Search

Soil penetration resistance (SPR) is an important indicator for soil strength which not only affects the growth of crop roots and crop yield but also is crucial in the design and selection of agricultural machinery. The determination of SPR in the laboratory is complex and time-consuming, while measuring SPR on-site shows high uncertainty at different times and locations due to soil heterogeneity. Therefore, this paper investigated the impact of soil parameters on SPR for paddy soils in the plastic state and then established a simple regression model to predict SPR using easy-to-obtain soil physical properties, including clay content, water content and density. Using the combined approaches of central composition rotatable design (CCRD) with response surface methodology (RSM), SPR of 20 soil samples from five paddy fields were measured in the laboratory. The results from the experiments showed that the contribution rate of each single factor to SPR from high to low was soil density, clay content and water content. Statistical analysis for the established equation suggested that the p-value for goodness of fit was significant (p < 0.001) and the p-value for lack of fit was insignificant (p > 0.05); meanwhile, the coefficient of determination (R2) was 0.95, indicating that the model was effective in predicting the SPR. Subsequently, the performance of the regression model was validated by comparing the estimated SPR with in situ field measurements, which showed high accuracy, with percent errors within 10%. Our study successfully proposed a method to estimate SPR using easy-to-measure soil properties that could be obtained from sensors in the soil or field investigations, including soil clay content, water content and wet bulk density. [ABSTRACT FROM AUTHOR]

There are many studies related to using alkali activated binders for the improvement of clayey soil mechanical properties. In this study, alkali activated slag (AAS) for the improvement of clayey soil strength was used and it reinforced the clay. This paper presents results of an investigation on the utilization of ground-granulated blast-furnace slag in the reinforcement of clay soils. Therefore, significant cost savings could be achieved by using alkali activated slag as binding material. These samples were analyzed by X-Ray fluorescence analysis (XRF), X-Ray diffraction (XRD), scanning electron microscopy (SEM) and strength tests after the curing. The clay samples reinforced with AAS showed higher shear stress, cohesion and internal friction angle compared with the samples without reinforcement. The highest shear strength was achieved by using the highest amount of AAS (30%). This shear stress of the unreinforced clay samples could be increased from 63.2 to 137.4 kPa (117.4%) and from 123.2 to 257.4 kPa (108.9%) when the normal stress value of 100 and 500 kPa was used, respectively. The increase in shear strength is closely related to the compact contact zone between AAS and clay. Moreover, the new formed cementitious compounds of AAS had a positive influence on the shear strength of samples as well. [ABSTRACT FROM AUTHOR]

The number of sensors, ground-based and remote, exploiting the relationship between soil dielectric response and soil water content continues to grow. Empirical expressions for this relationship generally work well in coarse-textured soils but can break down for high-surface area and intricate materials such as clayey soils. Dielectric mixing models are helpful for exploring mechanisms and developing new understanding of the dielectric response in porous media that do not conform to a simple empirical approach, such as clayey soils. Here, we explore the dielectric response of clay minerals and clayey soils using the mixing model approach in the frequency domain. Our modeling focuses on the use of mixing models to explore geometrical effects. New spectroscopic data are presented for clay minerals (talc, kaolinite, illite and montmorillonite) and soils dominated by these clay minerals in the 1 MHz–6 GHz bandwidth. We also present a new typology for the way water is held in soils that we hope will act as a framework for furthering discussion on sensor design. We found that the frequency-domain response can be mostly accounted for by adjusting model structural parameters, which needs to be conducted to describe the Maxwell–Wagner (MW) relaxation effects. The work supports the importance of accounting for soil structural properties to understand and predict soil dielectric response and ultimately to find models that can describe the dielectric–water content relationship in fine-textured soils measured with sensors. [ABSTRACT FROM AUTHOR]

Deformations monitoring in airport runways and the surrounding areas is crucial, especially in cases of low-bearing capacity subgrades, such as the clayey subgrade soils. An effective monitoring of the infrastructure asset allows to secure the highest necessary standards in terms of the operational and safety requirements. Amongst the emerging remote sensing techniques for transport infrastructures monitoring, the Persistent Scatterers Interferometry (PSI) technique has proven effective for the evaluation of the ground deformations. However, its use for certain demanding applications, such as the assessment of millimetric differential deformations in airport runways, is still considered as an open issue for future developments. In this study, a time-series analysis of COSMO–SkyMed satellite images acquired from January 2015 to April 2019 is carried out by employing the PSI technique. The aim is to retrieve the mean deformation velocity and time series of the surface deformations occurring in airport runways. The technique is applied to Runway 3 at the "Leonardo da Vinci" International Airport in Rome, Italy. The proposed PSI technique is then validated by way of comparison with the deformation outcomes obtained on the runway by traditional topographic levelling over the same time span. The results of this study clearly demonstrate the efficiency and the accuracy of the applied PSI technique for the assessment of deformations in airport runways. [ABSTRACT FROM AUTHOR]

