Soil development on Late Quaternary river terraces in a high montane valley in Bhutan,Eastern Himalayas

We examined the geochemistry and micromorphology of the soils on a suite of morphologically well-defined and visually distinct fluvial terraces, up to 40 m elevation above the current riverbed, at Thangbi in the upper Bumthang Valley, Bhutan. The alluvia forming each of the terraces are lithologically and structurally similar, with shallow or moderately deep, clast-free sandy loam overbank deposits capping deep clast-supported beds of rounded boulders and interstitial sand. The topsoils on the 40 m terrace have more silt than those on the lower terraces. The soils are interpreted mainly as a monoclinal post-incisive chronosequence. Features that indicate progressive pedogenesis with increasing elevation include subsoil rubefaction, crystallinity of free Fe sesquioxides, and weathering of susceptible primary minerals, such as biotite and hornblende. However other soil attributes show no systematic trends and the overall impression is of limited pedogenesis, even in the soils on the higher terraces. We examine possibilities that the immaturity of the soils is due to pedogenic rejuvenation by post-incision additions to the soil parent materials.     

Soil genesis along a chronosequence on marine terraces in eastern Taiwan

Soil chronosequences developed on elevated marine terraces are ideal for studying changes in soil-forming processes with time. The coastal range of eastern Taiwan is a product of active arc–continent collision. Vertisols, Mollisols and Entisols are generally found on the different levels of marine terraces herein, but no detailed investigations of soil chronosequence have been conducted by integrating field morphology, physio-chemical characterization, micromorphology and mass-balance interpretations. Five soil pedons were selected on the three marine terraces including Tt-1 and Tt-2 pedons (Typic Hapluderts) on the first higher level with the oldest soil age (9–10 ka), Tt-3 (Vertic Hapludolls) and Tt-4 pedons (Typic Hapludolls) on the second intermediate level (5–6 ka), and Tt-5 pedon (Typic Udipsamments) on the third lower level with the youngest soil age (≤ 3.5 ka). The morphological characteristics showed that strongly developed angular blocky structures, pressure faces and slickensides are more common in higher terrace soils than in lower terrace soils. In this study, depth to C horizon, solum thickness, and thickness of the clay-enriched zone increase with relative terrace age. Although only one to two profiles per terrace were characterized, the following soil analytical characterizations increase with time: the degree of sand grains weathering, pH (H₂O), organic carbon, CEC, contents of Fe_d, Fe_o and Mn_d. Based on X-ray diffraction analysis of the clay-size fraction, soils on all terraces have a mixed mineralogy. Mica, smectite, and kaolinite have slightly increased with increasing terrace age. Furthermore, the dominant processes identified with mass-balance analysis include loss of bases (Ca and Mg), iron, and clay with time. The soil properties, including analytical and mineralogical characterizations, which do not have notable changes with time are primarily due to relatively young soil age (< 10 ka).     

Soil chronosequences, soil development, and soil evolution: a critical review

Soils chronosequences are valuable tools for investigating rates and directions of soil and landscape evolution. Post-incisive chronosequences are the most common type of chronosequence. They are found in many landscapes, including sand dunes, glacial moraines, landslide scars, old pasture, burnt landscape patches, old mining areas, lava flows, alluvial fans, floodplains, river terraces, and marine terraces. They register pedogenic change over time-scales ranging from years to millions of years. Soil chronosequences help in testing rival theories of pedogenesis. Traditional soil formation theory sees a soil developing progressively under the influence of the environmental state factors until it is in equilibrium with prevailing environmental conditions. This developmental view of pedogenesis is supported by the classic soil chronosequence studies. A new evolutionary view of pedogenesis, which was prompted by the omnipresent inconstancy of environmental conditions and the notions of multidirectional changes and multiple steady states (as predicted by non-linear dynamics), proposes that environmental inconstancy and non-linear behaviour in soil-landscapes lead to soil evolution, rather than to soil development. Soils ‘evolve' through continual creation and destruction at all scales, and may progress, stay the same, or retrogress, depending on the environmental circumstances. Some recent soil and vegetation chronosequence investigations support an evolutionary view of pedogenesis. It is concluded that soil chronosequences are still potent instruments for pedological investigations and that they have a starring role to play in the testing of pedological theories.     

