Aggregation Concentration Research Articles

Effects of multiple microplastic types on growth of winter wheat and soil properties vary in different agricultural soils

Societal Impact StatementWinter wheat is one of the most important crops in the world. Microplastics, as an emerging pollutant, are widespread in agricultural soils due to various modern agricultural practices and can have adverse impacts on agricultural soils and plant growth. Herein, we investigated the effects of 10 types of microplastics on the properties of three agricultural soil types and the growth of winter wheat. This study contributes insights toward the conservation of agricultural soils and potential wheat yield responses to microplastic. Understanding the mechanisms that underpin the differences in responses to this pollutant class is of great importance for management recommendations.Summary Microplastics (MPs) (size < 5 mm) are increasingly recognized as anthropogenic contaminants that severely affect terrestrial ecosystems. These particles are always detected as a mixture of various polymer types and shapes. However, we have limited knowledge of the effect of combined MPs on plant–soil systems. To address this, we selected 10 types of MP, applied to three soil types singly and in combination along an increasing gradient of 1, 2, 5, 8, and 10 MP types at a content of 0.4% (w/v). After 8 weeks of pre‐incubation, winter wheat (TOBAK) was grown in each pot for another 8 weeks. Shoot and root biomass, soil aggregation, and carbon and nitrogen content were measured. The effects of the same MP on both soil and plant properties were drastically different (in size and effect direction) in the different soil types. However, no clear patterns were observed along an increasing number of microplastic types, suggesting that knowing the number of microplastic types in a sample, at equity of overall concentration, does not help predict effects. In contrast, our findings reveal the complex effects of multiple MPs on the soil–plant system and highlight that soil properties need to be taken into consideration when studying MP effects on terrestrial systems.

Chestnut soil organic carbon is regulated through pore morphology and micropores during the seasonal freeze–thaw process

Soil aggregates are basic structural units in soil organic carbon (SOC) protection. In alpine ecosystems, the seasonal freeze–thaw (FT) process characterizes soil formation and nutrient cycling. However, previous studies were mostly based on simulated FT experiments, which amplified the effects of natural FT processes. And, the regulations of pore structure on SOC protection/loss of aggregates during the FT processes were still not well understood. To investigate the effect of the seasonal FT process on SOC and pore structure of aggregates, as well as the interactions among them, soil samples were selected during a whole seasonal FT cycle, which can be divided into four periods: unstable freezing (UFP), stable frozen (SFP), unstable thawing (UTP), and stable thawed periods (STP). The results demonstrated that freezing increased SOC concentration as the total organic carbon (TOC) content of all aggregate fractions peaked in the SFP (17.46 g/kg on average). The TOC content of aggregates in the UFP dropped to 7.91 g/kg on average, which revealed a dramatic SOC loss after thawing began. Thawing also decreased the proportions of particulate organic carbon (POC) compared with mineral-associated organic carbon (MAOC). The highest microbial abundance was also found in the SFP. Freezing promoted the formation of pores > 80 μm while thawing increased the regularity of pore morphology. Pore structure explained 48.77 % of the SOC variance in the thawing period, but only 19.29 % of that in the freezing period. Overall, in the freezing process, soil pore structure impacted the SOC input by mediating pore morphology. In the thawing process, soil pore structure inhibited SOC loss by enhancing the formation of pores < 15 μm. These results demonstrate new perspectives on the soil aggregate microstructure–microbe–SOC interactions.

Effect of accelerated carbonation on fine cement paste aggregates

Accelerated carbonation is suggested as a potential alternative for carbon dioxide sequestration, which also improves the microstructure of recycled concrete aggregates. In this study, the carbonation parameters of model aggregates derived from cement pastes with two different water/cement ratios (i.e., 0.5 and 0.7) were evaluated in order to maximize the benefits of the carbonation process on their density and absorption. For this purpose, in a first phase, the initial moisture content of the model aggregates and the reaction time were evaluated. Furthermore, in a second phase of mortar production, the fraction of fine natural aggregates was replaced, considering each type of unprocessed and carbonated model aggregate at volumetric replacement percentages of 50% and 100%, varying the amount of water in the mortar mix to maintain a similar workability in all the series. In this way, the properties of the eight series of mortars are evaluated in comparison with the control series made only with natural aggregates. The results indicate that the accelerated carbonation process positively influences density and absorption in the model aggregate. Regarding the parameters of the accelerated carbonation environment analyzed, for a higher w/c ratio in the original model aggregate, higher initial water content was necessary for the carbonation process to be efficient. As for the mechanical performance of the mortars with model aggregate, the series that incorporated model aggregate aggregates with a w/c ratio of 0.5 achieved better mechanical behavior compared to the series replacing model aggregate with a w/c ratio of 0.7; this was related to the formation of a more compact matrix in the mortar with model aggregate of cementitious pastes.

