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Society calls for protection of agricultural soils in order to sustain the production of foods for a growing population. Compaction of subsoil layers is an increasing problem in modern agriculture and a cause of serious concern because of the poor resilience in natural amelioration. The concept of soil precompression stress has been adapted from civil engineering, although in soil science it is applied to unsaturated soils that have developed a secondary structure from the action of weather, biota and tillage. It assumes strain is elastic at loads up to the precompression stress, while plastic deformation is expected at higher stresses. To determine this threshold we performed uniaxial, confined compression tests for a total of 584 minimally disturbed soil cores sampled at three subsoil layers on nine Danish soils ranging in clay content from 0.02 to 0.38 kg kg-1. The cores were drained to either of three matric potentials (-50, -100 or - 300 hPa) prior to loading. Stress was applied by a constant-strain rate method. We estimated the point of maximum curvature of the strain-log10(normal stress) relation by a numerical procedure. This point is considered here as a compactive stress threshold, typically labeled the soil precompression stress, σpc. The preload suction stress (PSS) was calculated as the product of initial (i.e., before loading) water suction and initial degree of pore water saturation. Multiple regressions were performed to evaluate the effect of soil properties (textural classes, volumetric water content, bulk density (BD), soil organic matter (SOM), and PSS) on σpc. The best model explained 39% of the variation in σpc, and indicated that σpc increases with increasing PSS, BD and SOM. For a given combination of clay, BD and SOM, PSS affected σpc negatively. We recommend our regression model for use in risk assessment tools for estimating sustainable traffic on agricultural soils. The model was validated by five independent data sets from the literature. Our study shows that caution should be applied when regarding σpc as a fixed threshold for compressive strength. We hypothesize that plastic deformation is initiated over a range of stress rather than at a distinctive single value. Further studies are needed to better understand--and potentially quantify--to what extent the predicted σpc can be regarded a central estimate of allowable stress for a given soil. [ABSTRACT FROM AUTHOR]

Finding the particle size distribution is one of the main objectives in soil science as well as any other area to be worked on soil. There are many methods to accomplish this task, both traditional and technology-oriented. While traditional methods have many disadvantages, such as being dependent on the laboratory medium and expert knowledge, being carried out manually etc., technology-oriented devices on the other hand, are quite expensive due to hardware and production costs. In order to propose an optimized solution in between, an automated soil texture analyzer, supported by microcomputer and machine learning method, is proposed, which can eliminate the incomplete and error-prone disadvantages of the traditional hydrometer method, focusing only to find ratios of sand, silt and clay materials in a soil sample. In the light of a previous study, the structure and working principle of an automated soil texture estimation device, which works depending on the change of ultrasound intensity passed through the soil-water mixture in the 3D-printed measurement cup, has been explained in detail. The signals obtained from 80 soil samples, the contents of which were analyzed by the traditional hydrometer method, have been collected on the computer using the proposed device, pre-processed, and then feature extraction steps have been applied to be given as input to the machine learning methods. Rates of sand, silt and clay fractions of the soils have been predicted using Support Vector Regression (SVR), Multi-Layer Perceptron Neural Network (MLPNN) and Long Short-Term Memory (LSTM) machine learning methods. Best results are achieved using MLPNN structure in terms of Mean Absolute Error (MAE). Using MLPNN 54 soils for sand, 48 for silt, and 48 soils for clay, are found having estimation error of less than 10%. Worst results are obtained using LSTM method. There are 38 soils for sand, 38 for silt, and 41 soils for clay with MAE value below 10% with LSTM method. Statistical validations are presented with RMSE and Correlation Coefficient values and the achieved results are thought to be moderate especially considering the many of the competing studies are carried out using thousands of dollars worth laser diffraction based machines. The temperature effect has also been investigated by performing tests at varying temperatures from 9 to 38 ∘ C. [ABSTRACT FROM AUTHOR]

Reaching the land-related UN Sustainable Development Goals (SDGs) and similar goals articulated by the EU Green Deal (GD) by 2030 presents a major challenge and requires a pragmatic approach focused on joint learning by land users (mostly farmers), researchers and other stakeholders in "Living Labs" and system experiments at experimental farms of research organizations. Defining specific indicators and thresholds for ecosystem services in line with land-related SDGs is crucial to establish "Lighthouses" that can act as inspiring examples if they meet the various thresholds. This exploratory paper discusses indicators and thresholds for an arable farm operating on marine, calcareous light clay soils in the Netherlands. Studies of a system experiment are used to discuss and test operational methodology to be widely applied when characterizing many "Living Labs" in future, as planned by the European Union. The important role of soils in contributing to ecosystem services is discussed in terms of soil health. Recommendations are made for innovative methodology to be associated with all land-related SDGs. Satisfying the thresholds of ecosystem services, which will vary by soil type, region and farm type, can be the basis for farm subsidies, such as the Common Agricultural Policy (CAP). Research on Living Labs and in system experiments has to be judged by different criteria than those associated with traditional linear research. The important contributions of soils to achieve ecosystem services are framed in terms of soil health and are the most effective way to promote soil science in a by now widely desired inter- and transdisciplinary context. [ABSTRACT FROM AUTHOR]

• Traditional methods for soil specific surface area (SSA) are costly and laborious. • We propose models to estimate SSA from a single hygroscopic water content (w h) • Separate SSA models are developed for soil samples grouped by clay mineralogy. • Considering soil clay mineralogy in SSA models significantly improved performance. • Models based on w h were superior to models based on texture, carbon or CEC. The soil specific surface area (SSA) is an important variable for soil science and geoenvironmental engineering applications, but traditional measurement methods are difficult and time-consuming. Regression models or pedotransfer functions are often used to estimate SSA from other soil properties (e.g., clay content and cation exchange capacity), but these models do not consider the impact of clay mineralogy. Hygroscopic water content (w h) is intimately linked to these soil properties, which suggests that w h may be a better parameter for SSA estimation. This study (i) proposes regression models that estimate SSA from w h at different relative humidity values (5 to 90%) for kaolinite-rich samples (KA), illite-rich or mixed clay samples (IL/MC), montmorillonite-rich samples (ML), and a combination of all samples (ALL) and (ii) compares the performance of the w h models to other published models that comprise clay, silt and soil organic carbon contents and cation exchange capacity. We found that the sample-specific w h regression models accurately estimated SSA for KA, IL/MC and ML samples. For KA and IL/MC samples, the performance of the KA model (e.g., for adsorption, average RMSE = 10.5 m2/g) and IL/MC model (average RMSE = 21.3 m2/g) were better than the ALL-calibration model (KA: average RMSE = 18.7 m2/g; ML: average RMSE = 22.4 m2/g). For ML samples, similar model performance between the ML-calibration model (average RMSE = 41.4 m2/g) and the ALL-calibration model (average RMSE = 41.1 m2/g) was observed. In addition, the model performance of regression models based on w h was superior to models published in the literature that are based on clay, silt and soil organic carbon contents and cation exchange capacity. Overall, this study confirms that a single measure of w h can provide reliable estimates of the SSA while revealing a significant impact of clay mineralogy on model performance. [ABSTRACT FROM AUTHOR]