Simple Summary: Termitaria are nests of termites built from clayey soils. These nests can protrude to several meters high above the ground-surface. They serve not only as habitats for termites but also as foraging hotspots for grazing and browsing animals due to an increase in nutrient recycling that results in the growth of nutrient-rich vegetation around termitaria. There have been suggestions that a relationship exists between termitaria and groundwater due to the high demand of water by termite colonies for their nest building, to maintain high humidity and for their metabolism. However, few studies are available to directly or indirectly indicate this relationship. In this study, effort was made to investigate the direct relationship between termitaria and groundwater and to further answer the question on whether termitaria can indicate the presence of groundwater. A small parcel of land with a termitarium was selected for this study where nine resistivity soundings were made with one at the foot of the termitarium. The result obtained indicated a suitable geoelectrical signature around the termitarium and the integration of six geoelectrical parameters revealed the termitarium as falling in the middle of the most suitable zone of groundwater and hence can be used as a biomarker. Termite nests have long been suggested to be good indicators of groundwater but only a few studies are available to demonstrate the relationship between the two. This study therefore aims at investigating the most favourable spots for locating groundwater structures on a small parcel of land with conspicuous termite activity. To achieve this, geophysical soundings using the renowned vertical electrical sounding (VES) technique was carried out on the gridded study area. A total of nine VESs with one at the foot of a termitarium were conducted. The VES results were interpreted and assessed via two different techniques: (1) physical evaluation as performed by drillers in the field and (2) integration of primary and secondary geoelectrical parameters in a geographic information system (GIS). The result of the physical evaluation indicated a clear case of subjectivity in the interpretation but was consistent with the choice of VES points 1 and 6 (termitarium location) as being the most prospective points to be considered for drilling. Similarly, the integration of the geoelectrical parameters led to the mapping of the most prospective groundwater portion of the study area with the termitarium chiefly in the center of the most suitable region. This shows that termitaria are valuable landscape features that can be employed as biomarkers in the search of groundwater. [ABSTRACT FROM AUTHOR]

There has been a growing interest in polymer applied for soil reinforcement in recent years. However, there little attention has been paid to the effects of polymer on soil cracking behavior, and cracks significantly change soil strength and hydraulic properties and alter reinforcement effectiveness. This study investigated the desiccation cracking behavior of polyurethane (PU) and polyacrylamide (PAM) admixed clayey soils with different polymer concentrations by performing desiccation cracking tests. Scanning electron microscope (SEM) observation was also carried out to obtain the internal structure of these soils. The results show that PU and PAM addition both prolonged the initial evaporation stage, accelerated later evaporation processes, and the effects were related to polymer concentration. Final cracks morphology analyses show that PAM addition slightly reduced the cracking and crushing degree and kept the soil relatively intact, while PU addition slightly enhanced the cracking and crushing degree of soil. In addition, PU and PAM addition both increased the width and length of cracks. The scanning electron microscopy (SEM) analyses show that the effects of polymer on soil evaporation and cracking could be concluded as: (1) storing water in voids, (2) influencing water immigration channel, (3) providing space for soil shrinkage, and (4) enhancing the connection between aggregates, which did not fully come into play because of the existence of hydrogel form. These achievements provide a certain basis for the research of desiccation cracking behavior of polymer treated soil and make significant sense for the safe and effective running of related projects. [ABSTRACT FROM AUTHOR]

The research study described in this paper investigated the potential to use steel furnace slag (SFS) as a stabilizing additive for clayey soils. Even though SFS has limited applications in civil engineering infrastructure due to the formation of deleterious expansion in the presence of water, the free CaO and free MgO contents allow for the SFS to be a potentially suitable candidate for clayey soil stabilization and improvement. In this investigation, a kaolinite clay was stabilized with 10% and 15% ladle metallurgy furnace (LMF) slag fines by weight. This experimental study also included testing of the SFS mixtures with the activator calcium chloride (CaCl2), which was hypothesized to accelerate the hydration of the dicalcium silicate phase in the SFS, but the results show that the addition of CaCl2 was not found to be effective. Relative to the unmodified clay, the unconfined compressive strength increased by 67% and 91% when 10% and 15% LMF slag were utilized, respectively. Likewise, the dynamic modulus increased by 212% and 221% by adding 10% and 15% LMF slag, respectively. Specifically, the LMF slag fines are posited to primarily contribute to a mechanical rather than chemical stabilization mechanism. Overall, these findings suggest the effective utilization of SFS as a soil stabilization admixture to overcome problems associated with dispersive soils, but further research is required. [ABSTRACT FROM AUTHOR]

Predictive models able to provide a reliable estimate of hydraulic conductivity can be useful in various geotechnical applications. Since most of the existing predictive methods for saturated hydraulic conductivity estimation are valid only for a limited range of soils or can be applied under certain restrictive conditions, a new method applicable to clayey soils and clayey or silty sands having a wide range of values of soil index properties is proposed in this study. For this purpose, 329 saturated hydraulic conductivity values, obtained by laboratory tests carried out on different soils, were collected in a database and used to develop five equations using a multiple regression approach. Each equation correlates the hydraulic conductivity with one or more geotechnical parameters. An equation was developed that predicts, within an order of magnitude, the saturated hydraulic conductivity in the range from 1.2 × 10−11 to 3.9 × 10−6 m/s, based on simple geotechnical parameters (i.e., clay content, void ratio, plastic limit, and silt content). [ABSTRACT FROM AUTHOR]

This experimental laboratory study examines the potential use of tire-derived aggregate (TDA) products as an additive to alleviate the inferior geotechnical properties of a subgrade deposit of clay soil with high expansivity. A total of ten mix designs—the unamended soil and nine soil–TDA blends prepared at 5%, 10% and 20% TDA contents (by dry mass) using three different TDA gradations/sizes—were examined. The experiments included standard Proctor compaction, oedometer swell and unconfined compression tests. The TDA materials' lower specific gravity, hydrophobic character and higher energy absorption capacity compared with the soil solids led to notable reductions in the soil compaction characteristics. The amendment of the soil with TDA resulted in notable decreases in the rate and magnitude of swelling—the observed reductions were in favor of higher TDA contents, with larger TDA particle size being a secondary factor. Further, for any given TDA size, the variations of strength and toughness with respect to TDA content exhibited rise–fall relationships, peaking at 5% TDA and then decreasing for higher TDA contents. The stiffness and ductility parameters, however, were found to monotonically decrease and increase with the TDA content, respectively. Finally, TDA contents of up to 10%, with gradations equivalent to those of medium and coarse sands, were found to reduce the soil's swelling potential from high to moderate expansivity, while simultaneously improving its strength-related features, and thus can be deemed as optimum mix design choices from a geotechnical perspective. [ABSTRACT FROM AUTHOR]

