Total Clay Research Articles

Long-lasting Effects of Bentonite on Properties of A Sandy Soil Deprived of the Humus Layer

Abstract Bentonite has been recognized as a very good material for the improvement of coarse textured soils. In microplot experiment, of a sandy soil deprived of the humus layer was enriched in 1973 with waste bentonite at the rates of 0, 3, 6 and 12 kg m-2. Until 2002, the microplots were planted with different crops and regularly enriched with mineral and organic fertilizers. Since 2003, the microplots were left barren. In 2009, determinations of several features of the soils (in 5-30, 30-55 and 55-80 cm layers) showed that the historical amendment of the sandy soil with bentonite (especially its highest dose) ensured significantly higher contents of water, organic C, clay, silt and a sand fraction with particle diameter <0.1 mm in 5-30 cm layer. Proportions of non-dispersible clay in the total clay of bentonite soils in the two upper soil layers were significantly lower than those of the control soil. A significant increase in the penetrometer resistance was observed in 40-58 cm layers of the control soil and the soil with 3 kg m-2 bentonite amendment, contrary to the soils with two highest bentonite doses.

Rapid estimation of soil engineering properties using diffuse reflectance near infrared spectroscopy

Materials testing involve complex reference methods and several soil tests have been used for indexing material functional attributes for civil engineering applications. However, conventional laboratory methods are expensive, slow and often imprecise. The potential of soil diffuse reflectance near infrared (NIR) spectroscopy for the rapid estimation of selected key engineering soil properties was investigated. Two samples sets representing different soils from across the Lake Victoria basin of Kenya were used for the study: A model calibration set (n = 136) was obtained using a conditioned Latin hypercube sampling, and a validation set (n = 120) using a spatially stratified random sampling strategy. Spectral measurements were obtained for air-dried (<2 mm) soil sub-samples using a Fourier-transform diffuse reflectance near infrared (NIR) spectrometer. Soil laboratory reference data were also obtained for liquid limit (LL), plastic limit (PL), plasticity index (PI), linear shrinkage (LS), coefficient of linear extensibility (COLE), volumetric shrinkage (VS), clay activity number (Ac), total clay content, air-dried moisture content, and cation exchange capacity (CEC). Soil reference data were calibrated to smoothed first derivative NIR spectra using partial least squares (PLS) regression. At the calibration stage, coefficient of determination for full cross-validation (R2) of ≥0.70 was obtained for CEC, mc, LL, PI, LS, COLE and VS. Further independent validation gave R2 ≥ 0.70 and RPD (ratio of reference data SD and root mean square error of prediction) 1.7–2.2 for LL, PI, mc and CEC. The results suggested that NIR–PLS has potential for the rapid estimation of several key soil engineering properties. Further work should focus on extending calibration libraries using more diverse soil types and testing alternative infrared diffuse reflectance based methods.

Water retention of the loess-derived Luvisols with lamellic illuvial horizon in the Trzebnica Hills (SW Poland)

Abstract The aim of work was to characterize the water retention in the silt-textured Luvisols with lamellic illuvial horizon (argic) that occur in the loess covered northern part of the Silesian Lowland. Soil pits were localized on the Trzebnica Hills near the villages: Machnice (profile 1), Skarszyn (profile 2) and Zaprężyn (profile 3 and 4). Profiles Machnice 1 and Skarszyn 2 were situated in the upper parts of the hills covered with beech stands with an admixture of oak, linden and maple. Profiles Zaprężyn 3 and 4 were situated in the central and lower parts of the arable slope. During the field work conducted in April 2011, 29 soil samples were collected for texture, bulk density and water properties analysis. The soils under study were characterized by texture of silt loam with lower clay content in humus horizons (.loamy silt. according to Polish classification), and higher clay content (.clayey silt.) in the illuvial and subsoil horizons. The texture of all examined profiles was dominated by the „loess“ fractions. Variable abundance of the massive lamellae causes variations in water properties of the illuvial (sub-)horizons. It was found that lamellic illuvial horizons in the loess-derived Luvisols have higher field water capacity than the homogenous illuvial horizons, apart of the clay content. There was no apparent effect of the horizon kind (homogeneous versus lamellic) on the soil bulk density. These properties mainly depended on the total clay content in a particular horizon (sub-horizon).

