Copper distribution among physical and chemical fractions in a former vineyard soil.

摘要

In a former vineyard soil, copper (Cu) concentration was detected in different soil chemical and physical fractions, with the aim: (I) to identify soil fractions more important in Cu retention; (II) to reveal if pain symptoms shown by herbaceous crops were attributable to phytotoxicity of available Cu forms; (III) to compare the effectiveness of different methodological approaches in detecting Cu concentration and distribution. A comparison of aqua regia and H₂SO₄+HNO₃ mixture as soil digestion procedures, in moist and dry soil samples, was performed. Both methods were valid in Cu determination, giving comparable results for this soil. Differently, a 21% lower Cu concentration was found in moist samples with both methods. Two sequential procedures were used to chemically fractionate total Cu. The first one separated exchangeable, sorbed, organically bound, and precipitated forms. The second one separated water soluble, exchangeable, Fe and Mn and organic matter bound fractions. Despite the intrinsic differences of the sequential extractions, Cu concentrated mostly in the Fe and Mn and organically bound forms. Cu distribution in particle-size fractions revealed a high concentration of this heavy metal in silt and clay. From the results obtained we confirm the essential role of soil organic matter (SOM) in decreasing Cu toxicity, in particular through the adsorption of the metal on humified SOM and clay-SOM complexes. Pain symptoms shown by herbaceous crops could be attributable to the presence of available Cu forms, still phytotoxic after more than 20 years from land use change.