The small deformation of the model pile in a pile jacking test makes its accurate measurement very difficult. Based on the installation method of clamping at both ends, a sensitized miniature fiber Bragg grating (FBG) strain sensor was developed to measure the pile strain of small-size model piles. This study investigated the working principle of the sensitized miniature FBG sensor and analyzed the strain transfer characteristics of the sensor by calibration test. The lateral resistance and the earth plug resistance of the model pile were measured accurately by the grooves embedded in the outer tube of the double-wall opening model pile and the sensors directly pasted on the surface of the inner tube. The results of this study show that the sensitized miniature FBG strain sensor has the advantages of high sensitivity, strong interference resistance, and high test accuracy. The FBG strain sensor was completely fixed on the pile by clamping supports at both ends, and the strain measured using the FBG strain sensor was found to be consistent with the pile deformation. [ABSTRACT FROM AUTHOR]

Soil physical and chemical properties play a central role in plant growth, influencing the availability of air, nutrients, and water. The aim of this two-year study was to evaluate the effect of soil texture and chemical properties (pH, electrical conductivity, organic carbon, organic matter, total, and active lime) on saffron (Crocus sativus L.) growth, yield, and quality. Corms were planted in pots filled with seven different soil textures obtained mixing an increasing quantity (33% and 66%) of sand to a clay soil (S1) and to a clay loam soil (S2) compared to a full (100%) sandy soil as a control (S7). A randomized complete block design comprising of seven pots with different types of soil (S1, S2, S3, S4, S5, S6, and S7) replicated three times was used. The results showed that the highest flower number (320.3 n m−2), stigma yield (2.0 g m−2), daughter corm production (7.9 kg m−2), and horizontal diameter (3.1 cm) were derived from S3 and S4 soils. These were characterized by a loam and sandy-loam texture, not very calcareous, with a sub-alkaline and neutral pH, low electrical conductivity, a content of organic matter between 5.46 and 8.67 g kg−1, and a content of active lime between 21.25 and 26.25 g kg−1. According to International Organization for Standardization (ISO) references, although all spice samples belonged to the first qualitative category, S1, S3, and S2 soils recorded the highest value for coloring power (290.5, 289.1, and 287.6 A1%1cm 440 nm, respectively). The highest values of bittering (109.2 A1%1cm 257 nm) and aromatic (26.6 A1%1cm 330 nm) power were reached by S3 soil. Positive correlations were found both between color with clay and organic matter, and aroma with total calcium carbonate. In conclusion, the assessment of soil conditions is particularly important to obtain the best saffron performance in terms of stigma and daughter corms yield as well as spice qualitative traits. [ABSTRACT FROM AUTHOR]

In order to have a better understanding of the real contact area of granular materials, the white light interference method is applied to explore the real surface morphology of clay soils under high stress. Analysis of the surface profile indicates that there exists a support point height z0 with the highest distribution frequency. A concept of a real contact region (from z0 to z0 + d90; d90 represents the particle size corresponding to 90% of the volume fraction) is proposed by combining a surface profile with the particle size distribution of clay soil. It was found that under the compressive stress of 106 MPa–529 MPa, the actual contact area ratio of clay soil varies between 0.375 and 0.431. This demonstrates an increasing trend with the rise of stress. On the contrary, the apparent porosity decreases with an increasing stress, varying between 0.554 and 0.525. In addition, as the compressive stress increases, the cumulative frequency of apparent profile height (from z0 − d90 to z0 + d90) has a concentrated tendency with a limited value of 0.9. [ABSTRACT FROM AUTHOR]

The influence of suction on the mechanical behaviour of unsaturated chemically stabilised soils is still mostly unknown and unquantified. This is also motivated by the difficulties associated with the experimental procedure required to fully characterise the unsaturated response of the soil, including its direct influence on traditional strength tests. The present paper presents the soil water retention curves obtained for a Portuguese soil before and after being stabilised with Portland cement (OPC) and an alkali-activated cement (AAC). Saturated undrained triaxial tests were also performed for the same curing conditions (0, 28, and 90 days). Previous attempts to characterise the retention curve of soils stabilised with AAC are unknown, and the results showed that the pore volume structure is already formed after 28 days, prior to the full development of the gel matrix responsible for the strength increase between 28 and 90 days. The curve changed after stabilisation, and with each binder, as the OPC presented a higher air-entry value and a narrower suction range compared to the AAC solution. The significant differences between the curves obtained from each binder suggest the future development of a methodology to assess the quality of the AAC stabilisation. [ABSTRACT FROM AUTHOR]

The long term effects of applying livestock manures as soil amendment are well known. However, these manures usually contain high soluble salts content, which could increase the soil salinity and sodicity within a short time after their application. The aim of this study was to investigate the short term effects of animal manure application on soil structure stability, infiltration rate (IR), and runoff and soil erosion formation under rainfall conditions. Two soils, a non-calcareous, sandy soil with 0.2% organic matter, and a calcareous, clayey soil with 4.7% organic matter were sampled from a semiarid region. The soils were mixed with raw cattle manure or with compost, and soils with no addition were considered as a control. The two soils with the three treatments were incubated for 21 days, and then subjected to 80 mm of simulated rainstorm. In contradiction to previous works, it was found that the manure reduced soil structure stability, reduced infiltration, increased surface runoff and led to soil loss. The negative impact of the raw manure on soil structure was stronger than that of the mature compost. The findings of this study indicate the high sensitivity of arable soils to erosion processes during the first few weeks following the addition of manure to the soil, and therefore could contribute to the decision-making process of the timing of manure application, namely to make sure that the manure is applied well before the rainy season, in order to avoid the aforementioned soil erosion. [ABSTRACT FROM AUTHOR]