Influence of aggregate size on pervious concrete properties with and without construction and demolition waste

This research evaluates the impact of aggregate sizes on pervious concrete properties, comparing aggregates of 12.5 mm and 19 mm, as well as replacing natural aggregates with recycled aggregates set at 0% and 50%. Four types of pervious concrete were produced, and their properties were determined: density, porosity, permeability coefficient, compressive strength, flexural tensile strength, and abrasion resistance. The results indicate that water permeability is directly related to pore size and is influenced by aggregate size (90% of the variation in pervious concrete permeability) and, to a lesser extent, by recycled aggregate content (10% of the variation). Mixes with larger aggregates (19 mm) demonstrated higher permeability coefficients. Replacing natural aggregates with recycled aggregate did not significantly affect the mechanical properties of pervious concrete, highlighting the effectiveness of waste processing and mixing procedures, allowing for the incorporation of 50% of recycled aggregate. The concretes met the requirements of the American Concrete Institute, suggesting technically feasible conditions for sustainable practices in the construction industry.

A study on the mechanisms and influencing factors of interfacial physicochemical interactions between asphalt and mineral aggregates based on multiscale evaluation methods

The elucidation of interfacial physicochemical mechanisms between asphalt and mineral aggregates is vital for comprehending the interface formation in asphalt mixtures and enhancing their performance. To this end, multiscale evaluation methods were used to investigate the mechanisms and influencing factors of interfacial physicochemical interactions between asphalt and mineral aggregates (IPIAMA). Initially, the dynamic shear rheometer (DSR) was used to measure the complex shear modulus (G*) of various asphalt mastics. Subsequently, the interface film thickness was calculated using G* in conjunction with the Hashin and Mori-Tanaka (MT) micromechanical models. This indicator facilitated quantitative assessments and the analysis of influencing factors. The results indicated that the MT model underestimated the interface film thickness by approximately 0.08–0.29 % compared to the Hashin model, a discrepancy attributable to assumptions regarding aggregate particle interlocking. Moreover, the interface film thickness systematically varied with factors such as aggregate content, type of aggregate, and type of asphalt, ranging from 0.24 to 0.53 μm. To further elucidate the IPIAMA mechanisms behind these variations, the fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), and the ultraviolet test (UV) testing were conducted. FTIR tests demonstrated that the primary components of mineral aggregates—dolomite, calcite, and quartz—contributed to the physical adsorption increments on asphalt functional groups by 0.0185, 0.0509, and 0.004, respectively. SEM images revealed that dolomite and calcite possessed more surface fissures and pores than quartz. XPS tests showed that calcium carbonate and magnesium carbonate chemically reacted with asphalt, resulting in electron shifts of 0.9 eV and 1.1 eV, respectively, while silicon oxide only exhibited electron shifts when combined with a silane coupling agent-modified asphalt. UV tests demonstrated that lighter asphalt fractions were preferentially absorbed into the pores and micro-cracks of mineral aggregates. Consequently, the complex IPIAMA involved physical adsorption, chemical reactions, and selective absorption, strongly correlating with factors such as mineral composition, surface morphology, and asphalt type.

