Relationships between available Cu and its chemical fractions in some calcareous soils of East Azerbaijan province

Information about chemical forms of copper (Cu) is important for the evaluation of its status in soil and also understanding of soil fertility, plant nutrition and soil chemistry. To obtain such information, in this research available Cu was determined in 21 calcareous surface soil samples (0-30 cm) by six methods including DTPA, AB-DTPA, AC-EDTA, hydroxylamine, reference ammonium oxalate and rapid ammonium oxalate. Cu fractions were also determined by the modified sequential extraction procedures introduced by Singh et al. According to the results, rapid ammonium oxalate and DTPA-TEA methods extracted the maximum (25.69 mg kg-1) and minimum (1.57 mg kg-1) amounts of Cu, respectively. Also, Cu-residual and Cu-CFeox forms the greatest amount of Cu in studied soils respectively. AC-EDTA extraction method, in addition to Cu-Residual, extracted other fractions of copper such as Cu-Exchangeable, and Cu-CFeoxide. Hydroxylamine method extracted Cu mostly from the manganese oxides source compared to other methods. Regression analysis indicates that Cu-CFeox forms the maximum copper extracted by extractants AB-DTPA, AC-EDTA and DTPA in soils was studied. According to the statistical relationships presumably Cu-CFeox, does seem a potential source of available Cu in studied soils. Among chemical properties of soil, CCE content of the soils appear the most influential properties that predict available Cu in the studied soils.