Earth observation (EO) has an immense potential as being an enabling tool for mapping spatial characteristics of the topsoil layer. Recently, deep learning based algorithms and cloud computing infrastructure have become available with a great potential to revolutionize the processing of EO data. This paper aims to present a novel EO-based soil monitoring approach leveraging open-access Copernicus Sentinel data and Google Earth Engine platform. Building on key results from existing data mining approaches to extract bare soil reflectance values the current study delivers valuable insights on the synergistic use of open access optical and radar images. The proposed framework is driven by the need to eliminate the influence of ambient factors and evaluate the efficiency of a convolutional neural network (CNN) to effectively combine the complimentary information contained in the pool of both optical and radar spectral information and those form auxiliary geographical coordinates mainly for soil. We developed and calibrated our multi-input CNN model based on soil samples (calibration = 80% and validation 20%) of the LUCAS database and then applied this approach to predict soil clay content. A promising prediction performance (R2 = 0.60, ratio of performance to the interquartile range (RPIQ) = 2.02, n = 6136) was achieved by the inclusion of both types (synthetic aperture radar (SAR) and laboratory visible near infrared–short wave infrared (VNIR-SWIR) multispectral) of observations using the CNN model, demonstrating an improvement of more than 5.5% in RMSE using the multi-year median optical composite and current state-of-the-art non linear machine learning methods such as random forest (RF; R2 = 0.55, RPIQ = 1.91, n = 6136) and artificial neural network (ANN; R2 = 0.44, RPIQ = 1.71, n = 6136). Moreover, we examined post-hoc techniques to interpret the CNN model and thus acquire an understanding of the relationships between spectral information and the soil target identified by the model. Looking to the future, the proposed approach can be adopted on the forthcoming hyperspectral orbital sensors to expand the current capabilities of the EO component by estimating more soil attributes with higher predictive performance. [ABSTRACT FROM AUTHOR]

Wireless Underground Sensor Networks (WUSNs), an important part of Internet of things (IoT), have many promising applications in various scenarios. Signal transmission in natural soil undergoes path loss due to absorption, radiation, reflection and scattering. The variability and dynamic of soil conditions and complexity of signal attenuation behavior make the accurate estimation of signal path loss challenging. Two existing propagation models for predicting path loss are reviewed and compared. Friis model does not consider the reflection loss and is only applicable in the far field region. The Fresnel model, only applicable in the near field region, has not considered the radiating loss and wavelength change loss. A new two stage model is proposed based on the field characteristics of antenna and considers four sources of path loss. The two stage model has a different coefficient m in the near field and far field regions. The far field distance of small size antenna is determined by three criteria: 2 D2/λ, 5 D, 1.6 λ in the proposed model. The proposed two stage model has a better agreement with the field experiment data compared to Friis and Fresnel models. The coefficient m is dependent on the soil types for the proposed model in near field region. It is observed from experiment data that the m value is in the range of 0~0.20 for sandy soils and 0.433~0.837 for clayey silt. [ABSTRACT FROM AUTHOR]

Cyprus has a long tradition in grape cultivation and wine making and grapevine is important for the sustainability of the agricultural sector, like in other Mediterranean areas. Water scarcity, which is projected to increase due to climate change, could negatively affect the sector. In this research, the effects of irrigation and tillage treatments on various aspects of vine growth and product quality (e.g., yield, physiology and quality attributes), were studied in Chardonnay and Xynisteri cultivars grown in clay soils in Cyprus. Regarding soil properties and water content, N and K were more abundant in the soil than P and through the growing period irrigation tended to increase electrical conductivity (EC) in the soil. Soil water content (volumetric) was 22%–27.5% and 13%–16%, when irrigation was applied or not, respectively. Vegetative soil cover occupied 50%–55% of the surface and contained species typically present in Mediterranean farms (e.g., Poaceae, Fabaceae and Brassicaceae). Tillage increased yield in Xynisteri (4–5 kg plant−1) but negatively affected other parameters such as chlorophyll levels (in Xynisteri). In combination with irrigation, tillage increased antioxidant activity in Chardonnay (assessed by FRAP and DPPH), at harvest. Total phenolics at harvest were higher in the grape juice of Xynisteri, compared to Chardonnay (30–40 and 20–25 mg GA g−1 fresh weight, respectively). Irrigation influenced phytohormone levels in the two cultivars. ABA increased in non-irrigated Xynisteri, reflecting an increased capacity to react towards water stress. Water stress is considered to increase polyphenols in grapes, but in the case of Xynisteri it seems that irrigation water is required to obtain better quality grapes as without irrigation volumetric water content (VWC) is close to the permanent wilting point. Titratable acidity and total tannins decreased in Chardonnay, when tillage and irrigation were applied. In addition, tillage and irrigation tended to elevate the pH of the grape juice. Tillage and irrigation on the other hand, had no effect on the levels of ascorbic acid and total anthocyanin content. The results of this research may help to select management strategies that support the adaptation of viticulture to climate change in Cyprus and other Mediterranean areas. [ABSTRACT FROM AUTHOR]

