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The evaluation of dynamic soil characteristics is a crucial task in understanding the geotechnical engineering problems associated with dynamic loads. Most of the investigations concentrated on non-expansive materials, and there is a dearth of information on the dynamic performance of fibre reinforced expansive soil. This research paper presents the experimental soundings on unreinforced and reinforced expansive soil with randomly distributed polypropylene fibre with varying confining pressures under cyclic loading. Furthermore, to understand the micro structural behavior of the fibre reinforced soil, samples are examined under SEM analysis after being subjected to cyclic loading. Quantitative analysis of soil micro pores was done through image processing. In addition, the study also included the presentation of maximum shear modulus, a modulus reduction curve and a pore pressure variation curve. Experimental results indicate that, the addition of fibres caused an improvement in the dynamic shear modulus and damping ratio with a rise in confining pressure. Inclusion of fibres reduces the permanent strain. The change of dynamic shear modulus and damping ratio over shear strain amplitude and the dynamic shear stress–strain curves were analyzed under different confining pressures. From the SEM analysis, fibre reinforced soil has a fabric with large packets of soil particles. Moreover, the presence of fibres enhanced pore distribution and diminished considerable amount of voids. The results of image processing shown the area porosity of unreinforced soil is 25.3% and that for 1% of fibre reinforced soil is 6.9%. This shows the enhancement of the interface effect of soil reinforced with fibre, which strengthens the soil and integrity. • A scarcity of data on the dynamic performance of fiber-reinforced expansive soil. • Fibre reinforced soil is made of a fabric that contains large packets of soil particles. • The presence of fibres improved pore distribution and reduced the amount of voids significantly. • Image processing results show that the area porosity of unreinforced soil is 25.3% and 6.9% for fibre reinforced soil. • Improving the interface effect of soil reinforced with fibre, which strengthens the soil and its integrity. [ABSTRACT FROM AUTHOR]

Ecological restoration is considered an effective strategy for increasing soil carbon storage and mitigating climate change. However, the impact of revegetation in desert areas on the stability of soil organic carbon (SOC) is still unclear. We investigated the content and stability of SOC in restoration sites along a chronosequence in the Tengger Desert, focusing on the mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) fractions. The content of SOC significantly increased with site age from 0.37 g kg−1 at year 0–5.32 g kg−1 at year 66. Revegetation significantly changed the SOC fraction and improved SOC stability as a factor of site age. In the 66-year-old site, the levels of MAOC and POC were increased by 255.67 and 9.24 times, respectively. The percentage of MAOC was increased from 1.50% to 28.92%, whereas that of POC was decreased from 98.50% to 71.08%. Based on our findings, the content and proportion of MAOC and POC are closely related to plant input, soil variables, and the soil microbial community. We estimate that the maximum content and proportion of MAOC are 2.65 g kg−1 and 36.71% with continuous succession, based on the soil clay and silt contents. Overall, revegetation improved the stability of SOC. Our study highlights the importance of the revegetation of temperate desert areas to further mitigate climate change. [Display omitted] • Revegetation significantly changed the SOC fraction and improved SOC stability as a factor of stand age. • Revegetation increased the content and proportion of MAOC, whereas it increased POC content while decreasing its proportion. • The MAOC and POC are closely related to plant input, soil variables, and the soil microbial community. • The maximum content and proportion of MAOC are 2.65 g kg−1 and 36.71% with continuous succession. [ABSTRACT FROM AUTHOR]

Soil compaction combined with water deficit may cause a significant decrease in microbial functions. Two texture-contrast sugarcane soils were exposed to the combined stresses of compaction and drought, and microbial responses were investigated going into stress (phase I) as well as their response coming out of stress (phase II). We artificially applied a gradient of bulk densities (0.9–1.5 g cm−3) and water-filled pore space (WFPS, 21–100%) to simulate compaction and drought conditions. PCA results clearly demonstrated the separation of impacts of soil types and the moisture treatments. Additionally, it is evidenced that soil texture can strongly regulate soil microbial response to compaction, as finer texture provides a better local environment for soil microbial community growth, supported by two folds higher microbial biomass carbon content and significantly higher CO 2 respiration in Nitisol (clayey soil) than Planosol (sandy soil). The Structural Equation Modelling (SEM) analysis showed a strongly direct negative effect (path coefficient= −0.59 to −0.61, p < 0.01) of WFPS on the labile C at Phase I and Phase II in both Nitisol than Planosol. Further, soil moisture would govern microbial respiration cross soil types, particularly after removal of compactions which supported by the SEM result (path coefficient= −0.36 to −0.47, p < 0.05). Results from this study have implied the importance in considering the combined effects of soil texture and moisture in assessing compaction impacts and developing associated management regimes. [Display omitted] • Microbial response to compaction varied with soil moisture levels and texture. • Water filled pore space regulates microbial activity at the low moisture level. • Clayey soil showed a greater microbial response to compaction and moisture level. • Clayey soil showed higher resistance to compaction in comparison to sandy soil. [ABSTRACT FROM AUTHOR]

Recent studies have shown that long-term irrigation with treated wastewater (TWW 1 1 Treated wastewater irrigation (TWW): Freshwater (FW): Blended TWW:FW in a 1:1 ratio (MIX): Low-frequency TWW-irrigation (LFI): TWW irrigated tuff trenches (TUF)) can lead to land degradation and reduction of crop performance in clayey soils due to additions of salts and organic compounds. This study investigated the effects of two remediation and two mitigation methods intended to alleviate the damage to soil properties following long-term irrigation with TWW. The experiment was conducted in a 'Hass' avocado orchard (Persea americana Mill.) grown on a clayey soil irrigated with TWW since 2009. The treatments implemented in 2016 included: TWW (control), freshwater (FW), blended TWW:FW in a 1:1 ratio (MIX), low-frequency TWW-irrigation (LFI), and TWW irrigated tuff trenches (TUF). The results showed that FW and MIX significantly reduced total salinity, salinity-related ions (Na and Cl), and sodium adsorption ratio (SAR) to (i) depths of 90 cm and 30 cm under drippers, respectively, and (ii) depths of 60 cm (except for chloride) and 30 cm between drippers, respectively, compared with TWW. TUF and LFI reduced soil salinity and sodicity under drippers but not between drippers compared with TWW. Moreover, FW significantly increased aggregate stability to a depth of 30 cm. TUF had the highest oxygen concentration in the root zone (35 cm depth), followed by FW. Considering the scarcity of freshwater, MIX and TUF are suggested as possible measures for reducing soil salinity and sodicity, and increasing aeration of clayey soils under long-term irrigation with TWW, respectively. Our findings contribute valuable insights into strategies for remediating and mitigating the detrimental effects of TWW irrigation on soil, thus promoting sustainable agriculture in regions facing water scarcity. • FW reduced EC, Na and SAR than TWW both under and between drippers to 60 cm depth. • FW reduced salinity and sodicity at 15 cm away from drip laterals to 30 cm depth. • MIX significantly reduced EC, Na and SAR than TWW to 30 cm depth under drippers. • TUF increased oxygen concentration to 35 cm depth than all treatments. • TUF effects on EC and SAR was restricted to the wetted area bellow the drippers. [ABSTRACT FROM AUTHOR]

To achieve sustainable agricultural activity, phosphatase determination is an important practice for improving the efficiency of phosphorus (P) management in tropical agriculture. The objective of this study was to evaluate acid phosphatase activity in different soil textures and P stress levels affecting the nutritional, chemical, biochemical, and agronomic aspects of soybean. Treatments resulted from factorial combination in a 3 × 3 factorial scheme, consisting of three soil textures (clay, medium, and sandy) and three P stress levels (severe, moderate, and control) with four replications. Three different soil textures were used in the research: Latossolo Vermelho Distrófico (LVd) with clay texture, collected in the native forest, equivalent Oxisol (Soil Taxonomy); Cambissolo Háplico Tb Distrófico (CXbd) with medium texture collected in the natural field equivalent Inceptisols (Soil Taxonomy); and Latossolo Amarelo Distrófico (LAd) with sandy texture collected in the natural field equivalent Oxisol (Soil Taxonomy). Soil electrical conductivity, P available (method Mehlich-1), and acid phosphatase activity (ρ-nitrophenol released) (μg h−1 g−1 soil) were analyzed and the samples were collected at a depth of 0–20 cm. Also evaluated were the height of plants, number of leave and branches, dry mass (root, leave, and stem), P total concentration in leaf, and P translocation (transport from root to shoot) of soybean plants 45 days after sowing. Results showed the clayey textured soil provided the best results for plant growth, root, stem, and leaf dry matter content, P total concentration of P in leaf, P translocation (transport from root to shoot), P available in the soil, and higher acid phosphatase activity of under P stress. Results showed that the Latossolo Vermelho Distrófico (LVd) provided the best results in managing P in different soil textures. However, based on growth and development results, a reduction in phosphate fertilization (P stress moderate) may favor acid phosphatase activity. Acid phosphatase activity can be used as an option in the management of P soluble activity in different soil textures. However, in front of the complexity of soil–plant–P–environment interactions, further research needs to be conducted to investigate better these effects of the da acid phosphatase on different soil textures. • Different soil textures affect acid phosphatase activity. • Phosphatase is an important practice to improve phosphorus efficiency. • Different soil textures affect root and dry matter production in soybean. • Moderate P stress may favor acid phosphatase activity. [ABSTRACT FROM AUTHOR]

• Soil texture effect in temperate grassland region of China is examined. • A strong inverse soil texture effect on vegetation is evidenced. • Loam soil can be used as a benchmark to quantify effect of various textured soils. • Precipitation threshold for inverse texture effect increases with soil coarseness. The inverse texture effect of soil on vegetation has been reported in a few arid regions, but no information is available on the vast Chinese temperate grassland. In addition, no consistent criteria and approaches have been used to classify soil texture groups, determine the precipitation threshold (P θ) below which the inverse texture effect occurs, and quantify the effect size (Z), which has limited the generalization of the rules of the soil texture effect in different ecosystems. We analyzed the soil texture effect on vegetation using the remotely sensed vegetation data (MODIS/NDVI) and the Chinese soil profile texture data at 6851 sites in temperate grasslands of China. We found, first, a strong inverse texture effect, i.e., a higher NDVI on coarse- (>50 % sand) than fine-textured soil in low precipitation areas, and P θ was variable with annual precipitation and averaged 260 mm in the region. Second, we proposed a novel method to use the loam soil as a benchmark against which to quantify the effect of various textured soils, and determine P θ as the point on precipitation gradient where the soil texture effect shift from positive to negative or vice versa. As such, P θ decreased with soil coarseness, and increased with precipitation; and the texture effect decreased from positive to negative for sandy soils, whereas it increased from negative to positive for silt or clay soils, on the gradient of precipitation increase. Our results provide new insights into the relations of vegetation pattern and dynamics with precipitation and soil texture, and a method for quantifying and comparing soil texture effect across ecosystem types. [ABSTRACT FROM AUTHOR]