Alkaline clayey soil is considered to be a degraded soil, which causes serious issues in engineering and construction projects. The formation and development of desiccation cracks in alkaline clayey soils is a complex process affecting the strength, stability, and permeability of these soils. Therefore, to investigate how soda content can inhibit the development of desiccation cracks in alkaline clayey soils in Ulanhot, Inner Mongolia, China, free desiccation tests were performed to examine the cracks in alkaline clayey soil samples with different soda (Na2CO3) contents in the laboratory. During the cracking process, the changes in water content and the occurrence and evolution of cracks were recorded with a camera. Digital image processing was performed to analyze the structure characteristics of the surface cracks. The results indicated that the characteristics are influenced by the different soda contents. The soda inhibited the development of desiccation cracks in alkaline clayey soils. Three stages were found in the process of desiccation cracking in accordance with the rate of water loss: the residual, normal, and structural shrinkage stages. At <0.4 mol L-1 Na2CO3, the "three straight lines" model could be used to describe the volume shrinkage. However, at >0.4 mol L-1 Na2CO3, the structural shrinkage stage disappeared. Moreover, based on the general soil volume change equation and fractal theory, a model was formulated to quantitatively explain the relationship between the fractal dimension and the volume changes in the soil. The experimental results and equations are important for reducing subgrade deformation and slumps.

There is a need for improved knowledge of the limits to the available water range for root growth in the subsoil. The objective of this study was to recalculate the upper and lower limits of the least limiting water range (LLWR) concept by using respectively the air-filled porosity (εa) at which 0.005 of the relative gas diffusivity (Ds/Do) is reached and readily available water (RAW). The refined upper limit estimates the variation in εa related to pore connectivity and the refined lower limit expresses the boundary at which plants suffer physiological water stress. This study was based on soil sampled in compaction trials on two sandy loam soils. Soil samples were taken from plots with no compaction (Control), and compaction with 78 kN (M8) and 58 kN (M6) wheel loads with multiple wheel passes. The soil cores were analyzed for εa, Ds/Do, bulk density (rb) and penetration resistance (PR). Heavy farm machinery impact of M8 and M6 led to subsoil compaction up to depth of 0.5 to 0.7 m for the soils under study. The subsoil structure was affected by compaction across depths with the decrease in εa (~33-46%) and Ds/Do (~37-61%) and increase in rb (~4-8%) and PR (~40-50%, at -100 hPa at 30-cm depth). The refined LLWR showed a wider water range compared to the original approach. We anticipate that the refined LLWR well reflects the limiting soil physical conditions for root growth for the studied soils, but validation by combined soil physical and plant growth measurements is needed.

[Display omitted] • Soil sampling methods were assessed using 720 samples at two locations. • Calculated composite sampling decreased significant effects especially in sandy soils. • Sampling in-row resulted in greater crop effect on research results. • Soil enzyme activities required more samples compared to other soil properties. • A Monte Carlo simulation can be used to estimate needed sample size. A wide variety of soil sampling methods have been adopted, yet limited research has addressed how sampling methods can impact research results particularly for spatially variable soil properties. To address these concerns, we intensively sampled two existing soil health trials in Texas for analysis of soil extracellular enzymatic activities (EEAs), permanganate oxidizable C (POXC), soil organic C (SOC), and pH. The data generated was used to quantify the effect of composite sampling, sampling position (in-row vs between-row), and number of samples on statistical results. We compared a Monte Carlo simulation approach with a traditional power analysis to quantify the impact of the number of samples on our results. Calculated composite sampling resulted in lower statistically significant results compared to discrete sampling, demonstrating lower sensitivity of composite sampling. Sampling in-row resulted in greater values specifically for EEAs, pH, POXC, and SOC. Simulation generated estimated number of samples were mainly driven by the effect size and spatial variation. EEAs were highly variable, resulting in a higher estimated number of samples as compared to other soil properties such as POXC and SOC. In our study with two sites, soil with greater clay content resulted in overall lower estimated number of samples compared to a relatively sandy soil, demonstrating a greater sampling requirement for sandy soil. The simulation approach had a weak correlation with traditional power analysis. The simulation predicted lower estimated number of samples when compared to power analysis, which can help save cost in the long run. Overall, factors like composite sampling, sampling in-row vs between-row, and number of samples taken did impact research results. The impact of these sampling strategies on soil parameters of interest needs to be investigated to achieve the most accurate research results in soil science. [ABSTRACT FROM AUTHOR]

