Clay Soil Research Articles

Identification of plant soil water and soil aeration corequisites: A management tool

AbstractPlant‐available soil‐water and adequate soil aeration within the root zone are essential corequisites for successful plant growth. Characterization of these two requirements for plant growth is generally done by independent measurements of water and air phase properties and functions in soil, with limited emphasis on their combined effect. This study investigated soil‐water characteristic (SWC) measurements in vadose soil profiles (up to 117‐cm depth) in six pasture soils to examine the combined behavior of soil‐water and diffusion‐controlled aeration within the root zone. The soil moisture measurements were made over matric potentials ranging from −1 to −1500 kPa using tension table and pressure plate apparatus. The van Genuchten model was used to parameterize the measured SWC curve, while the Millington–Quick model was used to derive soil‐gas diffusivity from measured soil physical properties. Based on two simple indices, derived to represent plant‐available soil‐water and soil aeration status at a given moisture content, we propose an assessment matrix, which illustrates how a soil satisfies the corequisites for successful plant growth, as it drains to different matric potentials upon irrigation. Results show a pronounced effect of soil texture and, to a lesser extent, soil structure on satisfying these corequisites. With the aid of the assessment matrix, we observed that loam, sandy loam textures exhibited a good overall performance, while sand, clay loam, and clay soils struggled to meet these corequisites during drainage.

Dampak Penggunaan Abu Marmer terhadap Kuat Geser Tanah Lempung

Soil is an important part of the building structure because it has a function as a support for the building. Therefore, soil stability must be considered so that building construction is safe and durable. There are types of clay soils that have high plasticity values and low shear strength. Soils like this require stabilization with the addition of additives such as marble ash. The purpose of this study was to determine whether the addition of marble ash content has an optimal impact on improving the plasticity, density, and shear strength properties. The added material used was marble ash with a content of 3%, 6%, 9%, and 12% by weight of dry soil. The specimens were differentiated based on their curing age before being tested by triaxial. Based on the research results, it was found that the use of marble ash had the maximum impact on improving the plasticity properties and maximum density at an addition of 6%. This was followed by a significant increase in shear strength at the same addition. A good curing age for increasing the angle of internal friction in the soil was obtained at 14 days.

Performance of Bitumen Emulsion Mixtures utilized as Gravel Road Base incorporating Lateritic Clay Soil and Calcined Sugarcane Bagasse Ash Filler

Performance of Bitumen Emulsion Mixtures utilized as Gravel Road Base incorporating Lateritic Clay Soil and Calcined Sugarcane Bagasse Ash Filler

Three-Dimensional Site Response Analysis of Clay Soil Considering the Effects of Soil Behavior and Type

To understand changes in bedrock motion at the ground surface, frequency effects, and spatial distribution within the soil, it is important to look at how a site responds to earthquakes. This is important for soil–structure interaction in structural and geotechnical earthquake engineering. This study deals with the effect of classifying clays according to shear wave velocity (stiff/medium/soft) and nonlinearity in behavior (linear/nonlinear) on the analysis of the site response. A 3D soil model with a combination of free fields and quiet boundaries and advanced constitutive models for soil to obtain accurate results was used to conduct this study. A strong TABAS earthquake was used to excite the compliant base of the model after converting the velocity record of TABAS to an equivalent surface traction force using a horizontal force–time history proportional to the velocity–time history. This study reveals that the site response analysis is affected by the type of clay soil and the soil material behavior, with soft clay soil causing higher PGV and PGV values in the linear case and lower values in the nonlinear case due to soil yielding, which causes soil response attenuation. This results in extremely conservative and expensive building designs when linear soil behavior is adopted. On the other hand, the applied earthquake exhibits greater attenuation at longer frequencies and greater amplification at mid and short frequencies. However, at frequencies near the applied earthquake frequency, neither attenuation nor amplification occurs. Furthermore, nonlinear soil behavior is crucial for soil evaluation and foundation design due to higher octahedral shear strain and settlement values, especially in softer soils, resulting from extensive plastic deformation.