• Soil temperature temporal variations are in-phase with heat fluxes 10-cm deeper. • Moisture depression occurs in the seasonally frozen soil. • Spatiotemporal heterogeneity of moisture is stronger than that of temperature. • Strong thermohydraulic coupling exists in cold season, but not in warm season. • Zero curtain occurs in both dry and wet soils and varies from region to region. Frozen soil properties and thermohydraulic processes are still not fully understood due to lack of in-situ measurements, especially in the high altitudes and high latitudes (HAHL). Based on hourly measurements at 10, 40, 80 and 120 cm depths at 21 sites in the west, south and northeast regions of the Tibetan Plateau (TP) during July 2018 - July 2019, we examined soil particles, spatiotemporal variations of soil thermohydraulic processes and their connections with environmental factors to reveal the heterogenous frozen soil properties on the TP. Sand and silt are the dominant soil particles and clay is less than 10% at the sites. Existing and widely used soil products underestimates (significantly overestimates) sand (clay) content on the TP which raises the uncertainty in the thermohydraulic parameters derived from these products. Diurnal soil moisture and temperature variations are seen only above 40 cm, but seasonal variations occur down to 120 cm due to the soil memory effect. Seasonally frozen soil and permafrost soil show different freezing and melting processes. Dry soil features greater soil temperature temporal variability and deeper maximum frozen depth than wet soil. Zero curtain occurs in both dry and wet soil, and displays high (low) frequency but short (long) duration at 10 (80) cm that vary spatially. Moisture depression exists in seasonally frozen soil and is determined by the initial soil moisture and temperature gradient strength. The strong thermohydraulic coupling existed in cold season collapses in warm season. Soil moisture exhibits higher spatiotemporal variability than soil temperature. At daily time scale, the influences of precipitation, wind speed and relative humidity on soil moisture and temperature vary under different climate conditions. These findings fill the knowledge gaps in the soil thermohydraulic processes in the HAHL, and improve the understanding of frozen soil properties and heat-water coupling processes in soil in the HAHL. The study will benefit the Earth system model development and improve the quality of soil temperature and moisture assimilation and remote sensing products in the HAHL. [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]

Different types of soil water, such as bound water and capillary water, have distinct effects on the physicochemical and engineering properties of soils, particularly unsaturated clayey soils. Therefore, it is crucial to develop an accurate and physically meaningful experimental method for identifying and quantifying these components. This study pioneers the use of a multi-step kinetic model to identify and quantify different soil water components across a wide range of relative humidity (RH) using thermogravimetric analysis (TGA) data. To validate the determined kinetic parameters (i.e., activation energy, preexponential factor, and reaction model) and the identification and quantification results of soil water components, TGA with multiple heating rates, nitrogen adsorption method, cation exchange capacity measurement, and nuclear magnetic resonance (NMR) were performed on kaolin samples equilibrated under various RH conditions. These experimental results cross-validate the superior performance of the kinetic model in determining soil water components and predicting the thermal desorption behaviors of soil water. Based on the cross-validation results, the soil water components obtained from the kinetic analysis are further identified as tightly-bound, loosely-bound, and capillary water, which exhibit variations consistent with empirical soil water isotherm models. The T 2 cutoff value between bound and capillary water is determined to be 1.79 ms based on TGA and NMR results. The determined thermal kinetic parameters of different soil water components can exhibit their distinct retention mechanisms. The method and results in this study provide a new perspective on identifying different soil water components, as well as understanding the mechanism of soil-water interactions in unsaturated soils. • A method based on thermogravimetric and kinetic analysis is developed to identify and quantify soil water components. • Kinetic model can detect tightly-bound, loosely-bound, and capillary water in kaolin. • Different soil water components exhibit distinct kinetic triplets. • Bound water content increases with humidity regardless of capillary condensation. • NMR T 2 cutoff value between bound and capillary water is 1.79 ms. [ABSTRACT FROM AUTHOR]

The thermal volumetric behaviour of soils plays a critical role in designing energy geostructures, withstanding temperature fluctuations. This study examined, for the first time, the thermal deformation of the partially saturated kaolin clay (matric suction of 0–300 kPa) within the operating temperature range of energy geostructures (8 °C to 45 °C), subjected to varying most recent stress histories (normal stress of 0–400 kPa). The thermal cycle has been applied to samples with identical hydro-mechanical stress histories initiated by heating or cooling from room temperature. Scanning electron microscopy (SEM) tests have been performed to investigate the impact of temperature on soil microstructure as a potential determining mechanism of thermal deformation. The volumetric deformation associated with thermal cycles is analysed, considering the concurrent role of the overconsolidation ratio and the most recent stress. Secondary thermal consolidation (i.e., particle rearrangement) mainly depends on the most recent stress history, occurring only in samples heated beyond the yield limit, with cooling preventing secondary thermal consolidation. A clear relationship between thermal volume change and matric suction was observed, with higher matric suction resulting in less pronounced particle rearrangement. Further SEM analysis revealed that heating beyond the yield limit alters the soil microstructure permanently, with cooling showing no impact. • Thermal behaviour is determined by the most recent stress history, suction, and OCR. • Clayey soils in the loading stage might experience plastic deformations upon heating. • Cooling leads to elastic deformations, regardless of OCR and most recent stress history. • In contrast to cooling, heating permanently changes soil microstructure. • The secondary compression index increases significantly with temperature. [ABSTRACT FROM AUTHOR]

• Ratio of peak areas of MIR quantified OM dynamics in soil. • Using ratio of peak area increases our understanding of soil aggregate dynamics. • High C/N OM resulted in slow decomposition and gradual aggregation. • Low C/N OM fostered rapid macroaggregate formation and subsequent reorganisation. • Assigning a MIR band to a C group indicating its stability can be misleading. Soil organic carbon is a crucial parameter for assessing soil quality, and it significantly contributes to soil aggregation. However, the influence of different organic carbon components and groups on the formation of soil water-stable aggregates has not been thoroughly investigated. To examine it, a clay soil amended with two different types of organic matter (OM) at four input levels for 84 days. The ratio of peak area (RPA) of the mid-infrared (MIR) spectra was used to investigate the dynamic of specific compounds and soil aggregation during the decomposition of OM. The results showed three important aspects. Firstly, the amount and nature of OM input strongly influenced the formation of organic compounds during incubation, as well as the degree of soil aggregation. Furthermore, we observed that the C groups identified by MIR spectroscopy were highly dynamic. Thus, the approach of using a band of soil MIR spectra to infer the stability of a C group can be misleading. Secondly, the low C/N of alfalfa stimulated more microbial activity with 1.1 to 2.3 times more cumulative respiration than high C/N barley straw. The rapid degradation of alfalfa immediately formed water-stable aggregates and subsequently, the macroaggregates were reorganized by microbial activities and physical disturbance. In contrast, the slow decomposition of barley straw built up aggregates gradually in a hierarchical manner and in proportion to the amount of OM added. Alfalfa amendment caused a significant increase in the mean weight diameter (MWD) and a strong correlation with the RPA in the range of 1747–1500 cm−1 (r = 0.78). While aggregation due to barley straw treatment led a stronger relationship between MWD and RPA of 3000–2800 cm−1 (r = 0.89). The results suggest MIR spectra can be used to understand the dynamics of OM that build stable aggregates. [ABSTRACT FROM AUTHOR]

• Studied forests in Western Ghats had weathered and mature profiles of Ultisols. • Abundance of 2:1 and mixed layer minerals in natural forests than plantation. • Co-dominance of gibbsite with 2:1 minerals discounts the antigibbsite hypothesis. • Losses of SiO 2 in the non-clay fractions indicate active weathering in all horizons. • Clay formation assessments provide insights into ecosystem regulated pedogenesis. Clay minerals formed during soil formation are imprints of ecosystem functioning and pedogenic processes in landscapes. The study evaluated the variations in taxonomy, soil weathering and pedogenic changes in contrasting forest soils in the Southern Western Ghats, India. Three different forest systems with comparable soil-forming factors vis-a-vis evergreen, moist deciduous and a man-made system (rubber plantation) were evaluated for physical, chemical, morphological, and pedogenic characteristics of the related soils. Soil profiles were dug up to 1.50 m in the selected ecosystems and horizon-wise soil samples were collected. All the pedons were classified in the soil order of Ultisols and subclassified as Ustic Palehumult (evergreen forest), Ustic Haplohumult (moist deciduous forest) and Typic Haplustult (rubber plantation), respectively. The soil pH was found to be acidic in all the ecosystems ranging from 4.6 to 5.8. Chlorite, hydroxyl interlayered vermiculite (HIV), mica, kaolinite, feldspars, gibbsite and quartz dominated the mineral assemblages in the clay fractions of soils of natural forest systems. The losses of SiO 2 in the non-clay fraction and corresponding enrichment of the component in the clay-sized fraction in all horizons indicated an active continuous weathering process in all the systems of this region. Clay accumulation by way of formation and translocation was highest in the lower horizons of the soils of evergreen (Bt2 at a depth range of 28–57 cm) and moist deciduous (Bt3C at a depth range of 23–150 cm) forest, whereas it was highest at Bt1 at a depth range of 15–28 cm in the plantation soil. The depth variations in the clay formations in natural and manmade forest systems provide insights into ecosystems regulated profile development under natural and man-made systems in the humid tropics, a vital information gap hitherto in soil pedogenesis of the humid tropics. Such pedogenic assessments along with the factors responsible for such modifications would provide important inputs in developing soil health management strategies in the humid tropics. [ABSTRACT FROM AUTHOR]