Heavy clay soils are globally widespread but their poor drainage and poor aeration limit their use for agriculture. This study was designed to test the effect of the amendment of biochar (BC) from woody shrubs on drainage/saturated hydraulic conductivity (Ksat), soil aeration/air capacity, available water capacity and biomass and grain yields of maize. In a field experiment, BC from Gliricidia sepium was applied in planting basins or rip lines at 2.5% and 5% w/w in addition to a control without BC. The maize biomass and grain yields were higher in BC treated plots compared to control (p<0.05) during the 2012 and 2013 seasons. There was no significant difference in the yields between 2.5% and 5% BC treatments (e.g. grain yield were 6.6 and 8.1 t ha-1 in 2012 and 9.3 and 10.3 t ha-1 in 2013 compared to control with 4.2 and 6.7 t ha-1 in 2012 and 2013, respectively). Soil from the same field site was also mixed with a similar woody shrub BC from Eupatorium adenophorum in the laboratory at rates of 2.5%, 5% and 10% BC w/w and a control without BC. The mixtures were then incubated and subjected to two wet-dry cycles for two weeks. Core samples were taken from the incubated soil and tested for bulk density, Ksat and pF measurements. Total porosity and moisture at field capacity and wilting point were 72.3%, 43.7% and 23.7%, respectively, and not affected by BC amendment (p>0.05). In contrast, bulk density decreased linearly by 0.011±0.002 g cm-3 per percent BC added (p<0.001). Ksat and air capacity of the soil were 288 cm day-1 and 30.9%, respectively falling within the generally accepted optimal range. Both Ksat and air capacity followed a significant quadratic relation (p<0.05) upon BC addition, decreasing at low BC doses, reaching a minimum at 3–5% BC and increasing at higher doses. Results allowed a partial attribution of the yield increases to changes in soil physical properties such as changes in bulk density and not clearly to Ksat and air capacity. [ABSTRACT FROM AUTHOR]

Effective pretreatment of spectral reflectance is vital to model accuracy in soil parameter estimation. However, the classic integer derivative has some disadvantages, including spectral information loss and the introduction of high-frequency noise. In this paper, the fractional order derivative algorithm was applied to the pretreatment and partial least squares regression (PLSR) was used to assess the clay content of desert soils. Overall, 103 soil samples were collected from the Ebinur Lake basin in the Xinjiang Uighur Autonomous Region of China, and used as data sets for calibration and validation. Following laboratory measurements of spectral reflectance and clay content, the raw spectral reflectance and absorbance data were treated using the fractional derivative order from the 0.0 to the 2.0 order (order interval: 0.2). The ratio of performance to deviation (RPD), determinant coefficients of calibration (), root mean square errors of calibration (RMSEC), determinant coefficients of prediction (), and root mean square errors of prediction (RMSEP) were applied to assess the performance of predicting models. The results showed that models built on the fractional derivative order performed better than when using the classic integer derivative. Comparison of the predictive effects of 22 models for estimating clay content, calibrated by PLSR, showed that those models based on the fractional derivative 1.8 order of spectral reflectance ( = 0.907, RMSEC = 0.425%, = 0.916, RMSEP = 0.364%, and RPD = 2.484 ≥ 2.000) and absorbance ( = 0.888, RMSEC = 0.446%, = 0.918, RMSEP = 0.383% and RPD = 2.511 ≥ 2.000) were most effective. Furthermore, they performed well in quantitative estimations of the clay content of soils in the study area. [ABSTRACT FROM AUTHOR]

• A regular evaluation of satellite soil moisture (SM) products was conducted. • Their accuracies in detecting SM anomalies and seasonality were identified. • l -band products can effectively capture SM seasonality over forest covers. • Products had difficulties in detecting SM variations over organic-rich soils. • AMSR2 showed higher accuracy to detect SM seasonality over arid areas. Satellite-based soil moisture (SM) products exhibit distinct error patterns at various timescales. Knowledge of their accuracy characteristics for capturing different SM signals is significant for many real-world applications in soil sciences. This study conducted a comprehensive evaluation of the following eight satellite-based SM products: the Soil Moisture and Ocean Salinity-Institut National de la Recherche Agronomique and Centre d'Etudes Spatiales de la BIOsphere version 2 (SMOS-IC-V2), the Level 3 (L3) Soil Moisture Active Passive V7 (SMAP-V7), the combined European Space Agency Climate Change Initiative V06.1 (ESA CCI-V06.1), the L3 SMOS V3, the L3 Advanced Microwave Scanning Radiometer (AMSR2) V3 from the Japan Aerospace Exploration Agency (JAXA), the L3 Land Parameter Retrieval Model (LPRM) C1- and X- band AMSR2 V001, and the Chinese FengYun-3B V1. By using >1,500 sites from the International Soil Moisture Network and triple collocation analysis, this study aimed to identify not only the relative strengths of the products for detecting original SM signals, short-term SM anomalies, and long-term SM seasonality, but also the impacts of land cover, soil organic carbon (SOC), and soil texture on their retrieval accuracy. In terms of capturing the temporal dynamics of SM anomalies, SMAP-V7 outperformed SMOS-IC-V2 and ESA CCI-V06.1. In arid and semi-arid areas, LPRM C1-band AMSR2 V001 outperformed SMOS-ICV2 and SMAP-V7, in terms of detecting SM seasonality. SMAP-V7, SMOS-ICV2, and ESA CCI-V06.1 effectively captured SM seasonality over most forest zones and effectively detected short-term SM anomalies over croplands and grasslands. The l -band products showed the highest accuracy in terms of capturing the temporal dynamics of all the SM signals when the clay fraction was in the range of 20 %–25 %. Most products had difficulties in detecting SM variations over bare deserts, sandy and clay soils, and soils rich in organic matter (SOC content > 8.72 %). [ABSTRACT FROM AUTHOR]

Understanding the effects of external organic and inorganic components on soil fertility and quality is essential for improving low-yielding soils. We conducted a field study over two consecutive rice growing seasons to investigate the effect of applying chemical fertilizer (NPK), NPK plus green manure (NPKG), NPK plus pig manure (NPKM), and NPK plus straw (NPKS) on the soil nutrient status, enzyme activities involved in C, N, P, and S cycling, microbial community and rice yields of yellow clayey soil. Results showed that the fertilized treatments significantly improved rice yields over the first three experimental seasons. Compared with the NPK treatment, organic amendments produced more favorable effects on soil productivity. Notably, the NPKM treatment exhibited the highest levels of nutrient availability, microbial biomass carbon (MBC), activities of most enzymes and the microbial community. This resulted in the highest soil quality index (SQI) and rice yield, indicating better soil fertility and quality. Significant differences in enzyme activities and the microbial community were observed among the treatments, and redundancy analysis showed that MBC and available N were the key determinants affecting the soil enzyme activities and microbial community. The SQI score of the non-fertilized control (0.72) was comparable to that of the NPK (0.77), NPKG (0.81) and NPKS (0.79) treatments but significantly lower compared with NPKM (0.85). The significant correlation between rice yield and SQI suggests that SQI can be a useful to quantify soil quality changes caused by different agricultural management practices. The results indicate that application of NPK plus pig manure is the preferred option to enhance SOC accumulation, improve soil fertility and quality, and increase rice yield in yellow clayey soil. [ABSTRACT FROM AUTHOR]

