Changes in the profile properties and chemical weathering characteristics of cultivated soils affected by anthropic activities

The study of the pedogenic process in response to natural evolution, gradual anthropogenic shifts and engineering upheavals is of great significance for understanding, utilizing and transforming nature in the future. Although scholars have considered anthropic activities to be an important factor affecting pedogenesis, research on how and how much anthropic activities influence the soil-forming process is scant. This paper was conducted to analyse pedogenic characteristics dominated by anthropic activities. In this study, the parent materials and soils undergoing natural evolution (NE), tillage perturbation (TP) and engineering perturbation (EP) were selected as research objects. The genetic characteristics of soils undergoing NE, TP and EP are investigated mainly from three aspects: soil profile macromorphological characteristics, soil physical and chemical properties and chemical weathering characteristics. The results indicated that the influence of anthropic activities (TP and EP) on the process of pedogenesis is complicated. First, compared with NE, TP decreases the thickness of topsoil from 22.2 to 21.2 cm, while EP increases the thickness of topsoil from 22.2 to 23.2 cm, and EP causes the soil to have a high profile development index. Second, compared with TP, EP can improve bulk density (BD), soil organic carbon (SOC), total nitrogen (TN) and cation exchange capacity (CEC), Finally, the chemical weathering intensity differed among NE, TP and EP and followed the order of TP > NE > EP. Therefore, in the future, the genetic characteristics of soils dominated by anthropic activities should be considered. This will help us systematically understand the genesis and evolutionary characteristics of soil and lay a foundation for further perfecting the diagnostic horizon and diagnostic characteristics of the Soil Taxonomy and World Reference Base.

Sea spray and land use affect clay mineral and soil organic matter properties in soil on machair (Harris, Scotland)

<p>‘Machair’ describes a landscape form that is present along the Atlantic seaboard of Scotland and Ireland, and that is characterized by a gently sloping coastal plain developed from aeolian carbonate and quartzose sand. We characterized three grassland soil profiles along a coastal transect on Harris (Outer Hebrides, Scotland) by standard methods (colour, texture, pH, wet-chemical extractions), infrared spectroscopy, X-ray diffractometry, X-ray fluorescence spectrometry and differential scanning calorimetry. Our aim was to understand the impacts of humankind, matter input, weathering and accumulation of soil organic matter (SOM) on chemical processes and soil properties. One of the profiles differed distinctly from the other two, in particular regarding depth, texture, carbonate and SOM contents, and properties of SOM (relative content of rather labile permanganate-oxidizable SOM, transformation state), presumably caused by earlier land use as arable land. We classified the soil with the least depth as Hypereutric Leptosol, and the others as Cambic and Calcaric Phaeozem. Thermally stable SOM was present in all samples, likely pointing to pyrogenic SOM, i.e. black carbon. The mineralogical composition differed among the profiles and reflected the intermediate character of the local rocks. In all topsoil horizons, we identified Mg-hydroxy-interlayered minerals (HIMs), which are rather rare, given the commonly low abundance of Mg ions in the soil solution relative to Ca, or Al in acidic soil. The share of Mg-HIMs of the total minerals in the clay fraction ranged from 25% in a subsoil to 71% in a topsoil horizon. We suggest that sea spray is the source of subsequently intercalated Mg. This composition of the clay fraction, which is possibly typical of soil on certain machair sites, and is the result of a pedogenic process, surely affects soil properties and processes such as cation exchange capacity and SOM storage and thus element cycles.</p>

Structural composition of organic matter in particle-size fractions of soils along a climo-biosequence in the main range of Peninsular Malaysia

Information on structural composition of organic matter (OM) in particle-size fractions of soils along a climo-biosequence is sparse. The objective of this study was to examine structural composition and morphological characteristics of OM in particle-size fractions of soils along a climo-biosequence in order to better understand the factors and processes affecting structural composition of soil organic matter. To explore changes in structural composition of OM in soils with different pedogenesis, the A-horizon was considered for further analyses including particle-size fractionation, solid-state 13C nuclear magnetic resonance (NMR) spectroscopy and scanning electron microscopy (SEM). Due to the increase in the thickness of organic layer with increasing elevation, the A-horizon was situated at greater depth in soils of higher elevation. The relationship between relative abundances of carbon (C) structures and particle-size fractions was examined using principal component analysis (PCA). It was found that alkyl C (20.1-73.4%) and O-alkyl C (16.8-67.7%) dominated particle-size fractions. The proportion of alkyl C increased with increasing elevation, while O-alkyl C showed an opposite trend. Results of PCA confirmed this finding and showed the relative enrichment of alkyl C in soils of higher elevation. Increase in the proportion of alkyl C in 250-2000 μm fraction is linked to selective preservation of aliphatic compounds derived from root litter. SEM results showed an increase in root contribution to the 250-2000 μm fraction with increasing elevation. For the <53 μm fraction, pedogenic process of podzolization is responsible for the relative enrichment of alkyl C. This study demonstrates that changes in structural composition of OM in particle-size fractions of soils along the studied climo-biosequence are attributed to site-specific differences in pedogenesis as a function of climate and vegetation.

