Relationship Between Available Fe and its Chemical Fractions in Some Calcareous Soils of East Azarbaijan Province

In this research available iron was measured in 21 calcareous surface soil samples (0-30 cm) by five methods including DTPA, AB-DTPA, AC-EDTA, hydroxylamine, reference ammonium oxalate and rapid ammonium oxalate. Fe fractions were also determined by the modified sequential extraction procedures introduced by Singh et al. According to results, rapid ammonium oxalate and AC-EDTA methods extracted the maximum (856.03 mg.kg-1) and minimum (4.46 mg.kg-1) amounts of Fe, respectively. Rapid ammonium oxalate extraction method, in addition to Fe-Afeox, extracted other fractions of iron such as Fe-Ex, Fe-Om, Fe-CFeox and Fe-Res. Hydroxylamine method compared to other methods, ectracted Fe mostly from the amorphous oxides source. Regression analysis indicates that Fe-Ex, Fe-AFeox and Fe-Res fractions have major and Fe-Car and Fe-Mnox have minor role in releasing available Fe (with AB-DTPA and DTPA) in the studied soil. According to the statistical relationships, carbonates associated Fe, does not seem a potential source of available Fe in calcareous soils. Organic carbon content and cation exchange capacity of the soils appear the two most influential soil properties that predict available Fe in the studied soils.