滩涂围垦和土地利用对土壤微生物群落的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 滩涂围垦和土地利用对土壤微生物群落的影响 DOI: 10.5846/stxb201305271198 作者: 作者单位: 复旦大学生命科学学院生态与进化生物学系,复旦大学生命科学学院生态与进化生物学系,复旦大学生命科学学院生态与进化生物学系,复旦大学生命科学学院生态与进化生物学系 作者简介: 通讯作者: 中图分类号: 基金项目: 科技部气候变化专项资助项目（2010CB950600）；上海市科委资助项目（09DZ1900106） Effects of reclamation on tidal flat and land use on soil microbial community Author: Affiliation: The Institute of Biodiversity Science, Fudan University,The Institute of Biodiversity Science, Fudan University,The Institute of Biodiversity Science, Fudan University,The Institute of Biodiversity Science, Fudan University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:土壤微生物在生态系统营养物质循环过程，特别是碳、氮循环过程中扮演着重要的角色。上海市崇明岛位于长江入海口，因其土壤发育时间较短、土地利用历史背景清晰、土壤本底均一，不同土壤围垦年代的土壤，代表了土壤发育年代的不同时期。以空间变化代替时间变化，对崇明岛稻田和旱地6个不同围垦年代土壤的磷酸脂肪酸（PLFA）指纹图谱研究表明，湿地滩涂围垦16a后土壤微生物总PLFA、细菌PLFA、革兰氏阳性菌（G+） PLFA和革兰氏阴性菌（G-） PLFA含量显著降低。随着围垦时间的逐步增加，PLFA含量逐步上升。经过长时间的农业种植，G+ PLFA在围垦120a和300a稻田和旱地土壤中没有显著性差异；而总PLFA、细菌和G- PLFA在围垦75、120a和300a的土壤中含量趋于稳定且没有显著性差异。围垦16a和40a稻田土壤中总PLFA和G+ PLFA显著高于旱地土壤；围垦40a稻田土壤中细菌和G- PLFA显著高于旱地土壤。不同围垦年代土壤总PLFA、细菌PLFA与土壤总氮、粘土含量成显著的正相关关系。河口湿地围垦后微生物数量的变化与土壤营养含量存在强烈相关关系，提示土壤围垦及演替过程中微生物与土壤肥力之间的紧密关系，对探讨土壤演替过程中微生物群落的变化具有重要意义。 Abstract:Soil microbes play a vital role in nutrient cycling, especially in carbon and nitrogen cycling. Microbes are influenced and regulated by many factors, such as anthropogenic disturbances, environmental conditions and soil properties. Little has been reported on soil microbial response to long term cultivation after reclamation of estuary wetland. One of possible reasons may be the heterogeneity of soil background and complicated land use history. The Chongming Island, located in the estuary of Yangtze River, was originated mainly from periodical reclamation on tidal flat. Because of an excellent homogeneous soil background and a relatively short and clear land use history on the island, the chronosequence of soils reflects mainly microbial response to soil development and cultivation. Phospholipid Fatty Acids (PLFA) are principle components of microbial cell membranes. Its pattern can be used as a fingerprint of soil microbes to provide insight information of soil bacterial and fungal communities because different microbes show different PLFA profile patterns.This research focused on a chronosequence of 6 soil ages under two different cultivation (paddy rice and upland cropping) systems, including 0 (unclaimed wetland soil), 16, 40, 75, 120 and 300 years old soils. PLFA analysis results showed that after reclamation of coastal wetland, soil total PLFA, bacterial PLFA, Gram-positive (G+) PLFA and Gram-negative (G-) PLFA all reduced significantly in both paddy rice and upland cropping soils. Microbial PLFA abundance then increased gradually over several decades in both paddy rice and upland cropping soils. After a long-term human cultivation, no significant difference in G+ PLFA was observed in 120 or 300 years old soils, either in paddy rice or upland cropping soils. No significant difference in total PLFA, bacterial PLFA or G- PLFA was observed among 75, 120 or 300 years old soils. Principle component analysis (PCA) showed that two principle components, PC1 and PC2, could explain 51.12% and 18.57% of the total PLFA variation, respectively. PCA also revealed that PLFA profiles of 75, 120 and 300 years old soil were clearly different from those of 0, 16 and 40 years old soil. Cultivations of paddy rice and upland crops have significantly affected soil microbial structure. Total PLFA and G+ PLFA were significantly higher in 16 and 40 years old paddy soils than those of upland cropping soils. Bacterial and G- PLFA were significantly higher in 40 years old paddy rice soils than those of upland cropping soils. Soil total PLFA and bacterial PLFA were significantly correlated to soil total nitrogen and clay content, suggesting strong relations between soil microbes and soil nutrient status. The PLFA results indicated that human cultivations have led to environmental stress on soil microbes and this stress was gradually relieved along with long-term cultivations, because of improved soil nutrient conditions due to inputs of carbon, nitrogen and phosphorus fertilizers.This study provided deep insights into soil microbial structures of different soil ages based on PLFA analysis under paddy and upland cultivation systems, which are two major cropping systems in China. It was helpful for us to better understand the development of soil microbial communities along with soil succession in arable soils. 参考文献 相似文献 引证文献

