Determination of Iron Fractions and their Relations with Soil properties in Some Soils of East Azerbaijan Province

Information about different forms of Fe and determining the amount of each one of them is important for evaluation of soil Fe status and also understanding of soil Fe chemistry. To obtain such information, amount and distribution of Fe in different fractions of 21 soil composite samples of East Azerbaijan Province were determined by modified sequential extraction procedures introduced by Singh et al and the relationships of these types with each other and with soil properties were also investigated. According to the results, total Fe concentrations of soils, determined by Sposito et al method ranged from 15.25 to 50.84 g kg-1 with a mean of 29.84 g kg-1 and by aqua-regia method ranged from19.54 to 47.75 g kg-1, with a mean of 30.38 g kg-1. The amount of different forms of iron was determined to be as follow: Residual iron (Fe-Res)> iron associated with the crystalline iron oxides (Fe-CFeOX)> iron associated with the amorphous iron oxides (Fe-AFeOX)> manganese- oxide- associated Fe (Fe- MnOX)> organic matter-associated Fe (Fe-OM)> exchangeable iron (Fe-Ex) ≥ carbonates-bound iron (Fe-Car). Simple correlation coefficients showed that soil pH had a significant negative correlation with Fe-CFeOX, active calcium carbonate equivalent had a significant negative correlation with Fe-MnOX and CEC had a significant positive correlation with Fe-Ex, Fe-Res and total iron. Clay content had a significant positive correlation with Fe-Ex, Fe-Res and total iron and had a significant negative correlation with Fe-MnOX. Also silt content had a significant positive correlation with organic matter and significant negative correlation with manganese- oxide- associated Fe. In this study, a significant correlation was also observed between the Fe forms themselves, which is presumably a reflection of the existence of a dynamic relationship between the chemical forms of an element in soil.