This paper presents the influence of temperature on the residual strength by analyzing shearing tests carried out in a temperature- and velocity-controlled ring shear apparatus. Temperature was applied in steps of cooling and heating ranging between 6 °C and 50 °C at a constant shearing velocity of 0.442 mm/min. Additional tests include the evaluation of the strength at 0.890 mm/min before and after the imposed temperature change. Six basic soil types characterized by different mineralogy, grain size and plasticity, as well as, mixture soils having different proportions of sand and clay, are evaluated and the results are interpreted in terms of their properties. The experimental results reveal that the temperature effect becomes relevant when fine particles and plasticity increase being negligible in the case of the sandy soil. Shear strength reacts immediately to temperature changes and a new residual strength establishes soon. The temperature effect is symmetric. An increase in temperature leads to a decrease in strength, and an equal and opposite trend is observed when temperature decreases. The magnitude of the strength variation is significant in clayey soils. For the case of high plasticity soils, the residual friction angle variation observed during cooling and heating (±50 °C) is around 2°. The strain rate effect evaluated in a smaller number of tests indicated a strain rate strengthening in all the materials tested except for the case of the sandy soil, which also was not reactive to temperature changes. The experiments are calibrated with a velocity, state, and temperature-dependent friction model. • Influence of temperature on residual shear strength have been characterized. • Heating leads to decrease in friction and cooling leads to an increase for high shearing rates. • Relevance of residual friction change with respect of temperature correlates with the soil plasticity. • No effect of temperature was measured for the clean sand tested. • The friction constitutive model developed by Chester (1994) can reproduce the tests performed. [ABSTRACT FROM AUTHOR]

• Waste materials from different sources have been utilized in chemical stabilization of expansive pavement subgrade soils. • Engineering properties of expansive pavement subgrade soils can be improved with waste material stabilization. • The issue needs further investigation, since durability properties of expansive soils are affected by many parameters. • Microstructural characteristics of materials are a key factor that need more attention in expansive soils stabilization. • Waste materials-based stabilization can be sustainable, economic and eco-friendly alternative to traditional ones. Expansive soils, also known as swell-shrink soils, are one of the most problematic soils in highway construction and exhibit significant volume changes by swelling and shrinking while wet and dry, respectively. These changes in soil cause cracks, heaves, differential settlements, and damages to the overlying pavements leading to high maintenance costs. The annual average maintenance cost of structures built on expansive soils ranges from $9 to $15 billion, with 50% of the expenses associated with highways and streets. Chemical stabilization techniques such as cement and lime stabilization are one of the most efficient ways to treat expansive soils. However, there is a need to develop environmentally friendly approaches to stabilize expansive soils due to worldwide growing interest in sustainable developments and concerns about greenhouse gas emissions and climate change. In this context, using waste materials in soil stabilization has been considered an important issue for sustainability concerns. The aim of the current study is to review the relevant studies performed to improve the geotechnical and engineering properties of expansive subgrade soils of pavements by using waste materials arising from industrial, agricultural, and other activities in the last decade. In the organization of this study, characteristics of expansive soils including plasticity, compaction, strength & stiffness, microstructural characteristics, shrink-swell properties, and durability were focused to point out the effect of the waste materials. The overall results obtained throughout the scope of the current study indicated that the use of waste materials in soil stabilization improves the engineering properties of expansive soils, significantly. This paper also provides key information and creates awareness for researchers and sector representatives about sustainable soil stabilization. [ABSTRACT FROM AUTHOR]

Earth pressure balance shield (EPBS) has become the mainstream construction method for metro tunnels in China, which inevitably generates a large amount of discharged soil, putting enormous pressure on the environment and the cost. In order to realize the resource utilization of shield dregs, this paper explored the feasibility of recycling the waste silty clay as a soil conditioner in EPBS tunnel construction. Mixtures of bentonite, wasted silty clay, carboxymethyl cellulose (CMC), and tap water in different ratios were prepared. Defining the substituted ratio as the mass ratio of silty clay to (bentonite + silty clay), the effect of the substituted ratio on the apparent viscosity, flow curve, rheological model and physical stability of bentonite-silty clay composite slurry were investigated. Furthermore, the relationship between slurry microstructures and macroscopic rheological properties was revealed by scanning electron microscopy (SEM). The results show that the constitutive relationship of bentonite slurry (0% substituted ratio) can be well described by Herschel-Bulkley model. The silty clay has a deteriorating effect on the rheological behavior and physical stability, and changes the flow pattern of the composite slurry. Microscopically, CMC makes the clay particles in slurries form agglomerates with larger particle sizes, and can absorb excess free water from the slurry, thus significantly increasing the yield stress and apparent viscosity. The recycling scheme proposed in this study can not only greatly reduce the procurement cost of raw materials, but also eliminate the transportation and disposal costs of discharged soil, which has significant environmental benefits and promising application prospects. [ABSTRACT FROM AUTHOR]

Soil with persistent macroaggregates should maintain its integrity following wetting disturbance. This study determined how wetting-drying cycles affect two pre-sieved macroaggregate size fractions (2–4 mm and 0.6–2 mm) of clay and organic soils pretreated with organic carbon substrates. Soil aggregates were unamended or treated with organic carbon (4 g C from soluble glucose or insoluble wheat straw per kg soil) before being exposed, during three months of incubation, to nine sequential wettings at three wetting intensities (no wetting, slow wetting at the rate of 1 g of water per second or fast wetting with 2 g water per second). The glucose-treated macroaggregates from the clay soil were minimally disturbed by wetting-drying cycles, maintained their shape (shown by high aggregate circularity and low major/minor axis ratio) and were more cohesive, possibly because of a higher microbial activity provided by the glucose treatment. In contrast, the clay soil macroaggregates mixed with wheat straw, which had the same carbon content as glucose, did not persist when exposed to wetting-drying cycles. Macroaggregates from organic soil resisted nine wetting events with or without glucose addition, implying a distinct aggregate binding mechanism in organic soil compared to the clay soil. The persistence of clay soil macroaggregates treated with glucose may be related to microbial processes that promote macroaggregate stability, with glucose physical adhesion expected to substantially improve aggregate stabilization in this mineral soil as well. Glucose-mediated aggregate stabilization can apparently persist for many weeks in an environment with recurring wetting-drying cycles. • Macroaggregates from clay soil disintegrated with 9 repeated wetting events. • Macroaggregates from organic soil resisted 9 wetting events during 3 months. • Glucose improved the persistence of clay soil macroaggregates to repeated wetting. • Glucose maintained aggregate morphology and improved aggregate stabilization. [ABSTRACT FROM AUTHOR]

Expansive soils have been inevitable during road constructions due to its widespread availability. Conventional stabilizers; cement and lime have not been quite reliable in terms of economic, environmental, and durability perspectives. Thus, geopolymer has come into limelight as a sustainable alternative. However, the complexity of geopolymer-soil behaviour makes it challenging to predict their strength development patterns and it requires a large number of trial and error tests in laboratory scale due to the soil specific nature of such mixes. To date, no research has been attempted to develop design charts for geopolymer-expansive soil stabilization field applications. This study proposes design charts using Artificial neural networks (ANN) to predict the 28-day unconfined compressive strength (UCS) of Class F fly ash (FA) based geopolymer stabilized expansive soil (PI = 32% – 46%) to support field implementation of this novel geopolymer based soil stabilization. The model was developed based on a robust collection of literature data; FA/Soil, Activator/FA, Na 2 SiO 3 /NaOH, alkaline molarity, and their respective 28-day UCS values. Three contour plots for mix design: FA/soil vs. NaOH molarity, activator/FA vs. Na 2 SiO 3 /NaOH, and Na 2 SiO 3 /NaOH vs. NaOH molarity were proposed based on the model predictions. The proposed mix design charts were validated through the in-house tests which showed reasonable match in comparison with the predicted 28-day UCS using the contour plots. The proposed mix design charts can be employed for in-situ geopolymer-expansive subgrade stabilization to achieve strengths between 0.6 and 2.1 MPa. [ABSTRACT FROM AUTHOR]

Multi-scale evidence of rapid, climate-induced soil structural changes occurring at yearly to decadal timescales is mounting. As a result, it has become increasingly important to identify the properties and mechanisms controlling the development and maintenance of soil structure and associated macroporosity. This is especially relevant since macroporosity has disproportionate effects on saturated hydraulic conductivity (K sat) which strongly influences water storage and flux, thus, affecting the water cycle. In this study, we use decision trees and piecewise linear regression to assess the influence of soil and climate properties on effective porosity (EP; a proxy of macroporosity) in both surface and subsurface horizons under varying land-use and management practices. Data from 1,491 pedons (3,679 horizons) spanning five ecoregions representing bioclimate (e.g., potential vegetation) across the conterminous US demonstrate that, at a continental scale, EP in surface (A) and subsurface (B) horizons is strongly dependent on the complexed fraction of the total mass of soil organic carbon (SOC) and clay; a combined fraction that we refer to as complexed organic carbon and clay (COCC). EP showed a slight positive response to COCC in A horizons but increased steeply with increasing COCC in B horizons. This is because the smaller values of COCC in B horizons reflect a larger pool of clay that has a greater potential to accommodate and complex additions of SOC promoting stronger organo-mineral bonds and the concomitant development and maintenance of soil structure in these horizons. In contrast, larger values of COCC in A horizons reflect conditions where all or most of the clay fraction is effectively complexed with SOC resulting in a larger pool of non-complexed soil organic matter with varying contrasting effects on macroporosity that ultimately mute the response of EP to increases in COCC. In surface horizons, indirect factors such as mean annual precipitation and land use were important predictors of EP, whereas COCC was more influential in controlling EP within the subsoil. The EP-COCC relationship also holds within ecoregions but its effect is mitigated by soil and climate interactions suggesting that the effect of climate on this relationship is indirect and complex. Plowed surface horizons and horizons underlying plowed layers showed greater homogenization (due to disturbance effects reducing heterogeneity in the soil) as well as a reduction in the magnitude and rate of change of EP as a function of COCC compared to undisturbed horizons. Our findings suggest that the complexed fraction of clay and SOC is important for controlling macroporosity and K sat at ecoregion scales and that the EP-COCC relationship may be an important framework for understanding and predicting future land use- and climate-induced changes in soil hydraulic properties. • Effective porosity (EP) depends on complexed organic carbon and clay (COCC). • The nature of the EP-COCC relationship changes for A and B horizons and land use. • Large A horizon SOC contents saturate clay sites muting the effect of COCC on EP. • B horizons contain more clay which is able to complex greater amounts of SOC. • EP and soil hydraulic properties are more impacted by SOC content in the subsurface. [ABSTRACT FROM AUTHOR]