Saturated hydraulic conductivity (Ksat) in relation to some soil physical properties of some ferralitic soils with hydromorphic segregation in Delta State, Nigeria

The study was conducted in a ferralitic soil with hydromorphic segregation in Anwai, Asaba, Delta State. A grid of 12m x 12m were mapped out and pegged 4m apart to give a total of sixteen (16) experimental points. At each point, soil samples were taken at a pre-determined depth of 0-20cm and routinely processed and analyzed for particle size fractions, bulk density, particle density and total porosity. Saturated hydraulic conductivity was determined using a locally fabricated 12 cm iron core-cylinder which was carefully driven into the soil and core samples collected for laboratory determination and conductivity calculated using Darcy’s law. Data collected were analyzed using mean, standard deviation and coefficient of variation, while the relationship between saturated hydraulic conductivity was established using regression models. The results of the study showed that the particle size fractions of the soils varied from sandy loam to clay loam. Bulk density and particle density were low to moderate with mean values of 1.44 gcm-3 and 2.34 gcm-3. Total porosity was low with mean value of 38.06% and a coefficient of variation of 9.56%. Saturated hydraulic conductivity correlated positively with total sand (0.98xx), Clay (0.52x), bulk density (0.94xx) and total porosity (r = 0.56x) silt content showed poor correlation significant (r = 0.34ns). The general results showed that key soil physicl properties such as sand, clay, bulk density and total porosity can be used to predict hydraulic functions in the soil matrix. Keywords: Saturated hydraulic conductivity, soil physical properties, hydromorphic segregation, Delta StateNigerian Journal of Technological Research, 8(2), 2013

Spatiotemporal Distribution Characteristics of Soil Organic Carbon in Newborn Coastal Wetlands of the Yellow River Delta Estuary

The distribution and seasonal variation of soil organic carbon (SOC) in newborn coastal wetland of the Yellow River Delta (YRD) estuary at eastern China were studied based on monitoring data in 2009 at two transects from the bank of the Yellow River to the seaside. The results showed that SOC contents of 0–60 cm soil layer in transects ranged from 0.46 to 10.15 g kg−1 and average values of soil profiles ranged from 2.15 to 5.00 g kg−1. The SOC contents tended to increase from the river flood land to the salt beach, which could be accounted for the organic matters including large algae, the bodies and excretion of marine animals due to the feedback of tides. The significant difference of SOC contents at different vegetation communities was observed, while the difference of SOC in soil profiles was not obvious. The SOC contents in 0–30 cm soil layers decreased with plant growth period, while in 40–60 cm soil layers were relatively stable. The mean soil organic carbon density was 3.05 kg C m−2 in study region, which was much lower than that reported in other ecosystems, and its spatiotemporal variations were consistent with that of SOC content. Further analysis revealed that SOC was positively correlated with total nitrogen and clay contents. Our findings indicated that the newborn coastal wetland in the YRD should be a potential sink of SOC.

