1,721,176 research outputs found
Simulating the effects of wet and dry on aggregate dynamics in argillic fragipan horizon
No full textFragipan is a dense and usually brittle subsurface soil horizon, limiting the penetration of roots and the infiltration of water. The genesis of fragipan is still unclear, but a general agreement exists on the importance of wet-dry cycles. In addition, in argillic Bx horizon, the presence of cations affecting the clay dispersion/flocculation behaviour might be a key factor in fragipan dynamics. In order to gain knowledge on the specific effect of alternating moisture conditions on the evolution of aggregates collected from a Btx horizon, we evaluated the variations of physical properties caused by a wet-dry cycle using both deionized and Ca-enriched water on the 1â2 mm aggregate, and on newly formed aggregates (i.e. 2â5 and > 5 mm size classes) obtained after a lab experiment. The results were compared with a Bt horizon that did not show fragipan properties. Btx and Bt samples were collected from a Typic Fragiudalf developed on fluvio-glacial terraces in NW Italy. The two horizons had comparable clay content (around 13%), and their mineralogical composition was dominated by hydroxy-interlayered vermiculite and smectite. The fragipan 1â2 mm aggregates showed a low clay dispersion ratio (11.5%) before the treatments, together with low volume of macropores (74 mm3gâ 1), high volume of mesopores (111 mmâ 3gâ 1), high slaking (30.1%), close packing of coarse particles and open arrangement of fine particles. The water treatment increased the amount of flocculated-clay in the new-aggregates, and Ca-treatment enhanced clay flocculation both in the newly formed and in the remaining 1â2 mm aggregates. The clay flocculation induced a denser arrangement of clay particles (⥠0.44), and a consequent reduction of mesopores (from 56.2 to 66.1 mmâ 3gâ 1), combined with the opening of the coarser particles packing (⤠0.78). This new particle arrangement did not correspond to the specific combination of coarse/fine particles arrangement of fragipan. The relative percentage of slaking also decreased. Therefore, upon both deionized water and CaCl2wetting and drying, the newly formed aggregates (i.e., 2â5 and > 5 mm) from disturbed fragic materials, as well as those that did not take part in the new aggregate formation (1â2 mm), did not show the specific physical properties of fragipan. The simulation of wet and dry cycle acted on clay colloidal behaviour, and the results suggested the degradation, rather than the enhancement, of Btx physical properties measurable in laboratory
Soil aggregation, erodibility, and erosion rates in mountain soils (NW Alps, Italy)
Full text linkErosion is a relevant soil degradation factor in mountain agrosilvopastoral
ecosystems that can be enhanced by the abandonment of agricultural land and
pastures left to natural evolution. The on-site and off-site
consequences of soil erosion at the catchment and landscape scale are
particularly relevant and may affect settlements at the interface with
mountain ecosystems. RUSLE (Revised Universal Soil Loss Equation) estimates
of soil erosion consider, among others, the soil erodibility factor (K),
which depends on properties involved in structure and aggregation. A
relationship between soil erodibility and aggregation should therefore be
expected. However, erosion may limit the development of soil
structure; hence aggregates should not only be related to erodibility but
also partially mirror soil erosion rates. The aim of the research was to
evaluate the agreement between aggregate stability and erosion-related
variables and to discuss the possible reasons for discrepancies in the two
kinds of land use considered (forest and pasture).
Topsoil horizons were sampled in a mountain catchment under two vegetation
covers (pasture vs. forest) and analyzed for total organic carbon, total
extractable carbon, pH, and texture. Soil erodibility was computed, RUSLE erosion
rate was estimated, and aggregate stability was determined by wet sieving.
Aggregation and RUSLE-related parameters for the two vegetation covers were
investigated through statistical tests such as ANOVA, correlation, and
regression.
Soil erodibility was in agreement with the aggregate stability parameters;
i.e., the most erodible soils in terms of K values also displayed weaker
aggregation. Despite this general observation, when estimating K from
aggregate losses the ANOVA conducted on the regression residuals showed
land-use-dependent trends (negative average residuals for forest soils,
positive for pastures). Therefore, soil aggregation seemed to mirror the
actual topsoil conditions better than soil erodibility. Several hypotheses
for this behavior were discussed. A relevant effect of the physical
protection of the organic matter by the aggregates that cannot be considered
in computation was finally hypothesized in the case of pastures, while in
forests soil erodibility seemed to keep trace of past erosion and depletion
of finer particles. A good relationship between RUSLE soil erosion rates and
aggregate stability occurred in pastures, while no relationship was visible
in forests. Therefore, soil aggregation seemed to capture aspects of actual
vulnerability that are not visible through the erodibility estimate.