Micromorphological evidence of paleoenvironmental changes in Northern Cilento (South Italy) during the Late Quaternary

Three representative soil profiles developed during the Late Quaternary in Northern Cilento (South Italy) were studied by optical microscopy and SEM-EDS observation of thin sections to examine soil features as evidence for past climatic fluctuations.Two of the profiles are polygenetic and the third monogenetic. All these have a clear interglacial imprint, whereas the polygenetic profiles also contain other features, which can be related to periglacial conditions during the stadial glacial periods although in midlatitude coastal areas. All the paleosols show a strong marine influence during development, which probably resulted from windblown processes or submergence during past interglacial phases.     

Chrono-toposequences of soils on the river terraces in Transylvania (Romania)

A sequence of surface soil profiles and buried soils described on the 4th, 3rd, 2nd and 1st terraces of different rivers in Transylvania is presented as part of an attempt to perform a paleopedologic interpretation of the dominant soil types of this area. Excepting the first terrace, the described soils were formed from Pleistocene slopewash deposits of Würm, or possibly of Riss age, which overlay alluvial terrace deposits. On the basis of fossil animal remains, periglacial cryostructures, prehistoric artifacts (Coţofeni culture of the transition period from the Neolithic to the Bronze Age) and Scythian graves an approximate age of different soil horizons, as well as the polycyclic nature of soils was established. There is no essential difference between a Würmian buried soil horizon and the argic Bt horizon of the surface soils; moreover, in some cases, the buried paleosols become the Bt horizon itself of the surface soils, through the thinning of the overlying deposits. Even if the possibility of formation of the argic Bt horizons during the postglacial until the end of Neolithic, cannot be excluded, from the presented situations it seems that these horizons in the Transylvanian Basin are Würmian relics, formed in the periglacial interstadials. In most of the cases Bt horizon has nothing in common genetically with the topsoil.     

Smectite formation produced by weathering in a coarse granite saprolite in Galicia (NW Spain)

Weathering of a calcalkaline granite was studied in the south of Galicia (NW Spain) where the average annual precipitation is 1400 mm and the average annual temperature is 12°C. The original rock contains perthitic K-feldspars, plagioclases with inclusions of muscovite and opaque minerals, quartz and chloritized biotite, with apatite, zircon, sphene and opaques as accessories. In the saprolite the structure of the rock is preserved, the plagioclases show up to grade 4 weathering and the biotites, between 2 and 3. Weathering in quartz and potassium feldspar crystals is manifested only by fracturing. Biotite changes following the parallel linear model and its weathering products are interstratified biotite–vermiculite and iron oxyhydroxides. The plagioclases change to a microgranular material by pseudomorphic transformation. This material, which substitutes the plagioclase, includes small clearly delimited units which retain zones with the optic characteristics of muscovite. X-ray diffraction analyses of microsamples show that they are formed by 1:1 diocthaedral phyllosilicate, smectite and a small quantity of mica. From these facts we concluded that smectite is formed inside the plagioclase crystals, and probably originates from the inclusions of muscovite contained in these crystals, as it is suggested by the microscopic study which shows the increase in volume which occurs when the crystals of muscovite are transformed.     

Assessment of soil degradation in the Canary Islands (Spain)

In the Canary Islands a number of factors, both natural and induced by human activity, act on the fragile ecosystems and agricultural land to cause increasing problems with desertification and progressive degradation of soil productivity. the results of an assessment of soil degradation in the Canary Islands, The processes, causes and impacts, are presented in this paper. Although several processes and factors contribute to soil degradation in the Canary Islands, two have been found to exert a greater qualitative influence: (a) accelerated erosion (water and aeolian); (b) salinization-sodification (natural and induced by agricultural use). Approximately 40 per cent of the Canary Islands' land is undergoing rapid erosion. the factors involved May, be grouped into: natural erosion—torrential rainfall, sparse vegetation, high soil erodibility, rugged relief; and erosion due to human activities—unsuitable management of arable soils on the steep slopes, overgrazing and deforestation. About 60 per cent of the surface of the archipelago, including areas given over to intensive agriculture, is affected by salinization.The main factors responsible are: natural—an arid climate and a regime of oceanic winds; and human activities—overexploitation of the aquifers, irrigation with water having a high salt and/or sodium content, intensive monoculture, and excessive and indiscriminate use of chemical fertilizers and other agrochemicals.     

