The skeleton water-extractable fines (SWEF) is a soil fraction smaller than 2mm located at the interface between rock fragments (RF) and fine earth (FE). It is made of illuvial and/or RF weathering products comprising neoformed clay-size particles and organic substances. Contrary to FE and even to soil RF, SWEF represents a poorly documented soil fraction despite its unique ion exchange properties. To fill this knowledge gap, we compared mineralogy, effective cation exchange capacity (ECEC), and exchangeable cation composition of SWEF with those of FE and RF from three acidic soils derived from either mica schist (Mottarone, Italy), granite (Aubure, France) or glacial till of varied lithology (Gårdsjön, Sweden), and subjected to distinct climatic conditions. Further, we provided a general hypothesis on the formation of SWEF. The SWEF had a different acidity level, a significantly higher accumulation of organic C, a higher Alp and/or Fep content (in two over three soils), was enriched in neoformed minerals, and had a larger concentration of exchangeable cations than both FE and RF. A key role in the development of the SWEF properties was attributed to mineralogy, weathering and pedogenesis. The interactions between mineralogical composition, pH, and organic C content not only determined the extent of ECEC in SWEF but also the source of exchangeable cations originating either from organic complexes (Mottarone soil) or from the dissolution of the mineral phases (Aubure and Gårdsjön soils). However, the abundance of SWEF appeared to be independent from the actual abundance of RF. Its formation was rather controlled by the combination of mineralogy of the parent material, weathering intensity, pathway of mineral dissolution (congruent and/or incongruent dissolution), and to the duration of pedogenesis.

Il presente lavoro è una serie di osservazioni raccolte negli anni, riguardo alle esigenze dell'abete bianco e del pino laricio in fatto di terreno e agli effetti di queste due specie forestali sulla pedogenesi. Le esigenze sono molto diverse: mentre l'abete bianco pretende suoli profondi, ben strutturati e costantemente umidi, il pino laricio riesce a vegetare addirittura su accumuli di detriti rocciosi, privi di materiale fine. In particolare, l'abete soffre la presenza di orizzonti compatti vicino alla superficie. In questa situazione è spesso soggetto ai crolli, perché le radici non riescono a svilupparsi in profondità per assicurargli un adeguato ancoraggio al suolo. Entrambe le specie possono influire negativamente sulla conservazione del suolo tramite lo stemflow. Nell'abete, su superfici declivi, questo tipo di soluzione provoca un’erosione localizzata alla base del tronco, mentre nel pino, in virtù della sua elevata acidità, causa la degradazione delle porzioni di suolo poste allo sbocco dei canali corticali.

Of the remarkably few Antarctic pedological studies, many have been made in the Dry Valleys of VictoriaLand. To these Campbell and Claridge have contributed greatly in over 20 years' extensive work. Their research has culminated in this book, the most detailed and comprehensive account of soils of this formidable continent, where weathering and soil-forming processes are unique. The first four chapters introduce the continent, its environment and biota as they relate to soils; thus the geology, geomorphology, climate and biology of soils, with particular regard to development, are admirably summarized. There follow chapters on physical weathering and rock disintegration, and chemical weathering. Detailed coverage is then given to the soils themselves and to soil properties, followed by soil distribution and factors influencing soil pattern, the salts in Antarctic soils, and soil weathering and glacial history. The penultimate chapter discusses schemes of Antarctic soil classification; the final chapter sets the soil ecosystem in a conservation context, outlining the uniqueness of Antarctic soils, their value in the study of global pedology, the fragility of the soil ecosystem, its vulnerability to human impact, and the ease with which it can be damaged and polluted. This excellent account is largely a personal record of the authors' extensive and detailed research. It includes a bibliography of over 400 references, though the relatively small number relating directly to soils and weathering processes illustrates how little work has actually been carried out in Antarctica. Only half of the 50 post-1979 references relate to soils, but unfortunately several important recent publications, particularly on the maritime Antarctic, are not included. This suggests that the book has had a rather long gestation period, and that the few 1983 and 1984 references were slipped in at the last minute. The book is profusely illustrated with black and white photographs and line illustrations, and 25 colour plates, all of sites in Ross Dependency. If it has a weakness it must be the inadequate coverage of regions beyond the Dry Valleys, in particular of the maritime Antarctic and its relatively diverse soil types. Typographic errors are very few. This is an invaluable addition to Antarctic scientific literature, greatly expanding and updating J. C. F. Tedrow's 'Antarctic soils and soil forming processes' (1966, Antarctic Research Series 8, American Geophysical Union, Washington DC) and 'Soils of the polar landscapes' (1977, Rutgers University Press, New Brunswick). Because of the dearth of pedological research currently being undertaken in Antarctica, 'Campbell and Claridge' will be the standard reference for a long time to come. Unfortunately the cost will make it prohibitive for many individuals and restrict its purchase mainly to libraries. (R. I. Lewis Smith, British Antarctic Survey, Madingley Road, Cambridge CB3 OET.)

