Salvatore Raimondi

Effect of climate and vegetation on soil organic carbon, humus fractions, allophanes, imogolite, kaolinite, and oxyhydroxides in volcanic soils of etna (sicily)

A soil sequence along an elevational gradient ranging from subtropical to subalpine climate zones in the Etna region (Sicily, southern Italy) was investigated with respect to organic C, kaolinite, and crystalline to noncrystalline Al and Fe phases. Special emphasis was given to the stabilization of soil organic carbon (SOC) and its interaction with the inorganic phases. The soils were variations of Vitric Andosols that developed on a trachy-basaltic lava flow with an age of 15,000 years. Two main vegetation systems dominated the sites: at the lower sites, it was mainly maquis vegetation and, at the higher elevated sites, predominantly coniferous forest. The concentration of SOC in the topsoil, the SOC stocks in the profiles, the humus fractions such as humic and fulvic acids, functional groups and substances of organic matter, imogolite-type materials (ITM), and oxyhydroxides were found to be strongly related to elevation and, thus, climate (precipitation and temperature) and vegetation. The C/N ratio in the topsoil was especially indicative of the vegetation type. The amount of SOC, ITM, and crystalline Fe oxyhydroxides decreased with increasing altitude. Weathering, as related to the proportion of crystalline Fe-oxyhydroxides or the kaolinite concentration in the clay fraction, seemed to be greater at the lower elevated sites. At these sites, maquis vegetation led to a higher accumulation of SOC as compared with the coniferous trees at the higher sites. Fire activity, as indicated by aromatic compounds in the humic acids and by the presence of charcoal in the soil, has most probably influenced several important soil processes. The identification and radiocarbon dating of charcoal revealed evidence that repeated bush fires had played a significant role in soil formation. The better stabilization of SOC at lower altitudes might be due to the specific climatic conditions with a more pronounced change in periods of humidity alternating with periods of droughts and resultant fire activity. The positive correlation between mean annual temperature and SOC content supports such a hypothesis. The climate- and vegetation-dependent stabilization of organic matter in the soil can be ascribed to the proportion of aromatics in the humic acids, to the presence of noncrystalline Al and Fe phases, to the kaolinite concentration, to the amount of clay, and to a lesser extent to the silt fraction.

ORIGIN OF CLAY MINERALS IN SOILS ON PYROCLASTIC DEPOSITS IN THE ISLAND OF LIPARI (ITALY)

The island of Lipari (Italy) is characterized by calc-alkaline to potassic volcanism and a Mediterranean-type climate. The mineralogical and chemical features of two different soil profiles with ages of 92,000 and 10,000–40,000 y, respectively, have been investigated. There were no Andisols, but Vitric and Vertic Cambisols have developed at both sites. Although the morphology of the soils was similar, remarkable differences in the clay mineralogy between the two sites were observed. The site with the Vitric Cambisol was associated with the weathering sequence: glass → halloysite → kaolinite or interstratified kaolinite-2:1 clay minerals. Both sites had smectite in the clay fraction and, to a large extent, this smectite had a low charge and could be characterized as a dioctahedral montmorillonite. At the site with a Vertic Cambisol, smectite was the predominant mineral phase in the clay fraction. The smectites (predominantly montmorillonite) found in this soil were probably not of pedogenetic origin and are, therefore, inherited from the parent material. Their formation is due to hydrothermal alteration of glass particles during or immediately after the emplacement of the pyroclastic flow. The octahedral character of the smectites did not change from the C to the A horizon indicating that they are resistant to weathering processes. A high-charge expandable mineral was detected in small concentrations in the Vertic Cambisol and had a dioctahedral structure. In this case also, no signs of significant weathering or transformation could be detected in the soil profile. In contrast to many other investigations, no active smectite formation within the soil profiles could be measured. The subtropical and rather dry climate in Lipari might, therefore, favor the persistence of dioctahedral low-charge montmorillonites that are associated with a small amount of a high-charge expandable mineral in the soil.

