Existing strength criteria are mostly formulated to describe the mechanical properties of reconstituted soils. However, the engineering characteristics of structured soils are different from those of reconstituted soi...Existing strength criteria are mostly formulated to describe the mechanical properties of reconstituted soils. However, the engineering characteristics of structured soils are different from those of reconstituted soils in many aspects, especially in their strength properties, Thus, the influence of soil structure （bonding and fabric） on the mechanical properties of structured soils cannot be correctly described, By analyzing the breakage mechanism of natural soils, the structured soils can be conceptualized as binary medium materials consisting of bonded blocks and weakened bands. On this basis, a new strength criterion is pro- posed for structured soils, The expressions of the strength criterion on both meridian and deviator planes are given to describe the strength properties of structured soils on these planes. The proposed strength criterion is compared with available test data under conventional and true triaxial stress conditions in the literature. It is observed that the proposed strength criterion agrees well with the test data.展开更多
Structure is an evident determinant for macroscopic behaviors of soils.However,this is not taken into account in most constitutive models,as structure is a rather complex issue in models.For this,it is important to de...Structure is an evident determinant for macroscopic behaviors of soils.However,this is not taken into account in most constitutive models,as structure is a rather complex issue in models.For this,it is important to develop and implement simple models that can reflect this important aspect of soil behavior.This paper tried to model structured soils based on well-established concepts,such as critical state and sub-loading.Critical state is the core of the classic Cam Clay model.The sub-loading concept implies adoption of an inner(sub-loading)yield surface,according to specific hardening rules for some internal strain-like state variables.Nakai and co-workers proposed such internal variables for controlling density(p)and structure(ω),using a modified stress space,called tij.Herein,similar variables are used in the context of the better-known invariants(p and q)of the Cam Clay model.This change requires explicit adoption of a non-associated flow rule for the sub-loading surface.This is accomplished by modifying the dilatancy ratio of the Cam Clay model,as a function of the new internal variables.These modifications are described and implemented under three-dimensional(3D)conditions.The model is then applied to simulating laboratory tests under different stress paths and the results are compared to experiments reported for different types of structured soils.The good agreements show the capacity and potential of the proposed model.展开更多
Evaluating the stabilized lead(Pb)-contaminated soils through sampling and laboratory testing involves costly and time-consuming processes.Therefore,this study employed a low-cost and non-destructive resistivity tool ...Evaluating the stabilized lead(Pb)-contaminated soils through sampling and laboratory testing involves costly and time-consuming processes.Therefore,this study employed a low-cost and non-destructive resistivity tool to evaluate the Pb-contaminated soils stabilized by electrolytic manganese residue(EMR)-based geopolymer(EG-OPC)from the strength and environmental benefits perspective.First,unconfined compressive strength(UCS)and leaching tests were conducted to study the stabilization effectiveness of EG-OPC.Results indicated that the UCS values of soil(5000 mg/kg of pollutants)stabilized by 20%EG-OPC were 4.87 MPa and 8.13 MPa after 7 d and 60 d of curing,respectively.After 60 d of curing,the Pb concentration in the leachate reached 44 mg/L,far lower than the control group(321 mg/L).Second,soil,pore water,and leachate resistivity(ERS,ERW,and ERL)were measured to establish fitting relationships with strength parameters and pollution risk.The good fitting results(e.g.ERS/ERW versus UCS/secant modulus(E50):correlation coefficient R2 z 0.9,ERS/ERW versus Pb contents:R2 z 0.9,and ERL versus Pb2þconcentration:R2¼0.92)and well used Archie's law(ERS versus ERW:R2>0.9)indicate that the resistivity can be used to evaluate the stabilization effectiveness.Furthermore,the microscopic results revealed two behaviors,demonstrating the reliability of resistivity:(1)with the hydration process,resistivity increases due to a denser structure and lower amounts of free water and Pb ions,and(2)the addition of Pb reduces resistivity due to its inhibition or even destructive effects on cementation and formation of hydration products.展开更多