Specimen size effect on compressive strength of 3D printed concrete containing coarse aggregate with varying water to binder ratios

This study aims to investigate the specimen size effect of compressive strength in 3D printed concrete containing coarse aggregate (3DPCA). Firstly, we compare the specimen size effect of compressive strength in mold-cast concrete (CC) and 3DPCA. Through X-CT scans and image analysis, the underlying mechanisms of this specimen size effect in 3DPCA are revealed. The results indicate that 3DPCA exhibits a less pronounced specimen size effect on compressive strength when loaded along the Z direction compared to CC, due to the presence of interlayer weak zones that mitigate the influence of size variations. Specifically, when the water-binder ratio varies between 0.3 and 0.5, the size coefficient of printed sample is reduced by 0.01–0.07 compared to cast sample. Similarly, variations in coarse aggregate content result in a size coefficient for printed sample that is 0.01–0.05 lower than cast sample. Higher porosity increases the specimen size effect of 3DPCA, but good printing quality can mitigate this influence. A modified Weibull model integrating water-binder ratio and coarse aggregate content was proposed, providing precise predictions of the specimen size effect on 3DPCA's compressive strength, with a correlation coefficient exceeding 93 %.

Effect of key design parameters on the physical / mechanical properties of coarse aggregated UHPC and its structural response subjected to bending

This study experimentally investigates the effect of key design parameters on the physical, mechanical and structural performance of coarse aggregated ultra-high performance concrete (CA-UHPC), with an aim to provide design guidance for on-site engineering applications. The variables of maximum aggregate size, aggregate content, fiber dosage and curing condition are selected for investigation. The results showed that increasing aggregate size does not significantly affect the compressive strength, but somewhat increases the elastic modulus and fracture energy; the increase of aggregate content results in a reasonable increase of compressive strength and elastic modulus. In particular, the 480 kg/m3 coarse aggregated UHPC shows a compressive strength of ∼150 MPa, elastic modulus of ∼50 GPa, autogenous shrinkage of <200 µε, and outstanding durability. The structural specimens fabricated with coarse aggregated UHPC exhibit excellent load-carrying capacity and ductility when subjected to four-point bending. More importantly, it was found that the effect of curing condition on the structural performance is insignificant. The results of this study can provide insights into the development of advanced UHPC materials and structures and promote their applications in practice.

Design and optimization of a colorimetric biosensor using functionalized gold nanoparticles and bi-functional linker for agriculture and food industry

This study aims to develop a highly sensitive colorimetric detection system utilizing functionalized gold nanoparticles (f-AuNPs) and bifunctional linkers (BLs) for the detection of pathogens and contaminants in food matrices. The primary objective was to explore and optimize key parameters, including reaction time, system volume and the concentration of bifunctional linkers, in order to enhance the system’s detection capabilities. The core mechanism of the bi-functional linker-based detection system is based on the aggregation of streptavidin-functionalized AuNPs (stAuNPs), which varies in accordance with the concentration of the bifunctional linkers (BLs) and reflects the quantity of effective linkers (EALs) available in the system. The process comprises the binding of the targets and BLs, a reduction in EAL concentration, an increase in the BLs concentration required for the aggregation of the stAuNPs, and a shift in the range exhibiting a visible color change (REVC). In systems without a target, all BLs induce aggregation. In contrast, in systems with a target present, some BLs are bound by the target, reducing EAL concentration and altering the optimal BLs concentration for stAuNP aggregation. The system was shown to be capable of detecting protein in PBS at concentrations as low as 2 nM, as well as Salmonella at 101 CFU/mL. In whole milk, the detection limits were 20 nM for protein and 102 CFU/mL for Salmonella. The principal conclusion is that the BLs-based system provides a robust and adaptable platform for pathogen detection, even in complex food matrices, obviating the need for preprocessing. The findings demonstrate the system’s potential for practical applications in the fields of food safety and agricultural contaminant detection, offering clear visual signals and high sensitivity.

Distribution Characteristics of Soil Aggregate Stability and Organic Carbon of Different Grassland Types in the Temperate Desert of Longzhong Loess Plateau