• Regional geochemical baseline values can well model the background values of studied metals. • Cd was the main pollutant in the riparian sediment. • The contamination and risk of Cd was high in upper downstream and site of 24. • Influencing factors explained variation of metals better at 1 km buffer scale. • Land use composition contributed most to the high explanation at 1 km scale. In this study, we assessed pollution status and potential risk of metals in riparian sediment of Yangtze River with geo-accumulation index (I geo), ecological risk index (RI) and health risk index (THQ) by calculated regional geochemical baseline (RGB) values. We explored the influence of natural factor (sediment property) and anthropogenic factors (land use composition and landscape configuration) at different buffers (500 m, 1 km and 5 km) on metals in sediment using redundancy analysis (RDA) and variation partitioning analysis (VPA). Results indicated that RGB values can effectively model background values of metals (p < 0.01). I geo and RI assessment showed that Cd was the primary pollutant, which showed no contamination to moderate contamination (I geo > 0) and moderate ecological risk (ecological risk factor > 40) in upper downstream of the river. Besides, Cd showed moderate to strong contamination (I geo > 2) and considerable ecological risk (ecological risk factor > 160) at site 24, which is located in the intersection of Poyang Lake and Yangtze River and strongly affected by natural erosion and human activities of Poyang Lake drainage. THQ assessment indicated low health risk of metals from consuming fish influenced by suspended sediment. RDA and VPA analysis indicated that explanation rate of land use composition, sediment property and landscape configuration on metals was 27.01–55.1 %, 36.66 %, 9.77 %-12.52 %, respectively. The total explanation rate was significantly higher at 1 km scale (82.5 %), which was mainly contributed by land use composition and its interaction with sediment property and landscape configuration (55.11 %). Specifically, percentage of farmland, grassland, wetland and forest, content of TN, TOC, silt and clay in soil and landscape configuration index of NumP were positively correlated with metals, and content of sand in soil and landscape index of MSI negatively correlated with metals in riparian sediment at different buffer scales. Our results offer valuable insights for safeguarding riparian zone. [ABSTRACT FROM AUTHOR]

• C:N ratios in soils and particle-size fractions were assessed in tropical highlands. • Sand C:N ratios increase with depth, whereas silt and clay C:N vary little. • C:N ratios decrease with increasing Ca and Mg contents, CEC, and clay activity. • N-enrichment in clays is likely controlled by mineralogy. • R-NH 3 + sorption onto clays can be critical to organic matter stabilization. Factors affecting soil organic carbon (SOC) retention in the tropics are relatively well known, but this is not the case for N retention and thus C:N ratios, a common proxy for organic matter stability. Recent data suggest that SOC and N concentrations vary with climate, whereas soil C:N ratios depend on particle-size fractions contents. However, such knowledge is still incipient for tropical soils, native vegetations and deeper soil layers, which are critical to understand how land use and climate change affect C and N fluxes. We assessed SOC, N and C:N ratios in bulk soils and sand, silt and clay fractions, and their correlations with other soil properties under native tropical forests in the highlands near Lavras, Brazil. Soil samples were collected to 1-m depth in soils of contrasting texture and mineralogy, formed on quartzite, sericite-schist, gabbro, itabirite, ironstone, meta -limestone, gneiss, and phyllite. Mean SOC and N concentrations were generally high, whereas mean soil C:N ratios varied from 9.5 to 18.7 among parent materials, and only in three soils C:N ratios varied considerably with depth. Enrichment factors (EFs) were generally < 1 in the sand and silt fractions for SOC and especially N. Conversely, EFs for clay were mostly > 1 for SOC and even higher (up to 6.58) for N. Such trend indicates that SOC and N are concentrated in clays, and more importantly, that N sorption is favored compared with SOC, and likely dependent on clay mineralogy. Soil C:N ratios decreased with increasing values of exchangeable bases, due to higher N in the most fertile soils, suggesting that a mechanism of R-NH 3 + cationic sorption is likely involved. Our results suggest that soil N is a critical component of the overall stabilization of soil organic matter onto clays of tropical soils, deserving further investigation also under temperate climate and other zones. [ABSTRACT FROM AUTHOR]

Unraveling the distributions and controls of soil carbon (C) and nitrogen (N) accumulation is conducive to providing guidance for sustainable ecosystem management. Although the factors that affect soil C and N accumulation have been widely investigated, the relative importance of these factors and whether they confer direct or indirect effects remain unclear. Herein, we examined the distributions of soil organic carbon (SOC), soil inorganic carbon (SIC), and total nitrogen (TN) stocks across the 0–200 cm soil profiles in grasslands, forestlands, and shrublands on the Loess Plateau. Moreover, we determined the relative contributions of land use, topography, and soil properties (texture, water, phosphorus, and available nitrogen) to their variations. The results showed that with increasing soil depth, SOC and TN stocks decreased, while SIC stocks fluctuated. However, large amounts of SOC, SIC, and TN were stored in the deep soil layers (100–200 cm), with values of 3.06, 26.63, and 0.50 kg/m2, respectively. In the 0–200 cm soil layers, the total SIC stock was 53.40 kg/m2 and was 6.8 times higher than the total SOC stock. Among different plant communities, grasslands had the highest SIC stock (54.83 kg/m2), while Armeniaca sibirica and Robinia pseudoacacia had the highest SOC stock (10.06 kg/m2) and TN stock (1.49 kg/m2), respectively. Furthermore, approximately 85% of the variations in SOC, SIC, and TN stocks were jointly affected by land use, topography, and soil properties, in which soil properties acted as the most important driving factors, followed by topography and land use. In particular, topography affected SOC, SIC, and TN stocks mainly through its effects on soil texture and water. Overall, vegetation restoration scenarios incorporating grasslands and Robinia pseudoacacia are highly recommended and should be tailored according to specific topographic features. • SIC stock was 6.8 times higher than SOC stock in the 0–200 cm soil layers. • Grasslands performed better in soil C accumulation than forests and shrubs. • Land use, soil property, and topography explained 80% of the changes in C and N. • Land use played a less important role in affecting C and N than topography. • Topography affected soil C and N accumulation by influencing soil clay and water. [ABSTRACT FROM AUTHOR]

The aim of the study is to determine the correlations between mechanical impacts on clay soil samples and resulting changes in the microstructure of the samples and their IR spectra. For research, soil from a railway subgrade under construction in the Azov-Black Sea region was used. The soil was examined by traditional and modern physical methods and classified as light clay. Clay properties were modified by adding alabaster to the soil, after which the samples with different amounts of alabaster were subjected to mechanical load. A cyclic mechanical impact by the compression method was applied to a clay sample without alabaster, an equivalent to the passage of 400 freight trains along the railway track. The microstructure of samples was studied by electron microscopy which allowed determining the microstructure parameters of the fragments of samples before and after the mechanical action. Samples of clay and clay with the addition of alabaster were subjected to a semi-quantitative express analysis by IR spectroscopy, as a result of which the concentrations of minerals were determined with an accuracy of no worse than 10%. Clay and clay samples with the addition of alabaster were subjected to static uniaxial compression, after which the samples were examined by IR spectroscopy. Comparison of the results of spectral and compression studies made it possible to investigate the correlations between changes in the peak intensities of the IR spectra bands and the concentration of alabaster, as well as the strength properties of the soil. • Adding modifiers to clay soil leads to a change in its strength properties. • Addition of modifiers to the clay soil results in a change in the shape of the infrared spectra. • Changes in the intensity of IR band peaks correlate with the concentration of modifiers and strength properties of clay soil. • Correlation relations are individual for types of clay soils, method of spectra normalization and composition of modifiers. [ABSTRACT FROM AUTHOR]

• The combination of MgO and fly ash effectively solidifies salt-bearing clay in areas subjected to seasonal freeze–thaw cycles. • The substitution of conventional solidifying materials with fly ash constitutes a sustainable and ecologically responsible approach to consolidating clay soils. • The cementation of soil particles is efficiently accomplished by the carbonate compounds generated from magnesium and calcium. This paper presents an innovative method for improving the strength of salt-bearing clay under freeze–thaw cycles. The active magnesium oxide (MgO) and industrial waste fly ash were employed as primary solidifying materials in the seasonal freezing soil reinforcement process, and the reinforcement effect is achieved through carbonate crystals generated through carbonization tests. The solidification effect was investigated with varying ratios of solidifying materials, salt content, and freeze–thaw cycles. The experiment results revealed that the combination of active MgO and fly ash effectively enhances the strength of salt-bearing clay. Specifically, compared to unsolidified soil, the soil solidified with 8 % active MgO (8M0F) and a combination of 4 % active MgO and 4 % fly ash (4M4F) demonstrated a significant increase in ultimate strength by 14 and 12 times, respectively. Moreover, the number of freeze–thaw cycles exhibited a negative correlation with ultimate strength, whereas the salt content demonstrated a similar negative correlation. Microscopic analysis revealed that the 8M0F sample produced mainly magnesium carbonates and hydrogen and oxygen compounds, whereas the 4M4F sample generated primarily magnesium and calcium carbonates. The resulting compound crystals efficiently filled the internal pores and cemented the soil particles, leading to a substantial increase in strength. Overall, these results indicate that the active MgO combined with fly ash solidifying method can offer a viable and sustainable solution for improving the strength of salt-bearing clay in areas with seasonal freeze–thaw cycles. [ABSTRACT FROM AUTHOR]

• The use of a residual alkaline solution to enhance the clay properties is examined. • UCS , ITS , UPV and microstructural (SEM , XRD) tests are conducted. • High- and low- calcium fly ash are introduced into the alkaline activation process. • A microstructural analysis showed the formation of binding gels. • An environmental assessment is performed to compare the CO 2 emission. This study aims to evaluate the usability of a recycled alkaline solution, a residue from cleaning iron plates in the car manufacturing industry, to enhance the strength and stiffness of clayey soil by carrying out unconfined compressive strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity (UPV) and microstructural (SEM , XRD) tests. High- and low- calcium fly ashes with percentages of 10% to 40% and 10% to 30%, respectively, were independently introduced into the alkaline activation process to determine the proper type and content of precursors at room temperature. Two mixtures of the residual cleaning solution blended with 2 M and 4 M NaOH solutions at a weight ratio of one were also utilized to determine how efficiently binary solutions could improve the performance of the parent clay soil. These experiments revealed that all mixtures of the residual alkaline solution work better to activate high-calcium fly ash as compared to the low-calcium fly ash in terms of both mechanical strength and stiffness. The sample of high-calcium fly ash with fly ash/solid and Na/ash ratios equal to 30% and 0.037, respectively, experienced the highest improvement. A microstructural analysis showed the formation of C-(A)-S-H and N–(C)–A–S–H gels in the corresponding sample, thus providing a considerably dense structure, which in turn significantly contributed to the enhancement of the maximum strength and stiffness of the treated soil. In fact, the high-calcium precursor proved to be the best candidate for a low-range alkaline activator because it contributes more calcium to a low-alkaline environment. An environmental impact assessment was also carried out to compare the CO 2 emissions of clays treated with the 4 M NaOH binary solutions tested in this study with those conventionally stabilized by cement and lime and also those treated traditionally with commercial 2, 4, and 8 M NaOH. The samples in this study treated with environmentally friendly binary solutions (residual cleaning solution blended with 2 M and 4 M NaOH solutions at a weight ratio of one) performed better in terms of both CO 2 emissions and strength gain compared to the samples stabilized with conventional materials. [ABSTRACT FROM AUTHOR]

