Abstract
Understanding both the concentration and distribution of aluminum (Al) in agricultural soils is essential to provide a benchmark on the productivity of such soils. In this study, a combination of sequential chemical extraction and mineralogical investigation of the fine fraction was used in order to evaluate Al pools in agricultural soils in Galicia (NW Spain), an Atlantic European region where the wet climate favors leaching of soil basic cations. Determination of Al (soluble/exchangeable/specifically adsorbed, bound to manganese oxides, associated with amorphous compounds, bound to oxidizable organic matter, associated with crystalline iron oxides, and residual fraction) in the topsoil samples was performed to evaluate its potential environmental availability in the study area. Aluminum contents were determined by flame atomic absorption spectrophotometry and the mineralogy of the fine fraction of these soils was studied by X-ray diffraction (XRD). The results showed that Al is mainly in the residual phase, which represents Al incorporated in the lattice minerals, and consequently the threat of toxicity to plants and the environment is reduced. The XRD results showed the presence of hydroxy-Al interlayered vermiculites and kaolinite, accompanied by small amounts of goethite, mica, and quartz.
Highlights
Aluminum exists in the Earth’s crust as the most abundant metal representing 8% of its content in weight
Apart from Al integrated into the structure of soil minerals, Al in the soil solution and Al reactive associated with solid phases occurs, including exchangeable Al, weakly and strongly organically bound Al, forming non-crystalline minerals, and as interlayer hydroxy-aluminum polymers in clay minerals [2, 3]
A combination of sequential chemical extraction and mineralogical investigation of the fine fraction was used to evaluate Al pools in agricultural soils in Galicia (NW Spain), an Atlantic European region where the wet climate favors leaching of soil basic cations
Summary
Aluminum exists in the Earth’s crust as the most abundant metal representing 8% of its content in weight. It is a major element in soils and component of the solid phase, such as primary (e.g., feldspar, mica, amphibole, and pyroxene) and secondary minerals (e.g., kaolinite and Al-hydroxides, such as gibbsite and bayerite). The stability of the aluminum pool in the solid phase controls its facility to be released in the soil solution, Al integrated into the mineral structure being the most stable pool and less likely to be released.
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