Influence of Soil Salinity on Sensory Characteristics and Volatile Aroma Compounds of Nero d'Avola Wine

The influence of soil salinity on the chemical composition, volatile aromatic compounds, and sensory characteristics of Nero d’Avola wine was examined. Data on vineyard productivity, such as grape yield, are also reported. Physicochemical parameters were determined on the samples analyzed. Solid-phase microextraction was used for the extraction of aromatic volatile compounds, followed by capillary gas chromatography-mass spectrometry. Sensory analyses were performed by visual inspection, smelling, and tasting. Statistical analysis showed that most of the physicochemical parameters and volatile constituents, both primary and fermentation aromas, were influenced by the soil salinity. The composition differences observed among the samples had little influence on the sensory characteristics; the increase in soil salinity enhanced color intensity, purple reflexes, salty, citrus, and fruit in the aroma. Results indicate that Nero d’Avola vine may be well suited to increased soil salinity, even given reduced plant productivity.

Pedogenesis and Variability in Soil Properties in a Floodplain of a Semiarid Environment in Southwestern Sicily (Italy).

We performed a pedological study of the variability in soils in a floodplain area of a semiarid region in southwestern Sicily. The objectives of our research were to (i) investigate the role of parent material, erosion, and distribution processes on soil pedogenesis and horizon differentiation; (ii) evaluate the statistical distribution of soil properties; and (iii) interpret these distributions in terms of pedogenic and other processes. Our results showed that not all soil properties examined followed a normal distribution and that even when log-transformed, the degree of normality of the soil salinity data did not improve. Furthermore, principal component analysis was performed to investigate the role of parent material and erosion and distribution processes on soil pedogenesis and horizon differentiation. Although all soils tested had developed on alluvium, great variability was found among them, mostly related to the grain size of the substrates. Soils that had developed on finer alluvium had higher clay content, cation exchange capacity, exchangeable bases, soil salinity, exchangeable sodium percentage, and sometimes organic carbon accumulation with depth because of hydromorphic conditions and chemical stabilization by Ca++ ions. Soils that had developed on coarser deposits showed a clear differentiation between the topsoil and subsoil in terms of a decrease in clay content from the surface soil to the subsoil. The accumulation of clay on the surface of a floodplain can result in a high risk of loss of productivity because of the significant relationship between clay content, hydromorphic conditions, and exchangeable sodium percentage.

Prediction of Soil Formation as a Function of Age Using the Percolation Theory Approach

Recent modeling and comparison with field results showed that soil formation by chemical weathering, from bedrock or unconsolidated material, is limited largely by solute transport. Chemical weathering rates are proportional to solute velocities. Nonreactive solute transport described by non-Gaussian transport theory appears compatible with soil formation rates. This change in understanding opens new possibilities for predicting soil production and depth across orders of magnitude of time scales. Percolation theory for modeling the evolution of soil depth and production was applied to new and published data for alpine and Mediterranean soils. The first goal was to check whether the empirical data conform to the theory. Secondly we analyzed discrepancies between theory and observation to find out if the theory is incomplete, if modifications of existing experimental procedures are needed and what parameters might be estimated improperly. Not all input parameters required for current theoretical formulations (particle size, erosion and infiltration rates) are collected routinely in the field; thus, theory must address how to find these quantities from existing climate and soil data repositories, which implicitly introduces some uncertainties. Existing results for soil texture, typically reported at relevant field sites, had to be transformed to results for a median particle size, d50, a specific theoretical input parameter. The modeling tracked reasonably well the evolution of the alpine and Mediterranean soils. For the Alpine sites we found, however, that we consistently overestimated soil depths by approximately 45%. Particularly during early soil formation, chemical weathering is more severely limited by reaction kinetics than by solute transport. The kinetic limitation of mineral weathering can affect the system until 1kyr to a maximum of 10kyr of soil evolution. Thereafter, solute transport seems dominant. The trend and scatter of soil depth evolution is well captured, particularly for Mediterranean soils. We assume that some neglected processes, such as bioturbation, tree throw, and land use change contributed to local reorganization of the soil and thus to some differences to the model. Nonetheless, the model is able to generate soil depth and confirms decreasing production rates with age. A steady state for soils is not reached before about 100 kyr.