Pedovariability and Expression of Andic Soil Properties on the Basalts of Macomer (Sardinia): Influence of Vegetal Cover

Although it is well known that soil genesis and development are functions of several factors, the nature of the geo-lithological substrate is often regarded as the prevailing one. This paper deals with the pedovariability and the different expressions of andic properties of soils developed on basalt substrate. The study was carried out in a central-western area of Sardinia, Italy (St. Antonio mountain, Macomer) characterized by the presence of basalt from an extinct shield volcano. Eleven profiles, developed under different land uses (pasture, agriculture, sylvicultural management) and vegetal cover, but under the same climatic (mean annual precipitation 905 mm, mean annual temperature 14.6°C), geological (plio-quaternary alkaline basanites, altered phonolite and colluvial coverage) and morphologic (mean altitude 670 m a.s.l.) conditions, were investigated. The physiognomic vegetation clearly shows human influence over the last fifty years, with the presence of natural woods of Quercus pubescens, semi-natural woods of Quercus pubescens, Quercus suber, Quercus ilex and anthropogenic vegetation (reforestation with Pinus, Acacia, Eucalyptus, Quercus). Despite the small extension of the area, the pedovariability is clearly defined, with moderately to well-developed profiles (A-C or A-B-C/R) belonging to Andisols, Entisols, and Inceptisols, solum depth between 30-75 cm, loamyloamy sandy texture, low base saturation (<60%), high organic carbon content (ave. = 48.5 g/kg), high C.E.C (ave. = 38.1 cmol[+]/kg). The andic properties are varied, showing a (Alo+½Feo) content from 0.32% to 3.19%, bulk density from 0.616 to 1.259 kg m-3 and P-retention from 44.8% to 86.8%. The basanite rock matrix does not contain any native quartz or volcanic glass. However, such mineralogical phases were detected in the surface horizon of some profiles under different vegetal cover, with more or less expressed andic properties.