Soil aggregate stability is a fundamental measure for evaluating soil structure.While numerous tests exist for assessing soil aggregate stability,ultrasonic agitation(UA)is widely recognized for its effectiveness.None...Soil aggregate stability is a fundamental measure for evaluating soil structure.While numerous tests exist for assessing soil aggregate stability,ultrasonic agitation(UA)is widely recognized for its effectiveness.Nonetheless,a significant limitation of UA is the lack of standardized methodologies and stability assessment criteria,resulting in inconsistency and incomparability across studies.Several critical factors influence the assessment of soil aggregate stability,including sample preparation(e.g.,drying,sieving,and settling duration),initial and final aggregate size classes,the definition of final energy form and its calculation,variations in instrumentation and laboratory procedures,and the absence of standardized criteria.Unlike some stability methods,UA produces a broad range of results,with dispersion energy varying significantly(0.5–13440 J g^(-1))across different soil and aggregate types due to divergent procedural settings.These settings encompass factors such as initial power and amplitude,temperature fluctuation,soil/water ratio,probe specification(diameter and insertion depth),and the choice of liquid used during the process.Furthermore,UA faces challenges related to limited reproducibility,raising doubts about its status as a standard stability assessment method.To address these issues,standardization through predefined procedures and stability criteria has the potential to transform UA into a precise and widely accepted method for both qualitative and quantitative assessments of soil stability.In this comprehensive review,we outline the challenges in standardizing UA,elucidate the factors contributing to dispersion energy variation,and offer practical recommendations to establish standardized protocols for UA in soil aggregate stability assessments.展开更多
Global climate change exerts profound effects on snow cover,with consequential impacts on microbial activities and the stability of soil organic carbon(SOC)within aggregates.Northern peatlands are significant carbon r...Global climate change exerts profound effects on snow cover,with consequential impacts on microbial activities and the stability of soil organic carbon(SOC)within aggregates.Northern peatlands are significant carbon reservoirs,playing a critical role in mitigating climate change.However,the effects of snow variations on microbial-mediated SOC stability within aggregates in peatlands remain inadequately understood.Here,an in-situ field experiment manipulating snow conditions(i.e.,snow removal and snow cover)was conducted to investigate how snow variations affect soil microbial community and the associated SOC stability within soil aggregates(>2,0.25-2,and<0.25 mm)in a peatland of Northeast China.The results showed that snow removal significantly increased the SOC content and stability within aggregates.Compared to the soils with snow cover,snow removal resulted in decreased soil average temperatures in the topsoil(0-30 cm depth)and subsoil(30-60 cm depth)(by 1.48 and 1.34°C,respectively)and increased freeze-thaw cycles(by 11 cycles),consequently decreasing the stability of aggregates in the topsoil and subsoil(by 23.68%and 6.85%,respectively).Furthermore,more recalcitrant carbon and enhanced SOC stability were present in microaggregates(<0.25 mm)at two soil depths.Moreover,reductions in bacterial diversity and network stability were observed in response to snow removal.Structural equation modeling analysis demonstrated that snow removal indirectly promoted(P<0.01)SOC stability by regulating carbon to nitrogen(C:N)ratio within aggregates.Overall,our study suggested that microaggregate protection and an appropriate C:N ratio enhanced carbon sequestration in response to climate change.展开更多
It has been well documented that natural normally-consolidated marine soils are generally subjected to the effects of soil structure. The interpretation of the resistance of soil structure is an important issue in the...It has been well documented that natural normally-consolidated marine soils are generally subjected to the effects of soil structure. The interpretation of the resistance of soil structure is an important issue in the theory study and engineering practice of ocean engineering and geotechnical engineering. It is traditionally considered that the resistance of soil structure gradually disappears with increasing stress level when the applied stress is beyond the consolidation yield stress. In this study, however, it is found that this traditional interpretation of the resistance of soil structure can not explain the strength behavior of natural marine deposits with a normally-consolidated stress history. A new interpretation of the resistance of soil structure is proposed based on the strength behavior. In the preyield state, the undrained strength of natural marine deposits is composed of two components: one developed by the applied stress and the other developed by the resistance of soil structure. When the applied stress is beyond the consolidation yield stress, the strength behavior is independent of the resistance of soil structure.展开更多
Naturally deposited or residual soils exhibit more complicated behavior than remolded clays. A dual-surface damage model for structured soils is developed based on the thermodynamics framework established in our first...Naturally deposited or residual soils exhibit more complicated behavior than remolded clays. A dual-surface damage model for structured soils is developed based on the thermodynamics framework established in our first paper. The shift stresses and the transformation between the generalized dissipative stress space and actual stress space are established following a systematic procedure. The corresponding constitutive behavior of the proposed model is determined, which reflects the internal structural configuration and damage behavior for geomaterials. Four evolution variables κj^i（i=D, R;j=V, S） and the basic parameters λ, s, v and e0 are introduced to account for the progressive loss of internal structure for natural clays. A series of fully triaxial tests and isotropic compression tests are performed for structured and reconstituted samples of Beijing and Zhengzhou natural clays. The validation of the proposed model is examined by comparing the numerical results with the experimental data.展开更多
