Distribution of zinc forms and the relationship of these fractions with soil properties in some soils of Golestan Province

The bioavailability and mobility of metals in soils are dependent upon distribution of these metals between solution and solid phases and among solid phase components. A sequential extraction procedure was used to investigate the distribution of Zn among soil fractions for 15 soils of Golestan province that varied in physical and chemical properties. The results revealed that about 0.51, 0.41, 1, 0.44, 8.24, 22.15 and 67.23% of the total soil Zn was present in water-soluble and exchangeable (Ex), carbonates-bound (Car), organically bound (OM), Mn-oxidebound (Mnox), amorphous Fe-oxide-bound (AFeox), crystalline Fe-oxide-bound (CFeox) and residual (Res) forms, respectively. Organic carbon was significantly positively correlated with Zn associated with Mnox, CFeox and total Zn. Cation exchange capacity was significantly positively correlated with Zn in Mnox and AFeox fractions, but did not show correlations with other fractions including Ex- Zn. Organically bound Zn did not show significant correlations with any soil properties. Correlation coefficient between calcium carbonate equivalent and carbonate-bound Zn was not significant. No correlations were observed between soil pH and Zn fractions except with organically bound Zn. Total Zn shows significant correlations with all Zn fractions except Ex-Zn, OM and Mnox fractions. DTPA erxtractable Zn was significantly positively correlated with Zn associated with AFeox and total Zn.