Soil aggregate stability and organic carbon （SOC） are important indicators of soil structure and quality and play a key role in the improvement of soil quality in temperate deserts. This study aimed to investigate the distribution patterns, stability of soil aggregates, and variation characteristics of the content of aggregate organic carbon in different grassland types in temperate deserts and their interrelationships. Four grassland types in a temperate desert （Kalidium foliatum type, Reaumuria songarica type, Salsola passerina type, and Sympegma regelii type） in the Longzhong Loess Plateau as research objects, and the soil aggregate particle size distribution characteristics were determined using the wet sieving method. The stability of soil aggregates was analyzed by calculating aggregate stability indicators and the contribution of aggregate particle size SOC to bulk soil SOC content. Correlation analysis, principal component analysis, and linear fitting equations were used to reveal the relationship between the soil aggregate content and aggregate particle size SOC and aggregate stability. The results showed that the content of &gt;0.25 mm aggregates （R0.25）, mean weight diameter （MWD）, geometric mean diameter （GMD）, and bulk soil SOC content in each soil layer （0-10, 10-20, and 20-30 cm） of the K. foliatum type grassland were significantly higher than that of the R. songarica type and S. regelii type （P&lt;0.05）. The SOC content of 0.053-0.25 mm and &lt;0.053 mm particle size in each soil layer of the K. foliatum type grassland were significantly higher than that of the S. regelii type （P&lt;0.05）. Surface and subsurface soils （0-10 cm and 10-20 cm） had the significantly highest contribution of 0.25-2 mm particle size SOC to the bulk soil SOC content （P&lt;0.05）. Additionally, as the soil layer deepened, the R0.25, MWD, GMD, bulk soil, and aggregate SOC contents of the K. foliatum type grassland showed a tendency to increase first and then decrease, with the highest contents from 10-20 cm. Kalidium foliatum type grassland aggregate content was dominated by 0.25-2 mm aggregates, whereas the other three grassland types were dominated by 0.053-0.25 mm aggregates. In addition, bulk soil SOC content was significantly correlated with R0.25, MWD, GMD, and ELT （P&lt;0.01）, and the 0.25 mm aggregate was the critical size of positive and negative correlation. R0.25, MWD, GMD, and ELT values were the key factors influencing bulk soil SOC in grassland. The equation fitted to bulk soil SOC content, and GMD was the most suitable to describe the relationship between SOC content and the stability of soil aggregates. Therefore, compared with other grassland types, K. foliatum type grassland had a promoting effect on the soil aggregate stability and the improvement of soil quality.

Effects of Terracing on Soil Aggregate Stability and Erodibility in Sloped Farmland in Black Soil (Mollisols) Region of China

Soil aggregates are important indicators of soil structure stability and quality. The black soil region of northeast China, known for its high agricultural productivity, faces significant challenges due to soil erosion. This study investigates the impact of terracing on the stability and erodibility characteristics of soil aggregates in sloped farmlands, which is crucial for this important agricultural area. Three research sites with the same basic management modes were selected along a latitudinal gradient, from the mid-temperate zone to the cold temperate zone, in the black soil region of northeast China. The Savinov method was used to analyze the differences in soil aggregate size distribution, stability characteristics, and soil erodibility between terraced and non-terraced slopes at each research site. The results showed that terracing increased the content of large soil aggregates (&gt;0.25 mm) by 5.38–6.35%, with the increase becoming more pronounced from north to south. The improvement in soil structure varied by location and slope position, with the most significant improvement at the middle slope position. Terracing enhanced soil aggregate stability, reduced soil erodibility, and improved soil structure by increasing clay and soil organic matter (SOM) content and reducing soil bulk density (BD), promoting the conversion of small aggregates to large aggregates. Soil stability indicators such as water-stable aggregates (WSAs), mean weight diameter (MWD), and geometric mean diameter (GMD) were dominated by aggregates &gt; 5 mm, while erodibility indicators such as fractal dimensions (Ds) and the soil erodibility factor (K values) were mainly influenced by aggregates &lt; 0.25 mm. Terraces can improve the soil structure and stability of sloping farmland by increasing the content of large soil aggregates and enhancing overall soil quality. The benefits of these improvements increase with latitude. These findings provide critical insights for determining effective management practices for sloped farmlands in the black soil region under various site conditions. They offer scientific evidence for preventing soil erosion and improving soil quality, thus supporting the sustainable development strategy for protecting black soil and ensuring long-term agricultural productivity.

