DISTRIBUTION AND FORMS OF COPPER, IRON, MANGANESE, AND ZINC IN CALCAREOUS SOILS OF INDIA

Abstract

The distribution of trace metals among various chemical forms may vary significantly in response to changing soil properties. Therefore, we conducted a study to investigate the distribution of Cu, Fe, Mn, and Zn among soil fractions for 11 soils that varied in physical and chemical properties. A sequential extraction scheme was used that fractionated Cu, Fe, Mn, and Zn into exchangeable (EX), carbonates-bound (CARB), organically bound (OM), Mn-oxide-bound (MnOX), amorphous Fe-oxide-bound (AFeOX), crystalline Fe-oxide-bound (CFeOX), and residual (RES) forms. A sequential fractionation showed that about 62, 52, 53, and 82% of the total soil Cu, Fe, Mn, and Zn, respectively, was present in RES fraction; about 17, 41, 11, and 7% of the total soil Cu, Fe, Mn, and Zn, respectively, was associated with the CFeOX fraction. The AFeOX fraction averaged to 12, 6, 9, and 5% of the total soil Cu, Fe, Mn, and Zn, respectively. The amounts of metals in the OM fraction were generally <1.0%. Metals associated with the MnOX fraction amounted to 0.7, <0.1, 22, and 2% of the total soil Cu, Fe, Mn, and Zn, respectively. Carbonates-bound Cu, Fe, Mn, and Zn accounted for 6, <0.1, 4, and 2%, respectively, of the total present in soils. EX-Cu or EX-Zn averaged to 2%, whereas EX-Fe or EX-Mn were nonsignificant fractions averaging to <0.1% of the total present. Exchangeable metals did not show significant correlations with any soil properties except EX-Zn and free Fe. In general, such soil properties as sand, silt, clay, free Fe, and free Mn were significantly correlated with metals in AFeOX, CFeOX, and RES fractions. No consistent correlations were observed between soil properties and metals associated with CARB, OM and MnOX fractions.