This paper addresses the influence of fluidized bed combustion fly ash (FBCA) and further liquefying additives on the formation of structure and on the resulting properties of self-compacting grouts based on clay soil. In order to give the best account of the influence of individual input materials, tests were conducted on samples without the use of fluidized bed combustion fly ash. Clay soil (Cl) and cement were used as input materials, and fluidized bed combustion fly ash (10% and 30%) and a liquefying additive (sodium carbonate 0.1%) were used as an admixture. It has been experimentally determined that the use of 10% FBCA with clay soil is most suitable for achieving the optimal spillage parameter of self-compacting grout (class SF2 (660–750 mm) and class SF3 (760–850 mm)). It was also found that fluidized bed combustion fly ash and the liquefying additive have a significant influence on the formation of the structure of the self-compacting grout and, due to their presence, the compressive strength of the samples increased up to 0.5 MPa after seven days of hardening. The reaction between 0.1% of sodium carbonate and clay soil increased the electrokinetic potential, which reduced the viscosity of the self-compacting grout. Within the research work, the verification of the developed self-compacting grout in situ was also carried out. [ABSTRACT FROM AUTHOR]

Spherical cavities made by explosive charge activation in a clay soils differ in size and shape. The mass of explosive charge lowered on the bottom of the borehole in a one-time blasting is typically relatively small and is calculated by a desired and planned performace. The effect of smaller explosive charge for spherical cavities is in principle different than continuously filled borehole in mining and blasting operations. Detonation of smaller explosive charge crushes the material in proximity of activated explosive charge. With the increase of distance from the explosive charge, the released energy in not enough for crushing of the materials, but instead compacts it. This paper is an extension of the previous research, which resulted in a smallest error of estimated in a model shown as the sum of square residuals (SS), largest value of determination coefficient (R2) and smallest loss of information through Akaike's Information Criteria (AIC and AICc). This paper presents an extended power model of dependence of spherical cavity volume expansion on explosive charge. Extended model is a basic model with an additional parameter to ensure more precise mathematical description and further decrease of error of estimate for all efficiency indicators and for both types of explosive used. [ABSTRACT FROM AUTHOR]

Adding biochar to excessive compost amendments may affect compost mineralization rate and nitrogen (N) availability. The objective of this 371-day incubation study was to evaluate the effects of four proportions of woody biochar (0%, 0.5%, 1.0%, and 2.0%) from lead tree (Leucaena leucocephala (Lam.) de. Wit) biochar produced at 750 °C through dynamic mineral N and N mineralization rates in three rural soils (one Oxisol and two Inceptisols). In each treatment, 5% poultry–livestock manure compost was added to serve as an excessive application. The results indicated that the biochar decreased available total inorganic nitrogen (TIN) (NO3−-N+NH4+-N) by on average 6%, 9% and 19% for 0.5%, 1.0% and 2.0% treatments, respectively. The soil type strongly influenced the impact of the biochar addition on the soil nitrogen mineralization potential, especially the soil pH and clay content. This study showed that the co-application of biochar and excessive compost benefited the agricultural soils by improving NO3−-N retention in agroecosystems. The application of biochar to these soils to combine it with excessive compost appeared to be an effective method of utilizing these soil amendments, as it diminished the net N mineralization potential and reduced the nitrate loss of the excessive added compost. [ABSTRACT FROM AUTHOR]

A large part of Australia's broad acre irrigation industry, which includes cotton, is farmed on heavy clay Vertosols. Recent changes in nematicide chemical availability, changes in rotations and the observation of the reniform nematode in central Queensland has highlighted that we need to improve our understanding of nematodes in these soils. We undertook preliminary investigations into distribution by depth under a cotton-cotton and cotton-maize rotation as well as vertical movement experiments in microcosms to better understand nematode distribution and movement in heavy clay soils. Analysis revealed that field populations decreased with soil sample depth, but there were also differences between rotations. In microcosm experiments, vertical movement of nematodes in these heavy clay soils was restricted, even in the presence of plant roots and moisture, both of which were hypothesised to improve nematode migration. The results imply that crop rotation currently remains a plausible option for nematode control, and that we still have a lot to learn about the ecology of nematode populations in Vertosols. [ABSTRACT FROM AUTHOR]

Particle size distribution is one of the most significant factors determining physical soil properties. Laser diffraction analysis (LDA) is an alternative method to the traditional hydrometric methods (HM) used to determine particle size distribution in soils. However, significant differences in fraction content are found in relation to the applied methods of a particle size test. Above all, measurements performed by LDA for clayey soils usually produce different results to those based on Stokes' equation. Methodical problems, such as an appropriate method of dispersing the sample and the selection of LDA calculation theory, also play a significant role in fine soils. This paper contains the results of analyses of Neogene clays from Poland, which are characterized by differentiation with regard to the content of clay fraction particles. In this article, the validity of using laser diffraction analysis (LDA) for the identification and characterization of clayey sediments with common genesis is assessed. The possibility of finding reliable pedotransfer functions to the convert LDA results to a hydrometric analysis is discussed. [ABSTRACT FROM AUTHOR]

The use of saline water for the irrigation of forage crops to alleviate water scarcity has become necessary in semi-arid and arid regions and researchers have been seeking ways to offset the harmful results of soil salinity. Soil amendments with compost, manure and other organic material provide a valuable source of plant nutrients and appear to speed up soil recovery. The aim of this study was to compare the benefits of farmyard manure and a municipal solid waste (MSW) compost (40 mg ha−1) for raising alfalfa (Medicago sativa, cv. Gabès) under salt-water irrigation. Both compost and manure improved plant mineral uptake and growth of alfalfa cultivated in clay soil. Using compost in clay soil increased the content of copper (Cu), cadmium (Cd), and zinc (Zn) in plant tissues compared to manure, while the bio-accumulation factor (BAF) of Cu, Pb and Zn was higher in plants grown with manure compared to MSW compost with salt stress. Compost addition could enhance alfalfa growth under salt stress, which depends on salt doses and can greatly improve the recovery effects in a cost-effective way, although additional amendment type should receive special attention in order to be used as a tool for sustainable agriculture. [ABSTRACT FROM AUTHOR]