An intensive experimental investigation by means of triaxial and oedometer tests was performed on a clayey loess that was retrieved from two depths at a location on the southern Chinese Loess Plateau. Intact and reconstituted samples were used to identify the effects of the natural structure on soil behavior in saturated conditions. The behavior in compression was clearly affected by structure with the intact samples reaching well-defined gross yield points outside the intrinsic compression line of the reconstituted soil, after which the compression paths converged towards the intrinsic compression lines, behavior which is consistent with destructuration. However, very high stresses were required to give complete convergence. Similarly the triaxial tests that were carried out at lower stress levels also did not give convergence of the critical states so that different critical state lines could be defined for the intact and reconstituted soils. This was consistent with qualitative observations from scanning electron micrographs that natural elements of fabric and possibly bonding persisted even after triaxial shearing. The effects of structure at the two depths on the compression and shearing behavior were slightly larger for the shallower samples. Despite the very different genesis of the soils, it was found that similar frameworks could be applied to those used for sedimentary clays and that the degree of structure was equivalent to a clay of medium sensitivity. [ABSTRACT FROM AUTHOR]

The standard penetration test (SPT) and Menard's pressuremeter test (PMT) are among the available in-situ techniques. This research has been carried out with the aim to develop correlations among the in-situ parameters obtained by both methods. [ABSTRACT FROM AUTHOR]

Treated wastewater (TWW) is an important water resource, especially in semiarid and arid regions. However, there are concerns that irrigation with TWW could lead to degradation of soil physical and hydraulic properties. The objective of our study was to determine the effects of long-term (≥ 15 years) irrigation with secondary TWW on some basic and hydraulic soil properties of a clay soil. Undisturbed soil samples (cores) were taken to a depth of 4.5 m (in sections of 0.5 m) over a diagonal cross section of a five year old orchard irrigated with TWW. Samples were taken from five sites within the tree rows (i.e., representing soil directly affected by TWW; referred to as “within rows”) and four sites between the rows of trees (i.e., the control treatment representing soil that was not directly subjected to the irrigation water; referred to as “between rows”). Soil analyses included an array of basic properties, determination of a continuous particle size distribution and measurement of the saturated hydraulic conductivity (HC). The latter two were used for the computation of soil characteristic curve, Θ ( ψ ), and the unsaturated HC curve, K ( ψ ). Similar bulk density, moisture content, cation exchange capacity, pH and exchangeable sodium percentage (ESP) levels were observed for the TWW irrigated samples and the control ones. However, irrigation with TWW caused a significant reduction in the saturated HC, Ks . The computed Θ ( ψ ) curve at a given soil depth, averaged over the different sites, was similar for the TWW-irrigated samples and the control ones. On the contrary, the computed K ( ψ ) curve at a given soil depth, averaged over the different sites, for the TWW-irrigated samples were lower than those for the control samples at matric potential ≳− 100 cm (= pF ≲ 2); similar K ( ψ ) values were noted at pF > 2 for the two treatments. The observed differences in the hydraulic properties between the TWW-irrigated samples and the control ones in this specific matric potential range, albeit the similarity in their ESP, suggest that long term irrigation with TWW affected structural porosity via narrowing macro- and mesopores (> 70 and 30–70 μm, respectively). It is further postulated that this adverse impact of irrigation with TWW on structural porosity might be associated with previously reported effects of TWW on the composition of the dissolved organic matter in the soil solution. [ABSTRACT FROM AUTHOR]

Accessible information on Galápagos soils is very limited. Much of the existing, although still scarce, information is several decades old and not easily retrieved. The aim of this paper is to present a critical synthesis. Three local soilforming factors (parent material, climate, and vegetation) are briefly highlighted, followed by a more detailed discussion of the hypsometric soil sequence on Santa Cruz, the only island where systematic information was recorded by a Belgian geopedological mission in 1962. Five zones are distinguished from the coast toward the top of the island: a dry coastal area, containing superficial and interstitial reddish, smectite-bearing soils between basalt blocks; a transition zone of brown, also smectite-bearing soils; and three subsequent higher zones covered by deeper, brown soils with probably andosolic characteristics. Trace element analyses point to a uniform composition of the parent material and a more progressed weathering on the higher slopes. Micromorphological characteristics of the soils are discussed. Soils of Santa Fé are comparable with those of the coastal zone of Santa Cruz but show higher amounts of P and S, probably of avian origin. Deeper, reddish clayey soils cover San Cristóbal and are at least partly pre- Holocene. On the younger islands, no soils seem to be present. [ABSTRACT FROM AUTHOR]

A large amount of field and experimental data has been devoted to rectangular excavations thus far. In contrast, very few data were available for cylindrical excavations, especially those with large diameters in thick soft clay deposits. Via a comprehensive instrumentation program on a unpropped (self-supported) cylindrical excavation constructed by the bottom-up method in Shanghai soft clay, the characteristics of this large-sized circular excavation were extensively investigated. This cylindrical shaft was a part of a large-scale deep foundation pit excavated by the central-island technique. The investigated items included (1) lateral wall deflections, (2) vertical wall movements, (3) lateral ground movements, (4) ground settlements, (5) subsurface settlements, (6) basal heaves, (7) vertical column movements, (8) column stresses, and (9) variation of pore pressures along depth and artesian water levels. Analysis of the field data indicates that discharging of the deep artesian water was one of the key factors affecting the excavation behaviors. The influence zone of basal heave caused by soil removal (stress relief) reached very deep soil layers, far beyond the depths reported in literature. Column movement and stress were shown to be reliable indicators of the relative movement between basal soils, diaphragm walls, and interior columns. Finally, the comparisons of this study with other bottom-up excavations in Shanghai, including 11 cylindrical excavations, 92 building basement excavations, and eight metro station excavations, demonstrate that self-supported (unpropped) cylindrical excavations had much stronger capabilities of resisting deformation than both multipropped regular basement excavations (in terms of deformation magnitudes) and long and narrow metro station excavations (in terms of scale of influence zones). For cylindrical shafts, their diameters, and not wall penetration ratios, played a dominant role in the determination of excavation behaviors. However, when the shaft diameter reached 90 m or more, the advantage of cylindrical shafts over rectangular pits in constraining wall deflection was no longer obvious. [ABSTRACT FROM AUTHOR]