Efficacy of Acacia Gum Biopolymer in Strength Improvement of Silty and Clay Soils under Varying Curing Conditions

Acacia gum (AG), a polysaccharide biopolymer, has been adopted to improve the strength of three cohesive soils by subjecting them to diverse environmental aging conditions. Being a polysaccharide and a potentially sustainable construction material, the AG yielded flexible film-like threads after 48 h upon hydration, and its pH value of 4.9 varied marginally with the aging of the stabilized soils. The soil samples for the geotechnical evaluation were subjected to wet mixing and were tested under their Optimum Moisture Content (OMC), as determined by the light compaction method. The addition of AG modified the consistency indices of the soils due to the presence of hydroxyl groups in AG, which also led to a rise in OMC and reduction in Maximum Dry Unit weight (MDU). The Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR) were determined under thermal curing at 333 K as well as on the same day of sample preparation. The least performing condition of the soil’s CBR was evaluated under submerged conditions after allowing the AG-stabilized specimens to air-cure for a period of 1 week. The UCS specimens tested after 7 days were subjected to the initial 7 days of thermal curing at 333 K. A dosage of 1.5% of AG yielded the UCS of 2530 kN/m2 and CBR of 98.3%, respectively, for the low compressible clay (LCC) after subjecting the sample to 333 K temperature for 1 week. The viscosity of the AG was found to be 214.7 cP at 2% dosage. Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and average particle size determination revealed the filling of pores by AG gel solution, adsorption, and hydrogen bonding, which led to improvements in macroproperties.

Digging into Detectability: Uncovering How Temperature Influences Detection Probability of the Fossorial Temblor Legless Lizard

Abstract Knowledge of species distributions is critical for conservation, but surveying for rare, understudied species presents many challenges. A two-phase occupancy study can increase knowledge gained from early occupancy studies of a species by quickly using data from the first survey period to revise the study design for a second period. The Temblor legless lizard Anniella alexanderae is a recently described fossorial species found in the southwestern San Joaquin Valley, California, and its status is currently under review by state and federal wildlife agencies. As a fossorial species that is rarely surface active, Temblor legless lizards might be unavailable for detection at certain times of year or under inhospitable conditions (e.g., hot, dry weather), indicating the importance of accounting for false-negative surveys when determining its distribution. We used a multiscale occupancy model to disentangle detection probability, availability for detection, and occupancy for Temblor legless lizards. Focusing our effort from mid-February to mid-April when temperatures are mild and soil moisture is expected to be higher near the surface, we surveyed a total of 89 sites in 2022 (n = 60) and 2023 (n = 68) and detected Temblor legless lizards at 12 sites, including 5 new localities. Detection probability was positively related to temperature during our late winter-early spring survey period, and availability for detection was consistently high with minimal fluctuation within each year. Nevertheless, repeated surveys with nondetection can increase confidence that this fossorial lizard does not occur at a site. Temblor legless lizards were more likely to occur at sites near ephemeral streams and in areas without high clay soil content, but more investigation could help to discern drivers of occurrence. Our study provides valuable information for optimizing surveys for Temblor legless lizards and suggests promising directions for future research on this species’ ecology.

Life cycle assessment of green binder for organic soil stabilization

Increasing construction on soils with low bearing capacity is a geotechnical challenge currently faced in several parts of the world. Highly compressible organic soils require intervention to improve their mechanical behavior. In this case, mass stabilization with binder is an applicable technique, however the commercial cement used (Ordinary Portland Cement) generates environmental impacts that can be minimized with its replacement by environmentally friendly binders. Blended binders can use secondary materials from the industry (waste or by-products) and promote environmental gains. In this case, this research proposes the use of carbide lime and granulated blast furnace slag with the complement of Portland cement for the stabilization of an organic soil. A comparison of the strength obtained with the blended binder versus Portland cement is analyzed in soil stabilization. A Life Cycle Assessment is performed to verify if the proposed blended binder has environmental benefits in replacing conventional cement. Results show that the blended binder has similar capacity to stabilize the organic clay soil compared to commercial cement. The life cycle analysis showed that the use of secondary materials from industry in the composition of blended binder promotes a significant reduction in environmental impacts assessed.