A liquid culture enrichment-polymerase chain reaction (E-PCR) assay was investigated as a potential tool to overcome inhibition by chemical component, debris, and background biological impurities in soil that were affecting detection assay performance for soil samples containing Bacillus atrophaeus subsp. globigii (a surrogate for B. anthracis). To evaluate this assay, 9 g of matched sets of three different soil types (loamy sand [sand], sandy loam [loam] and clay) was spiked with 0, ~4.5, 45, 225, 675 and 1350 endospores. One matched set was evaluated using a previously published endospore concentration and colony-forming unit spreadplate (CFU-S) assay and the other matched set was evaluated using an E-PCR assay to investigate differences in limits of detection between the two assays. Data illustrated that detection using the CFU-S assay at the 45-endospore spike level started to become sporadic whereas the E-PCR assay produced repeatable detection at the ~4.5-endospore spike concentration. The E-PCR produced an ~2-log increase in sensitivity and required slightly less time to complete than the CFU-S assay. This study also investigated differences in recovery among pure and blended sand and clay soils and found potential activation of B. anthracis in predominately clay-based soils. [ABSTRACT FROM AUTHOR]

Soil salinization is a serious environmental issue that significantly influences crop yield and soil fertility, especially in coastal areas. Numerous studies have been conducted on the salinity status in Pakistan. Information about the geospatial and temporal distribution of salinity in the Sujawal district is still lacking. The present study examines the soil salinity status and the impact of seawater intrusion in the entire district from 1990 to 2017 using field and remote sensing (RS) data. In addition, 210 soil samples at different depths (0–20, 20–40, and 40–60 cm) were collected from randomly selected locations for lab measurements of physiochemical properties. The results showed that the soil texture classes were mainly fine to medium particles. The samples collected at the 0–20 cm depth were mostly dominated by three textural classes of soil: clay at 19.5%, clay loam at 25.6%, and loam at 32.9%. The electrical conductivity (EC) of 65.7% soil samples collected from the top layer exceeded the normal range. The quantitative results indicated that the exchangeable sodium percentage (ESP) ranged between 1.38 and 64.58, and 72.2% of the top layer soil samples had ESP >15, while 81.5% of soil samples were in the normal range of soil pH. Furthermore, the results indicated that the vegetation decreased by 8.6% from 1990 to 2017, while barren land and water bodies increased significantly, by approximately 4.4% and 4.2%, respectively. The extreme and high salinity classes were characterized by high contents of soluble salt on the surface in the Jati and Shah Bandar subdistricts. In addition, the soil EC values at the 0–20 cm depth were significantly correlated with the salinity index (S1). Therefore, it was concluded that more than 50% of the top layer of soil was affected by salinity due to seawater intrusion, low rainfall, climate change, and erratic river flow. It is suggested that remote sensing (RS) data are more suitable for the detection of the soil salinity status of a region and impose a lower cost compared to other conventional approaches. However, this study could provide significant knowledge to land managers, policymakers, and government officials to allow them to take action to implement salinity control measures in the study area. [ABSTRACT FROM AUTHOR]

A two-year study was conducted to determine how soil texture affects calcium (Ca) absorption and partitioning in potted 'Hass' avocado trees. Trees were planted in 200 L pots in one of four soil types: clay (C), clay loam (CL), sandy loam (SL) or sand (S). Prior to planting, Ca content in each soil was in the normal range of availability, although the Ca concentration was highest in C soil. After two years of tree development, dry weights of shoots and roots were significantly higher in the SL and S soils than in C soil. Trees in the C soil had higher wood dry weight than trees in SL or S soils. The Ca contents (absolute quantities, not concentrations) in the roots, shoots and whole tree were significantly lower in the C soil than in the SL or S soils. The K/Ca ratio of trees in the C soil (K/Ca = 1.5) was significantly higher than that in the other soil types. Stem water potential was significantly lower for trees in the C soil compared to the other soils. These results indicate that Ca absorption and partitioning in young avocado trees varies with soil texture, probably associated with soil effects on root growth and/or plant water status. [ABSTRACT FROM AUTHOR]

With the increase in offshore wind farms, the demands for umbilicals and power cables have increased. The on-bottom stability of umbilicals and power cables under the combined wave and current loading is the most challenging design issue, due to their light weight and the complex fluid–cable–soil interaction. In the present study, the methodology for dynamic lateral stability analysis is first discussed; and the reliable hydrodynamic load model and cable–soil interaction model based on large experimental test data are described in detail. The requirement of the submerged weight of a cable w s to obtain on-bottom stability is investigated for three types of soil (clay, sand and rock), using the finite element program PONDUS, and the results are w s , r o c k > w s , c l a y > w s , s a n d under the same load conditions. Several different aspects related to optimization design of the on-bottom stability are explored and addressed. There is a significant benefit for the on-bottom stability analysis to consider the reduction factors, due to penetration for clay and sand soil. The on-bottom stability is very sensitive to the relative initial embedment z 0 / D for clay and sand soil, due to the small diameter of the cables, and therefore, reliable prediction of initial embedment is required. In the energy-based cable–soil interaction model, the friction coefficient μ and the development of penetration affect each other and the total effect of friction force F f and passive resistance F r is complicated. The effect of the friction coefficient μ on the on-bottom stability is different from engineering judgement based on the Coulomb friction model. The undrained shear strength of clay is an important parameter for the on-bottom stability of umbilicals and cables. The higher the undrained shear strength of the clay, the larger the lateral displacement. Meanwhile, the submerged weight of sand has a minor effect on the lateral displacement of cables. The method used in the present study significantly improves the reliability of the on-bottom stability analysis of umbilicals and power cables for offshore wind application. [ABSTRACT FROM AUTHOR]

