Ermanno Zanini

Iron oxides and clay minerals within profiles as indicators of soil age in Northern Italy

Abstract Nine profiles representing the Alfisol, Inceptisol and Entisol orders were sampled on three terraces forming a chronosequence. Total iron, dithionite-extractable iron and oxalate-extractable iron were determined for all horizons of all profiles, and the clay mineralogy for horizons of three profiles. The percentage of total Fe (Fet) extracted by dithionite (Fed) increased with age of terraces, as did the difference between Fed and Feo (oxalate-extractable). Analysis of variance (ANOVA) of the horizon data showed that the ratios Fed/Fet and FedFeo/Fet were closely related to the ages of the terraces. Clay minerals were also related to terrace ages, with 2:1 minerals dominant in the profiles on the youngest and mixed-layer minerals and kaolinite more abundant in profiles on the older terraces.

Pedogenesis in a soil catena on serpentinite in north-western Italy

Serpentinite is a fairly common parent material for soils of the Alps and Apennines in Italy. In the Apennines these soils may show very different degrees of development even over small areas. This work was undertaken to study the pedogenesis on a soil catena occurring on a very small hill, with a particular attention to the clay mineral transformations. The catena is only 100 m long, but four orders of the Soil Taxonomy were represented, ranging from Entisols to Alfisols. In the clay fraction of the Entisol and of the Inceptisol located respectively at the summit and at the backslope positions, we found that serpentine is the main mineral in the clay fraction and that traces of some interstratified low charge vermiculites are present in the surface horizon. The two Alfisols at the footslope positions have different clay minerals: one of them shows some low charge vermiculites in the surface horizons and smectites in the deepest ones, while in the other one smectites were found in the surface horizon too. These two profiles have different drainage regimes as seen in the field and from laboratory determination of water content and porosity. Significant differences (p < 0.01) of porosity were found in the catena between the horizons with smectites and those with low charge vermiculite. In the Mollisol, located at the toeslope position, a trend towards acidification was found in the surface horizon but the presence of serpentine acts as a continuous magnesium source thus preventing the base saturation to become < 50%. The main pedogenic processes in this catena are: lessivage of clays; formation of different 2 : 1 phyllosilicates depending probably on the porosity; acidification caused by organic materials. In some horizons an enrichment of organic matter is possible, but the acidification is hindered by the parent rock. No clear evidence of chlorite formation from serpentine was found. The weathering of serpentine minerals seems to give rise to a low charge vermiculite in upper and drier horizons or to a smectite in poorly drained conditions. Vermiculite in turn may transform into smectite under a moister environment.

Soil Organic Matter Changes In A Spruce Chronosequence On Swedish Former Agricultural Soil: I. Carbon And Lignin Dynamics

Afforestation of former agricultural soils is an important tool to reduce atmospheric CO2 levels because of the high capacity of both biomass and soil to store carbon (C). The long-term effect of afforestation on the role of soil as C sink was investigated in a chronosequence of 18-, 29-, 64-, 73-, and 91-year-old Picea abies stands, established on former agricultural soils in southwestern Sweden. The forest floor was sampled both as a whole and in the three horizons (unaltered, semialtered, and altered organic horizons), whereas the mineral soil was sampled at 0 to 5, 5 to 15, and 15 to 30 cm depth. The physicochemical characterization of soil, C and nitrogen content, and lignin characterization by the cupric oxide oxidation method was conducted. Within the first decades of afforestation, the soil properties reflected the former soil management, and C accumulation involved mainly the organic layer (3.41-5.92 Mg C ha−1), where the new litter was accumulating, and coniferous lignin showed a low degree of degradation. Meanwhile, the mineral soil behaved as a C source (95.5-80.2 Mg C ha−1), loosening the C inherited from the previous land use probably because of the nutrient needs of the growing trees that accelerated organic matter mineralization. Vanillyl moieties were almost absent, and the syringyl units, derived from angiosperms, were considerably oxidized, indicating a low C input from the conifer litter and high degradation of the inherited organic material. With age, the C stock started to increase both in the organic and mineral layers, reaching 191.5 Mg ha−1 in 91 years. The accumulation in organic soil was accompanied by a litter nitrogen impoverishment and decrease of soil pH, which probably limited the microbial community to fungi, able to degrade lignin. In the oldest stands, the lignin material seemed to be intensively altered, mainly in the deeper organic horizons, where aromatic, mobile, acidic compounds were produced and/or translocated down in the profile. This could contribute to organic matter incorporation into mineral layers and to mineral weathering, driving the soil toward the restarting of the podzolization process. From these results, it seemed that even if the previous land use caused an initial acceleration of organic matter mineralization, soil started to accumulate C when the influence of the new vegetation dominated. The soil became a major C sink with a long forest growth of about a century. The accumulation was strongly affected by litter composition, which changed with spruce age.