Decade-long effects of integrated farming systems on soil aggregation and carbon dynamics in sub-tropical Eastern Indo-Gangetic plains

Integrated farming system (IFS) aims to diversify the agricultural landscapes by incorporating different components to meet the multifarious needs of the burgeoning population. The present study was undertaken to understand the impact of different cropping systems on soil organic carbon (SOC) stock, aggregate distribution, and aggregate associated organic carbon (AAOC) in 2-IFS models of varying sizes (0.4 and 0.8 ha) established during 2008–2009. After 10 years of the study, the fodder system registered the greatest TOC and carbon stocks across IFS models, with surface soil (0–15 cm) accumulating 17 and 13% higher TOC and C stock, respectively, in 0.4 and 0.8 ha models. In 0–15 cm, macroaggregates (Ma) represented the highest proportion (75–76%) in both models. Among cropping systems, the fodder system recorded the highest large macroaggregates in both IFS models. Within 0–30 cm depth, small macroaggregates are mostly found in the perennial system (fodder, guava+turmeric, and lemon intercropping system), indicating the potential to improve the aggregate stability over the seasonal (shorter duration) system. In general, micro aggregate (Mi) fraction was pre-dominant in sub-surface soil (17.35%). The maximum AAOC was found in Ma compared to Mi fractions, with approximately 67 and 63% of total carbon associated with Ma in 0.4 and 0.8 ha IFS models, respectively. Interestingly, the 0.8 ha IFS model had higher TOC (~11%) and carbon stock (~12%) than the 0.4 ha model, but AAOC did not show a similar result, indicating the influence of cropping systems on AAOC. The study indicated that the fodder-based production system had better performance in terms of soil physical health and increased aggregate stability and content of soil carbon. This is indicative of the advantages of perennial-based systems over seasonal- or annual-based cropping systems for soil sustainability in Eastern Indo-Gangetic Plains.

Meso-crack propagation of RC induced by non-uniform rebar corrosion and the predictive model of time to concrete cover cracking

Non-uniform corrosion expansion in reinforced concrete (RC) structures will lead to concrete cracking, bond degradation, and an overall reduction in load-bearing capacity, severely threatening structural safety and durability. Accordingly, meso-crack propagation of RC induced by non-uniform rebar corrosion and the predictive model of time to concrete cover cracking are investigated in this paper, and the theoretical solutions for the critical corrosion rate and the corresponding time are proposed for structural durability evaluation and design. Firstly, based on the mesh-mapping technique of multi-shape random aggregates, a finite-element generation method for three-dimensional concrete three-phase meso-scale model is proposed, with modeling corrosion-expanded cracking of RC, reproducing the crack morphology and propagation process of concrete cracking due to non-uniform rebar corrosion. Subsequently, single factor influence analysis and multi-factor orthogonal test were employed to reveal the degrees of influence of various factors on the critical corrosion rate as follows: concrete strength > cover thickness > interface layer strength > aggregate content > aggregate grading > aggregate shape. A theoretical predictive model for the corrosion expansion cracking time of the RC cover was proposed, considering the influence of key factors including concrete strength and cover thickness. Finally, the validity of theoretical prediction method and the numerical model’s damage mode are verified through accelerated corrosion tests of RC.

Smooth vetch covering alters soil aggregate microbial metabolic limitations in citrus orchards