Predictive Modelling and Functional Group of Clay Soil Treated with Steel Slag and Calcium Carbide Residue

Swell-shrink subgrade soils like clay are rich in sulphate and exhibit a high rate of volume change by swelling and shrinking during wet and dry cycles, respectively, leading to heaves, cracks, and differential settlement of pavement layers. The aim of this study was to establish predictive simulation models and functional group of clay soil treated with steel slag and calcium carbide residue. Physical and geotechnical tests (such as California bearing ratio (CBR), compaction characteristics, and consistency parameters) were carried out on the unstabilised and stabilised clay soil. Using SPSS statistical software (version 23), multiple linear regression analysis was applied to the experimental data that relate CBR to compaction parameters and additive contents (steel slag and calcium carbide residues). The generated models gave a reliable coefficient of determination, R2 , of 0.990, and 0.998, which can be used to successfully predict both unsoaked and soaked CBR of the stabilised clay soil, respectively. Fourier transform infrared spectroscopy (FTIR) analysis was examined on the clay soil, the additives, and the stabilised clay soils. The FTIR analysis showed weak peaks at 1115 and 1103 cm-1 for all the stabilised clay soils, and this revealed that both additives drastically reduced the sulphate content in the clay soil, which consequently reduced the expansion, cracking, and disintegration rates. As a result, the clay soil's chemical bonding was enhanced through physico- chemical mechanisms.

Does the presence of mineral nutrient enhance the carbon sequestration, soil aggregation, and microbial biomass in the subtropical clay soil?

Crop residue incorporation is considered as a promising approach for improving carbon sequestration coupling with soil aggregation (MWD). However, better understanding is needed regarding to the mechanism of carbon sequestration and aggregation following crop residue return in subtropical clay soil. A short-term field experiment (1.5 years) was conducted to explore the underlaying potential mechanism of carbon sequestration after crop residues return in the subtropical clay soil. Four treatments were applied as follows: (1) Control, (2) Inorganic fertilization (NPK), (3) Crop residue at 8-ton ha−1, (6) NPK + Crop residue at 8-ton ha−1. MWD, soil organic carbon (SOC), microbial biomass carbon (MBC), glomalin protein (GRSP), mineral and aggregate-associated SOC, and Fe oxides were determined. Results exhibited that the mineral nutrients with or without crop residue enhanced the SOC significantly in comparison to the only straw and control treatments (P < 0.05). The short-term residue return enhanced the MWD compared to the baseline soil, which was less than control due to the greater concentration of amorphous Fe oxides. Moreover, GRSP and MBC were significantly increased upon crop residue return in presence of mineral nutrients treatment (P < 0.01). SOC was reduced in the order of NPK > NPK + Crop residue > Crop residue > control, while MBC and GRSP were increased in the order of control < Crop residue < NPK < Crop residue + NPK. Aggregate-associated and mineral-associated SOC of aggregates were enhanced in presence of mineral nutrients (P < 0.001). Our results suggest that the nutrients addition in presence or absence of crop residue return under short-term field experiment is considered as a promising and sustainable clay soil management approach for enhancing carbon sequestration to mitigate climate change.