Soil moisture variability along transects over a well-developed gully in the Loess Plateau,China

Knowledge of soil moisture distributions in gullies, which are highly variable spatially and temporally, is important for both restoring vegetation and controlling erosion in them, but little attention has been paid to this spatio-temporal variability to date. Therefore, we examined soil moisture profiles and their variability along three transects traversing sidewalls of a well-developed gully with steep slopes in a hilly area of the Chinese Loess Plateau. We took intensive measurements at 20-cm intervals from 0 to 160 cm depth, using a portable time domain reflectometer, from September 3 to October 20 2009 and from April 5 to July 20 2010. The results indicate that the mean, standard deviation and coefficient of variation of moisture content vary with time, their responses to precipitation vary at different depths, and moisture content is most variable when mean values are moderate (15–20%). Revised fitting functions developed and introduced by Famiglietti et al. (2008) captured with confidence the relationship between spatial variability (SD and CV) and spatial mean of moisture content (RMSE ranging from 0.0015 to 0.0293). Soil moisture clearly varied along the transects, the vertical distribution of soil moisture differed in different seasons, and correlation analysis showed that soil texture influenced the variability of surface soil moisture more strongly than terrain attributes (except during distinct rainfall events, when this pattern reversed). The results presented here should improve understanding of spatio-temporal variations in soil moisture profiles in well-developed gullies in the Loess Plateau, and potentially elsewhere.     

Classification of Urban and Industrial Soils in the World Reference Base for Soil Resources (5 pp)

Background, Aim and Scope   Historically, built areas were ignored in soil mapping and in studies of soil formation and behaviour. It is now recognized that these areas, and therefore their soils, are of prime importance to human populations. Another trend is the large increase in reclaimed lands and new uses for old industrial areas. In several countries there are active projects to map such areas, either with locally-developed classification systems or ad-hoc names. Soil classification gives unique and reproducible names to soil individuals, thereby facilitating correlation of soil studies; this should be possible also for urban soils. The World Reference Base for Soil Resources (WRB) is the soil classification system endorsed by the International Union of Soil Science (IUSS). The 2006 edition has important enhancements which allow urban and industrial soils to be described and mapped, most notably a new reference group, the Technosols. Main Features   Urban soils are first defined, followed by the philosophical basis of soil classification in general and the WRB in particular. WRB 2006 added a new Technosols reference soil group for soils whose properties and function are dominated by technical human activity as evidenced by either a substantial presence of artefacts, or a impermeable constructed geomembrane, or technic hard rock. Technosols are one of Ekranic, Linic, Urbic, Spolic or Garbic; further qualifiers are added to show intergrades to other groups as well as specific soil properties. Soils from fill are recognized as Transportic Regosols or Arenosols. Toxic soils are specifically recognized by a qualifier. Results   - Discussion   The limit between Technosols and other groups may be difficult to determine, because of the requirement that the technic nature dominate any subsequent pedogenesis. Conclusions   - Perspectives   The WRB should certainly be used in all urban soil studies to facilitate communication and correlation of results. In the period leading up to the next revision in 2010, the quantitative results from urban soil studies should be used to refine class definitions.     