This paper reports an investigation of the influence of waste stone powder and lime on the geotechnical properties of clayey soil. The plasticity and changes in the chemical properties of the soil with pH test when mixed with varying proportions of waste stone powder and lime were investigated. The results show significant reduction in plasticity and increasing in the pH value of clayey soil with increasing amount of waste stone powder and lime. Also there is a decrease in liquid limit and increase in plastic limit with increasing waste stone powder and lime content. The behavior of the geotechnical properties of the clayey soil when blended with waste stone powder and lime indicates that these materials are a good modifier for this soil. [ABSTRACT FROM AUTHOR]

The combined action of physical, chemical and biological soil processes, which occur at different intensities and scales, causes complex spatial variation in soil that is difficult to characterize. The presence of non-stationarity and non-linearity increases this complexity. Wavelet transforms have been used to analyse non-stationary soil spatial variation. In this study we used the wavelet transform to characterize the spatial variation of non-linear soil systems. In the wavelet transform, a mathematical function (mother wavelet) is used to examine the frequency behaviour of a spatial series by translating or dilating the function. The effective resolution in identifying the frequency is dependent on the translation-dilation parameter, which is further dependent on the central frequency of the mother wavelet. The central frequency of the commonly used mother wavelet (Morlet) has been modified in this study to capture up to 95% of the uncertainty in identifying frequency components present in spatial series. Increased central frequency resulted in more oscillations within a localized window and thus provided enhanced frequency resolution, which helped to identify the instantaneous (≡ localized) frequency ( IF). Identification of the IF can reduce the local unpredictability and enable characterization of non-linear systems. We have demonstrated the method with a case study using soil water storage and clay content data. The wavelet spectra and the wavelet IF spectra provided improved spatial resolution in identifying the dominant frequency (scale) of variation in the spatial series. Information on dominant scales can be used for scale-specific prediction of soil properties and multiscale soil mapping and modelling. [ABSTRACT FROM AUTHOR]

Highlights: [•] Soil and crop observations together with modeling were used to study the yield. [•] Soil PAWC did not significantly correlate with yield. [•] Soil K sat correlated with yield only in few cases. [•] The simulated variation of the potential yield was lower than the observed. [Copyright &y& Elsevier]

Abstract: Soils with subsoil clay accumulation account for more than 20% of the global land surface. These soils are characterized by vertical differences with respect to soil texture and increasing bulk density below the topsoil, which in turn affects root penetration into the subsoil. Biopores are preferential pathways for roots and assist in overcoming physical barriers like high density soil layers. An integration of these relationships into cropping systems models at the field scale is on-going. This paper presents a new approach to model the effect of biopores on root development in soils with clay accumulation at the plot scale. In this approach, the effect of biopores on root elongation rate depends on bulk density and on a biopore-root growth threshold (MPRT), which is the biopore volume at which the resistance of soil strength to root penetration is completely offset by the density of the biopores. The approach was integrated into a model solution of the model framework SIMPLACE (Scientific Impact assessment and Modeling PLatform for Advanced Crop and Ecosystem management). MPRT was parameterized for spring wheat using the inverse modeling approach based on root observations from a multi-factorial field experiment on a Haplic Luvisol. The observed biopore densities (>2mm diameter) were between 300 and 660poresm−2 (equivalent to a volumetric proportion of 0.38–0.83%) depending on the preceding crop. Observed soil bulk densities ranged between 1.31 and 1.62gcm−3. For spring wheat, the best fit between simulated and observed root densities in different layers was obtained with a MPRT of 0.023m3 m−3 (equivalent to 2.3% of soil volume). The mean simulated total above ground biomass was sensitive to MPRT and had the best agreement with observed values when a MPRT between 0.023 and 0.032 m3 m−3 was used in the simulations. Scenario simulations with the parameterized model at the same site demonstrate the importance of biopores for biomass production of short-cycle spring wheat when prolonged dry spells occur. The simulations allow a rough quantification of the biopore effects with respect to root elongation rate and biomass production at the plot scale with the potential to be extended to the field scale. [Copyright &y& Elsevier]

A comprehensive study of expansive soil behavior includes understanding the surface phenomena of clay particles within the soil matrix. This research studies four micro-scale properties of four remolded expansive soils--matric suction, pH, surface conductance and percentage of montmorillonite--in order to predict soil swelling. An approach to approximate surface conductance is presented. Linear regression analyses were undertaken in an attempt to predict percent swell and swell pressure based on each of these micro-scale properties. Matric suction was found to be the most accurate predictor of the swelling behavior of the studied soils, which were initially compacted at optimum moisture content. Surface conductance, which is a combination of specific surface area, cation exchange capacity and cation mobility, also gave good predictions, except for one soil with high acidity. [ABSTRACT FROM AUTHOR]

Abstract: Within this work we present a revised pedotransfer function (PTF) that predicts water sorption isotherms for dry soils based on the clay content of the soils. When the water sorption isotherm is plotted as a water retention curve (log water potential plotted against the water content) it typically results in a log linear function as described by Campbell and Shiozawa (1992). The linear function is defined by its slope and a fixed endpoint at zero water content. The reciprocal of the slope shows a strong correlation with the clay fraction. For the calibration of a PTF we measured water sorption data for 18 soils with clay contents from 2% to 61%. The final predictions of the water sorption isotherms from the clay mass fraction were very good if the clay content was higher than 7%. The use of a revised theoretical endpoint at the dry end of the WRC did improve the prediction as compared to the endpoint that has been used in the literature before. In addition Literature data for 22 soils and 3 pure clay minerals were used for validation. The good performance of the PTF only occurred if the clay fraction was dominated by 2:1 clay minerals. The water retention isotherm of soils rich in the 1:1 clay mineral kaolinite could not be predicted by this approach; the actual water content was strongly over-predicted and the water retention curve did not follow a log linear relationship. [Copyright &y& Elsevier]

