Forms of Copper in Soils of Grape Orchards

Copper accumulating in surface (0–15 cm) soils (red sandy clay loam) of grape growing orchards was fractionated into water soluble plus exchangeable, weakly held on inorganic charge sites, organically bound, occluded by oxide materials and residual form present in mineral structure. The average contents of the respective fractions were 0.96, 3.4, 33.3, 16.5 and 33.6 ppm, constituting 1.3, 4.5, 40.0, 19.7 and 42.7% of the total copper. The levels of total and individual fractions of copper were much higher than those reported for field soils. While the various fractions were mutually related, their contents were governed by pH, organic carbon, clay and oxides of iron and manganese in soils. Stepwise regression analysis showed that water soluble plus exchangeable Cu and that bound to inorganic sites were influenced by pH, organically bound fraction by organic carbon, occluded form by oxides of Mn and residual mineral and total Cu by organic carbon and clay.