• The actively heated FBG technology measures the moisture content of expansive soil. • The influence of cracks on measuring soil moisture content is investigated. • A modified function is proposed to eliminate the measurement error. • The root mean square error after modification is reduced to 0.030 m3·m−3. Accurately moisture content measurement is crucial in addressing engineering problems of expansive soil with cracks. In this study, the actively heated fiber Bragg grating (AH-FBG) sensing technology was used to measure in-situ moisture contents of expansive soil. The impact of soil cracks on the measurements was investigated through a series of numerical simulations, and a modified function was proposed to eliminate measurement errors. The results show that the Cai model can accurately describe the relationship between the thermal conductivity and moisture content, and is thus utilized as the calibration model. Under the heating strategy, the influence range of the sensor is roughly 4 cm in the radial direction. Cracks within that range hinder heat transmission, leading to underestimation of moisture contents. The RMSE of the measurements after modification is reduced to 0.030 m3·m−3, which verifies that AH-FBG sensing technology can be extended to the reliable measurement of expansive soil moisture. [ABSTRACT FROM AUTHOR]

[Display omitted] • High performance paradigm for predicting UCS of stabilized expansive soil. • Waste glass powder (WGP) and Fly Ash (FA) were used for stabilization of expansive soil. • Effect of the WGP, FA, and Clay content on microstructural behavior of expansive soil. • The MEP predicted the UCS of stabilized expansive soil more robustly. Expansive soils (ES) are unsuitable for construction because of their low shear strength, bearing capacity, unconfined compression strength (UCS), and high shrink-swell potential. The traditional experimental techniques for obtaining the optimized mixes of stabilized ES using a variety of waste additives are laborious, time-consuming and uneconomical. Therefore, this study determines the optimized mixes by evaluating the UCS of waste glass powder (WGP) and Fly Ash (FA) modified ES by deploying a robust computational technique, i.e., multi-expression programming (MEP). The ES was modified using WGP at 0, 5, 10, 15, 20, 25, and 30%, in order to determine the optimum dosage of WGP. Furthermore, FA was incorporated at 0, 5, 8, 11, 14, and 17% in the ES at the optimum WGP content, and their synergistic effect was determined. An experimental dataset was compiled with 180 test results on the untreated ES to develop the MEP model. The proposed optimal MEP model relates the UCS at 28 days (UCS 28d) to its plasticity index, specific gravity, swell potential, UCS 3d , and UCS 7d. It was also evaluated using different statistical indices, such as correlation coefficient (R = 0.995), Nash-Sutcliffe efficiency (NSE = 0.989), coefficient of determination (R2 = 0.989), and error analysis indices (MAE = 6.87 kPa, RMSE = 11.42 kPa, and performance index ρ = 0.016) for the test dataset. These values suggest the robust predictive capability of the MEP model, thus enabling the designers and practitioners to readily use these equations where cost-effectiveness and time are to be considered in engineering projects. In addition, the inclusion of these industrial waste-based additives would lead to sustainability in the field of geoenvironmental engineering. [ABSTRACT FROM AUTHOR]

• First study on the response of box-shaped buried tunnel under BLEVE. • Critical factors on tunnel responses under BLEVE are identified. • Tunnel responses to BLEVE and its TNT equivalent explosion are compared. • Measures to mitigate tunnel damage are examined. Box-shaped road tunnels have been widely used in urban areas and might face the threats of accidental Boiling Liquid Expansion Vapor Explosions (BLEVEs) due to ever-increasing liquified petroleum transportation. However, very limited study has investigated the response of popularly used buried box-shaped road tunnels (i.e., box-shaped tunnels buried in soil mass) subjected to internal BLEVEs. In this study, the dynamic response of a typical two-cell box-shaped road tunnel buried in soil subjected to internal BLEVEs induced by the burst of a 20 m3 liquified petroleum gas (LPG) tank is numerically investigated by using LS-DYNA. The results show that the tunnel experiences severe damage under BLEVEs with liquid-filling ratios equal to or more than 65% while it suffers only minor damage with the load carrying capacity not compromised under BLEVE with 50% filled-liquid. The effects of BLEVE occurring locations on the tunnel response are then investigated. It is found that the tunnel subjected to the BLEVE occurring on the lane near middle wall experiences more significant response in general than that away from the middle wall. In addition, to mitigate the tunnel damage under BLEVEs, strengthening soil mass around the tunnel using soil–cement mixture is considered and its performance is examined. An empirical formula is also proposed for the design of using soil–cement mixture to enhance the buried box-shaped tunnel against internal BLEVEs. [ABSTRACT FROM AUTHOR]

Soil pores play a critical role in the complex physical coupling process and are closely associated with the mechanism of soil salinization. This research used mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and laser particle size analysis on a soil profile about 230 cm deep in Qian'an, where soda saline–alkali soil is distributed and the deepest underground freezing depth is 180 cm. The material composition of the soil in active layer was identified, and the soil pores were classified as micropores (<0.04 μm), small pores (0.04–0.4 μm), mesopores (0.4–4 μm), and macropores (>4 μm). The soil deposited at a depth of 0 to 80 cm was affected by freeze–thaw cycles and dry–wet cycles, developing longitudinal cracks. During the rainy season, clay particles and salt were carried downward by rainfall, whereas at a depth of 30 to 80 cm, the exchangeable sodium ions and clay particles in the soil created a thick diffused layer and hindered rainfall infiltration, resulting in salt accumulation. The small pore diameter and low porosity of the soil in this depth range caused pores degradation, further exacerbating the salinization process. The soil deposited at a depth of 80 to 120 cm had low clay content, resulting in limited upward migration of unfrozen water during freezing periods. Upon thawing, the salt and fine clay particles moved upward with capillary water, leading to a lower salt content than the upper soil. Additionally, this depth range had a high content of macropores with a large average pore diameter. The soil deposited at a depth of 120 to 180 cm had high clay content, and during short freezing periods, salt migrated upwards with unfrozen water along poorly connected longitudinal cracks with limited clay particle migration. The macropore content was low, and the average pore diameter was small due to clay particles filling the pores. The salt content in this depth range was lower than in the upper soil. The pore structure characteristics of the saline soil in the active layer provide insights into salt deposition mechanisms, and this research offers data support from a pore-scale perspective for preventing the salinization process. • A salt accumulation layer is identified at certain ground depth. • The influence of soil material composition on pore structure is bidirectional. • The magnitude of the water absorption gradient is related to the freezing duration. [ABSTRACT FROM AUTHOR]

Understanding wave propagation across rock joints is of great importance in rock engineering, petroleum engineering, and other geophysical applications. Previous studies have shown that wave behaviours across filled rock joints are highly affected by the properties of filling materials. However, how clay minerals and water saturation of the infilling affect wave attributes across filled rock joints is still poorly understood. In this study, ultrasonic tests were conducted on kaolinite- and bentonite-filled rock joints to investigate the roles of clay minerals and the water saturation of infillings on elastic P-wave behaviours across individual filled rock joints. The test results show that the infilling's water saturation and mineralogical compositions have combined effects on P-wave signatures of single rock joints filled with clayey soils. Particularly, for the kaolinite-filled rock joint, P-wave velocity and attenuation first increase and then slightly decline with the increasing water saturation. By contrast, for the bentonite-filled rock joint, an increase in water saturation causes gradual decreases in velocity and attenuation. The integrated interpretation of the experimental results indicates that the difference in heterogeneity saturation due to clay hydration is the first-order reason for the discrepancies in saturation-dependent P-wave attributes between kaolinite- and bentonite-filled rock joints. The findings of this study can help further understand wave propagation and attenuation across rock joints filled with fluid-saturated clayey soils. [ABSTRACT FROM AUTHOR]

Variations in soil radon concentrations are a potential precursor of earthquake and volcanic events. However, the unclear migration and variation mechanisms of radon concentrations in soil still limit its effective application. To elucidate the temporal variation and its possible influence factors on radon concentrations at different soil depths, a case study was performed at a suburban site in Beijing. A long-term continuous measurement system consisting of ten radon-in-soil monitors at depths from 0.1 to 5.0 m and other meteorological sensors was employed. The monitoring was carried out from January 8th to July 29th, 2022, covering 3445 h in total. Radon concentrations generally increased with soil depth. Diurnal variation of soil radon concentrations at depths of 1.2 and 1.6 m in winter and spring was observed, and a negative correlation between the soil radon concentration and the residual air pressure was found. This finding indicates a possible air exchange channel between the soil and the atmosphere at the study site. In addition, the soil radon concentration at 4.0 m depth was unexpectedly lower than that of neighboring depths and was steady throughout the measurement period. This is attributed to a possible clay layer in the soil structure at 4.0 m depth. The results of this field study indicate that the complexity of temporal variation of soil radon concentrations should be considered for its application in predicting earthquake and volcanic events. • Continuous monitoring of radon concentrations in ten soil depths to 5.0 m. • Bi-periodic diurnal variation of radon concentrations at 0.8–3.0 m depth. • Negative correlation between radon concentration and air pressure. • Air exchange channel between soil and atmosphere might exist. [ABSTRACT FROM AUTHOR]