Abstract: The purpose of this paper is to outline a procedure for soil block extraction, which is highly appropriate for clay soils. The method described here is rapid and cheap and has been used successfully by us in clay soils in southern Spain for the last six years. A wooden box is used to shape the soil block in situ and protect it during its transport from the field to the laboratory. Polyurethane foam was selected as the bonding agent, between the wooden framework and the soil block in order to avoid any possible alterations of the soil. This type of foam is used because it is strong, durable and non-toxic. The polyurethane foam is applied to the soil block as a permanent coating. This technique allows us to extract the clay soil solution in the laboratory. [Copyright &y& Elsevier]

Environmentally Smart Nitrogen (ESN) is a polymer-coated urea fertilizer with potential to increase crop recovery of fertilizer nitrogen (N). Our research objectives were to characterize ESN N retention across time as affected by soil series, temperature, moisture, and incubation method. A rumen bag containing 38 to 44 mg ESN N was placed in 400 g soil, and the amount of ESN N remaining in prills was measured every 5 d for 40 d. Soil was incubated at 25 °C and 250 g H2O kg-1 soil, except in experiments where soil temperature or moisture was varied. Nitrogen retention in ESN was linear for three silt and sandy loams and curvilinear in two clayey soils with retention declining more rapidly in clayey soils. Soil temperature had the greatest effect on N retention with the rate of ESN N release increasing as soil temperature increased. Near complete release of ESN N was achieved by 40 d with temperatures ≥ 20 °C. [ABSTRACT FROM AUTHOR]

Liquid limit is one of the important soil index parameters and it is determined by means of two standard methods; Casagrande and fall-cone methods. Determination of liquid limit by fall-cone is based on penetration of cone shaped metal object into a homogeneously prepared soil mud with free fall. Even though it is less operator dependent and it gives more accurate results, compared to the Casagrande method, standard 4 point fall-cone method as imposed in TS 1900, takes long time when too many samples are to be tested for identification purposes. In this study 138 clay samples were tested with fall-cone method, test results were evaluated statistically and determination of liquid limit by means of one point fall-cone was investigated. After the experimental and statistical studies, 3 empirical equations were developed and “LL= W/(0.33* P/20)+0.66)” equation seemed to be more reliable. Faults to happen during the application of standard 4 point method are reflected on the graph and after drawing a trend line, these faults will be distributed along the trend line. However in the one point method faults will be reflected directly on a single liquid limit value. Therefore, in one point method, test procedure should be obeyed carefully. Although the fall-cone liquid limit test method is proposed method in Turkish Standards, one point method is not mentioned. As in the standards of other countries, it is thought to be appropriate that Turkish Standards include one point fall-cone method. [ABSTRACT FROM AUTHOR]

The article discusses a study which investigated the aspects of the compacted soils' behaviour along wetting paths. The study conducted wetting and oedometric loading tests on clayey compacted soils. Results revealed the effect of compaction stress and compaction water content on wetting paths. It notes that when compaction stress is higher, the soil's swelling is larger.

Little is understood about chemical weathering processes in Alaskan arctic soils, where moisture is generally not limited but acidity varies and the average soil temperature is close to or below freezing. Weathering reactions in soil convert primary minerals into secondary clay minerals. Silty loam textured soils from three sites in moist acidic tundra (MAT) and three sites in moist nonacidic tundra (MNT) in the northern Arctic Foothills, Alaska, were characterized with emphasis on the origin of the clay minerals. The MNT soils had a discontinuous and thinner organic layer, which leads to a deeper summer thaw and greater cryoturbation than the MAT soils. The MNT had higher cation exchange capacity and base saturation than MAT. These buffer against acidification and account for the pH differences of MAT and MNT. Other chemical characteristics including C and N content as well as Fe and Al were similar (by horizon) across the MAT/MNT boundary. X-ray diffraction of coarse (0.0002-0.002 ram) and fine clay (<0.0002 mm) fractions indicate that illite, vermiculite, and kaolinite are the predominant clay minerals. Presumably, kaolinite is detrital and vermiculite is weathered from illite. The proportion of vermiculite to illite is higher in MAT and the illite to vermiculite proportion is higher in MNT. This shows that soil acidity does affect weathering processes despite the low soil temperature. [ABSTRACT FROM AUTHOR]

The rate-dependent rheological behaviour of soils of different origins and characteristics was studied and the applicability of the power law model was examined. The studied soils were divided into three groups: (i) low-activity soils, (ii) high-activity soils, and (iii) silt-rich soils. The results show that the power law applies to all these soils and is representative of soil behaviour in a strain rate range corresponding to debris flows, which is generally not the case with the Bingham model. For low-activity clays, the power law index, n, is typically equal to 0.12 and seems to increase with the plasticity index; it is larger (i.e., in the range of 0.2–0.6) for silt-rich soils. Comparison of n values for tests performed on intact and remoulded low-activity clay specimens indicates that the power law index is possibly strain-rate dependent. [ABSTRACT FROM AUTHOR]

Regression models were developed to estimate the optimum moisture content and maximum dry density of clayey and fine-grained soils using physical and index properties from 30 soil samples collected in Central Italy and 41 soils described in the literature. The liquid limit of the soils analyzed ranged between 18 and 82%, the plasticity index between 1 and 51%, and specific gravity between 2.47 and 3.09. The most significant regression variables were the specific gravity and the Atterberg limits. The developed models are accurate and can be used as a simple tool to approximate the maximum dry density and optimum water content of clayey and fine-grained soils. [ABSTRACT FROM AUTHOR]

Abstract: An analysis of results from published laboratory tests on Jossigny silt and Barcelona clayey silt is presented to confirm the existence of a unique capillary bonding function linking the quotient between unsaturated and saturated void ratio, at the same mean average skeleton stress, to a single capillary bonding scalar variable. The analysis confirms that the same capillary bonding function applies to both normally consolidated and critical stress states. The above two experimental sets with the addition of further published data for Speswhite Kaolin are also used to study the relationship between unsaturated critical shear strength, mean average skeleton stress and capillary bonding variable. The results of such analysis are assessed in the light of a similar modelling framework proposed in the literature. [Copyright &y& Elsevier]