Unfrozen water in frozen soils In continental Antarctica, the intense cold, the paucity of liquid water and low biological activity posed the question on whether the surficial, grayish, sandy, material devoided of plants and humus could be legitimately called soils. This question was raised since 1916 when Antarctic soils were first analyzed. The question was later resolved by waiving the U.S.D.A requirements for the presence of higher plants. Nevertheless, one cannot usher the apparently lifeless, unconsolidated material into the realm of soils just by changing a definition! Proofs are required to show that soil formation in continental Antarctica is a present day process. This confermation was obtained by detecting ionic migration in frozen xeric soils. The experiment showed that radioactive ions, 36Cl− and Na, moved in the unfrozen interfacial films of water at the surface of soil particles. The higly dissociated and corrosive nature of the unfrozen water could explain, also, the observed weathering in situ.

In the Hisma Basin, southern Jordan, the selection of a virtually monomineralic parent material allowed the unequivocal determination of allogenic minerals to an Aridisol. Quantitative XRD analyses combined with optical microscope observations reveal a suite of minerals—calcite, gypsum, 2:1 clay minerals, K-feldspar, plagioclase and dolomite, and possibly goethite, palygorskite and chlorite—in the soil that contrast markedly with the almost monomineralic composition of the bedrock—quartz, with minor kaolinite and traces of illite. The distribution of allogenic minerals follows a decreasing depth-trend, thus supporting an aeolian provenance. Gypsum and quartz are the only exceptions to this trend, the former due to its solubility and the latter because the quartz rich bedrock at depth is a source. Quartz and kaolinite may also be partly of aeolian origin, but to a great extent with increasing depth must be sourced in situ from the bedrock. The presence of secondary calcite and gypsum is consistent with the fact that the soil receives scanty precipitation. Other features observed include a varnished desert pavement and a distinctive vesicular A horizon. Although no evidence was found for salt shattering, an increase in the porosity of the clasts of the desert pavement is ascribed to the growth of CaCO3 crystals. The desert varnish consists of a glossy blackish patina rich in Fe and Mn apparently deposited with carbonate and left as an insoluble residue upon dissolution of the carbonate. The A horizon tends to grow upward due to infilling of dust and to the heaving caused by the formation of vesicles in response to wet/dry cycles. These processes result in a “floating” desert pavement.

The first mention of Antarctic soils dates back to 1916, when Jensen reported on analyses of samples collected in the McMurdo area during the British Antarctic Expedition, 1907–1909. With the advent of the International Geophysical Year in 1958, and the establishment on the continent of permanent bases by many nations, an era dedicated to scientific investigations was inaugurated. New Zealand and American field parties explored the soils of the McMurdo Dry Valleys region and published their findings in the early 1960s. Questions about the legitimacy of calling soils a loose, sandy, grayish material devoid of plants and of an organic layer were often raised but also answered. A number of soil-forming processes were identified and also verified was the role of the soil- forming factors such as of time, lithology, and exposure. In continental Antarctica the biota, except for microorganisms, was only present in small areas occupied by Bryophyta. An organic cover, in the form of guano, was also restricted to penguin rookeries. Chemical weathering and the origin and distribution of salts were topics investigated by pedologists, geologists and geochemists.