Green manure covering alters the supply-demand relationship between soil resources and microorganisms by improving soil structure and increasing carbon inputs. However, it remain unclear how soil microorganism respond to the imbalance between resources and demands at the aggregate scale. The present study analyzed the stoichiometric ratios of organic carbon, nitrogen, and phosphorus nutrients, microbial extracellular enzyme activities, and biomass in large macroaggregates (LMA, 2–8 mm), small macroaggregates (SMA, 0.25–2 mm), and microaggregates (MIA, < 0.25 mm) under smooth vetch covering. The relationship between microbial carbon use efficiency and nutrient restriction in soil aggregates was elucidated and the alteration was revealed in microbial metabolic pathways and carbon sequestration functions within soil aggregates under green manure covering. The results showed that: (1) Smooth vetch covering significantly increased the C: N resource imbalance (ln(MBC: MBN)/ln(SOC: TN)) in soil aggregates from 0.50 to 0.69, and thus increased the nitrogen requirement of soil aggregates. However, the N:P resource imbalance (ln(MBN: MBP)/ln(TN: TP)) decreased from 2.25 to 1.78, especially in microaggregates. (2) To mitigate the limitation imposed by nitrogen availability at the aggregate level, microorganisms have ramped up the activity of C- (46.72 %–98.64 %), N- (2.32 %–121.00 %), and P- acquiring enzymes (119.11 %–187.78 %). Nevertheless, the spatial heterogeneity inherent in soil aggregates, characterized by varying particle sizes, has led to a pivotal shift in microbial nutrient limitation. As soil aggregate size diminishes, the primary constraint on microbial activity transitions from nitrogen limitation to phosphorus limitation, reflecting the dynamic interplay between soil structure and nutrient availability. (3) In addition, smooth vetch covering increased the microbial carbon use efficiency of soil aggregates, and it increased with the increase of the particle size of soil aggregates: LMA (178.80 %) > SMA (147.23 %) > MIA (9.99 %). Microorganisms allocated more energy to generate biomass instead of obtaining limiting nutrient elements. These results indicate that smooth vetch covering could increase the organic carbon content of soil aggregates. In addition, in order to adapt to nutrient imbalance, soil aggregates microorganisms choose a “egoistic” metabolic pathway, which alleviates nutrient limitation and assimilated more energy and nutrients into their own biomass and reduces the release of organic carbon. It is evident that integrating Vicia villosa Roth var. glabresens Koch as a ‘green manure’ in orchards serves a dual purpose: it mitigates the environmental impact of chemical fertilizers while simultaneously promoting soil carbon sequestration. This approach offers a robust theoretical framework for achieving the harmonious integration of ecological sustainability and economic viability in economic forestry, such as citrus orchards.

Poly-γ-glutamic acid enhanced the yield and photosynthesis of soybeans by adjusting soil aggregates and water distribution.

Poly-γ-glutamic acid (γ-PGA) is employed extensively in agriculture to enhance soil water retention; however, the underlying mechanism by which γ-PGA improves soil structure and soybean productivity in arid regions remains poorly understood. A micro-scale field experiment was conducted in the arid region of northwest China, employing five concentrations of γ-PGA to investigate its impacts on soybean yield, photosynthesis, and water-use efficiency, as well as soil aggregates and water distribution. The five levels of γ-PGA were 0 (CK), 10 (P1), 20 (P2), 40 (P3), and 80 kg ha-1 (P4). The results demonstrated that the application of γ-PGA significantly improved soybean yield, photosynthesis, and chlorophyll content. It resulted in a decrease in soil aggregate content with a maximumdiameter of less than 0.053 mm and an increase in the stability of soil aggregates in the uppermost layer of the soil (0-30 cm). The application of γ-PGA significantly increased soil water content, particularly in the uppermost layer of the soil, and effectively reduced water consumption and improving water use efficiency in soybeans. Overall, the P3 treatment exhibited the most pronounced improvement of soybean yield, photosynthesis, water-use efficiency, as well as distribution of soil aggregates and water. The correlation matrix heatmap also revealed a strong correlation between improvement of soybean yield or photosynthesis at various γ-PGA application levels and the enhancement of soil stability or soil water content. The multivariate regression analysis revealed that an optimal application level of 46 kg ha-1 γ-PGA could enhance effectively both yield and water use efficiency of soybean in the arid region of northwest China. © 2024 Society of Chemical Industry.

Long-term straw return increases fungal residual contribution to soil microaggregate nitrogen pool: An eco-enzymatic stoichiometric study