Clay ball is a pavement surface defect which refers to a clump in which clay or dirt is mixed with hot asphalt mixture. Clay ball is typically caused by a combination of aggregate contamination of clay or soil, high aggregate moisture, and low production temperature at the asphalt plant. It usually appears a few weeks or months after paving under traffic load, after being liquefied and knocked from the pavement surface. Clay balls can be the source of potholing, raveling, and other issues such as moisture infiltration and reduced ride quality. This paper presents an investigation of the clay balls on US-31 one winter after construction in Hamilton County, Indiana. In order to understand the pavement condition, their severity was measured using both visual observation and infrared image collection system. In addition, a clay ball amount, its distribution pattern, and cores condition were evaluated. A precipitation effect on clay ball formation was investigated for finding a cause of the clay balls. The investigation found that infrared image collection system was appropriate in detecting the clay balls. The clay balls were elliptic in shape with 2.5 cm to 10 cm in diameter, and the maximum clay ball depth was almost penetrating the entire surface course. It was also found that the asphalt paving on the raining days or right after raining could increase the potential of clay balls. Monitoring of aggregate moisture during construction on or after raining days should be able to reduce the risk of clay balls. [ABSTRACT FROM AUTHOR]

This study aims to characterize the effect of microbial-induced calcite precipitation (MICP) on the desiccation cracking behaviors of compacted calcium bentonite soils. We prepare six groups of samples by mixing bentonites with deionized water, pure bacteria solution, pure cementation solution, and mixed bacteria and cementation solutions at three different percentages. We use an image processing tool to characterize the soil desiccation cracking patterns. Experimental results reveal the influences of fluid type and mixture percentage on the crack evolution and volumetric deformation of bentonite soils. MICP reactions effectively delay the crack initiation and remediate desiccation cracking, as reflected by the decreased geometrical descriptors of the crack pattern such as surface crack ratio. The mixture containing 50% bacteria and 50% cementation solutions maximizes the MICP treatment and works most effectively in lowering the soil cracking potential. This study provides new insights into the desiccation cracking of expansive clayey soils and shows the potential of MICP applications in the crack remediation. [ABSTRACT FROM AUTHOR]

Expansive soil shows dual swell–shrink which is not suitable for construction. Several mitigating techniques exist to counteract the problem promulgated by expansive clayey soils. This paper explored the potential mecho-chemical reinforcement of expansive clayey soil to mitigate the effect of upward swelling pressure and heave. The polypropylene fiber is randomly distributed in the soil for mechanical stabilization, and the industrial residual silica fume is used as a chemical stabilizer. The experimental analysis was made in three phases which involved tests on mechanically-reinforced expansive soil, using randomly distributed polypropylene fibers with different percentages (0.25%, 0.50%, and 1.00%), and which were 12 mm length. The second phase of experiments was carried out on chemical stabilized expansive soil with different percentages (2%, 4%, and 8%) of silica, and the next phase of the experiment focused on the combination of mecho-chemical stabilization of the expansive soil with different combinations of silica (i.e., 2%, 4%, and 8%) and polypropylene fibers (i.e., 0.25%, 0.50%, and 1.00%). Maximum dry density (MDD), optimum moisture content (OMC), liquid limit (LL), plastic limit (PL), plastic index (PI), grain size, and constant volume swelling pressure tests were performed on unreinforced and reinforced expansive soil, to investigate the effects of polypropylene fiber and silica fume on the engineering properties of expansive clayey soil. The experimental results illustrate that the inclusion of polypropylene fiber has a significant effect on the upward swelling pressure and expansion property of expansive soil. The reduction in the upward swelling pressure and expansion is a function of fiber content. These results also indicated that the use of silica fume caused a reduction in upward swelling potential, and its effect was considerably more than the influence of fiber. [ABSTRACT FROM AUTHOR]

Expansive Yazoo clay soil is susceptible to volumetric deformation and is dominant in central Mississippi and other neighboring southern states of the United States. Recurring shrink-swell behavior causes a significant problem to infrastructures in the area. Although Yazoo clay causes a significant problem in the deep southern states, limited study has been conducted on the behavior of Yazoo clay, especially in the presence of rainfall. The objective of this current study is to investigate the coupled effect of changes in void ratio due to wet-dry cycles and rainfall on the stability of highway slopes made of Yazoo clay. The finite element method in Plaxis 2D by Bentley System (https://www.plaxis.com/) has been utilized to investigate the coupled effect of changes in mechanical properties and rainfall using flow-deformation and stability analysis. Reconstituted expansive clay soil samples were used for the laboratory experiment. The reconstituted Yazoo clay samples were subjected to 3, 5, and 7 wetting and drying cycles in an enclosed chamber for a 24-h period. The axial deformation of the samples and the change in void ratios at each number of the cycle was closely monitored. The strength change at each wet and dry cycle was also investigated and used for slope stability analysis in the presence of rainfall. The test results indicate that the void ratio increases with the increasing number of wet-dry cycles. A continuous increment in void ratios from 0.99 in an undisturbed state with no wet-dry cycle to 1.49 at the 7th wet-dry cycle, indicating a 48.9% increase, as the wetting and drying cycle increases was recorded; in turn, decreasing the cohesion of the soil by 77%. The factor of safety considering the effect of two total rainfall periods of Rv = 126.2 mm (2 h) and Rv = 271.7 mm (3 days) reduced from 1.7 to 1.2 and 1.68 to 1.02, considering the effect of the 7th wet-dry cycle at the topsoil. The changes in the void ratio due to the wetting and drying cycle of Yazoo clay soil reduces the shear strength to a fully softened condition, increasing the possibility of slope failure. This condition further worsens in the presence of a perched water condition due to the infiltration of rain water. [ABSTRACT FROM AUTHOR]