Volcano flanks are usually covered by deposits of fine materials (tephra) with variable thickness originated by the explosive activity. The deposits form bedded sequences of tephra layers often alternated with paleosols. Pyroclastic successions on Etna volcano (Italy) are composed of scoria or pumice lapilli and ash deposits, representing separate eruptions, and volcanogenic sediments developed between eruptions. The origin of paleosols cropping out in three pyroclastic successions on Mt Etna is here discussed on the basis of stratigraphic, pedological, chemical and mineralogical data. The results suggest that the sequences originated from the accumulation of primary volcanic materials produced by explosive events, together with material of secondary origin derived from wind-transported materials originated by the alteration of the pyroclastic deposits formed at higher elevations. The vegetation present at the surface at any time would have favoured the aggrading of the soil by exerting a trapping effect on the wind-blown materials. At the same time, the presence of plants would have favoured enrichment in organic C and mineral alteration. In the studied paleosols, the pedogenetic processes were not sufficiently intense or did not act for a sufficient time to favour neogenesis of mineralogical phases, either crystalline or “amorphous”.

Maillard compounds were synthesized from D-glucose and glycine to mimic the separation of particles during a volcanic eruption so that the role of quartz and volcanic ash, fractionated into silt- and sand-size particles, could be tested under sterile conditions. The obtained polymers were separated into two fractions of 1000-8000 and > 8000 Daltons. The results evidence the formation of humus-like polymers from simple compounds and show the importance of substrate mineralogy. Specifically, a) humic-like polymers can form in the absence of microbial life, b) the role of particle size is important, c) mineral substrates enhance their yields, d) the polymers on volcanic ash and quartz show differences, e) their structure changes with time, f) at the end of the experiments there is an increase of unsaturation while the aliphaticity decreases, and g) the yields of the compounds of 1000-8000 Daltons decrease with time unlike those > 8000.

Abstract Soil science came into its own only in the 20th century. Before this, the study of soils was dominated by geologists, agronomists and chemists. It was Dokuchaev in 1886, who recognized soil as a physical entity with properties acquired from the impact of soil-forming factors, among which the geological substrate was only one. This vision resulted in the establishment of a new discipline, called pedology. With time, geologists began to appreciate soil in a pedological context. In fact, palaeosols in particular have been utilized to interpret the stratigraphy of metamorphic and sedimentary rocks and Quaternary deposits. Also, palaeosols have been used for correlating unconsolidated sediments, faults and neotectonics, or for the relative dating of deposits or surfaces. Weathering is a field where soil chemists have interacted with geochemists to evaluate chemical denudation and landscape evolution. Geological engineering in terms of water storage, pollutant transport, and critical load, in addition to location, design and construction of roads, is another area of interaction between soil researchers and geologists. The exploration of the planets of the solar system is a field which has assembled soil chemists and geochemists to collect, analyse and interpret data sent by space vehicles. Future interactions between geology and soil science will occur on issues such as: water in the vadose zone; risks due to Earth movements; and functions of soils in ecosystems. We predict and also welcome more communication between the two disciplines, as solutions to some of these problems are demanded by society.