Biocementation is a low carbon footprint soil improvement technique alternative to the use of hydraulic binders such as cement, mainly applied in sandy soils due to the need for vital room for bacteria and easy access for nutrient transport to feed them. This treatment is not suitable for natural clayey soils, however pore clogging caused by the presence of clay in low percentages may not be a problem, and clay minerals can be beneficial to increase the area for bacteria to attach and therefore to precipitate larger quantities of biocement. In addition, clay minerals can also have a positive influence on bacteria activity itself, and this is the novelty of this investigation. The influence of kaolin and bentonite clays on biocementation using Sporosarcina pasteurii was measured by (i) the amount of calcium carbonate precipitated in sandy soil prepared with known percentages of the two clays (1%, 5%, 10% and 20% in dry sand mass), relating it with unconfined compression strength, and (ii) evaluating bacteria growth and urease activity in liquid media with 1% and 5% of each clay. The best enhancement of biocementation was found for kaolin percentage between 5% and 10% and for 5% of bentonite, considering as reference the case where no clay was added. These relatively small percentages were linked to physical aspects related with the room occupied by the clay minerals causing dispersion of the precipitate in the clay matrix, although the presence of clay in the fluids of soil voids could contribute positively for bacteria growth and long-term survival. These results confirm that biocementation treatment may be effective on soils with relatively small clay percentages and opens the possibility that clay can be used in controlled fixed amounts to improve the efficiency of this treatment in clean sands. • The positive influence of clay on bacteria growth was confirmed by optical density measurements. • Urease activity measurements along time showed that clay minerals contribute to bacteria survival. • Kaolin can be more beneficial to biocementation than the bentonite. • The clay presence only becomes a negative influence above 5% for bentonite and 10% of kaolin. • Highest strength increment and calcium carbonate content were found for 5% of bentonite and 5% to 10% of kaolin. [ABSTRACT FROM AUTHOR]

Despite numerous individual studies evaluating the impact of straw return on soil organic carbon (SOC) stock in upland wheat and maize croplands in China using no-tillage (NTS), rotary tillage (RTS), and deep tillage (DTS) practices, the results have shown inconsistency. In addition, several factors influence the effects of various tillage practices with straw return on SOC stock that are not well understand. In this study, we conducted a meta-analysis of 764 comparisons to determine the combined impact of SOC stock in the topsoil (0–20 cm) and subsoil (20–40 cm) layers, while considering factors such as climate conditions, management practices, and initial soil properties. The results indicate that straw return with different tillage practices significantly improved SOC stock in both soil layers compared to straws removal. The increase in topsoil SOC stock was nearly identical for NTS (7.38 %) and DTS (7.17 %), compared to the RTS. However, the increase in subsoil SOC stock was significantly higher for DTS (28.8 %). According to subgroup analysis, NTS has been more effective in increasing topsoil SOC stock in regions with medium temperature (10–15 °C) and low precipitation (<400 mm), when used in a single cropping system. However, in regions with higher temperature (>15 °C) and precipitation (>800 mm), DTS is more effective in increasing SOC stock in both topsoil and subsoil layers in a double cropping system. Long-term (11–20 years) DTS resulted in a significant increase in SOC stock in the topsoil (19.2 %) and subsoil (18.5 %), while the increased effects of NTS on SOC stock were only in topsoil layer (17.1 %). The effects of straw return on SOC stock were also found to be associated with soil texture, with NTS having a greater impact on sandy to loam soils, and DTS having a greater impact on clay soils. Furthermore, a significant (P < 0.01) positive linear relationship was observed between annual carbon (C) input and SOC sequestration in the topsoil under NTS, as well as in both soil layers under DTS. These findings have important implications for enhancing SOC in Chinese upland wheat and maize cropland soils through optimizing straw return, given that more than 518 million tons of crop straw are produced annually. • Effect of straw return and different tillage practices on SOC stock was analyzed. • Topsoil SOC stock increased more in NTS than RTS in semi-arid regions. • DTS has greater effects on subsoil SOC stock than RTS and NTS. • C inputs contribute to SOC accumulation in topsoil and subsoil layers. [ABSTRACT FROM AUTHOR]

• Nematode abundance increased with aggregate size. • Soil type shifted nematode community composition by aggregate size. • Clay soils fostered more k-strategist nematodes compared to silt-loam soils. • Tillage had no impact on nematode distribution by aggregate size. • Predator-prey dynamics drive soil C accumulation in larger aggregates. Soil aggregates are critical for soil carbon (C) sequestration and serve as a habitat for microorganisms, including free-living nematodes. Yet, the interactions between nematode community composition and soil C cycling across aggregate fractions is rarely assessed. The objectives of this study were to 1) determine how soil type alters nematode community dispersal across aggregate fractions, 2) understand how soil type may alter the relationship between nematode communities and labile C pools, and 3) assess the impact that tillage intensity has on nematode community assemblage across aggregate fractions. Soil cores were taken at two identical long-term trials located in Ohio (silt loam vs. clay). Each trial compared two different tillage intensities (chisel till vs. no-till). Soils were fractionated into three aggregate fractions (>2000 μm, 2000–250 μm, and <250 μm). For each fraction, nematode communities were identified to feeding group and permanganate oxidizable carbon (POXC) was measured. Results indicated that silt loam soils had greater bacterivore nematodes in the >250 μm aggregate fraction (p < 0.05) and relatively lower predator-omnivore nematode proportions when compared to clay soils. Tillage did not have a significant effect on nematode feeding groups. Correlation analyses revealed that predator-omnivore nematodes and POXC were positively correlated in clay soils, but only in the largest aggregate fraction (p < 0.05). Bacterivore nematodes were positively correlated with POXC in clay soils but negatively correlated in silt loam soils (p < 0.05). These findings reveal that predator-prey dynamics likely drive soil C accumulation in larger sized aggregates. Moreover, shifts in nematode community composition by soil type demonstrates how inherent properties influence soil food web structure and ultimately, soil C cycling. [ABSTRACT FROM AUTHOR]

• Weathering paths and soil depth serve as a first order control of soil organic carbon. • Soil deeper than 100 cm, can store significant portions of the total SOC stock. • SOC stock and poorly crystalline mineral concentrations peak in soil <30 cm at 30 kyr. Characterizing the distribution and dynamics of organic carbon in soil is critical for quantifying changes in the global carbon cycle. In particular, weathering controls on near-surface and deep (>1 m) soil organic carbon (SOC) dynamics have been proposed but limited data prevents us from predicting SOC over topographically complex landscapes and quantifying how changes in climate and perturbations, such as wildfire or land management, influence SOC stocks. To advance our understanding of how weathering alters soil geochemistry and influences SOC storage, we synthesize previous data with a new analysis of the Siuslaw River soil chronosequence from terraces in the Oregon Coast Range, a region that harbors the richest SOC inventories in the continental US. We analyze how the relationships between soil geochemistry, physical properties, and SOC storage vary with weathering status and pathways across soils that span 0.041 to 990 kyr and vary in depth from 1 m to >10 m. To distinguish the key properties and processes influencing SOC storage at different depths, we break our analysis into three depth intervals: 0–30, 30–100, and >100 cm. Our results suggest that the processes that control SOC stocks vary systematically with time and depth owing to weathering impacts on soil properties and pedogenic development. At 30 kyr we observe a peak in SOC stock in the top 100 cm coincident with a peak in oxalate extractable Al and Fe concentrations, representing secondary poorly crystalline minerals, which is consistent with previous studies. We also observe a decline in shallow SOC stock for >30 kyr soils as poorly crystalline minerals are replaced by more stable crystalline forms and soils become clay dominated. At 120 kyr, SOC below 100 cm starts to contribute significantly to the total SOC profile inventory and by 990 kyr, this fraction composes >40% of the total SOC stock. Taken together, our results indicate that total SOC stock increases with soil age as the increased intensity of bedrock weathering deepens the critical zone, creating accommodation space for deep SOC storage. These findings reveal the intimate link between poorly crystalline minerals and SOC and suggest that systematic analysis of soil development in the critical zone provides a first-order constraint on SOC stocks. [ABSTRACT FROM AUTHOR]

• Manure had little effect on water vapour sorption isotherms (WSIs) in clayey soil. • Improvement in soil WSIs by manure varied with crop type in silty and sandy soils. • Permanent grass had the most positive effect on soil WSIs. • Improvement in soil WSIs by crop rotation varied with soil texture. • Multiple linear regression models based on soil properties well estimated WSIs. Increasing studies indicate that long-term experiments (LTEs) involving manure application and optimal cropping systems can significantly improve soil physicochemical properties, which may also affect the soil water retention curve (WRC) in the wet region (pF < 4.2). However, few studies have explored the effect of long-term manure application and cropping systems on soil WRC in the dry region (water vapour sorption isotherms, WSIs) (pF > 4.2) as well as the associated soil physicochemical properties. To overcome this knowledge gap, we investigated the effect of long-term manure application (24 to 177 years) and different cropping systems (71 to 82 years) on soil organic carbon (SOC) content, WSIs, hysteresis, and specific surface area (SSA). Soil samples were collected from five long-term manure experiments in Sweden, the United Kingdom, Spain, Germany, and Denmark, and two long-term cropping systems experiments in the United Kingdom. The five manure LTEs comprised three soil textures (silty clay, silt loam, and sandy loam) with one to four crops grown in the fields, including wheat, barley, maize, and grass/clover. The cropping system LTEs comprised silt loam and sandy loam including bare fallow (BF), arable rotation, ley–arable rotation, and permanent grass. Results showed that long-term manure application increased SOC content in each site, but it had little effect on the soil WSIs, hysteresis, and SSA in silty clay soils. The changes of soil WSIs, hysteresis, and SSA in silt loam and sandy loam arising from manure application largely depend on the crops grown in the field. For the long-term cropping systems experiments, permanent grass had the most significant effect in increasing SOC content, soil WSIs in silt loam and sandy loam, and hysteresis and SSA in silt loam compared to other treatments. Compared to BF, arable rotation and ley-arable rotation had no effect on SOC and soil WSIs in silt loam, and on hysteresis and SSA in silt loam and sandy loam. Multiple linear regression models including SOC, clay, and silt contents sufficiently explained the variabilities observed in the soil WSIs, hysteresis, and SSA for both manure and cropping systems LTEs. [ABSTRACT FROM AUTHOR]

