چكيده لاتين :
Introduction: Among essential plant micronutrients, iron (Fe) exerts the highest restriction to crop
production in Fars Province. Determination of iron chemical forms is one of the accurate methods to study the
status of this element (Fe) in the soil. Assessment of the relationships between the chemical forms and soil
characteristic helps to describe the chemical changes of iron in the soil. In this study sequential extraction to
determine iron forms in soils was conducted in order to provide a clear understanding of elements mobility and
availability to plants. Trace elements in the soil are classified into 5 groups of chemical forms. These are the
water-soluble and variable, adsorbed, chelate creating with complex compounds, secondary clay minerals, forms
of insoluble metal oxide minerals, and primary minerals. Trace elements in the forms of water-soluble,
changeable, adsorbed or chelates improve elemental balance in the soil and are known important for plant
nutrition.
Materials and Methods: In a greenhouse experiment, the effects of Fe chelate (FeEDDHA) fertilizer levels
on William cultivar of soybean (Glycine max L.) growth and chemical composition were studied using factorial
and completely randomized design with 3 replications. Treatments were consisted of 10 soil samples and 3 levels
of Fe applications (control, 5 and 10 mg.kg-1 as Fe EDDHA). The aerial parts of Soybean plant were harvested
at 8 weeks after plant emergence.Furthermore, many physical and chemical soil properties and extractable iron
content with DTPA and EDTA were determined. Furthermore, by using sequential extraction methods of Singh
et al ( 1988), chemical forms of Iron for example, exchangeable iron (Exch-Fe), organic bounded iron (OM-Fe),
amorph iron oxides bounded iron (AFeOX-Fe), crystal iron oxides bounded iron (CFeOX-Fe), carbonate and
residual forms of iron in the studied soils, were determined. Finally, concentrations of Fe, Mn, Cu and Zn were
detected in plant and soil.
Results and Discussion: Forms of carbonate, organic, amorphous oxide, crystalline iron oxide in the forms
of bounded and residual iron showed 0.0053, 0.0016, 0.44, 21.1 and 78.6% of the total soil iron, respectively.
Therefore, the content of carbonate, organically bound iron of soil, represented only a small fraction of total soil
iron and was considered unimportant in the total iron.In other words, crystalline iron oxide bound iron and
residual iron forms constituted an important part of total iron.
The average contents of chemical forms of iron were classified as follows:
Res-Fe>CFeOX-Fe>AFeOX-Fe>Car-Fe> OM-Fe >Exch-Fe
Applications of Fe had a significant effect on dry matter, concentration, and uptake of Fe, Zn, Cu and Mn,
extractable forms via extracting DTPA, EDTA, organic and exchangeable forms in soybean, when compared to
the control. Among the chemical forms of iron, organic form had a significant positive correlation with the
amount of available iron plant (extraction by DTPA). Moreover, most of the physical and chemical properties of
calcareous soils studied were significantly correlated with the chemical forms and amount of iron uptake by
plant. DTPA extractable iron had a negative significant correlation with pH (R2=0.514*) and EDTA extractable
iron had a positive significant correlation with organic matter (R2= 0.428*). The strongest correlation among the
different chemical forms was obtained between the total and residual iron forms. Furthermore, the form
connected to the amorphous iron oxides (AFeOX-Fe) showed a positive significant correlation with crystalline
iron oxide bound iron (CFeOX-Fe). Therefore, there were significant correlations between some chemical forms
of Fe, indicating the existence of a dynamic relationship between them in soils.
Conclusions: Application of Fe EDDHA resulted in significant increase in the organic and plant available
(DTPA) forms of iron and, then it can be inferred that due to significant regression equation (r=0.435*) between
two chemical forms of iron (organic and DTPA extracted), the form of organically bound formed the bulk of
available iron in the plant. The positive reaction of plant to the use of Fe EDDHA was attributed to a significant
increase in absorbable forms of iron in the studied soils. Furthermore, the highest level of iron (10 mgkg-1 as Fe
EDDHA) resulted in significant decrease of yield and a sharp drop in the concentration and uptake of other
nutrients such as Cu, Mn and Zn in plant. Thus, production and appropriate stability of the concentration of the
other nutrients and good balance should be achievedthrough using an optimum level of Fe EDDHA in the
Soybeancultivation.