The brittleness of fragipans is generally ascribed to the close‐packing fabric arrangement acquired at the initial step of pedogenesis thanks to physical processes. However, there is an on‐going debate over the agent causing soil densification. In this work, we tested the plausibility that ice segregation or liquefaction could have been the cause of the compaction of four fragipans. Two of them are located in nonseismic areas that have experienced periglacial conditions; one is from a strongly seismic area not affected by periglacial conditions, while the fourth site underwent moderate seismic activity and slight periglacial conditions. After disaggregation in the laboratory, soil specimens were submitted to freeze–thaw cycles and vibrations at different amplitude and duration, either dry or water‐saturated. Analyses of aggregate stability, bulk density, porosity, and pore‐size distribution were made on natural and treated specimens. Results indicated that the compactness arose mainly from the close‐packing arrangement of particles. The freeze–thaw cycles were able to reproduce only some of the features in the water‐saturated specimens, independent of whether they came from periglacial or seismic areas, while those from seismic areas successfully acquired the original arrangement after vibrations‐induced liquefaction. This different behavior could be partly explained by the fact that consolidation after liquefaction occurs only if a material with proper particle‐size distribution and mineralogical assemblage is saturated by solutions able to disperse phyllosilicates and promote their face‐to‐face arrangement. Our findings support the hypothesis that liquefaction of soil material due to earthquakes could indeed provide a dense parent material in which the fragipan may develop through pedogenesis.

Soils formed in volcanic ejecta have many distinctive physical, chemical, and mineralogical properties that are rarely found in soils derived from other parent materials. These distinctive properties are largely attributable to the formation of noncrystalline materials (e.g., allophane, imogolite, ferrihydrite) containing variable charge surfaces, and the accumulation of organic matter. Formation of noncrystalline materials is directly related to the properties of volcanic ejecta as a parent material, namely the rapid weathering of glassy particles. The composition of the colloidal fraction forms a continuum between pure Al–humus complexes and pure allophane/imogolite, depending on the pH and organic matter characteristics of the weathering environment. For soil management purposes, volcanic soils are often divided into two groups based on the colloidal composition of the surface horizons: allophanic soils dominated by allophane and imogolite, and nonallophanic soils dominated by Al–humus complexes and 2:1 layer silicates. Volcanic soils exhibit a wide range of agricultural productivity, depending on the degree or intensity of pedogenic development and the colloidal composition of the rooting zone. The different charge characteristics of allophanic and nonallophanic soils is the most important factor regulating chemical fertility attributes. Phosphorus fixation, strong acidity, and aluminum toxicity are the primary chemical limitations to agricultural productivity. Volcanic soils generally have high physical fertility (tilth) and mature soils are relatively resilient to erosion and compaction. To maximize the productivity of volcanic soils, proper management based on an understanding of the unique physical, chemical, and mineralogical properties of these soils must be practiced.

The paper deals with the role of Etnean broom [Genista aetnensis (Biv.) DC.] on the early stages of pedogenesis on basaltic pyroclastic deposits (Mt. Etna, Italy) of different age and altitude previously not vegetated. After a few decades, this plant has been capable to arrest erosion and produce some soil features in both Entisols. The soil of Mts. Rossi, at a lower altitude, formed from a centenary parent material and hosted a broom plantation of about 50 years old. Here, the regimes of soil moisture (ustic) and temperature (mesic) limited the diffusion of the grass to the projection of the broom crowns, but favoured the diffusion of microorganisms and pedofauna. These conditions favoured a generalised alteration of the parent material and induced a certain horizon organisation. The soil of Mt. Vetore, at higher altitude, formed from a millenary parent material, and hosted a broom plantation of about 35 years old. At this site, the soil moisture (udic) and temperature (frigid) regimes favoured the fort-nation of a thick and continuous carpet of gramineae. Yet, these conditions limited the activity of microorganisms and pedofauna, thus inducing a poorer horizon organisation. In this soil, because of the higher mean annual precipitation and root activity, most of the chemical modifications of the parent material occurred at the level of the rhizosphere, which acquired a thickness of 2-3 cm. From a chemical and mineralogical point of view, horizontal variations between rhizosphere and matrix were more evident than those among horizons. The most striking change occurring in the rhizosphere was the accumulation of secondary minerals such as oxalates and easily reducible Fe-oxyhydroxides.We also inferred that, in the environment of Mt. Etna, the excretion of oxalic acid from the roots of the broom could represent a strategy of nutrient uptake, in particular P, Mg and K. (C) 2003 Elsevier Science B.V. All rights reserved.

