Investigation of Iron Chemical Fractions in Some Calcareous Soils of Orange (Citrus sinensis L.) Orchards in Darab Region, East southern of Fars Province

Iron (Fe) deficiency in soil is a limiting factor for the growth of most plants. Fe availability in soil depends on distribution of Fe chemical forms among soil components which it is affected by physicochemical characteristics of soil. The aim of the present study was to investigate the distribution of Fe chemical fractions in some calcareous soils of orange orchards in Drab region (Fars province) and their relationships with some soil physicochemical properties and Fe concentration in leaves of orange trees. A sequential extraction procedure was used to fractionate Fe chemical forms in the studied soils. The results showed that the distribution of Fe chemical fractions in the studied soils were in the order: CFeOx > Fe-Res > AFeOx > Fe-WsEx > Fe-OM > Fe-Car > Fe-MnOx. There was about 98.2 percent of total soil-Fe in both CFeOx and Fe-Res fractions which it indicates the presence of Fe in unavailable forms for plant in the studied soils. Among the Fe chemical forms, AFeOx fraction only showed a significant and positive correlation with DTPA extractable Fe in soil and Fe concentration in leaves of orange trees. Also, among the soil properties, organic matter, calcium carbonate equivalent and cation exchange capacity were the effective characteristics of soil in determining the bioavailability of Fe and content of AFeOx form in soil. There were significant and positive correlations among some Fe chemical forms in soil that it represents a dynamic relationship between Fe chemical forms in soil. According to the results, it seems that the amount of soil organic matter can have an effective role on the availability of Fe in calcareous soils of orange orchards.