Considering the relevance and extension of agrosilvopastoral ecosystems
partly left to natural colonization, further studies on litter and humus
protective action might improve the understanding of the relationship among
erosion, erodibility, and structure
Soil Science in Italian Universities
No full textThe community of soil scientists in Italian universities is small, approximately 100 people as permanent staff, distributed from North to South in groups of variable dimensions. Despite being a small community, their research activities show a wide range of topics, ranging from the molecular to the landscape scale, and encompassing evergreen themes and present-day hot topics. This chapter summarizes the main topics investigated over the last five years, as they appear in the Scopus database. The activities were grouped into seven main research fields that offer an overview of both the specific topics, and the scale at which a phenomenon can be investigated: (1) soil development, pedogenic processes and soil classification, (2) soil functions and ecosystem services, (3) soil organic matter characteristics and functions, (4) soil chemical and biochemical properties, (5) biowaste upcycling for soil remediation and fertility enhancement, (6) soil degradation, contamination and remediation and (7) land suitability and management, soil variability and mapping. In many cases, collaborations among Italian universities and with international partners are visible, testifying the need of joining efforts and expertise to address the present-day challenges
Relative Importance of Mineralogy and Organic Matter Characteristics on Macroaggregate and Colloid Dynamics in MG-Silicate Dominated Soils
No full textSoil aggregation and organic matter (OM) conservation are important in the prevention of land degradation. Aggregation processes and OM turnover influence each other and depend on the characteristics of both minerals and organic pools. We assessed the relative importance of the organic and mineral phases at the macroaggregate and colloidal scale in two soils (CHL and SRP, chlorite and serpentine-rich, respectively) where Mg-silicates dominated, by incubating them with a relatively degraded and oxidized organic fraction, that is the humic acids (HAs) extracted from the organic horizons of both CHL and SRP. The HA from SRP were more aromatic and richer in phenolic groups, whereas HA from CHL were N-richer, more aliphatic and richer in carboxyl groups. The SRP soil formed larger amounts of macroaggregates, more stable than in CHL. At the colloidal scale, SRP was more flocculated and clay had a lower electrophoretic mobility than CHL. HA enhanced aggregate formation in both samples but improved aggregate stability only in CHL. In CHL, slight differences in electrophoretic mobility were visible, while in SRP, differences were more pronounced, with a point of zero charge at lower pH and larger hydrodynamic diameter. The abundance of Mg in SRP may have favoured the formation of weaker outer-sphere interactions and the release of clay-HA associations upon water dispersion, while in CHL Ca formed more stable bonds with HA. In SRP, ligand exchange reactions can be ruled out, conversely to the dominant bonding mechanism occurring in Al-silicate dominated soils, with important consequences on the release of OM-loaded clay particles. Copyright © 2016 John Wiley & Sons, Ltd
Chemical and spectroscopic characteristics of humic acids and dissolved organic matter along two Alfisol profiles
No full textThe aim of this study was to elucidate the heterogeneous structural and functional composition of humic acids (HAs) and dissolved organic matter (DOM) isolated from two Alfisol profiles with different soil texture, in order to develop a better understanding of the organic matter dynamics. Soil samples were collected at different depths from three (Ap, 2AB and 2Bt) and eight (A1, A2, A3, E1, E2, 2Bt1, 2Bt2 and 2Bt3) soil horizons of two Alfisols located in the south (PR1) and north (PR2) of Italy, with a clay texture and a silt loam to loam ones, respectively. Chemical and spectroscopic methods were used to characterize the HAs and the DOM isolated from different soil horizons, including Ultraviolet-Visible (UV-Vis), Fourier Transform Infrared (FTIR), and Fluorescence spectroscopies. The HAs and the DOM isolated from the two Alfisols apparently showed significant differences in their compositional, structural and functional characteristics. In particular, the HAs isolated from the PR1 featured a higher degree of humification and molecular complexity with respect to those isolated from the PR2. On the contrary, the DOM samples isolated from the PR2 showed a more marked aromatic character and polycondensation degree. Both the HAs and the DOM obtained from the PR1 presented a greater qualitative homogeneity with respect to those obtained from the PR2. These results could be reasonably ascribed to the different texture and horizons of the two Alfisols, and to a greater pedogenesis occurred in the PR1. © 2014 Elsevier Ltd
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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