A toxicological approach was taken to determine the heavy metal binding capacity of soils. A soil heavy metal binding capacity (SHMBC) methodology was developed and was based on the use of the MetPLATETM toxicity test kit, a bioassay that is specific for heavy metal toxicity. SHMBC test is based on the heavy metal binding capacity (HMBC) concept that has been considered in the assessment of the metal binding capacity of surface waters (Huang et al., 1999) and solid wastes landfill leachates (Ward et al., 2005). SHMBC is the ratio of the EC50 of an added metal in a soil sample divided by the EC50 of a metal in a reference soil (clean Ottawa sand). A higher SHMBC value indicates higher metal binding to soil and lower bioavailability and potential toxicity to the test bacteria. Five soils (two sandy soils, two organic soils and a clay soil) were used to determine their binding capacity towards Cu, Zn, and Hg, using the developed SHMBC test. The test measured the ability of the solids to reduce metal bioavailability and toxicity. SHMBC was highest for the clay soil and lowest for the sandy soils. The potential application of this relatively rapid (a few hours) test to predict metal toxicity to terrestrial plants is discussed. [ABSTRACT FROM AUTHOR]

The objective of this work was to construct and validate a model that shows how the clay shrinkage curve, under the influence of a silt-sand admixture as well as an inter- and intraaggregate structure, is transformed to the soil shrinkage curve. To meet this objective, we investigated (i) the reference shrinkage curve, that is, one without cracks, because cracks lead to a multivalued shrinkage curve; (ii) the rigid superficial (interface) layer of aggregates, with changed pore-size range and distribution, compared with the intraaggregate matrix; and (iii) soils with sufficiently high clay content when large pores inside the intraaggregate clay (so-called lacunar pores) are nonexistent. The methodology is based on detail accounting for contributions of the interface aggregate layer and intraaggregate matrix to the soil volume and water content during shrinkage. The reference shrinkage curve is determined by six physical soil parameters: oven-dried specific volume; maximum swelling water content; mean solid density; soil clay content; oven-dried structural porosity; and the ratio of aggregate solid mass to solid mass of the intraaggregate matrix. Only the last parameter was fitted for lack of data and compared with an unfitted estimate. The model was validated using data for eight soils. The important new conclusion is that the mere existence of the rigid superficial aggregate layer leads to a soil reference shrinkage curve that is convex upward in the structural shrinkage area, unlike the shrinkage curve of the clay contributing to the soil. The model can have numerous applications. [ABSTRACT FROM AUTHOR]

Two separate field experiments were conducted to evaluate the effects of swine lagoon effluent relative to inorganic fertilizer at equivalent rates on phosphorus (P) status of an acidic Vaiden (very fine, montmorillonitic, thermic, Aquic Dystrudert) and an alkaline Okolona (fine, montmorillonitic, therimic, Typic Chromudert) silty clay soil. In each site, a randomized complete block design with a factorial arrangement of treatments was used. Treatments were replicated four times. Cumulative swine lagoon effluent P application rates for the year 1994 through 1996 were 0, 59, 121, and 175 kg P ha -1 on the Vaiden soil and 0, 72, 148, and 223 kg P ha -1 on the Okolona soil. In each replication, commercial fertilizer P at rates equivalent to swine effluent P application were also included. For both sites, soil P concentration increased with increasing swine effluent and commercial fertilizer P applications. No significant difference in soil P level was observed between two P sources. At high application rate, desorbed P was 1.20 and 0.59 mg P kg -1 in the Okolona and Vaiden soil respectively. In the Vaiden soil, P adsorption approached the maximum for equilibrium P concentration greater than 600 mg L -1 . However, Okolona soil displayed a linear adsorption potential with application of swine effluent P. Among P fractions, NH4Cl‐P and HCl‐P concentrations increased the most compared to the check in both Okolona and Vaiden soils. Results indicated that P status differs between the soils, but no significant differences in P concentration were obtained between swine lagoon effluent and commercial fertilizer, suggesting that both P sources had similar effect on soil P after 3 years of application. [ABSTRACT FROM AUTHOR]

We know much about the influence of management on stocks of organic matter in subtropical soils, yet little about the influence on the chemical composition. We therefore studied by CPMAS 13C NMR spectroscopy the composition of the above-ground plant tissue, of the organic matter of the whole soil and of silt- and clay-size fractions of the topsoil and subsoil of a subtropical Acrisol under grass and arable crops. Soil samples were collected from three no-till cropping systems (bare soil; oats−maize; pigeon pea + maize), each receiving 0 and 180 kg N ha−1 year−1, in a long-term field experiment. Soil under the original native grass was also sampled. The kind of arable crops and grass affected the composition of the particulate organic matter. There were no differences in the composition of the organic matter in silt- and clay-size fractions, or of the whole soil, among the arable systems. Changes were observed between land use: the soil of the grassland had larger alkyl and smaller aromatic C contents than did the arable soil. The small size fractions contain microbial products, and we think that the compositional difference in silt- and clay-size fractions between grassland and the arable land was induced by changes in the soil's microbial community and therefore in the quality of its biochemical products. The application of N did not affect the composition of the above-ground plant tissue nor of the particulate organic matter and silt-size fractions, but it did increase the alkyl C content in the clay-size fraction. In the subsoil, the silt-size fraction of all treatments contained large contents of aromatic C. Microscopic investigation confirmed that this derived from particles of charred material. The composition of organic matter in this soil is affected by land use, but not by variations in the arable crops grown. [ABSTRACT FROM AUTHOR]