This study reports on the formation of Maillard compounds (humic-like substances called "melanoidins") from D-glucose and L-tyrosine in the presence of volcanic ash and pure quartz. It was demonstrated that the synthesis occurred not only under non-sterile, but also under sterile conditions, and under moisture and temperature stress. The temperature remained for 30 days at 70degreesC for 63% of the time. The non-sterile environment with a contact time of at least 30 days was the most favorable condition for the synthesis. In sterile environment, only low molecular weight polymers were formed, while in non-sterile systems high molecular weight substances were synthesized. The presence and the nature of mineral substrates appeared important even if not essential for the formation of humic-like substances. in fact, these substances were also formed by the reaction of the precursors alone.

SummaryThe upper surfaces of trachyte outcrops and boulders in Tuscany and Latium have numerous cavities. The cavities have formed from the dislodgement of xenoliths and, if properly oriented, they collect water and accumulate mineral and organic debris. There is no drainage, and water stays in them for a long time, inducing a severe hydrological regimen, but supporting a variety of living organisms such as cyanobacteria, green algae and insects. The humic substances produced by the humification of organic matter and the organic acids released by organisms alter the underlying rock, thereby deepening and enlarging the cavities. Following the dissolution of the glassy cements, crystals detach from the matrix to join the accumulated material, where they are progressively comminuted and partly changed into clay minerals. With time, these accumulations increase in thickness sufficiently to allow the establishment of vascular plants and the development of horizons so as to become embryonic soils. We sampled the material from several such cavities and determined its chemical and mineralogical composition. We conclude that cavities contain miniature ecosystems supported by the tiny bodies of soil in them.

To evaluate the contribution of rock fragments to the soil's total carbon content, the soil of 26 sites, ranging from the Canadian Arctic to the Jordan desert, was analysed for the content of organic C and total N in both fine earth and skeleton fractions. The soils, uncultivated and cultivated, are derived from 11 parent materials: sandstone, mica-schist, granite, gneiss, basaltic pyroclastites, trachyte, dolomite, beach deposits, clay schist, marl and serpentinite. For each soil horizon the contents of fine earth and skeleton were determined by volume. Both fractions were analysed for bulk density, total and organic C and total N. Our results indicate that rock fragments contain amounts of C and N that depend on the nature of the parent material and on its resistance to the weathering processes. The C and N of both fine earth and skeleton were used to calculate the contents of these elements for three depths. At each depth, the skeleton contributes C and N to the soil depending on its abundance. We conclude that the contribution of the rock fragments to the soil C and N cannot be predicted from the soil taxa, but can from the parent material. Calculations that exclude C and N of the skeleton could lead to errors in the estimates of these two elements in soils.

SummaryRock fragments in soil can contain significant amounts of organic carbon. We investigated the nature and dynamics of organic matter in rock fragments in the upper horizons of a forest soil derived from sandstone and compared them with the fine earth fraction (<2 mm). The organic C content and its distribution among humic, humin and non‐humic fractions, as well as the isotopic signatures (Δ14C and δ13C) of organic carbon and of CO2 produced during incubation of samples, all show that altered rock fragments contain a dynamic component of the carbon cycle. Rock fragments, especially the highly altered ones, contributed 4.5% to the total organic C content in the soil. The bulk organic matter in both fine earth and highly altered rock fragments in the A1 horizon contained significant amounts of recent C (bomb 14C), indicating that most of this C is cycled quickly in both fractions. In the A horizons, the mean residence times of humic substances from highly altered rock fragments were shorter than those of the humic substances isolated in the fine earth. Values of Δ14C of the CO2 produced during basal respiration confirmed the heterogeneity, complexity and dynamic nature of the organic matter of these rock fragments. The weak 14C signatures of humic substances from the slightly altered rock fragments confirmed the importance of weathering in establishing and improving the interactions between rock fragments and surrounding soil. The progressive enrichment in 13C from components with high‐14C (more recent) to low‐14C (older) indicated that biological activity occurred in both the fine and the coarse fractions. Hence the microflora utilizes energy sources contained in all the soil compartments, and rock fragments are chemically and biologically active in soil, where they form a continuum with the fine earth.