Windthrow in riparian buffers affects the water quality of freshwater ecosystems in the eastern Canadian boreal forest

Despite the wide application of riparian buffers in the managed boreal forest, their long-term effectiveness as freshwater protection tools remains unknown. Here, we evaluate windthrow incidence in riparian buffers in the eastern Canadian boreal forest and determine the effect of windthrow on the water quality index of the adjacent freshwater ecosystems. We studied 40 sites—20 riparian buffers, aged 10 to 20 years after harvesting and 20 control sites within intact riparian environments—distributed among clay and sandy (esker) soils and black spruce (Picea mariana) and jack pine (Pinus banksiana) stands. We observed more windthrow in the harvested stands (36%) relative to the control sites (16%), regardless of substrate and species. We determined that the most important factors explaining windthrow were exposition, harvesting, aquatic environment size, and stand characteristics. These factors drive wind exposure, speed, and force, which determine post-harvest windthrow risk. Furthermore, windthrow negatively affected the water quality index of the adjacent aquatic systems, i.e., greater windthrow decreased the protective effect of the riparian buffer. We recommend increasing the use of partial harvest near riparian environments and adapting riparian buffers to site conditions to ensure the long-term protection of adjacent freshwater ecosystems.

Assessment of Fusarium wilt (Fusarium oxysporum f.sp. sesami) Disease Incidence in Sesame (Sesamum indicum L.) in Western Tigray, Northern Ethiopia

Fusarium wilt disease is one of the most serious diseases threatening sesame production in Tigray, northern Ethiopia. The aim of the present study was to assess Fusarium wilt disease incidence and its association with agronomic practices and environmental factors. Field survey was conducted in Kafta-Humera, Welkayt and Tsegedie districts in 2018 cropping season. A total of 92 farmers’ fields were assessed for the prevalence and incidence of the disease. Results indicated that 67% of farmers’ fields were infected by Fusarium wilt disease from the total assessed fields. Fusarium wilt disease incidence was varied from 0.22% to 80%. It was ranged from 0-72% in Kafta-Humera, 0-56% in Welkayt and 0-80% in Tsegedie. The mean disease incidence was 11.89% at Kafta-Humera, 11.14% at Welkayt and 10.69% at Tsegedie. According to the single predictor in the logistic regression model Fusarium wilt disease incidence was most affected significantly (p &lt; 0.05) with the previous crop and altitude. Higher levels of disease incidence were recorded when the previous crop was sesame, lower altitudes and in clay loam soil texture. Overall results of the present study indicated that Fusarium wilt disease is the major challenge to sesame production in study areas. Therefore, efforts should be put in place to manage the disease via integration of appropriate strategies.

Mechanisms of microbial diversity modulation of mineral black clay to achieve ecological restoration of open-pit mine dump

The harsh climatic conditions and severe scarcity of surface soil present significant challenges to ecological restoration in open-pit mine dumps within China's type II plant cold resistance zone. To address the topsoil shortage, mineral black clay was used to create synthetic soil. This study explored the application of an ecological restoration bacteria (ERB) consortium to accelerate the ecological restoration of synthetic soil-covered areas by enhancing soil ecosystem construction. The results demonstrated that ERB significantly influenced the native bacterial community structure in mixed black clay. Specifically, ERB disrupted the inhibitory effects of the Actinobacterota phylum on the development of native bacterial diversity, leading to an increase in unclassified_o_Solirubrobacterales sp., norank_f_norank_o_norank_c_KD4-96 sp., Sphingomonas sp., Luteitalea sp., norank_f_Vicinamibacteraceae sp., and other aerobic and anaerobic bacteria. These alterations in soil microbial structure directly impacted soil composition and vegetation diversity. The plant diversity survey and metabolomics analysis revealed that the reduction of harmful substances, such as HPED, HODE, and HOME, in black clay soil improved the growth and distribution of Salsola collina Pall. and Medicago sativa L. This increase facilitated the cycling of key nutrients, such as nitrogen (N) and phosphorus (P), and promoted the establishment of symbiotic relationships between plants, microorganisms, and soil. Ultimately, the ecological remediation of the synthetic soil was achieved through the synergistic effects of ERB, which included the degradation of inhibitory soil components, enhanced nutrient consumption by microbiota and plants, and the overall promotion of ecosystem stability in the reclamation area.