Indirect estimation of the clay content of clay-rocks using acoustic measurements: New insights from the Montiers-sur-Saulx deep borehole (Meuse, France)

This work benefited from a comprehensive set of logging and mineralogical data that was acquired from the 2-km-deep EST433 borehole of Montiers-sur-Saulx (Meuse, France). A multiple linear regression analysis was performed on three sets of data: (a) sonic data (P- and S-wave velocities), (b) total combinable magnetic resonance (TCMR) porosity data, and (c) X-ray diffraction (XRD) data. The analysis was performed to estimate the clay content in the Callovo-Oxfordian (COx) claystone and other clay-rocks of the stratigraphic column. The inferred statistical relationships were compared to results obtained from a conventional spectral gamma ray (GR) approach.The results indicate that simple linear regressions using only elastic wave velocities (a) accounted for more than 81% of the vertical variability of the clay content in the COx formation (i.e., coefficient regression R2 values greater than 81%) and (b) enable the estimation of clay content with the same accuracy as the spectral GR approach. Both approaches, our acoustic regressions and spectral GR methodology, provide estimate errors that are within the range of uncertainties associated with the XRD analysis applied. Moreover, using the whole set of XRD data showed that the elastic wave velocities and the TCMR porosity as explanatory variables are better predictors of total clay content than swelling clay mineral content.Blind estimations of clay content were performed using data acquired in clay-rocks from the same stratigraphic column and in the COx formation located a few kilometers distant in the EST423 borehole. The results demonstrated that the established regressions must be used with caution when vertically and horizontally extrapolating the estimated clay content. This difficulty is partly explained by the influence of the microstructure of the studied clay-rocks, which was insufficiently taken into account via the petrophysical variables considered in this work.

Improving on the Prediction of Cation Exchange Capacity for Highly Weathered and Structurally Contrasting Tropical Soils from Their Fine-Earth Fractions

The roles of fine-earth materials in the cation exchange capacity (CEC) of especially homogenous units of the kaolinitic and oxyhydroxidic tropical soils are still unclear. The CEC (pH 7) of some coarse-textured soils from southeastern Nigeria were related to their total sand, coarse sand (CS), fine sand (FS), silt, clay, and organic-matter (OM) contents before and after partitioning the dataset into topsoils and subsoils and into very-low-, low-, and moderate-/high-stability soils. The soil-layer categories showed similar CEC values; the stability categories did not. The CEC increased with decreasing CS but with increasing FS. Silt correlated negatively with the CEC, except in the moderate- to high-stability soils. Conversely, clay and OM generally impacted positively on the CEC. The best-fitting linear CEC function (R2, 68%) was attained with FS, clay, and OM with relative contributions of 26, 38, and 36%, respectively. However, more reliable models were attained after partitioning by soil layer (R2, 71–76%) and by soil stability (R2, 81–86%). Notably FS's contribution to CEC increased while clay's decreased with increasing soil stability. Clay alone satisfactorily modeled the CEC for the very-low-stability soils, whereas silt contributed more than OM to the CEC of the moderate- to high-stability soils. These results provide new evidence about the cation exchange behavior of FS, silt, and clay in structurally contrasting tropical soils.

Contamination profile of DDT and HCH in surface sediments and their spatial distribution from North-East India

Contamination status and spatial distribution of DDTs and HCHs were investigated in sediments collected from ponds and riverine system from districts Nagaon and Dibrugarh, North East India. A total of 113 surface sediment samples were collected from both the districts including 43 from ponds/wetlands and 70 from rivers/streams. Based on dry weight (dw), the mean concentration of ∑HCH and ∑DDT in sediments were found to be 287ng/g (71.2–834ng/g) and 321ng/g (30.1–918ng/g) for district Dibrugarh while 330ng/g (39.2–743ng/g) and 378ng/g (72.5–932ng/g) for district Nagaon, respectively. DDTs and HCHs in sediments were well influenced by total organic carbon, clay and silt content of sediments. Source identification revealed that sediment residue levels have originated from long and recent mixed source of technical HCH and Lindane for HCHs and mainly technical DDT for DDTs. Majority of samples exceeded the sediment quality guidelines (SQG) for γ-HCH, p,p′-DDT and ∑DDT indicating potential environmental risk. This baseline data can be used as reference for regular ecological and future POPs monitoring program.

