cu was studied. Most of Cu was retained by roots with very limited translocation to the upper plant parts of wheat. Both soil tests correlated well with the Cu content in the durum wheat (Triticum turgidum var. durum L.) plant (r(2)=0.99; P=0.0001). A significant correlation (r=0.960, P=0.0001) was found between the plant Cu content and the Cu associated with metal-fulvic complexes, indicating that copper was mainly available through the metal-fulvic complexes. The contaminated soils (soils nos. 9 and 10) had a significantly higher proportion (77%) of Cu associated with organic binding sites, in comparison to that of uncontaminated soil (soil no. 8) (21.3%), resulting in higher proportion of phytoavailable Cu.