DEM simulation of subsoiling in tropical sugarcane fields: Effects of opposing subsoiler design and model parameters

During the subsoiling operation of clayey soil in sugarcane fields in tropical areas, there are key limitations such as high resistance caused by high adhesion and unsatisfactory subsoiling effects of machines and tools. To address these issues, this study first explored the machine's structural characteristics using a mechanism analysis method to identify key optimization parameters. Then, simulation tests were conducted based on the root-soil complex model. Single factor analysis was conducted to evaluate the effects of backsweep angle, plow spacing, and penetration angle on tillage resistance and soil disturbance, determining their optimal ranges. Finally, a multi-factor orthogonal rotation combination experiment was designed using Box-Behnken theory to optimize the subsoiler's structural parameters. The regression analysis results show that the optimized model significantly improves the reliability of simulation results. Field verification test results show that under the conditions of a sweep angle of 50°, a plow spacing of 60 cm, and a soil penetration angle of 45°, the average tillage resistance of subsoiling operations is significantly reduced to 76.2 kN, and the amount of soil disturbance is reduced to 1780cm². The optimization reduced tillage resistance and soil disturbance by 34.42% and 30.50% respectively, significantly improving the subsoiling performance. To our knowledge, this is the first work applying discrete element methods to subsoiling operations in red clay soils in sugarcane growing areas. The proposed machine structure has higher efficiency and better performance, providing an effective reference for the design and application of sugarcane field subsoiling machinery.

Straw management and fertilization improve soil aggregate stability by inducing biological binding agents and specific keystone genera

Improving soil aggregate stability through proper fertilization management is essential for crop growth. However, how different fertilization regimes affect soil aggregate stability driven by microorganisms and biological binding agents remains largely unexplored. For this purpose, we conducted a 9-year field experiment involving two soil textures (i.e., loam and clay soils) and five fertilization regimes (i.e., no fertilizer or crop straw return (CK), crop straw return (S), chemical fertilization (N), crop straw return with chemical fertilizer (SN), and crop straw return with chemical fertilizer and 20% nitrogen substituted with chicken manure (SNM)). Mean weight diameter (MWD) of soil aggregates, glomalin-related soil protein (GRSP) content, and microbial community composition were investigated. The SN and SNM treatments had similar MWD, which was 70.08–76.45% higher than the CK, and the S and N treatments had similar MWD, which was 20.35–34.76% higher than the CK, indicating better effects of SN and SNM on the improvement of the soil aggregate stability than the S or N treatment. High easily extractable GRSP and total GRSP contents contributed to the improved MWD. Meanwhile, some specific keystone genera identified from the keystone modules (co-occurring groups of soil biota including arbuscular mycorrhizal fungi, bacteria, and nonmycorrhizal fungi) were recognized as the important factors regulating the MWD, though the selected specific genera in the loam soil differed from the clay soil. Altogether, our results highlighted the fundamental role of the GRSP and selected specific keystone microbial taxa in improving the soil aggregate stability and provided a list of microbial taxa linking to MWD in different soils, which could be specifically targeted in specific soil.

Evapotranspiration and Rainfall Effects on Post‐Storm Salinization of Coastal Forests: Soil Characteristics as Important Factor for Salt‐Intolerant Tree Survival

AbstractFlooding and salinization triggered by storm surges threaten the survival of coastal forests. After a storm surge event, soil salinity can increase by evapotranspiration or decrease by rainfall dilution. Here we used a 1D hydrological model to study the combined effect of evapotranspiration and rainfall on coastal vegetated areas. Our results shed light on tree root uptake and salinity infiltration feedback as a function of soil characteristics. As evaporation increases from 0 to 2.5 mm/day, soil salinity reaches 80 ppt in both sandy and clay loam soils in the first 5 cm of soil depth. Transpiration instead involves the root zone located in the first 40 cm of depth, affecting salinization in a complex way. In sandy loam soils, storm surge events homogeneously salinize the root zone, while in clay loam soils salinization is stratified, partially affecting tree roots. Soil salinity stratification combined with low permeability maintain root uptakes in clay loam soils 4/5‐time higher with respect to sandy loam ones. When cumulative rainfall is larger than potential evapotranspiration ETp (ETp/Rainfall ratios lower than 1), dilution promotes fast recovery to pre‐storm soil salinity conditions, especially in sandy loam soils. Field data collected after two storm surge events support the results obtained. Electrical conductivity (a proxy for salinity) increases when the ratio ETp/Rainfall is around 1.76, while recovery occurs when the ratio is around 0.92. In future climate change scenarios with higher temperatures and storm‐surge frequency, coastal vegetation will be compromised, because of soil salinity values much higher than tolerable thresholds.