Analysis of the developmental characteristics and major regulating factors of fractures in marine–continental transitional shale-gas reservoirs: A case study of the Carboniferous–Permian strata in the southeastern Ordos Basin, central China

Fractures play an important role in the formation of shale-gas reservoirs because they can enlarge the transport channels and aggregation spaces and increase the specific surface area of the gas shale. For artificial hydraulic fracturing of these reservoirs, the natural fracture system must be fully integrated with the artificial fracture system to form an intact fracture system. In this study, we first comprehensively examined the fractures in 42 shale-gas wells using several approaches, including a systematic examination and description of the cores and the casting of thin sections, a compilation of the statistics of fracture feature parameters, and observation of various analytical and test data, such as the mineral composition, the organic carbon contents, and the rock mechanics properties for specimens from the corresponding fractured intervals. The data enabled us to thoroughly explore the developmental features and major factors affecting organic-rich shale fractures in the upper Paleozoic Carboniferous–Permian marine–continental transitional coal-bearing formation, which is located in the southeastern Ordos Basin. Our results reveal that, in comparison with the Paleozoic marine shale in the United States and southern China, as well as the Paleozoic basin transitional shale in northern China, the upper Paleozoic black shale in the Ordos Basin is primarily characterized by a relatively low content of brittle minerals and a high content of clay ingredients. The total content of brittle minerals, e.g., quartz, feldspar, and siderite, was approximately 33%, which included 27% quartz and 0.3% K-feldspar but did not include carbonate. The total content of clay minerals reached 64% and was dominated by mixed-layer illite–smectite (I/S), which accounted for more than 41% of the total clay ingredients. The shale accommodated the widespread development of various types of macro- and microfractures. In the core specimens, medium-angle slip fractures and horizontal bedding cracks were the most common types of fractures, whereas vertical and high-angle fractures and horizontal bedding cracks were underdeveloped. In the thin sections, microfractures arising in organic matter laminations or at their edges as well as those of tectonic origin were the predominant type of fractures, and they were mainly short, narrow, and open. Overall, the surface/fracture ratios of the thin sections were concentrated in a range of approximately 0.1–0.3%. The developmental level of the fracture was influenced by various factors, including tectonism, lithology, rock mechanics, and organic matter and mineral content. Thus, increased developmental level of fractures was correlated with higher paleostructural elevation and increased sand content, whereas the developmental level of microfractures was correlated with high lamellation development, high level of organic carbon (leading to more pronounced laminations), and high contents of quartz, mixed-layer I/S, and illite (leading to low levels of kaolinite). These findings were corroborated by other data generated in this study, including the rock mechanics results for the upper Paleozoic black shale and silty shale, the observation results from the cores and from the thin sections sampled from more than 40 shale-gas wells, and the anomalies of gas logging.

Mapping of Total Carbon and Clay Contents in Glacial Till Soil Using On-the-Go Near-Infrared Reflectance Spectroscopy and Partial Least Squares Regression

Characterizing spatial variability of soil attributes, using traditional soil sampling and laboratory analysis, is cost prohibitive. The potential benefit of managing soils on a site-specific basis is well established. High variations in glacial till soil render detailed soil mapping difficult with limited number of soil samples. To overcome this problem, this paper demonstrates the feasibility of soil carbon and clay mapping using the newly developed on-the-go near-infrared reflectance spectroscopy (NIRS). Compared with the geostatistics method, the partial least squares regression (PLSR), with NIRS measurements, could yield a more detailed map for both soil carbon and clay. Further, by using independent validation dataset, the accuracy of predicting could be improved significantly for soil clay content and only slightly for soil carbon content. Owing to the complexity of field conditions, more work on data processing and calibration modeling might be necessary for using on-the-go NIRS measurements.

Perfluorooctane sulfonate (PFOS) distribution and effect factors in the water and sediment of the Yellow River Estuary, China

The distribution of perfluorooctane sulfonate (PFOS) was investigated in a total of 15 water and sediment samples from the Yellow River Estuary, China in April 2011. The results indicated that the concentrations of PFOS in the water and sediment samples averaged 157.5ng/L and 198.8ng/g and ranged from 82.30 to 261.8ng/L and 75.48 to 457.0ng/g, respectively. The concentrations of PFOS in the sediment column increased from 45.32 to 379.98ng/g with the decrease of the sampling depth, which showed that the increased PFOS pollution in the sediment appeared in this region in over recent years. The distribution coefficient (K d) of PFOS between water and sediment linearly increased from 0.37 to 4.80L/g as the salinity (S‰) increased from 0.18 to 4.47. Correlation analysis revealed that K d was significantly and positively correlated to the contents of total organic carbon and clay of the sediment, and salinity. Therefore, salinity was an important parameter in controlling the sediment-water interactions and the fate or transport of PFOS in the aquatic environment. The results of this study showed that the estuary was an important sink for PFOS and suggested that PFOS might be carried with the river water and transported for long distances before it reached to the sea and largely scavenged to the sediment in the estuaries due to the change in salinity.