Pedogenesis on volcanic rocks in protected landscape areas in Central and North Bohemia

The development of soil cover on volcanic rocks in Central and North Bohemia was analyzed. The study was performed in the protected landscape areas on basalt, andesite, and dolerite. Parent material was characterized on the basis of thin-section study. Petrography of the parent material makes it possible to document the differences in the texture, character, and amount of rock-forming minerals. All the studied sequences exhibit the same configuration of soil profiles but various thicknesses. The soil profiles were evaluated on the basis of particle size distribution, chemical properties, soil organic matter parameters, and mineral composition of clay fraction. The major specific pedogenic process in soils developed on volcanic rocks is weathering of parent material and development of the Bw horizon with the formation of mainly smectite from the group of swelling clay minerals. The results revealed differences in the formation of the Bw horizon which is significantly affected by the petrography of the parent material and local geological conditions. According to the type of volcanic rocks, the intensity of the developmental process of the Bw horizon is as follows: andesite (T&yacute;řovick&eacute; sk&aacute;ly) &gt; dolerite (Z&aacute;hrabsk&aacute;) &gt; basalt (Březina).

Mineralogical Composition Of Soils From Urir Char ? A Tiny Offshore Island Of Bangladesh

Mineralogical composition of three surface soils from Urir Char ? an environmentally vulnerable small offshore island of Bangladesh ? was determined by X-ray diffraction analysis. In the bulk soils layer silicates and quartz were the dominant minerals while the quantity of feldspars was around ten percent. Quantity of weatherable minerals was very high in the soils. Illite was the dominant mineral in the clay fraction of the soils. The second dominant clay mineral was smectite which comprised around one-fourth of the clay fraction closely followed by chlorite with a small quantity of kaolinite mineral. Soil vermiculite and mixed layer minerals were absent in these soils. These soils had a mixed mineralogical composition with a high cation exchange capacity and percent base saturation. Texturally the soils were silty loam. Exchangeable Ca++/ Mg++ ratio was less than unity. Magnesium solonization was considered as the dominant pedogenic process along with gleization. There was problem of salinity as the elevation of land was around one meter above the mean sea level. Natural calamities like tropical cyclones and tidal surges were highly devastating as the island was completely washed with sea water. J. Asiat. Soc. Bangladesh, Sci. 39(1): 95-104, June 2013 DOI: http://dx.doi.org/10.3329/jasbs.v39i1.16038

Brunisolic soils of Canada: Genesis, distribution, and classification

Smith, C. A. S., Webb, K. T., Kenney, E., Anderson, A. and Kroetsch, D. 2011. Brunisolic soils of Canada: Genesis, distribution, and classification. Can. J. Soil Sci. 91: 695–717. Brunisols are considered as moderately developed soils formed under forest cover. They have a wide range of physical and chemical properties and no single dominant pedogenic process drives the development of these soils. Brunisols are some of the more common soils in Canada, occupying over 1.2 million km2 of land, roughly equivalent to the area of Podzolic soils, and about half the area of the most common soil order in Canada, the Cryosols. Brunisols occur mainly within the boreal forest regions, but extend across the country with the exception of the Arctic and prairie regions. Within the zone of discontinuous permafrost they co-exist on landscapes with Cryosols. In humid regions of both eastern and western Canada they form a continuum of soil development with Podzolic soils. Within subhumid to semi-arid regions they often co-exist with Luvisolic soils, occurring on parent materials too coarse to enable Luvisolic soil formation. Brunisols equate closely to the Cambisol reference group in the World Reference Base taxonomic system and to several suborders of the Inceptisol order in Soil Taxonomy. Both Melanic and Sombric Brunisols are important agricultural soils in British Columbia, Ontario and the Maritime provinces. Eutric and Dystric Brunisols support commercial forest stands throughout the boreal forest and western cordillera of Canada.

Exploring pedogenesis via nuclide-based soil production rates and OSL-based bioturbation rates

