Abstract

Along the shoreline of the Pernambuco state-Brazil occurs of acid sulfate soils in mangrove ecosystems and floodplain areas. The floodplains are widely used for the cultivation of sugar cane along this region. Acid sulfate soils submitted to cultivation generate high acidity and release of heavy metals, like iron and prejudice to the environment and agricultural production. The objective was to identify the geochemical forms of iron present in floodplain soils of the Pernambuco state, Brazil searching to understand the genesis of these soils and the possible risks of environmental impact due to its use. To perform the sequential extraction were used soil samples from seven profiles located in floodplain areas of three rivers: Goiana (Profile 1), Sirinhaém (Profiles 2, 3 and 4) and Ipojuca (Profiles 5, 6.7). We used the methods of sequential extraction of iron proposed by Claff et al. (2010), Huerta-Diaz (1990), Shuman (1985) and Tessier et al. (1979). The iron concentrations in all fractions extracted were quantified by atomic absorption spectroscopy. The content of Fe in soluble/exchangeable fractions and organically bound were very low or undetectable in most of profiles. This indicates that despite the high acidity of these profiles the iron present in these floodplains cultivated with cane sugar has no risk of carrying this element to drain water or subsurface and damage to environment. The values the sequential extraction of iron also demonstrated a predominance of iron bound forms of non-crystalline oxides, being consistent with the environment hydromorphism, and high values of iron associated with pyrite in the subsoil, the profiles 2 and 3 were classified as acid sulphate soils.