NO TITLE AVAILABLE

The objective of this work was to identify the most important soil attributes to estimate the aggregate stability index. To identify these attributes, multiple stepwise regression was used on data collected from an Eutrorthox cultivated under a no-tillage system. To obtain the prediction models for the aggregate stability index (IeaE), ten independent variables were evaluated: total clay, bulk density, penetration resistance, organic matter, pH in water, effective cation exchange capacity, available water, total porosity, macroporosity, and gravimetric moisture. The attributes total clay (Arg), bulk density (Ds), penetration resistance (RP), organic matter (MO), and pH are the most important for the estimation of the IeaE, and the pedotransfer function that best describes this index is: IeaE = 27.80 + 0.04Arg + 27.97Ds + 12.35RP + 0.45MO - 9.72pH (R2 = 0.89).

Scale-dependent correlations between soil properties and environmental factors across the Loess Plateau of China

Traditional statistical analysis of the correlations between spatially distributed variables takes no account of their regionalised nature. Factorial kriging analysis (FKA) was developed and widely used to overcome this problem. In our study, we applied FKA to investigate scale-dependent correlations between selected soil properties and environmental factors across the Loess Plateau of China. Surface soil samples were collected from 382 sampling sites throughout the region, and soil organic carbon (SOC), soil total nitrogen (STN), soil total phosphorus (STP), soil total potassium (STK), soil pH, bulk density (BD), and clay and silt contents were determined. Five environmental factors (elevation, precipitation, temperature, land-use type, and soil type) were also included in the FKA to identify influential processes. A linear model of co-regionalisation, including a nugget effect and two spherical structures (effective ranges of 200 and 400 km), was fitted to the experimental auto- and cross-variograms of the variables. Scale-dependent correlations were calculated for nugget-effect scale (&lt;30–50 km), short-range scale with a range of 200 km, and long-range scale with a range of 400 km. Principal component analysis was conducted to clearly illustrate the correlations at each spatial scale. The scale-dependent correlations were different from the general correlations and varied at different scales. Generally, SOC and STN were strongly correlated at the nugget-effect scale and the long-range scale, but not at the short-range scale. Precipitation and clay content showed close correlations with STP at the nugget-effect scale and long-range scale. The STK was weakly correlated with the other variables at each spatial scale, and closely correlated with soil type at the long-range scale. Soil pH was closely correlated with BD, soil type, and elevation at the nugget-effect, short, and long spatial scales, respectively. Close correlations were found between BD and land-use type at each spatial scale. Land use and soil type were considered to be the important factors controlling spatial variation of soil properties at the short-range scale, while at the long-range scale the likely factors were identified as precipitation, temperature, and elevation. Our study provided an insight into the spatial-dependent correlations between soil properties and environmental factors from a regional perspective.

Spatial variability of particle size fractions of an Oxisol cultivated with conilon coffee

Information on the spatial distribution of particle size fractions is essential for use planning and management of soils. The aim of this work to was to study the spatial variability of particle size fractions of a Typic Hapludox cultivated with conilon coffee. The soil samples were collected at depths of 0-0.20 and 0.20-0.40 m in the coffee canopy projection, totaling 109 georeferentiated points. At the depth of 0.2-0.4 m the clay fraction showed average value significantly higher, while the sand fraction showed was higher in the depth of 0-0.20 m. The silt showed no significant difference between the two depths. The particle size fractions showed medium and high spatial variability. The levels of total sand and clay have positive and negative correlation, respectively, with the altitude of the sampling points, indicating the influence of landscape configuration.