Water balance simulation of a dryland soil during fallow under conventional and conservation tillage in semiarid Aragon, Northeast Spain

In Central Aragon, winter cereal is sown in the autumn (November–December), commonly after a 16–18 months fallow period aimed at conserving soil water. This paper uses the Simple Soil–Plant–Atmosphere Transfer (SiSPAT) model, in conjunction with field data, to study the effect of long fallowing on the soil water balance under three tillage management systems (conventional tillage, CT; reduced tillage, RT; and no-tillage, NT). This was on the assumption that soil properties would remain unchanged during the entire fallow season. Once the model was validated with data obtained before primary tillage implementation, the differences between simulated and observed soil water losses for the CT and RT treatments could be interpreted as the direct effect of the soil tillage system. The model was calibrated and validated in a long-term tillage experiment using data from three contrasting long-fallow seasons over the period 1999–2002, where special attention was paid to predicting soil hydraulic properties in the pre-tillage conditions. The capacity of the model to simulate the soil water balance and its components over long fallowing was demonstrated. Both the fallow rainfall pattern and the tillage management system affected the soil water budget and components predicted by the model. The model predicted that about 81% of fallow seasonal rainfall is lost by evaporation in long-fallow periods with both a dry autumn in the first year of fallow and a rainfall above normal in spring. Whereas, when the fallow season is characterised by a wet autumn during the first year of fallow the model predicted a decrease in soil water evaporation and an increase in water storage and deep drainage components. In this case, the predicted water lost by evaporation was higher under NT (64%) than under RT (56%) and CT (44%). The comparison between measured and simulated soil water loss showed that the practice of tillage decreased soil water conservation in the short term. The long-term analysis of the soil water balance showed that, in fallow periods with a wet autumn during the first year of fallow, the soil water loss measured under CT and RT was moderately greater than that predicted by the model.     

Soil fertility affected by land use history,relief position,and parent material under a tropical climate in NW-Vietnam

In Vietnam as much as half of the total land area is already degraded by soil erosion and nutrient depletion. In particular, degradation due to deforestation is increasingly affecting mountainous areas in north-western Vietnam. The necessity to safeguard the farmers' livelihoods requires sustainable resource management, which firstly requires a qualitative and quantitative evaluation of resources. The objectives of the present study were to (1) identify the dominant soil types and their vulnerability using elicitation of local soil knowledge, (2) characterise the physical and chemical properties of the soils and (3) link them to the relief position and land use in order to (4) initiate sustainable soil use based on recommendations deduced from objectives (1) to (3). These objectives were achieved also by the elicitation of local knowledge. The final aim of the study was to initiate sustainable soil use based on recommendations for sustainable land use scenarios. The Chieng Khoi commune in Son La province of northern Vietnam was chosen as representative for other erosion-prone Southeast Asian sloping areas. In a participatory approach, combining local and scientific knowledge, sixteen sites were selected, representative for distinct relief positions, parent material (sand stone and silt stone), land use history, and erosion hazard. Chemical (e.g. content of organic matter, nitrogen, cation exchange capacity, base saturation, and plant available phosphorous) and physical properties (e.g. air capacity, plant available water) were used to estimate soil fertility. The predominant reference soil groups in the study area are Alisols and Luvisols, with a high diversity in respect to soil fertility. These soils are locally named ‘red soil’ and ‘black soil’, respectively. Although the main physical processes are erosion and selective sedimentation, farmers tend to underestimate their impact and causes, whereas soil quality was well-evaluated. Soils with high fertility were found on less eroded upper parts of hills and at sites, where agricultural use started only recently. Once degraded by cultivation practices, soils derived from sandstone did not recover even after more than 50 years of fallow. As a result of unsustainable land use, soils on middle and lower slopes are often affected by severe soil erosion, whereas foot slope soils suffer from accumulation of eroded infertile subsoil material as well as stagnic conditions. This study showed that unsustainable land use at upslope landscape positions has a severe impact on downslope areas. The elicitation of local knowledge facilitated the identification of such hot spots, allowing the implementation of spatially targeted conservation measures.     

Effect of water erosion and cultivation on the soil carbon stock in a semiarid area of South-East Spain

An experiment to evaluate the impact of water erosion and cultivation on the soil carbon dynamic and carbon stock in a semiarid area of South-East Spain was carried out. The study was performed under three different land use scenarios: (1) forest; (2) abandoned agricultural field; and (3) non-irrigated olive grove. Experimental erosion plots (in olive grove and forest) and sediment traps (in the abandoned area) were used to determine the carbon pools associated with sediments and runoff after each event occurring between September 2005 and November 2006.

