The iron content of some red Mediterranean soils from northeast Spain and its pedogenic significance

Abstract

Alfisols cover 18% of the surface of the NE edge of the Garraf massif (SE of Barcelona, Catalonia). Most of these are Mediterranean red soils. Some representative pedons, especially over Mesozoic limestones, are discussed in this paper. Climate of the zone is littoral Mediterranean (mean temperature 16°C, precipitation 650 mm). Pedoclimatic regimes are xeric and thermic. Vegetation is Quercetum ilicis galloprovinciale. Horizon B is 5YR and 2.5YR in Munsell Hue with a pHw of 7.2 to 8.6. All of them are base saturated and the majority recarbonated. Organic matter content is 2.5%. Some have an “isohumic” character. The illuviation clay index ranges from 0.37 to 0.87 and the mean value of the illuviation Fe index is 0.76. The nearly constant Fe d/clay ratio indicates co-illuviation. Values for Fe d are between 0.40% and 2.81%. The mean Fe o is 0.057%, and it ranges between 0 to 0.14%. Generally redness rating (RR) increases with Fe d. Values of Fe d/Fe 1 vary from 0.22 to 0.82 and the mean is 0.54. Rubefaction according to redness rating is moderate. Taxonomically, Calcic Haploxeralfs predominate and are located at 50–70 m above sea level. Calcic Palexeralfs (at 70–80 m and again at 150 m) and Petrocalcic Palexeralfs (at 80–130 m) are also found. Typic Haploxeralfs are frequent over limestones at higher altitudes (260 m) or overlying silicic rocks found at 35 65 m. According to the 1967 French Classification System they are Red fersialitic and Brown fersialitic soils and some are integrades with Cinnamotnic soils (“marron encroûté”).