Understanding the effects of irrigation regime and soil texture on potassium-use efficiency (KUE) of rice (Oryza sativa. L) is essential for improving rice productivity. In this regard, experiments were conducted from July to October in 2016 and 2017 by using a randomized complete block design in a factorial arrangement with four replications. The rice plants were grown in three soils, with clay contents of 40%, 50%, and 60%, which were marked as S (40%), S (50%), and S (60%), respectively. For each soil type, irrigation regimes, namely, R (F, S100%), R (F, S90%), and R (F, S70%), were established by setting the lower limit of irrigation to 100%, 90%, and 70% of saturated soil water content, respectively, and the upper limit of irrigation with 30 mm of flooding water above the soil surface for all irrigation regimes. Results showed that the responses of the roots and shoots and the potassium accumulation (KA) and KUE of rice were significantly affected by the water regime and soil texture. In the same irrigation regime, increasing the soil clay content improved the K utilization of rice. Under the same soil type, R (F, S100%) was the optimal water management practice for growing rice. The R (F, S100%) S (60%) treatment presented the highest KUE, which was 56.4% in 2016 and 68.1% in 2017. The R (F, S70%) S (40%) treatment showed the lowest KUE, which was 13.8% in 2016 and 14.9% in 2017. These results enrich knowledge regarding the relationship among soil, water, and rice, and provide valuable insights on the effect of irrigation regime and soil texture on the KA and KUE of rice. [ABSTRACT FROM AUTHOR]

Over years of intensive cultivation and imbalanced fertilizer use, the soils of the Indian subcontinent have become deficient in several nutrients and are impoverished in organic matter. Recently, this region has started emphasizing a shift from inorganic to organic farming to manage soil health. However, owing to the steadily increasing demands for food by the overgrowing populations of this region, a complete shift to an organic farming system is not possible. The rice–wheat cropping system (RWCS) is in crisis because of falling or static yields. The nations of this region have already recognized this problem and have modified farming systems toward integrated nutrient management (INM) practices. The INM concept aims to design farming systems to ensure sustainability by improving soil health, while securing food for the population by improving crop productivity. Therefore, this paper was synthesized to quantify the impact and role of INM in improving crop productivity and sustainability of the RWCS in the context of the Indian subcontinent through meta-analysis using 338 paired data during the period of 1989–2016. The meta-analysis of the whole data for rice and wheat showed a positive increase in the grain yield of both crops with the use of INM over inorganic fertilizers only (IORA), organic fertilizers only (ORA), and control (no fertilizers; CO) treatments. The increase in grain yield was significant at p < 0.05 for rice in INM over ORA and CO treatments. For wheat, the increase in grain yield was significant at p < 0.05 in INM over IORA, ORA, and CO treatments. The yield differences in the INM treatment over IORA were 0.05 and 0.13 Mg ha−1, respectively, in rice and wheat crops. The percent yield increases in INM treatment over IORA, ORA, and CO treatments were 2.52, 29.2, and 90.9, respectively, in loamy soil and 0.60, 24.9, and 93.7, respectively, in clayey soil. The net returns increased by 121% (INM vs. CO) in rice, and 9.34% (INM vs. IORA) and 127% (INM vs. CO) in wheat crop. Use of integrated nutrient management had a positive effect on soil properties as compared to other nutrient management options. Overall, the yield gain and maintenance of soil health due to INM practices over other nutrient management practices in RWCS can be a viable nutrient management option in the Indian subcontinent. [ABSTRACT FROM AUTHOR]

This work presents a method to determine the plasticity of clay soils using Fourier transform mid-infrared (FT-MIR) spectroscopy. Samples of mono- and polymineral soils of varying water contents are studied. The FT-MIR results are compared with the results obtained from standard Russian and international methods for the plasticity range. The correlation between the consistency of clay soils, when displaying their plastic properties, and the position of the Si–O stretching band in the FT-MIR spectra is established. The possibility of, and interest in, determining the plasticity characteristics of clay soils using mid-infrared spectroscopy is demonstrated: it yields effectively higher precision results compared to standard test methods. It is shown that the method of IR spectroscopy allows the fixing of the start and the completion of the series of “phase transitions” of the soil in the plastic and liquid state. The significant effect of the concentration of non-clay minerals on the Si–O ν line is that a moisture content curve is noticed, which may help to predict the clay content of the soil without undertaking XRD analysis. [ABSTRACT FROM AUTHOR]

Semarang-Demak and other cities along the coast of North Java are vulnerable to land subsidence. The presence of saline groundwater in the coastal region is thought to affect the high subsidence rate, in this case the compressibility of the aquitard layer. We aimed to analyze the effects of groundwater salinity on the compression characteristics of the Semarang-Demak clay using physical analysis. Methods included the determination of groundwater salinity, clay mineralogy and fabrics, and consolidation tests under various salinity conditions. The Semarang-Demak clay is dominated by smectite of high activity, and saline clay exists at the depth of 10 to 35 m. Consolidation tests revealed that the increase insalinity increases the average consolidation rate and hydraulic conductivity up to 42% and 37.5%, respectively. Clay fabric analysis showed that the groundwater salinity modified the interconnectivity of pores by changing the fabric into parallel alignments, facilitating faster porewater dissipation, hence the clay is more readily compressed. These findings are useful for explaining the mechanism of the fast-subsiding coastal plains of North Java. [ABSTRACT FROM AUTHOR]