New dating techniques are available for soil scientists to test fundamental pedogenic ideas. Recent developments in applications of terrestrial in situ cosmogenic nuclides (TCN) from bedrock and saprolite allow the derivation of soil production rates, at scales ranging from local (sub-hillslope) to catchment wide, generally averaged over timescales of 104–105 years. Where soil depths are relatively constant over time, soil production rates equal transport rates and are thus essential to establishing sustainable erosion rates. TCN also allow the form of the soil production function to be compared to theoretical models—a difficult task previously. Furthermore, parameterised soil production functions can now be incorporated into numerical surface process models to test landscape evolution ideas. Bedrock and saprolite conversion to soil is demonstrably dependent on the overlying soil depth, and there is general agreement that weathering declines exponentially beyond maximum soil production, consistent with theory. Whether maximum soil production occurs under a finite or non-existent soil cover at particular sites remains unresolved. We suggest that, in general, soil production from saprolite declines exponentially with increasing depth, while production from bedrock follows a humped function. Estimates of the role of flora, fauna and processes such as freeze–thaw that mix soil mantles to depth, have been limited prior to optically stimulated luminescence (OSL) dating techniques. Recently derived OSL mixing rates extend the magnitude of previous partial, short-term bioturbation rates. In fact, bioturbation appears to be the most active pedogenic process operating in many soils, with freeze–thaw environments a noted exception. Although bioturbation far outweighs soil production, it does not always lead to homogenisation as is often reported. We maintain that the above-ground component of bioturbation, i.e. mounding, may alone, or particularly when combined with particle sorting via rainwash processes, lead to horizonisation and texture contrast soils in those materials that can be sorted such as mixtures of sand and clay. Together, TCN- and OSL-based estimates of hillslope soil transport and bioturbation, suggest significant rates of downslope soil mantle movement coupled with rapid mixing, contrary to in situ soil development models.

Conceptual Approaches to Pedogenesis

To fully appreciate and apply pedologic principals in archaeology, some of the theoretical underpinnings of pedology and especially soil geomorphology must be outlined. Pedologists and soil geomorphologists have attempted to describe, if not model, the processes of soil formation, the factors that drive the processes, and the evolution of soils as landscapes evolve (summarized by Smeck et al., 1983; Johnson and Watson-Stegner, 1987; and Gerrard, 1992, pp. 1–50, 217–220). The task is a difficult one, however, because of the complex and variable sets of processes responsible for soil development. Several of the resulting approaches have proven useful for conceptualizing pedogenesis and, more important, for interpreting soils. In addition to understanding soil-forming processes for interpreting soil profiles, understanding soil formation is important for understanding site formation. The conceptual approaches particularly useful in soil geomorphic and geoarchaeological research are summarized below. Soil-forming processes as components of site formation are discussed more fully in chapter 10. The following discussions of conceptual approaches to pedogenesis are roughly arranged in order of increasing complexity. The “multiple-process model” is essentially a categorization of soil-forming processes. It does not explain pedogenesis but is a useful way to sort and group the many soil-forming processes. The “state factor” approach and the “K-cycle” concept do not deal directly with soil formation, but instead focus on important external factors and processes that drive or affect pedogenesis such as climate and geomorphic evolution. The “soil evolution” model and the “new global view of soils” attempt to integrate pedogenic process with landscape evolution, climate, and other factors. This section closes with discussion of two important aspects of pedogenesis and pedogenic pathways that offer caveats in the use of soils for reconstructing the past. Soils are the result of biogeochemical processes determined and driven by the ecosystem (following Buol et al., 1997). This relationship is more simply described as “internal soil-forming processes” driven by “external soil-forming factors” (fig. 3.1; after Buol et al., 1984). A useful approach to categorizing the many and varied internal soil-forming processes responsible for pedogenesis is the multiple-process model of Simonson (1959, 1978).

Aspectos Pedogeomorfológicos e Mineralógicos de uma Topossequência de Solos Gnáissicos no Complexo Bação – Quadrilátero Ferrífero, MG, Brasil

The mineralogical association of the weathering rocks and their pedogenic process is fundamental in order to understand the erosive susceptibility of the soils. The regolith of the southern area of the Complexo Bação, Quadrilátero Ferrífero, Minas Gerais, was developed from gneiss and has as its predominant characteristic a thick saprolite (around 20 m) overlaid by a solum (A + B horizons) with of less than 3 m thick. This thickness is much thinner than those that frequently occur in the gneiss regolith from tropical and intertropical regions. In the toposequence investigated, the upper slope profile is a cambic soil with a poorly developed B horizon and with many relictal weathered gneiss nodules at the bottom, closer to the saprolite. The mineralogical composition of this B horizon is mainly kaolinite, gibbsite, quartz, hematite and goethite and secondarily pseudomorphous feldspars. The middle slope profile is a latosol with a well developed and thick B horizon. The mineralogical composition of this B horizon is essentially formed by kaolinite, gibbsite, quartz, hematite and goethite. The lower slope profile is a cambic latosol with the presence of relictal gneiss nodules in the B horizon analogously to the B horizon from the upper slope profile. Their mineralogical composition are also similar. The pedogeomorphological evolution of the studied catenary sequence shows that the middle slope profile is allochthonous with an accumulation of colluvial materials that formed a well developed latosol B horizon without primary minerals. The source of the colluvial materials is the upper slope profile. In the lower slope segment the lack of colluvial material suggests a process of incision, with channel and perennial flows that were originated from the adjacent gullies. The incipient fluvial plain that was formed occurs in abrupt altimetric unconformity (declivity rupture) with the lower slope segment.