Although much is known about the transformation of humic substances in the fine earth fraction of surface horizons, little is known about these processes in the coarse fragments (>2 mm) or about the changes with depth of humic and fulvic acids extracted from an entire soil profile. For each horizon of a forest soil developed on sandstone, the humic acids (HAs) and fulvic acids (FAs) were extracted from four fractions: fine earth, washing (i.e. fine material adhering to the clasts) and highly altered and slightly altered rock fragments. The HAs and FAs were also extracted from samples of the parent rock. The humic substances were then analyzed for their elemental composition and chemical structure by FT-IR and 13C NMR spectroscopy. In the A horizons (upper 20 cm of the profile), the HAs from all the fractions appeared highly aromatic, with a high degree of C substitution and an abundance of carboxyl groups; however, the HAs of the rock fragments were more aromatic and richer in carbohydrate and proteinaceous residues than those of the fine earth. The HAs showed a more condensed and unsubstituted aromatic pattern at depth than in surface horizons. In the Bw and BCb horizons the contribution of biological residues to the humic substances seems to be progressively replaced by the contribution of organic materials derived from the sedimentary parent rock. The presence of features ascribable to the HAs and FAs of the parent rock decreased following the order: slightly altered clasts > highly altered clasts > washing > fine earth. Conversely, FAs showed a high homogeneity throughout the profile and are considered mostly of pedogenic origin. The chemical characteristics of both HAs and FAs showed a break in the trend with depth between Bw and BCb horizons, confirming the presence of a pedogenic discontinuity between the upper modern soil (A-Bw2 horizons) and the buried paleosol (BCb horizons).

In alpine environments, natural or man-induced disturbances are fairly common and acknowledged as determining factors in pedogenesis and soil distribution. We have selected a representative alpine valley in the Italian Northwestern Alps to evaluate the effects of perturbations of different intensity and frequency on soil development and weathering during the last few centuries. In order of decreasing disturbances, we selected: (i) an active avalanche shoot; (ii) a man-built terrace; (iii) a park-like forest; and (iv) a coniferous forest. In the two most disturbed sites, independently of the intensity and frequency of the disturbances, the active pedogenic processes are restricted to the topsoil. At site 1, the acidity induced by the invading pioneer N-2-fixing tree species determines a certain degree of mineral dissolution, while at site 2, plowing and manuring influence the properties of organic matter and limit its mobility. At site 3, where coniferous species are associated to the herbaceous cover, the weathering proceeds further and a cambic horizon was detected in the field and supported by evidences of K depletion from illite. The higher polarity of the organic substances of mixed origin is certainly responsible for this more intense weathering. In the coniferous forest, the least disturbed situation, the vegetation is more representative of the climax in the area and pedogenesis further proceeds leading to the appearance of podzol-like features. These, even if scarcely displayed by a very shallow and discontinuous E horizon, are clearly manifested by the formation of interstratified minerals and by the amount of pedogenic iron oxides. This can be related to the organic matter dynamics, with a high FA/HA ratio and accumulation in the Bw horizons of acidic and highly polar aromatic molecules. However, podzols are not common at this elevation and this steady state condition seems to be very vulnerable to disturbances even of low intensity. In conclusion, in an alpine valley, the impact of different disturbances on soil development, independently from their intensity and frequency, leads to a pattern of development of soils in which the vegetation plays a key role. (C) 2002 Elsevier Science B.V. All rights reserved.