Temperature has a significant effect on the bulk electrical conductivity (σ b) of soils because fluid properties, such as viscosity, which affect σ b , are functions of temperature. The governing mechanisms between pore water conduction (K w) and surface conduction (K s) in terms of temperature dependency are completely different. Thus, soils with a higher relevance of K s can exhibit a different temperature dependency of σ b when compared to K w -dominant soils. Therefore, in this study, we aim to determine the temperature compensation parameter (α) of σ b of soils as a function of the ratio of K s to σ b. Silica sand and kaolin clay were selected as the K w - and K s -dominant materials, respectively. The electrical conductivity of tested materials with varying initial porosities and pore fluid concentrations was measured as a function of temperature in the range of 10 °C to 50 °C. The results of this study showed that K w -dominant soils have an α value of approximately 2%/°C, whereas the α value of K s -dominant soils ranges from 1%/°C to 2%/°C as a function of porosity and pore water conductivity. The experimentally determined α value was compared with the α value calculated from the theoretical series–parallel model. Additionally, an empirical model to capture the α value of soils with varying magnitudes of K s and K w was suggested. Finally, the suggested model was verified using the results of Korean residual soil (i.e., clayey sand) and two other clayey soils (i.e., kaolin and ca-bentonite clays). • Electrical conductivity (EC) of sand and clay was measured according to temperature. • Experimental results were compared with the theoretical series-parallel model. • Surface conduction-dominant soils show different temperature dependency of EC. • A model for temperature compensation parameter is newly suggested. • The suggested model accuracy was verified using the data of other three soils. [ABSTRACT FROM AUTHOR]

In a piled raft foundation, the stresses applied on the soil from the raft and piles overlap, which leads to changes in the settlement and bearing capacity of the raft and each individual pile. In this numerical study, settlement-dependent variation of three interaction factors, namely piles-to-piles (P-P), raft-to-piles (R-P), and piles-to-raft (P-R) have been investigated for large piled raft in stiff clay. The unpiled raft is flexible, the piles are friction piles and the effects of pile number, spacing and length on these interaction factors are presented. The P-P factor increases and then tends to become constant at a certain settlement. In contrast, the R-P factor always shows an increasing trend with settlement. However, the P-R interaction factor initially decreases and then increases with settlement. At the final settlement equal to 0.35% of raft width, the P-P, R-P, and P-R interaction factors range from 0.95 to 1.10, 0.86–1.04, and 0.25–0.92, respectively. Predictive equations have been proposed for these interaction factors and thereby determine the load-sharing ratio and mobilized safety factor. Within the allowable settlement range satisfying the serviceability limit, a good agreement between the results obtained from predictive equations and the finite element analyses is demonstrated for different piled raft configurations. • Three-dimensional finite element modeling of large piled rafts in clay. • Effects of pile number, spacing, and length on piled raft interaction factors. • Predictive equations for the interaction factors at any settlement level. • Predictive equations for load-sharing ratio and mobilized safety factor. [ABSTRACT FROM AUTHOR]

Upon completion of the operation on a site, spudcan foundations are pulled out of the seabed before relocating the jack-up platform to another candidate site. It is critical to predict the peak extraction resistance before commencing the jack-up extraction. Though sand-over-clay seabed is commonly found in active marine oil and gas exploration zones, the models for estimating the extraction resistance are very rare. This paper proposes a Bayesian prediction model based on 51 groups of centrifuge tests on foundations extracting from sand overlying clay soils. Model factors are introduced to define the uncertainties in the prediction. Combined with the monitored data during foundation extraction, possible breakout range of resistance and depth is predicted and updated in real time. The most likely breakout resistance and depth in the area are also estimated. The results show that (1) the predicted range of breakout resistance and depth may occur are concentrated around the measured values with the update of the monitored data; (2) the relative error between the most likely breakout depth and the measured value is kept within 10%; and (3) regardless the shape of the foundation, the Bayesian prediction model can effectively predict the extraction behaviour of the foundation. • The breakout resistance and depth for spudcan foundations extracting from sand-over-clay soils are predicted in real time. • The range of the predicted results concentrates to the measured breakout resistance and depth with increasing monitored data. • The relative error of the predicted breakout depth and resistance are within 10% and 20%, respectively. • The proposed method provides a powerful tool for the engineer for timely and safely extraction of jack-up foundations. [ABSTRACT FROM AUTHOR]

• Adhesion behavior of clayey soils are investigated through experimental tests. • Adhesion increases firstly and decreases thereafter with increasing water content. • Clay fraction and mineralogical composition significantly influenced the adhesion. • The updated semi-empirical diagram considering compositional factors is proposed. Clogging is common for tunnel boring machines, especially in clayey soil, and when it happens, the cutter heads or even the entire tunnelling device can become completely clogged, causing low excavation efficiency and high project costs. Because clogging stems from the adhesion of the excavated geomaterials, a better understanding of soil adhesion is required if clogging is to be avoided. Reported here are piston pull-out tests conducted to investigate the adhesion of natural clayey soils and artificial soils prepared using pure kaolin, montmorillonite, and silica sand, thereby enabling consideration of the effects of compositional factors (e.g., clay fraction, and mineralogy). The results show that with increasing water content, the adhesion stresses of the studied samples increased initially and then decreased. With increasing clay fraction, the adhesion stresses increased linearly because of the larger real contact area of the interface between the soil and a foreign object. With the addition of montmorillonite, the soil adhesion also increased significantly because of its microstructural properties. An updated semi-empirical diagram is proposed that allows the effects of compositional factors on clogging potential to be evaluated qualitatively. The measured maximum adhesion stresses of the studied samples occurred in the region of strong clogging in the semi-empirical diagram, showing the feasibility of using adhesion stress as an index for assessing the clogging of tunnel boring machines. This study provides valuable experimental data on soil adhesion and a better understanding of the adhesion behavior of clayey soils. [ABSTRACT FROM AUTHOR]

In this study, field-scale experiments were carried out to analyze the coupling effects of typical agronomic measures and soil types on soil antibiotic resistance genes (ARGs) using high-throughput fluorescence quantitative PCR. The results indicated that agronomic measures enhanced ARG abundance in different soil types. For the same soil type, the enhancement of ARG abundance in response to agronomic measures could be ordered as follows: livestock manure application (257.6–131.7 %) > sewage irrigation (57.6–35.0 %) > plastic film mulching (21.2–5.0 %). Under the same agronomic measures, enhancement of ARG abundance according to soil type was: clay (257.6–21.2 %) > loam (147.8–15.9 %) > sandy (131.7–5.0 %). Furthermore, the contributions of environmental factors in determining ARG abundance in different soil types differed in response to the application of different agronomic measures. Phthalates had the most and least pronounced effects on ARG abundance in sandy and loam soils, respectively. Effects of moisture on ARG abundance were minor in loam soil, but greater in clay and sandy soils. These findings provide new insights into the dissemination of soil ARGs promoted by the adoption of agronomic measures. • Under same measure, soil resistance gene abundance was in order: clay > loam > sandy. • Effects of phthalates on resistance genes in soils were in order: sandy > clay > loam. • Effects of moisture on resistance genes in soils were in order: sandy and clay > loam. [ABSTRACT FROM AUTHOR]

Current electro-osmotic consolidation theories and numerical models usually ignore the variation of chemical fields and are applicable to soft clay soils with a single chemical composition. In this paper, a numerical model, called EC4, is presented for one-dimensional large strain electro-osmotic consolidation with coupled electrical-hydro-chemical fields. The algorithm accounts for non-linear variation of soil parameters, ion transport and a variety of chemical reactions, including ionization-neutralisation reactions, ion adsorption–desorption reactions and electrolytic water reactions at electrodes. The laboratory electro-osmotic consolidation tests on kaolin samples with different NaCl concentrations were conducted. The laboratory results were used to verify the accuracy of EC4. Then EC4 was implemented to example problems to investigate the effect of important chemical characteristics on the electro-osmotic consolidation. The effects of electrical voltage and initial pH on settlement, degree of consolidation, excess pore pressure and energy consumption of multi-field coupled electro-osmotic consolidation were further analyzed. [ABSTRACT FROM AUTHOR]

A model for the one-dimensional consolidation of saturated clayey soils, considering creep, is proposed, based on the consolidation mechanism idealized by Terzaghi (1941). The effective vertical stress is divided into two parts: one corresponding to the "solid" contacts, and other relating to the "viscous" contacts, the void ratio changes being caused by variations solely in the solid portion. Based on experimental evidence, a non-linear viscosity law was adopted, described by a hyperbolic function, in addition to its dependence on the void ratio. The resulting differential equation system is solved through the Finite Difference Method. The main "secondary effects of time" – experimental deviations from the classical Terzaghi (1925) theory – were able to be reproduced using the model, as well as experimental results that support other categories of consolidation models, such as the isotache- and C α / C C -based models. A good fit was obtained for the results of long-term laboratory tests in clays from different parts of the world that reached the end of secondary consolidation. A good prediction was also reached for the evolution of settlements from the experimental embankment on the soft soils of Lilla Mellosa, monitored since 1947 in Sweden. [ABSTRACT FROM AUTHOR]

The expansion of sugarcane (Saccharum spp.) over extensive pasture areas has been one of the primary land-use change (LUC) scenarios in central-southern Brazil. However, LUC could negatively affect soil fauna along with the multiple functions and services associated with these organisms. Numerous groups of macroinvertebrates inhabiting the soil surface (i.e., epigeic) or the soil profile (i.e., edaphic) are fundamental for litter fragmentation, soil structuring and stabilization, water infiltration, biogeochemical cycling. In this study, both the edaphic and epigeic macrofauna communities were surveyed simultaneously to assess responses induced by the expansion of sugarcane cultivation over extensive pastures and to investigate whether the magnitude of such responses to LUC differs according to the community niche (i.e., soil profile versus surface). We hypothesized that LUC to a semi-perennial crop such as sugarcane would increase the density and diversity of the edaphic macrofauna, while the epigeic community would be negatively affected by LUC due to drastic changes in surface litter. The studied areas were two sites varying in soil texture (i.e., clay versus sandy soils) each including the following land uses: i) native vegetation, ii) extensive pasture, iii) newly planted sugarcane crop (sugarcane); and iv) established sugarcane (sugarcane ratoon). To evaluate edaphic macrofauna the TSBF methodology was adopted, while pitfall traps were installed at the same sampling points to collected epigeic macrofauna. The evaluated community attributes were density, Shannon diversity index, evenness index, richness of soil macrofauna taxa, as well as the chemical and physical attributes of the soil. Linear mixed effects analysis showed that LUC affected the relative abundance of edaphic (Land use p = 0.1191 r2 marginal = 0.28, r2 conditional = 0.33) and epigeic (Land use p = 0.0176; r2 marginal = 0.22, r2 conditional = 0.32) macroinvertebrates. Both groups showed the greatest density of organisms under native vegetation. Coleoptera and earthworms were associated with pasture areas, especially in clayey soil. Response ratios of LUC effects on macrofauna showed stronger responses of the epigeic compared to edaphic macrofauna, indicating a greater sensitivity of surface-dwelling organisms and their functions to disturbances such as those caused by LUC. In general, the density and diversity of macrofauna exhibited a positive correlation with soil organic matter, microbial carbon and nitrogen, macroporosity, and total porosity, and a negative correlation with soil density (p < 0.05). Also, the conversion of pasture to sugarcane cultivation (planting) causes significant macrofauna losses, particularly, in the clay soil. The cultivation of ratoon sugarcane led to a reduction of the density, taxonomic richness, diversity, and evenness of macrofauna. Given the importance of epigeic macroinvertebrates for litter fragmentation and decomposition, these results may indicate a rapid loss of key soil functions related to decomposition and carbon and nutrient cycling following LUC. [Display omitted] [ABSTRACT FROM AUTHOR]

