Forms of copper in vineyard soils as affected by pH and poultry litter application

The objective of this study was to evaluate the distribution of forms of copper as affected by pH and poultry litter addition in samples of surface layers (0 to 10 cm) of a Dystrophic Lithic Udorthent and a Humic Dystrudept, both from Serra Gaucha (Rio Grande do Sul highlands), Brazil, cultivated for more than 15 years with vines treated with successive applications of copper-based products. To evaluate the effects of pH variation and soil organic matter content in copper forms, five doses of HNO3 (50,100,200, 300 e 400 mmol kg(-1)) and four doses of poultry litter in dry basis (10, 20, 40 e 80 t ha(-1)) were added to the soils. The following fractions were evaluated: exchangeable; bound to organic matter; bound to Fe, Al, and Mn oxides; and residual. The largest proportion of copper of the soil was bound to organic matter fraction (from 70 to 80%). As the pH decreased from 6.8 to 3.8, the copper exchangeable contents increased, while copper bound to organic matter, oxides, and residual fractions decreased. The application of poultry litter did not significantly affect the distribution of forms of copper in both soils, except for the exchangeable fraction.