Enhancing clay soil reinforcement using the MICP-BIN method with biochar-induced nucleation

The microbially induced carbonate precipitation (MICP) method has gained extensive use in the realm of soil stabilization. The combination of MICP with biochar offers potential benefits in terms of simultaneous strength enhancement and vegetation cover enhancement. This study presents a novel microbial solidification technique known as the biochar-induced nucleation (MICP-BIN) method for reinforcing clay soil. Corn stover biochar was employed as an auxiliary material, mixed with dry clay powder, and subsequently reinforced using the MICP technique. Direct shear tests (DSTs), drying experiments, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were also conducted to investigate the efficacy of the MICP-BIN method. Compared with that of the remolded soil, the shear strength of the treated soil exhibited a substantial increase of 22.4%, the CaCO3 content increased by 30%, and the shear strength improved by 389.5%. Similarly, the internal friction angle exhibited increases of 22.7% and 405.2%, while the cohesion showed improvements of 9.4% and 344.3%, respectively. The MICP-BIN method is found to increase suction for a given water content. Further, biochar amended soil possesses highest water retention ability (especially at lower suction magnitude) followed by MICP amended soil, MICP-BIN amended soil and untreated soil. The difference in water retention abilities among various soils is negligible at higher suction magnitude. Further, there is no significant change in air entry value of MICP-BIN amended soil as compared to the untreated soil and MICP amended soil. This study demonstrated the promising results achieved by combining biochar and the MICP-BIN technique, providing a novel approach for reinforcing soft ground.

Unearthing the impact of land use on deep soil carbon−an example from the southwestern Australian wheatbelt

AbstractClimate change resulting from anthropogenic greenhouse gas (GHG) emissions is both a topic that is gaining greater societal attention and an area where greater efforts are being made for their mitigation. Increasing soil organic carbon (SOC) has been proposed as one of the mechanisms through which atmospheric carbon can be sequestered and has the potential co‐benefit of also improving soil productivity. A wide range of factors have been found to influence SOC contents, especially when depth is considered, and as such regionally specific sampling is useful to understand SOC dynamics. In this study, soil samples from an agricultural property in the West Australian Wheatbelt were analysed. The samples came from four different land uses: salinity revegetation, annual grazing, forage shrub, and perennial grazing. Samples were taken at four depth intervals up to 1 m and their general characteristics as well as each of their total organic carbon, dissolved organic carbon and microbial biomass carbon values analysed. A microbial incubation experiment was conducted over 28 days to assess the stability of the soil carbon and the extent to which this depends on the soil's clay content. This study found that depth and land use were statistically significant in both SOC concentrations and SOC stability. Soil clay content was a significant factor in the stability of SOC, explaining 38% of the variation in SOC stability. Furthermore, the study reveals that excluding soil below 30 cm depth in SOC analysis can result in a global underestimation of SOC values. An understanding of this is important for wheatbelt producers to be better equipped to understand and respond to, the market pressures exerted by societies and industries to move closer to their claimed net‐zero emissions targets.