Change in land use from forest to cultivated enhanced the risk of erosion (total soil loss in olive cropland seven-fold higher than in the forest area) and reduced the soil carbon stock (in the top 5 cm) by about 50%. Mineral-associated organic carbon (MOC) represented the main C pool in the three study areas although its contribution to soil organic carbon (SOC) was significantly higher in the disturbed areas (78.91 ± 1.81% and 77.29 ± 1.21% for abandoned and olive area, respectively) than in the forest area (66.05 ± 3.11%). In both, the olive and abandoned soils, the reduction in particulate organic carbon (POC) was proportionally greater than the decline in MOC.

The higher degree of sediment production in the olive cropland had an important consequence in terms of the carbon losses induced by erosion compared to the abandoned and forest plots. Thus, the total OC lost by erosion in the sediments was around three times higher in the cultivated (5.12 g C m⁻²) than the forest plot (1.77 g C m⁻²). The abandoned area displayed similar OC losses as a result of erosion as the forest plot (in the measurement period: 2.07 g C m⁻², 0.63 g C m⁻² and 0.65 g C m⁻² for olive, forest and abandoned area, respectively). MOC represented the highest percentage of contribution to total sediment OC for all the events analysed and in all uses being, in general these values higher in Olive (74–90%) than in the other two areas (55–80%). The organic carbon lost was basically linked to the solid phase in the three land uses, although the contribution of DOC to total carbon loss by erosion varied widely with each event.

Data from this study show that the more labile OC fraction (POC) lost in soil in the cultivated area was mainly due to the effect of cultivation (low overall biomass production and residue return together with high C mineralization) rather than to water erosion, given that the major part of the OC lost in sediments was in the form of MOC.     

Effects of Long-term Organic and Mineral N-fertilisation on Soil Microarthropods in Berlin (Germany), Madrid (Spain) and Tartu (Estonia)

Soil micro-arthropods play an important role in the nutrient cycle of agro-ecosystems and are considered to have a strong impact on microbial activity. The occurance of soil microarthropods was investigated in the International Organic Long-Term Field Experiment (IOSDV). The investigation took place in the experimental fields of Berlin/Germany, Madrid/Spain and Tartu/Estonia. Field plots "without organic fertisation", "farmyard manure" and "straw-beet-leaves-green manure" without mineral N-fertilisation and with 120kg/ha mineral N-fertilisation respectively have been investigated. Data shows that the effects of organic manure and mineral N-fertilisation are considerably influenced by specific site characteristics. The highest abundances were found in the experimental field of Madrid. In the two nothern sites soil microarthropods were found only in very low quantities. Data indicates that not only organic manure but also mineral N-fertilisation may influence the abundance of soil micro-arthropods positively.     

Effects of grazing on soil physical properties and soil erodibility in semiarid grassland of the Northern Loess Plateau (China)

Grazing animals provide a livelihood for farmers, but they may also produce adverse environmental effects. We investigated whether grazing leads to deterioration of soil physical properties that subsequently increases topsoil erodibility. We sampled three sites (an ungrazed grassland, a continuously grazed grassland, and a track trampled by stock) on the northern Loess Plateau of China. The bulk density, water content, proportion of stable aggregates, infiltration rate, and resistance to scouring were determined for each soil sample. The results showed that the track had the highest soil bulk density and the lowest soil water content, proportion of stable aggregates, infiltration rate, and ability to resist scouring. The ungrazed plots had the best results for these parameters, in terms of reduced erosion. Soil bulk density and the proportion of stable aggregates differed significantly with depth beneath the track. However, the effect of depth on water content, infiltration rate, and the soil resistance to scouring was not significant at any sampling site. The ability of the soil to resist scouring was negatively correlated with the soil's bulk density and positively correlated with the soil's water content, infiltration rate, and proportion of stable aggregates. Thus, soil physical properties played an important role in determining soil erodibility. Grazing and trampling by livestock therefore appear to cause deterioration of soil physical properties and to increase soil erodibility.     