Liming with 'structure lime', comprising approximately 80–85% ground limestone and 15–20% slaked lime, has been promoted in subsidised environmental schemes in Sweden since 2010 to increase clay aggregate stability and mitigate particulate phosphorus losses to surface waters. To date, approximately 65,000 ha have been structure-limed. Apart from stabilising aggregates, liming may also improve other physical properties, such as soil strength. This study examined the effect of increasing application rate (0–16 t ha-1) of structure lime on soil strength, approximated by horizontal (draught requirement) and vertical (penetrometer resistance) measurements, in eight field soils (clay content 26–38%) to which structure lime had been applied two, three, four or six years previously. Draught requirement when cultivating with a multipurpose cultivator significantly decreased (by 11%) with the highest application rate of structure lime (16 t ha-1) compared with an unlimed control. This reduced the wheel power requirement by 7.1 kW and diesel consumption by 1.2–1.4 L ha-1, and lowered CO 2 emissions by 3–4 kg ha-1. To clarify the general effect of structure liming, the mean value of all limed treatments was compared with that of the unlimed control. This showed that structure liming in general significantly reduced the draught requirement (by 7%). However, penetrometer resistance measurements revealed no significant effects of structure liming and no relation between draught requirement and penetrometer resistance measurements. Overall, the results indicate that structure liming can reduce fuel consumption, due to easier soil tillage, and thus lower CO 2 emissions. • Cultivator draught requirement was measured in structure limed field trials. • A towing eye with sensors that can measure forces in three directions was used. • Structure liming reduced horizontal draught requirement by 7%. • Reductions corresponded to decreases of 1.2–1.4 L diesel ha-1 and 3–4 kg CO 2 ha-1. • Structure liming did not affect penetrometer resistance in this study. [ABSTRACT FROM AUTHOR]

• We examine how sampling methods affect detecting inorganic N in 21 soils. • In situ microdialysis sampled proportionately less ammonium than soil extractions. • Ammonium was highest in salt extracts and correlated with soil properties. • Nitrate was correlated across methods implying minimal impact by disturbance. • Measurement of inorganic N is biased by methods-related soil disturbance. Measuring soil nitrogen (N) provides important information for ecosystem productivity and improving N use efficiency in agricultural systems. Conventional means of sampling N using soil extractions disturb soil structure and function, and likely distort accurate quantification. In situ microdialysis is a novel sampling method that generates differing N profiles compared to soil extractions. Here we test the hypothesis that differences observed between sampling methods are due to the minimal disturbance and sampling of a mobile N fraction when using microdialysis, with discernible patterns expected across soils with distinct clay and organic matter contents. In a short-term laboratory microcosm experiment with 21 sugarcane cropping soils, we compared salt (potassium chloride; KCl) or aqueous (H 2 O) extractants and microdialysis. KCl-extractable ammonium (NH 4 +) was highly correlated with the content of clay, total N and carbon, indicative of bound N being solubilised. In contrast, NH 4 + contributed significantly less to microdialysis fluxes and was not correlated with the measured soil properties, which we attribute to minimal disturbance of bound N·H 2 O extracts sampled proportionally more NH 4 + than microdialysis but were significantly correlated with fluxes. This suggests that while microdialysis and H 2 O extraction sample from a dissolved N pool, H 2 O extracts sample from an additional pool of loosely-bound NH 4 +. Nitrate (NO 3 −) measures were correlated between methods, but shared no relationship with the measured soil properties, indicating that NO 3 − sampling is less affected by the disturbance introduced by extractions. We conclude that sampling inorganic N is biased by the degree to which soil sampling methods disturb adsorbed N sources with implications for interpreting soil N measurements. [ABSTRACT FROM AUTHOR]

[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]

• Saltation bombardment is a main pattern of dust emission for compacted soils. • Wind tunnel was used to simulate the abrasion of compacted soils by blown sand. • Dust emission efficiency was positively correlated with the amount of abrader. • Clay and silt contents of soils had different influences on dust emission efficiency. • An integrated model of dust emission efficiency for compacted soils was established. Abrasion by blown sand is a main wind erosion process for compacted soils, such as dry lake basins and the undisturbed grassland that are widely distributed in arid land. Dust emission efficiency (δ) is defined as the ratio of the dust flux to the sediment transport rate from a soil surface. Previous studies mostly focused on the influence of wind velocity or soil properties on δ and rarely considered the amount of abrader in blown sand; furthermore, most of their experiments used loose soils involving three physical mechanisms of dust emission. In this study, we explored the mechanism of dust emission from compacted soils caused by saltation bombardment of the abrader making use of wind tunnel experiments and using the mass flux of the abrader (q) to represent the abrasion intensity of blown sand. The results showed that dust flux (F) generated from the compacted soil by abrasion and bombardment was linear with q , and δ was always positively correlated with q and with the silt and clay content in soils. Taking into account both the amount of abrader and the texture of the soil being abraded, we proposed and validated a model of dust emission efficiency for compacted soil. [ABSTRACT FROM AUTHOR]

• Effect of salinity in grout on the performance of soilcrete was evaluated. • Seawater has no effect on long-term UCS of soilcrete contains inactive clays. • In active clay at cement <15 %, curing time had a negative effect on the strength. • The change in LL and UCS with salinity is similar. S oil-cement columns created by the injection of grout into the soil are common in practice for stabilizing soft soil in coastal areas. The behavior of clay-cement under marine conditions, especially considering the effect of both the clay mineral type and water salinity, has been less considered. The current study investigated the effects of high salinity grout on the mechanical and the physical behavior of cement-stabilized marine clay at a range of cement contents and water-to-cement ratios. The performance of the cement-stabilized marine clay was compared with those of kaolinite as an inactive clay and bentonite as an active clay. The results showed that, when saline water was used in the soil–cement mixtures containing kaolinite or marine clay, there was no decrease in strength and the cement content had no effect on the results. For active bentonite at 5% and 10% cement contents, the curing time had a negative effect on the strength; over time, the strength of the mixtures decreased. In practice, there should be no concern about the use of saline water to create grout at cement contents greater that 15%. However, if the clayey soil contains active minerals, a cement content of less than 15% is not recommended. [ABSTRACT FROM AUTHOR]

• A meta-analysis to test rubber stand age and altitude effects on soil properties. • Forest-to-rubber conversion significantly reduced SOC pools by 24%. • Rubber monoculture-to-intercropping significantly increased SOC pools by 6%. • Improvement of intercropping occurred in 0–20 cm soil and at 500–800 m altitude. The rapid expansion of rubber plantations may have greatly influenced the carbon stocks of the ecosystem, with potential impacts on mitigating climate change and future carbon fluxes. Therefore, soil carbon pools and other properties must be reliably estimated after rubber-based land cover transitions. The aim of this meta-analysis is to understand how various land use changes based on rubber plantations affect soil physicochemical properties, especially soil organic carbon (SOC) pools. This study focuses on three land use changes: (1) forest-to-rubber conversion; (2) rubber monoculture vs. intercropping; and (3) the age and altitude of the rubber stand over a chronosequence in rubber plots. Results showed that the conversion of forest to rubber plantation significantly reduced the SOC, microbial carbon (MBC), total nitrogen (TN) and total magnesium pools by 24%, 35%, 13% and 94% respectively, whereas rubber intercropping with different crops profoundly increased the SOC and MBC pools by 6% and 24% on average, respectively. The improvement of rubber intercropping on SOC and properties mainly occurred in the surface soil at 0–20 cm and at altitudes of 500–800 m, but these effects were diminished in the subsurface soil at 20–60 cm and at altitudes higher than 800 m. Rubber intercropping plantations can significantly alleviate soil acidification. Changes in the response ratio of SOC were closely related to the variations in soil clay, bulk density, and C/N ratio. These results suggest that rubber-based land use management policies should promote intercropping plantations, especially those with woody plants, and the altitude of rubber planting should be manipulated to minimize the loss of soil C, N, and other nutrients. [ABSTRACT FROM AUTHOR]

The partitioning and migration of antibiotic resistance genes (ARGs) at the interfaces of soil, water, and air play a critical role in the environmental transmission of antibiotic resistance. This study investigated the partitioning and migration of resistant plasmids as representatives of extracellular-ARGs (eARGs) in artificially constructed soil-water-air systems. Additionally, it quantitatively studied the influence of soil pH, clay mineral content, organic matter content, and simulated rainfall on the migration of eARGs via orthogonal experiments. The findings revealed that the sorption equilibrium between eARGs and soil can be attained within 3 h, following the two-compartment first-order kinetic model. The average partition ratio of eARGs in soil, water, and air is 7:2:1, and soil pH and clay mineral content are identified as the main influencing factors. The proportion of eARGs migrating from soil to water and air is 8.05% and 0.52%, respectively. Correlation and significance analyses showed that soil pH has a significant impact on the soil-water and soil-air mobility of eARGs, while clay content affects the percentage of peaks during migration. Moreover, rainfall exerts a noticeable impact on the timing of peaks during migration. This study provided quantitative insights into the proportion of eARGs in soil, water, and air and elucidated the key factors influencing the partitioning and migration of eARGs from the perspectives of the sorption mechanism. [Display omitted] • The distribution ratio of eARGs in soil, water and air is 7:2:1. • The migration rate in soil-water and soil-air was 8.05% and 0.52%, respectively. • Soil pH dominates the soil-water/air migration rate of eARGs. [ABSTRACT FROM AUTHOR]