Development of an enhanced electrical injera baking pan (Ethiopian Traditional mitad) using steel powder additives and gypsum insulation

Electric Injera baking Pan are prevalent in Ethiopia but are highly inefficient, resulting in significant heat loss, high energy consumption, and increased energy bills. This research investigates improving these devices using steel powder as an additive and gypsum as an insulator. The study examines thermal conductivity, baking time, energy consumption, heat loss, and insulation effectiveness. The objectives of this research are to improve the thermal conductivity of the baking surface while ensuring even heat distribution, enhance the insulation properties of the pan to reduce heat loss, improve the safety of the user by reducing the risk of excessive heat exposure to the outer surfaces, and reduce the overall energy consumption of the Injera baking process. Temperatures were measured using an infrared thermometer, digital thermometer, and thermocouple. Four samples (A0, A1, A2, & A3) with different steel powder compositions (0 %, 15 %, 25 %, and 35 %) and a constant 75 % clay soil composition were tested. The analysis showed an average baking energy of 0.45 kWh per kg of injera (0.198 kWh per injera) and a thermal efficiency of 86.4 % when baking 4.395 kg of injera. The total heat energy loss was 1402.78 KJ (14.08 % of 10300 KJ input energy). The losses were distributed among the retained (92.17 %), the baking plate (3.95 %), the bottom enclosure (2.08 %), the side enclosure (1.04 %), and the cover lid (0.76 %).

Stabilization of clay soil using alkali-activated sewage sludge

This study investigates the innovative reuse of sewage sludge with eco-friendly alkaline solutes to improve clayey soil without conventional cementitious binders. The unconfined compressive strength (UCS) was the main criterion to assess the quality and effectiveness of the proposed solutions, as this test was performed to measure the strength of the stabilized clay by varying binders’ dosages and curing times. Moreover, the direct shear test (DST) was used to investigate the Mohr-Coulomb parameters of the treated soil. Microstructure observations of the natural and treated soil were conducted using scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), and FTIR. Furthermore, toxicity characteristic leaching procedure (TCLP) tests were performed on the treated soil to investigate the leachability of metals. According to the results, using 2.5% of sewage sludge activated by NaOH and Na2SiO3 increases the UCS values from 176 kPa to 1.46 MPa after 7 d and 56 d of curing, respectively. The results of the DST indicate that sewage sludge as a precursor increases cohesion and enhances frictional resistance, thereby improving the Mohr-Coulomb parameters of the stabilized soil. The SEM micrographs show that alkali-activated sewage sludge increases the integrity and reduces the cavity volumes in the stabilized soil. Moreover, TCLP tests revealed that the solubility of metals in the treated soil alkali-activated by sewage sludge significantly decreased. This study suggests that using sewage sludge can replace cement and lime in ground improvement, improve the circular economy, and reduce the carbon footprint of construction projects.

Integrating rhizosphere bacterial structure and metabolites with soil Cd availability in different parent paddy soils

Soil bacterial community structure and rhizosphere metabolites are important pathways for rice to respond to external Cd stress. The specific correlations between these microorganisms, metabolites and inherent soil properties, as well as the mechanisms they utilize to regulate Cd availability across different parent soils remain underexplored, emphasizing the need for deeper understanding to inform effective soil management strategies. In this study, five typical parent soils with large differences in properties (quaternary red clay soil (hereby defined as Q), granite soil (G), river sandy mud (R), yellow mud soil (Y), stucco field (S)) in Chinese paddy soils were collected, and extra Cd were added (CK: 0 mg·kg−1, Cd: 2.4 mg·kg−1).The result indicated that the toxicity impact of Cd in rice grains in G was the weakest, and the highest Cd bioavailability in S. The abundance of Proteobacteria, Bacteroidota and Firmicutes showed an increasing trend in G, while they decreased significantly in S. The contents of Cis-9-palmitoleic acid and phosphoethanolamine increased by 170.02 % and 154.03 % in G, decreased by 218.62 % and 181.58 % in S. MBNT15 and Desulfobacterota showed a significant negative correlation with humic acid molecular weight (MW) extracted from parent soils and Clay (montmorillonite, illite, kaolinite) contents, while they exhibited a positive correlation with soil organic matter (OM) content (P < 0.01). The MW played a crucial role in shaping rhizosphere metabolites with R2 value of 0.8498. These results elucidate how soil bacterial communities, rhizosphere metabolites, and inherent soil properties interact to regulate Cd availability across different parent soils.