SEM image analysis in the study of a soil chronosequence on fluvial terraces of the middle Guadalquivir (southern Spain)

A Quaternary fluvial chronosequence (Guadalquivir River, southern Spain), consisting of five soil profiles with estimated ages of 300 years (Haplic Fluvisol), 7000 years (Haplic Calcisol), 70 000 years (Cutanic Luvisol), 300 000 years (Lixic Calcisol) and 600 000 years (Cutanic Luvisol), was studied. Increasing soil age was associated with increases in: reddening, development of structure, clay content, dithionite-extractable iron (Fe _d ) and aluminium (Al _d ) and strengthening of X-ray diffraction (XRD) peaks for phyllosilicates and iron oxides; there were also decreases in pH and percentage of carbonates in the fine earth and lower XRD peaks for calcite and dolomite. These changes indicate that the principal pedogenic processes were weathering, clay illuviation, rubefaction and the weathering and leaching of carbonates. We have further characterized the pedogenetic chronosequence by quantification of ultramicrofabrics of ped interiors using image analysis (IA) techniques on images obtained with scanning electron microscopy (SEM). We have estimated morphometric ultramicrofabric parameters for particle clusters, skeleton grains and pore space. These are closely related to analytical, mineralogical and macromorphological properties. In the principal component analysis, the first two principal components of the combined morphological, analytical and mineralogical data accounted for 78% of the total variance. The first component (48%) is loaded by variables associated with clay illuviation, relative accumulation of iron and aluminium sesquioxides and the weathering and leaching of carbonates. The components are related to ultramicrofabric development trends. We tested several chronofunctions derived from analytical and morphometric attributes. The logarithmic model fitted best, and we interpret this as indicating pedogenetic processes that are converging towards a steady state.     

覆盖作物根系对砂姜黑土压实的响应

轮作直根系的覆盖作物被认为是缓解土壤压实的有效手段,但不同覆盖作物对土壤压实的适应性在不同气候和土壤条件下存在较大差异.为筛选更适宜缓解砂姜黑土压实的覆盖作物品种(模式),在安徽典型砂姜黑土设置不压实(Non-compacted,NC)与压实(Compacted,C)处理,通过种植不同覆盖作物(休闲、苜蓿、油菜、萝卜+...     

Soil erosion from a single rainstorm over an area in East Lothian, Scotland

Abstract. An area of about 24 km² in arable East Lothian, Scotland, was examined for soil erosion by water following a severe rainstorm in October 1990. Significant erosion was found in only 10 fields out of 26.5 in an area where topography, soils and cropping suggest a high erosion risk. Doubt is cast on some assessments of the widespread risk of significant soil erosion by water in arable areas of the UK.     

Differential weathering of granitic stocks and landscape effects in a Mediterranean climate,Southern Iberian Massif (Spain)

Mineralogical and structural features control the weathering processes and landform development of two different crystalline stocks in the Iberian Massif, Spain (the Santa Elena and Linares stocks). The Santa Elena stock shows irregular saprolite profiles and boulder landforms whereas the Linares stock develops broad and plain landscapes with uniform saprolites and less boulder forms. The Santa Elena stock is more closely jointed and fractured than the Linares body. The main secondary minerals are kaolinite, and illite; illite/smectite interstratification was only observed in deep samples from the Linares profile. The Linares profile is feldspar-enriched whereas in Santa Elena plagioclase is almost absent and clay mineral content, especially kaolinite, is higher. Feldspars show dissolution channels developed along cleavage planes filled by clay minerals. Biotite–kaolinite intergrowths have fanned-out textures of epitaxial disposition. Weathered materials are enriched in Al and H₂O and Fe, and depleted in Ca, Na, Mg, Ti, P. The Santa Elena weathered materials are richer in H₂O than those from Linares and have lower Si/Al ratios. Mineralogical and geochemical evidence indicate the Santa Elena materials are more intensely weathered. High fracturation and high Ca-richer plagioclase contents are key factors producing the pervasive Santa Elena stock weathering. Fluvial erosion removed the alteration products in incised tectonically controlled streams resulting in boulder accumulation.