Copper fractionation and release from soils devoted to different crops.

We studied copper release as a function of pH in eight samples of acid soils under vine and maize crops containing variable concentrations of total copper (Cu(t)) from 55 to 112 mg kg(-1). Although both types of soil had similar Cu(t) values, the origin of the copper was essentially anthropogenic in the vineyard soils and natural (as result of weathering of parent material) in those under maize. The disparate origin of the metal resulted in marked differences in its fractions, particularly as regards organically bound copper, which was much more abundant in the vineyard soils. This had a strong effect on copper release as a function of pH, which was one order of magnitude greater in the vineyard soils than in those under maize.