A Typic Palexerult in the raña formations of the northern plateau in the province of León (Spain) was subjected to acidity correction field tests over a period of three years. The experimental crop was a local rye variety (Secale cereale L. var. Petkus) and the amendments included gypsum, dolomite, limestone and sugar foam waste, all at a 6,000 kg ha -1 rate as CaCO 3 . General analyses were integrated with specific tests for soluble and easily exchangeable Al forms (AlCaCl 2 ) in addition to KCl, BaCl 2 and CuCl 2 extracted Al; adsorbed Al (NH 4 AcO) and amorphous Al. Two types of multiple linear regression models (OLS) for production each year were established; some encompassed all studied variables and others the six Al forms only. As shown here, Al-KCl, Al-CaCl 2 , base saturation and exchangeable Ca were the individual variables most strongly correlated with production, with R 2 = 0.865, within the topmost 12 cm of the soil layer receiving the calcareous amendments. A principal component analysis exposed a substantial share of pH-dependent charge in organic matter on the cation exchange capacity of the soil.Additional key words: acidity; biomass; cation-exchange capacity; OLS equation; pH-dependent charge; pH increment. ResumenFraccionamiento del aluminio extraíble y producción de biomasa en un suelo corregido con materiales calizos Se han realizado unos ensayos de campo de tres años de duración encaminados a la corrección de la acidez de un Typic Palexerult de las formaciones de raña de la meseta norte de la provincia de León (España). El cultivo ensayado fue una variedad local (Petkus) de centeno (Secale cereale L.), empleándose como materiales calizos en la enmienda del suelo yeso, dolomita, caliza y espumas de azucarería, con dosis de 6.000 kg ha -1 de CaCO 3 equivalente. Además de la analítica general, se determinaron las formas de Al solubles y fácilmente intercambiables (Al-CaCl 2 ), además del Al extraído con KCl, BaCl 2 y con CuCl 2 estimándose también el Al-adsorbido (NH 4 OAc) y el Al-amorfo. Se establecieron dos tipos de modelos de regresión lineal múltiple (OLS) de la producción anual de biomasa; el primero incluye todas las variables analizadas, mientras que en el segundo únicamente se consideran las seis formas de Al analizadas. Se comprueba que el Al-KCl, el Al-CaCl 2 , el porcentaje de saturación de bases y el Ca de cambio son las variables más correlacionadas con la producción, alcanzándose valores de R 2 = 0,865, al considerar únicamente los 12 cm superficiales del horizonte en el que incorporó la enmienda caliza. Finalmente, mediante el análisis de componentes principales, se deduce el importante efecto de la carga dependiente del pH de la materia orgánica en el aumento de la CIC del suelo.Palabras clave adicionales: acidez; biomasa; capacidad de intercambio catiónico; carga dependiente del pH; incremento de pH; regresión. *Corresponding author: mavidb@unileon.es Received: 18-07-11. Accepted: 07-05-12Abbreviations used: BS (base saturation); CEC (cation-exchange capacity); Dw (Da...

This paper presents detailed mineralogical results together with a geochemical characterization for a sequence of six natural soil profiles. Bedrock samples (R series) and overlying soil samples (S series) were characterized. The soil profiles are distributed in a series of Paleozoic lithological units from lower Ordovician to upper Carboniferous in age (Iberian Massif, NW Iberia). The lithological influence on mineral properties and geochemical composition and, how different weathering may be occurring under very similar temperate and acidic conditions, have been studied. Field observations together with laboratory analyses were indicative of differential weathering. So, a series of selected chemical indices and relations were applied to clarify this assumption. The mineralogy was analysed by Scanning electron microscopy (SEM-EDS), X-ray diffraction (XRD) of rock powder and soil oriented aggregates. X-ray fluorescence spectrometry (XRF) and inductively coupled plasma mass spectroscopy (ICP-MS) were applied to analyse chemical composition. The first results showed how major elements, SiO2, Al2O3 and Fe2O3, slightly enriched in the soil profiles, are consistent with the dominant mineralogy: quartz, chlorite, muscovite and/or illite, together with kaolinite and albite. The bases K2O, Na2O, CaO and MgO are also coherent with mineral composition and experience little variation, but are gradually removed in the profiles. The mobility of major elements leads to a general loss of bases and, in general, a slight enrichment in silica and sesquioxides. SiO2 is enriched, firstly accumulated in soils and partially depleted by dissolution as colloidal form. Al2O3 in some soils is slightly less than in former rocks, so other physical processes are expected to take place, involving clay removal with consequent aluminium depletion too. A special emphasis has been given to albite coexisting with kaolinite, firstly supposed to be directly inherited from parent substrates when present, but finally the chemical index PIA shows it was mainly due to mineral alteration of plagioclases. The best correlations to explain the albite alteration and kaolinitization progress were obtained with chemical indices PIA, CIW, CIA and Al2O3/Na2O ratio. This together with mineralogical signatures, suggest that kaolinite is the result of gradual dissolution due to the acid hydrolysis of albite in such acidic environments, which may also be attributed to the organic matter influence.

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