Impact of sedimentary processes and paleopedogenesis on Holocene Luvisol formation

stacking of periglacial layers: A differentiation of eluvial (E-) and illuvial (Bt-) horizon is already developed within the upper layer. The intermediate layer carries the main argillic horizon of those profi les whereas the within the upper layer. The intermediate layer carries the main argillic horizon of those profi les whereas the basal layer is only marginally affected by soil formation. By the help of soil micromorphology it was possible basal layer is only marginally affected by soil formation. By the help of soil micromorphology it was possible to identify numerous fragments of paleosol material within the intermediate layer (2Bt-horizon) accountto identify numerous fragments of paleosol material within the intermediate layer (2Bt-horizon) accounting for large proportions of the total clay content of this horizon. While the formation of the upper layer, ing for large proportions of the total clay content of this horizon. While the formation of the upper layer, parts of the intermediate layer were reworked and incorporated into the newly formed slope deposit. As a parts of the intermediate layer were reworked and incorporated into the newly formed slope deposit. As a result, the lower part of the upper and the whole intermediate layer contained large amounts of clay before result, the lower part of the upper and the whole intermediate layer contained large amounts of clay before the onset of Holocene pedogenesis. Recent lessivation, evidenced by undisturbed clay illuviations, affected the onset of Holocene pedogenesis. Recent lessivation, evidenced by undisturbed clay illuviations, affected the profi le. Consequently this soil formation masks prior differences in clay content due to included paleosol the profi le. Consequently this soil formation masks prior differences in clay content due to included paleosol material. Soil formation is dominated by the paleosol remnants and therefore elucidates the impact of late material. Soil formation is dominated by the paleosol remnants and therefore elucidates the impact of late glacial conditions on Holocene soils. glacial conditions on Holocene soils. Besides, a Luvisol was identifi ed which was not formed in periglacial slope deposits but in Holocene colBesides, a Luvisol was identifi ed which was not formed in periglacial slope deposits but in Holocene colluvium. In this case paleosol remnants were totally absent. Hence, a precise reconstruction of Luvisol-genesis luvium. In this case paleosol remnants were totally absent. Hence, a precise reconstruction of Luvisol-genesis is enormously improved by micromorphological analyses. is enormously improved by micromorphological analyses.

Sediment provenance and geomorphic development of soils in a blackwater ecosystem, South Carolina Coastal Plain

Mineral soil is a conundrum on southeastern U.S. blackwater floodplains because these freshwater ecosystems are known for slow-flowing streams bearing little suspended sediment. Investigations on soils along this riparian system revealed two distinct geomorphic surfaces, the modern swamp floodplain (classified as Inceptisols according to Soil Taxonomy) and slightly elevated landforms (intra-swamp terraces) with more developed soils (Alfisols and Ultisols). This study examined soil characteristics and sediment provenance on the Black River floodplain and its tributaries in the Atlantic Coastal Plain of South Carolina to determine the properties and pedogenic relationship between these two geomorphic surfaces and to propose a theory for the geomorphic evolution for soils on these landforms. Spatial characterization of the soils will benefit ecologists researching the biological aspects of blackwater ecosystems such as the concentration and flux of dissolved organic carbon (DOC). Results showed terrace soils had aquic moisture regimes while floodplain soils had peraquic moisture regimes. Floodplain surface horizons were organic carbon-rich (5% to 25% OC) but seldom with enough to qualify as organic soil material. Discontinuities occurred within the soils of both landforms indicating two distinct sedimentological environments. The fine-earth fraction of soil profiles on both landforms generally had upper strata composed mainly of silt and clay indicative of wash load sediments underlain with sandy strata indicative of bed load deposits. Fine clay distribution and fine clay:total clay ratios (FC/TC) showed argillic horizon development in the terrace subsoils but not in the floodplain soils. Micromorphology supported argillic horizons for the terraces, but also revealed modest clay accumulation in pores and channels of the floodplain soils. These floodplain clay features are interpreted to have formed during a period of subaerial weathering. The sandy strata were likely deposited during the beginning of the transgressions following the down cutting that occurred during the regressions and sea level lows. Silt fraction comparisons between the blackwater soils and soils on other landscapes in the region suggest the silts and clays likely were deposited in an estuarine environment late in the transgressions.

Colloidal properties and potential release of water-dispersible colloids in an agricultural soil depth profile

