Abstract

AUXTERO, Edgardo  and  MADEIRA, Manuel. Extractability of aluminium and forms in solution of soils derived from granite in Portugal. Rev. de Ciências Agrárias [online]. 2011, vol.34, n.1, pp.65-79. ISSN 0871-018X.

Extractable aluminium (Al) was determined in surface and subsurface horizons of eleven pedons derived from granite occurring in Portugal, under a wide range of precipitation. Five successive extractions with 1 M KCl, 0.5 M CuCl₂ and 0.33 M LaCl₃ were used. Monomeric (Al_m) and organic (Al_org) forms of Al in the soil solution, extracted at field capacity, were also determined. Amounts of extracted Al were greatest with the 0.5 M CuCl₂ and lowest with the 1 M KCl. These amounts showed strong positive correlation with soil organic C contents. Soil horizons having high contents (56-80 g kg^-1) of organic C showed the highest amount of extractable Al by the 0.5 M CuCl₂ (12.2-30.9 cmol_c kg^-1). Organically bound Al extracted by the 0.5 M CuCl₂ and 0.33 M LaCl₃ was also highest in these soils (7.6-10.1 and 4.7-8.3 cmol_c kg^-1, respectively). In contrast, lowest amounts of Al extracted by the 1 M KCl, 0.5 M CuCl₂ and 0.33 M LaCl₃ (0.9-4.3, 4.1-17.1 and 2.2-7.2 cmol_c kg^-1, respectively) were observed in horizons containing low organic C content (3-22 g kg^-1). Concentrations of total (Al_T), monomeric (Al_m) and organic (Al_org) Al in the soil solution of studied soils also increased with increasing soil organic C content, but only Al_m was significantly correlated with soil organic Ccontent. Solution of soils having low organic C contents (3-6 g kg^-1) showed the lowest concentrations of Al_T, Al_m and Al_org (0.09-1.60, 0.06-0.38 and 0.03-1.29 µg mL^-1, respectively). In contrast, the concentrations of Al_T (7.1-17.2 µg mL^-1),Al_m (0.8-0.9 µg mL^-1),and Al_org (7.6-16.9 µg mL^-1)were much higher in soils containing high amounts of organic C (37-73 g kg^-1). In order to monitor the effects of Al in the soil and quality of sub-superficial water, changes in the concentration of monomeric forms of Al and their activities in the soil solution need further study.

Keywords : Aluminium; organic carbon; pH; soil solution.

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