Pedogenesis in disturbed alpine soils (NW Italy)

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 N2-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.

Topsoil aggregate breakdown under water-saturated conditions

When the aggregate stability of soils is evaluated under water-saturated conditions by conventional methods of wet-sieving at fixed times (5 to 20 min), the dynamic features of aggregate breakdown are often lost or ignored. An exponential equation, y(t) = a[1 - exp(-t/c)] + b, is proposed to describe the dynamic features of aggregate breakdown as a function of wet-sieving time. Parameter a is the maximum estimated abrasion loss of aggregates, b is the incipient failure of the aggregates when saturated in water, and c is a parameter that links the rate of aggregate breakdown to wet-sieving time. The equation was validated with experimental data using 100 samples of a wide range of Italian topsoils developed on Tertiary deposits. With R 2 values close to unity for fitting data from all 100 soil samples, the equation described successfully the dynamics of aggregate breakdown, and the parameters accounted for variations among the soils based on soil type, parent material, and land use. We also scale the exponential equations for the 100 soils with scaling factors to define a scale mean curve for the aggregate breakdown of all soils. The scale factors were obtained by minimizing an objective function containing measured values of aggregate loss and the scale mean curve. The magnitude of the scaling factor gives a quantitative estimate of aggregate stability (the larger its value, the greater the aggregate stability) for each soil, whereas the particular values of parameters a, b, and c describe the kinetics of aggregate breakdown for each soil. A multivariate analysis showed that the value of the scale factors depends significantly on the amounts of amorphous iron oxides and organic carbon in the topsoil as well as on the topographical elevation of the soil surface.

Fire severity, residuals and soil legacies affect regeneration of Scots pine in the Southern Alps

Regeneration of non fire-adapted conifers following crown fires on the European Alps is often delayed or unsuccessful. Fire may limit establishment by eliminating seed trees, altering soil properties, or modifying microsite and soil conditions via disturbance legacies. However, the effect of soil legacies on post-fire establishment has rarely been discussed. We analyzed the abundance of Scots pine regeneration in a 257 ha wildfire in an inner-alpine forest. Our aims were (1) to model fire intensity at the soil surface and topsoil heating along a gradient of increasing fire severities; (2) to assess the differences in soil properties along the fire severity gradient; (3) to model the effect of disturbance and soil legacies on the density of pine seedlings. We reconstructed fire behavior and soil heating with the First Order Fire Effects Model (FOFEM), tested the effect of fire severity on soils by nonparametric distributional tests, and modeled seedling density as a function of site, disturbance and soil legacies by fitting a GLM following a variable selection procedure. Topsoil heating differed markedly between the moderate and high severity fires, reaching temperatures high enough to strongly and permanently alter soil properties only in the latter. High fire severity resulted in decreased soil consistency and wet aggregate stability. Burned soils had lower organic matter and cations than those unburned. Pine seedlings favored low-fertility, eroded, and chemically poor sites. Establishment was facilitated by the presence of coarse woody debris, but hampered by increasing distance from the seed source. These results suggest that in dry, inner-alpine valleys, fire residuals and soil legacies interact in determining the success of Scots pine re-establishment. High severity fire can promote favorable soil conditions, but distance from the seed source and high evaporation rates of bare soils must be mitigated in order to ensure a successful restoration.

Soil Erosion Caused by Snow Avalanches: a Case Study in the Aosta Valley (NW Italy)

Abstract Snow avalanches can exert considerable erosive forces on soils. If a snow avalanche flows directly over bare ground, basal shear forces may scrape away and entrain soil. Soil material entrained by the avalanche is transported to the deposition zone, changing the chemical composition of the soils and potentially contributing to unique landforms. The quantity of soil material eroded and accumulated depends on avalanche characteristics and on morphological features, as well as soil properties and vegetation cover. We monitored a channeled avalanche path in the Aosta Valley of NW Italy in order to assess the contribution of avalanche debris to the formation of soils in the runout zone. Sediment concentration estimates and measurements of the avalanche deposit volumes were used to estimate the total sediment load. The collected sediments were separated into fine sediments (<2 mm) and large (>2 mm) organic and mineral fractions. Results, obtained from the winter seasons of 2006, 2007, and 2008, showed that the amount of sediment deposited on the preexistent soil at the foot of the avalanche path was mainly the fine sediments fraction. The total carbon and nitrogen content in the fine sediment fraction ranged respectively from 6.6 to 9.0% and 0.37 to 0.42%. The total sediment load transported out of the 3.5 km2 basin was estimated to be 7585 kg in 2006, 27,115 kg in 2007, and 2323 kg in 2008. This mass transport resulted in basin averaged denudation rates ranging from 0.67 g m−2 event−1 in 2008 to 7.77 g m−2 event−1 in 2007. Annual accumulation in the runout zone was 240 Mg ha−1 in 2006, 38 Mg ha−1 in 2007 and 10 Mg ha−1 in 2008. The inorganic N concentration of the snow in the runout zone was significantly greater than in the starting zone and was correlated with the organic fraction accumulated by the avalanche. By redistributing snow, avalanches not only redistribute water but also nutrients that can be available for plants in the growing season. Moreover, avalanche paths are places where soil accumulates in some areas and erodes in others, contributing to potentially unique pedo-environmental conditions.

