Applicazione di metodologie geofisiche integrate per l'analisi della variabilità spaziale dei suoli

The traditional soil survey, aimed to the production of soil maps, encounters methodological difficulties and high costs, particularly if accurate measurements, necessary for the interpretation of the spatial variations of the soil properties, are essential to address management strategies, as in the case of precision agriculture. In effect, the traditional soil survey made by augering and soil profile excavation is totally incompatible with a spatially dense sampling strategy, which would destroy the soil. For these reasons, there is an increasing attention toward the application of geophysical methods with respect to the traditional soils survey. In fact, the geophysical methods, that are non-invasive, fast and cost-effective, can be of great help in soil mapping because they disturb neither the structure nor the dynamics of the soil. In this paper, the results of detailed soil mapping carried out by electromagnetic induction (E.M.I.) and Very Low Frequency (V.L.F.) methods in two areas of Southern Sardinia (Italy), together with direct investigation, are reported. Moreover, a numerical elaboration based on the spectral analysis of the V.L.F. electromagnetic signals, has been effected. For both studied areas, a 1:10,000 soil map, made using traditional soil surveys techniques, is available. Each area is located along a slope, where different soil units are present. Area 1 is characterised by terraced alluvial deposits of Pleistocene age, that cover sandstones, sometimes microconglomeratic, with silty and clayey intercalations, of Middle Eocene-Lower Pliocene age (Cixerri Formation). Calcic Palexeralfs are present in the upper (calcic horizon at the depth of 82 cm) and middle (calcic horizon at the depth of 115 cm) part of the slope, while Aquic Haploxeralfs characterise the lower part of the slope. Area 2 is characterised by the outcrop of Oligocenic andesites, that are in fault contact with the Cixerri Formation. The latter is not outcropping as it is covered by andesitic colluvia whose thickness increases downslope. From upslope to downslope, the following soils are present: rock outcrop associated with Lithic Xerorthents, Entic Haploxerolls, Vertic Calcixerepts, and Typic Haploxererts. From our analysis it was found that E.M.I. signals acquired in the above mentioned areas, are connected to the soil nature and composition. Furthermore, the spectral content of the V.L.F. electromagnetic can be considered as one of the key approaches used to improve the soil units characterization at field scale.