The effects of soil depth on the colloidal properties and potential release of water-dispersible colloids (WDCs) in an agricultural soil were investigated in batch experiments. Nine soil samples were collected along a trench at different depths (from −7.5cm to −127.5cm) from the TERENO test site located in Selhausen (Germany). A physical gentle soil fractionation confirmed the importance of the solution chemistry in controlling the depth distribution of WDC in the Luvisol soil. A maximal fraction of total clay (fWDC) equal to approx. 45% was released at a depth of −37.5cm to −52.5cm below the surface. This was found to be related to the lowest electrical conductivity of the soil electrolyte phase where Ca2+ concentration played a major role. A rather constant content of metal oxyhydroxide (MO(OH)) accounting for about 10% in WDCs was found along the soil depth after a dithionite-citrate-bicarbonate (DCB) extraction. However, a decrease from 40% to 25% in the contribution of MO(OH) particles to SSA of WDC was calculated along the soil depth. Using photon correlation spectroscopy (PCS) and N2 gas adsorption method, variations were measured in colloidal hydrodynamic diameters (dz) and the mineral specific surface area (SSA) for WDC in water-dispersed and dried states, respectively. A function structure f(np) was defined to relate the particle size variations between the two states along the soil depth. An inverse correlation was established between the particle size variations which assumed that the number of primary particle in the water-dispersed state increases in subsoil samples. The effects of different soil parameters such as pH, organic carbon (OC) coverage at MO(OH) surfaces and humification index (HIX) of dissolved organic carbon (DOC) on the WDC structure variations are discussed. It can be hypothesized that a maximal surface OC coverage at MO(OH) surfaces of WDCs facilitates the release of small particles through electrosteric dispersion in topsoil. Lower pHs and WDC(OC) content would favor the release of large WDC particles in subsoil where an OC content of a more aliphatic character can also facilitate hydrophobic interactions.

Soil microbial residue storage linked to soil legacy under biofuel cropping systems in southern Wisconsin, USA

Microbial residues can be a significant component of soil organic matter, and their component amino sugars are integrative indicators of biologically relevant ecosystem properties. We evaluate the impact of soil attributes, microbial functional group biomass, and cropping system type on soil amino sugar profiles in three model biofuel cropping systems in southern Wisconsin, USA. Total soil carbon and clay content explained differences in soil amino sugar profiles, with glucosamine and galactosamine more strongly related to soil carbon and muramic acid associated with clay content. Amino sugars were not correlated to cropping system or to microbial functional group lipid abundance, suggesting amino sugar differences among locations were due to differences in soil legacy properties such as total carbon, clay content and culture age rather than to current biotic drivers. The disconnect between the current biotic composition and legacies of past microbial activity suggests that microbial residues should be considered as trajectories over time rather than static system properties.

Performance of a reciprocal shaker in mechanical dispersion of soil samples for particle-size analysis

The dispersion of the samples in soil particle-size analysis is a fundamental step, which is commonly achieved with a combination of chemical agents and mechanical agitation. The purpose of this study was to evaluate the efficiency of a low-speed reciprocal shaker for the mechanical dispersion of soil samples of different textural classes. The particle size of 61 soil samples was analyzed in four replications, using the pipette method to determine the clay fraction and sieving to determine coarse, fine and total sand fractions. The silt content was obtained by difference. To evaluate the performance, the results of the reciprocal shaker (RSh) were compared with data of the same soil samples available in reports of the Proficiency testing for Soil Analysis Laboratories of the Agronomic Institute of Campinas (Prolab/IAC). The accuracy was analyzed based on the maximum and minimum values defining the confidence intervals for the particle-size fractions of each soil sample. Graphical indicators were also used for data comparison, based on dispersion and linear adjustment. The descriptive statistics indicated predominantly low variability in more than 90 % of the results for sand, medium-textured and clay samples, and for 68 % of the results for heavy clay samples, indicating satisfactory repeatability of measurements with the RSh. Medium variability was frequently associated with silt, followed by the fine sand fraction. The sensitivity analyses indicated an accuracy of 100 % for the three main separates (total sand, silt and clay), in all 52 samples of the textural classes heavy clay, clay and medium. For the nine sand soil samples, the average accuracy was 85.2 %; highest deviations were observed for the silt fraction. In relation to the linear adjustments, the correlation coefficients of 0.93 (silt) or &gt; 0.93 (total sand and clay), as well as the differences between the angular coefficients and the unit &lt; 0.16, indicated a high correlation between the reference data (Prolab/IAC) and results obtained with the RSh. In conclusion, the mechanical dispersion by the reciprocal shaker of soil samples of different textural classes was satisfactory. The results allowed recommending the use of the equipment at low agitation for particle size- analysis. The advantages of this Brazilian apparatus are its low cost, the possibility to simultaneously analyze a great number of samples using ordinary, easily replaceable glass or plastic bottles.