Soil properties under Norway spruce differ in spruce dominated and mixed broadleaf forests of the Southern Taiga

In natural forest, disturbance changes tree species composition which in turn affects soil properties. Two areas in the Central Forest State Biosphere Reserve, in the Russian Southern Taiga Zone, differed in the intensity of disturbance: Norway spruce was the dominant species at one site, while at the other spruce was mixed with broadleaves. The presence of broadleaves was due to large gaps in the canopy having been formed, which have triggered vegetation succession. At both sites, five plots were selected to evaluate how the presence of broadleaves influences the properties of the soils under spruce. Soil samples were taken close to spruce trees and the O, A and E horizons were analysed. A difference in the distribution of organic matter in the soil horizons was evident, with a higher concentration in the O and A horizons at the spruce dominated site, while a more homogeneous distribution was found under spruce at the site where broadleaves were abundant. The organic matter did not only differ in quantity, but also in quality as estimated by the C/N ratio, and therefore affected the CEC and element relative availability. No differences at the two sites were found for water-extractable and exchangeable elements, but the ratio between the exchangeable and the acid-extractable forms were different, suggesting a higher relative availability of the elements at the spruce dominated site, and thus potentially higher leaching. Both theoretical and empirical studies have suggested that podzolisation and accumulation of organic matter in the O horizon are related to stagnation of ecosystem processes and ecosystem decline. Our data suggest that the presence to windthrow sites and the inclusion of broadleaf species acts to slow or even reverse podzolisation even in spruce dominated sites.

Land suitability map for mountain viticulture: a case study in Aosta Valley (NW Italy)

Mountain vineyards are a valuable resource for high-quality wine production and landscape conservation. A suitability map (1: 50,000) for mountain vineyard cultivation was created for a study area located in Aosta Valley (NW Italy). We considered the following environmental variables that are known to influence wine production: slope, aspect, altitude and soil, producing a suitability map that allows the identification of areas that can be considered practical for sustainable mountain viticulture.

Early stages of soil development on serpentinite: the proglacial area of the Verra Grande Glacier, Western Italian Alps

PurposeClimate change is driving strong variations in mountain habitats, such as glacier retreat, which is releasing large surfaces soon colonized by vegetation and attacked by weathering and pedogenesis. Many proglacial soil chronosequences have been studied in different parts of the world, but no study is available on early soil development and pedogenesis on serpentinite.Materials and methodsWe analysed the development of the main chemical (pH, organic matter, nutrients and exchangeable cations) and morphological properties in three soil chronosequences in the Verra Grande Glacier forefield (Italian side of the Monte Rosa Group, Western Alps), characterized by slightly different parent materials (pure serpentinite or serpentinite with small gneiss inclusions) and topography (steep lateral moraines or flat basal till).Results and discussionOrganic matter accumulation, acidification and base and metal leaching are the most important pedogenetic processes active during early stages of soil formation on serpentinite in the upper subalpine altitudinal belt. These processes are associated with minor changes in color and structure showing weak mineral weathering. Biocycling of nutrients is limited on pure serpentinite because of weak primary productivity of the plant community. Pedogenesis is quite slow throughout the forefield, and it is slowest on pure serpentinite. On flat surfaces, where slow erosion permits a fast colonization by Ericaceae, the podzolization process begins after few centuries since moraine deposition, while on steep slopes more time is required.ConclusionsPedogenesis on serpentinite is extremely slow. The fast colonization by grassland species increases the speed of pedogenetic trends where serpentinitic till is enriched by small quantities of P-rich gneiss. The encroachment of forest-shrub species increases the speed of pedogenetic trends thanks to a strong nutrient biocycling.