The marshlands of western France provide the opportunity to relate the magnetic properties of a recent sedimentary clay soil to pedogenesis, including the impact of agriculture and drainage on magnetic mineralogy. We studied a plot of drained land that had been ploughed up to 1998 and under grass since. A new thermomagnetic method was used to identify and to quantify roughly the magnetic minerals, which represent less than 1 g kg−1. The most abundant Fe oxides are haematite (45%) and goethite (45%). However, trace amounts of the ferrimagnetic minerals maghemite (4%), magnetite (3%) and, to a lesser extent, iron sulphides (1%) provide most of the magnetic signal. This signal allowed us to identify magnetic horizons that relate to the soil horizons. The topsoil is characterized by a strong magnetic enhancement (4-fold), and the thickness of this layer increases close to the drains. Relative contents of ferrimagnetic phase also increase laterally with decreasing distance to the drains. Magnetic enhancement coincides with the most aerated and developed layer, in which water circulation, root colonization and hence soil fertility are greater. Ferromagnetic minerals sensu lato, especially maghemite and magnetite, can be considered as mineralogical tracers partly and indirectly reflecting soil fertility of these clay-rich marshland soils. [ABSTRACT FROM AUTHOR]

Morphological, geochemical and mineralogical studies were carried out in a representative soil catena of the low-elevation plateaux of the upper Amazon Basin to interpret the steps and mechanisms involved in the podzolization of low-activity clay soils. The soils are derived from Palaeozoic sandstones. They consist of Hydromorphic Podzols under tree savannah in the depressions of the plateaux and predominantly of Acrisols covered by evergreen forest elsewhere. Incipient podzolization in the uppermost Acrisols is related to the formation of organic-rich A and Bhs horizons slightly depleted in fine-size particles by both mechanical particle transfer and weathering. Weathering of secondary minerals by organic acids and formation of organo-metallic complexes act simultaneously over short distances. Their vertical transfer is limited. Selective dissolution of aluminous goethite, then gibbsite and finally kaolinite favour the preferential cheluviation of first Fe and secondly Al. The relatively small amount of organo-metallic complexes produced is related to the quartzitic parent materials, and the predominance of Al over Fe in the spodic horizons is due to the importance of gibbsite in these low-activity clay soils. Morphologically well-expressed podzols occur in strongly iron-depleted topsoils of the depression. Mechanical transfer and weathering of gibbsite and kaolinite by organic acids is enhanced and leads to residual accumulation of sands. Organo-metallic complexes are translocated in strongly permeable sandy horizons and impregnate at depth the macro-voids of embedded soil and saprolite materials to form the spodic Bs and 2BCs horizons. Mechanical transfer of black particulate organic compounds devoid of metals has occurred later within the sandy horizons of the podzols. Their vertical transfer has formed well-differentiated A and Bh horizons. Their lateral removal by groundwater favours the development of an albic E horizon. In an open and waterlogged environment, the general trend is therefore towards the removal of all the metals that have initially accumulated as a response to the ferralitization process and have temporarily been sequestrated in organic complexes in previous stages of soil podzolization. [ABSTRACT FROM AUTHOR]

The fate of pig (Sus scrofa) slurry labeled with 15N was investigated when applied on a clay soil (fine, mixed, frigid, Typic Humaquept) and a sandy loam (loamy, mixed, frigid, Typic Dystrochrept) cropped to maize (Zea mays L.) in 2000 and to barley (Hordeum vulgare L.) in 2001. The slurry was applied in spring 2000, and plant and soil samples were collected at 6 h (Day 1) and at Days 14, 42, 96, and 413 after application. The samples were analyzed for 15N content in plant, in whole soil, and in soil NH4+-N, NO3--N, organic N, and clayfixed N pools. Percentage 15N recovery was >93% in both soils at Day 1 and decreased slowly thereafter. Rapid clay fixation of slurry 15 occurred at Day 1, and was greater in the clay soil (34% of applied 15N) than in the sandy loam (11%). At Day 96, less of the applied slurry 15N was recovered in maize grown on the clay soil (29%), as compared with the sandy loam (50%). At the same period, the residual soil 15N was mostly present as organic N and NO3-N in the sandy loam, and as organic and clay-fixed N in the clay soil. At Day 413, 15N recovery in barley was about 3% of the initially applied N in both soils. The 15N recovery was generally higher in the clay soil than in the sandy loam, but total 15N recovery from the soil-plant system was similar for both soils. We conclude that soil type had little influence on the total 15 recovery from the soil-plant system, but significantly influenced the fate of slurry N in the various soil pools and plant N uptake on the year of application. [ABSTRACT FROM AUTHOR]

X-ray micro-computed tomography (μ CT) scanning is a proven technique with applications in geoscience, soil science, and geotechnical engineering. Here we apply the technique to investigate the effects of cation treatments on clayey soil micro-fabric in a frozen state. We imaged six suites of frozen cation-treated soils (montmorillonite, kaolinite, illite, illite-smectite, chlorite, and Copper River heterogeneous soil) at a resolution of 8.17 μm. Although this resolution was insufficient to observe differences in microaggregate formation as a result of cation treatment, we did observe micro-lenticular ice structures in the smectite-bearing soils that were invisible to the unaided eye. Quantitative analysis of the morphometric parameters from the illite-smectite and Copper River sample suites provided results that supported the visual observations, with the Copper River heterogeneous soil being more frost susceptible than illite-smectite, regardless of cation treatment. The μ CT results of these small soil cores also indicate that within the Copper River suite, the Ca2+-treated and Na+-treated samples are the most and least frost susceptible, respectively, which is in agreement with previous frost heave testing. Results from this study indicate that μ CT morphometric parameters can be used to quantify micro-lenticular ice lens formation in small samples and to serve as a quality control on sample preparation. • Uses μ CT scanning to visualize micro-fabric changes as a result of cation treatment on clayey soils • Provides images with high resolution (8.17 µ m), which is not typical for µ CT scanning of frozen soils • Discusses how μ CT scanning revealed the presence of ice lensing in certain types of soils and cation treatments [ABSTRACT FROM AUTHOR]

Principles of the classification of clayey soils are examined with respect to plasticity and flow indices. It is shown that determination of classification characteristics without consideration given to the content of +1-mm fractions may lead to incorrect estimation of soil properties. [ABSTRACT FROM AUTHOR]

Comments on a study which estimated the field hydraulic conductivity of compacted clay. Relationship between hydraulic conductivity and effective stress; Development of equations to relate change in hydraulic conductivity as a function of effective stress; Relationship between permeability and void ratio for soil types.