Straw return is a widespread agricultural practice for improving cropland nitrogen (N) stocks. However, the contribution of microbial N to the soil aggregate N pool and the underlying microbial metabolic regulation mechanisms remain uncertain. This study was based on a 13-year field experiment with rice (Oryza sativa L.) and wheat (Triticum aestivum L.) rotation, using only a chemical fertilizer alone (CF) as the control. We analyzed the effects of the chemical fertilizer combined with (CS, 9500 kg ha−1 y−1) and wheat (4000 kg ha−1 y−1) straw on microbial derived-N, microbial carbon (C) and N limitations. We also assessed microbial N use efficiency (NUE) in various aggregates of ferric lixisols (0–20 cm). Rotary tillage reached a depth of 20 cm. The CS significantly increased microbial-derived N concentrations in soil aggregates and enhanced the contribution of fungal residual N to the N pool in aggregates < 0.25 mm, but did not affect those > 0.25 mm. Conversely, the bacterial contribution to the N pool was not affected by CS. Meanwhile, CS significantly increased the soil organic C and microbial biomass in the aggregates. The results of our eco-enzymatic stoichiometric model revealed that the CS significantly alleviated microbial C limitations and increased microbial NUE in soil aggregates. Structural equation modeling further revealed that the microbial biomass and soil organic C contents are key drivers of the microbial C limitation. The increased contribution of fungal residual N to the N pools in < aggregates 0.25 mm was attributed to improved microbial NUE resulting from the straw, without altering net N mineralization rates or β-1,4-N-acetylglucosidase activity. Our findings suggest that straw return promotes microbial-derived N production and sequestration by alleviating microbial C limitation. The strategies governing these microbial-derived N responses in aggregates to straw return might vary. This might be valuable for designing cropland management practices to improve N storage.

A 44-year balanced fertilizer application affected rill erosion resistance by changing humus, aggregates, and polyvalent cation

Fertilizer application can affect the physicochemical properties of soil, such as the contents of large aggregates, humus, and exchangeable cations, thereby influencing soil erosion resistance. However, the rill erosion resistance and its key influencing factors of soil following long-term balanced fertilizer application remains unclear. This study aimed to analyze the change in rill erosion resistance following 44 years of balanced fertilizer application (No changes in the type of fertilizer) to non-calcareous soils and establish a Partial Least Squares Regression (PLSR) model of rill erodibility (kd) and soil critical shear stress (τc) to changes in the physical and chemical properties of the soil. Five treatments were designed: (1) CK (no fertilizer applied), (2) N (nitrogen), (3) NP (nitrogen plus phosphorus), (4) NK (nitrogen plus potassium), and (5) NPK (nitrogen, phosphorus, and potassium). Compared to CK, the N, NP, NK, and NPK application significantly increased τc by 49.6, 96.7, 73.6, and 36.2 %, respectively. Whereas, kd increased significantly only in the NPK treatment group. The optimal partial least squares regression model showed that mean weight diameter (MWD) had the greatest positive influence on soil critical shear stress, followed by fulvic acid (FA) content, whereas water-dissolved substances had a negative influence. Long-term balanced fertilizer application can increase MWD and τc by combining micro-aggregates and humus into large aggregates. Ca2+ content had the greatest positive effect on kd. Compared with that of CK, exchangeable Ca2+ content increased significantly with NP and NPK application (7.9 and 34.3 %, respectively). Ca2+ can increase kd by binding to the polar functional groups in FA to promote the shedding of hydration shells in large aggregates. Among all treatments, the NP treatment showed the best performance for reducing kd and increasing τc. This study could contribute to the understanding of the rill erosion process and modeling in non-calcareous soils and offer a reference for agricultural erosion control treatments.

Mesoscopic Numerical Simulation of Freeze–Thaw Damage in Hydraulic Concrete

To investigate the impact of freeze–thaw damage on the mechanical properties of concrete, this study utilized Python in combination with ABAQUS 2016 to generate a two-dimensional meso-scale model of concrete. Uniaxial compression tests were conducted on the concrete after freeze–thaw cycles to study the evolution of its mechanical properties. Using “relative compressive strength” as a variable, the relationships between this variable and the parameters of the freeze–thaw damage model were determined, leading to the establishment of the freeze–thaw damage model and the simulation of compressive tests on concrete after freeze–thaw cycles. This study also explored the changes in the mechanical properties of concrete with variations in ITZ parameters and coarse aggregate content. The conclusions drawn are as follows: A comparison with experimental data showed that the model ensures that the relative error of each mechanical property parameter does not exceed 7%, verifying the model’s rationality. Increasing the ratio of ITZ parameters improved the mechanical properties of the ITZ, enhancing the overall mechanical performance, but had almost no effect on the elastic modulus. Compared to ratios of 0.7 and 0.8, concrete with a ratio of 0.9 showed slower rates of decrease in compressive strength and elastic modulus and slower rates of increase in peak compressive strain after freeze–thaw cycles. The increase in coarse aggregate content had a similar effect on the strength and freeze–thaw resistance of concrete as the ratio of ITZ parameters. Concrete with a coarse aggregate content of 60% exhibited slower rates of change in mechanical properties after freeze–thaw cycles.

Mechanical Characteristics and Durability of Metakaolin-Based Self-Compacting Geopolymer Concrete as A Function of Recycled Aggregate and Steel Fiber Contents

Mechanical Characteristics and Durability of Metakaolin-Based Self-Compacting Geopolymer Concrete as A Function of Recycled Aggregate and Steel Fiber Contents

Study of the thermal stability of spent bleaching clay-based geopolymer with waste polypropylene plastic aggregates

This study incorporated polypropylene (PP) plastic waste into the spent bleaching clay (SBC)-based geopolymer as aggregates, aiming to address pollution from plastic and edible oil industry waste while promoting a transition into circular economy of repurposing waste. The geopolymer mixture paste, containing PP plastic aggregates in different mass ratios (SBC:PP = 1:0.4, 1:0.6, 1:0.8, and 1:1) is oven cured at 60 °C and 80 °C for 8 h followed by 7 days of room temperature curing. Thermal properties of PP-SBC-based geopolymer mortars with varying compositions of PP plastic were assessed using Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). The TGA results revealed that the geopolymer's thermal stability within the temperature range of 620 °C–700 °C improved with an increase in PP plastic aggregate content, up to an optimal amount of 1:08 PPSBCG sample ratio of SBC to PP cured at oven temperature of 80 °C has been chosen as the representative sample for further discussion based on analysis result of ATR-FTIR spectroscopy and BET analysis. Beyond this amount, a reverse trend was observed. The DSC analysis revealed that incorporating PP plastic aggregates reduced its thermal stability towards the melting reaction but improved its thermal insulation properties. However, this effect was observed only up to a composition of PP plastic relative to SBC of 0.6, beyond this threshold, a reverse trend was observed. In addition to TGA and DSC, the geopolymer samples were characterized using Attenuated Total Reflectance - Fourier Transform Infrared (ATR-FTIR) spectroscopy and N2 Brunauer-Emmett-Teller (BET) analysis. This study proved that the addition of high heat-resistant PP plastic into the geopolymer system increased the thermal stability of geopolymers, but only up to a certain optimal quantity. Excessive PP plastic resulted in a reverse trend due to significant effect of weakened interfacial bonding between the geopolymer matrix.

Long-term evolution of soil quality in citrus orchard terrace system: A whole life cycle perspective

Terracing is widely recognized as an effective strategy for mitigating soil erosion and preserving soil quality. This study aimed to evaluate the variations in soil aggregate C, N, and P composition, as well as the soil quality index (SQI), in subtropical citrus orchards of different plantation ages (PA) and across various terrace positions (TP). Surface soil samples (0–20 cm) were collected from four TP categories: terrace wall (TW), slub ditch (SD), under grove (UG), and between grove (BG), across varying PA (5, 15, 25, 35, and 45 years). The results showed the C, N, and P concentrations in most soil aggregates, along with the SQI of the slub ditch and under grove, increased significantly with plantation age. Compared to the 5-year-old plantations, the SQI of the slub ditch and under grove increased by 84 % and 66 % at 45 years, respectively. The aggregate stability and SQI of BG generally trended upwards but declined at 25 and 35 years. By 45 years, the SQI of the terrace wall was significantly lower than that of other positions, being 58 %, 61 %, and 39 % lower compared to the slub ditch, under grove, and between grove, respectively. Additionally, the C/P and N/P ratios of the terrace wall were higher than those of other positions, indicating phosphorus limitation in TW. Path analysis revealed plantation ages had greater effects on SQI. Aggregate stability and soil properties showed significant positive impacts on SQI. Overall, as plantation age increased, the differences in SQI among the slub ditch, under grove, and between grove decreased, while the terrace wall exhibited the weakest erosion resistance. Therefore, efforts should be made to restore the ecological function of the terrace wall, such as by colonizing it with moss. Additionally, reasonable tillage plans, including appropriate fertilization, should be formulated to enhance orchard soil quality.