The possibilities of the particle finite element method(PFEM)for modeling geotechnical problems are increasingly evident.PFEM is a numerical approach to solve large displacement and large strain continuum problems tha...The possibilities of the particle finite element method(PFEM)for modeling geotechnical problems are increasingly evident.PFEM is a numerical approach to solve large displacement and large strain continuum problems that are beyond the capabilities of classical finite element method(FEM).In PFEM,the computational domain is reconfigured for optimal solution by frequent remeshing and boundary updating.PFEM inherits many concepts,such as a Lagrangian description of continuum,from classic geomechanical FEM.This familiarity with more popular numerical methods facilitates learning and application.This work focuses on G-PFEM,a code specifically developed for the use of PFEM in geotechnical problems.The article has two purposes.The first is to give the reader an overview of the capabilities and main features of the current version of the G-PFEM and the second is to illustrate some of the newer developments of the code.G-PFEM can solve coupled hydro-mechanical static and dynamic problems involving the interaction of solid and/or deformable bodies.Realistic constitutive models for geomaterials are available,including features,such as structure and destructuration,which result in brittle response.The solutions are robust,solidly underpinned by numerical technology including mixedfield formulations,robust and mesh-independent integration of elastoplastic constitutive models and a rigorous and flexible treatment of contact interactions.The novel features presented in this work include the contact domain technique,a natural way to capture contact interactions and impose contact constraints between different continuum bodies,as well as a new simplified formulation for dynamic impact problems.The code performance is showcased by the simulation of several soil-structure interaction problems selected to highlight the novel code features:a rigid footing insertion in soft rock,pipeline insertion and subsequent lateral displacement on over-consolidated clay,screw-pile pull-out and the dynamic impact of a free-falling spherical penetrometer into clay.展开更多
Studies conducted over several decades have shown that the freeze-thaw cycles are a process of energy input and output in soil, which help drive the formation of soil structure, through water expansion by crystallizat...Studies conducted over several decades have shown that the freeze-thaw cycles are a process of energy input and output in soil, which help drive the formation of soil structure, through water expansion by crystallization and the movement of water and salts by thermal gradients. However, most of these studies are published in Russian or Chinese and are less accessible to international researchers. This review brought together a wide range of studies on the effects of freezing and thawing on soil structure. The following findings are summarized： i） soil structure after freeze-thaw cycles changes considerably and the changes are due to the mechanical fragmentation of soil coarse mineral particles and the aggregation of soil fine particles; ii） the particle size of soil becomes homogeneous and the variation in soil structure weakens as the number of freeze-thaw cycles increases; iii） in the freezing process of soil, an important principle in the variation of soil particle bonding is presented as： condensation →aggregation→ crystallization; iv） the freeze-thaw cycling process has a strong effect on soil structure by changing the granulometric composition of mineral particles and structures within the soil. The freeze-thaw cycling process strengthens particle bonding, which causes an overall increase in aggregate stability of soil, showing a process from destruction to reconstruction.展开更多
A trial of interplanting and non-interplanting villous amomum (Amomum villosum Lour.) under the canopy of Chinese fir (Cunninghamia lanceolata Hook.) at age 22 was established in Sanming, Fujian of China, and a survey...A trial of interplanting and non-interplanting villous amomum (Amomum villosum Lour.) under the canopy of Chinese fir (Cunninghamia lanceolata Hook.) at age 22 was established in Sanming, Fujian of China, and a survey on soil fertility was carried out 10 years after its establishment. Compared with the control (non-interplanting), the properties of soil humus in agroforestry system were ameliorated, with a higher level of humification and resynthesis of organic detritus. The soil microbial population and enzymatic activities were both higher under the influence of villous amomum. Both the nutrient supplying and nutrient conserving capacities of the soil were improved. This agroforestry system exhibited an advantage of improved soil fertility as well as an accelerated growth of Chinese fir, it was, therefore, a sustainable management system suited for Chinese fir in South China.展开更多
Soil properties were investigated in sites where three succeeding generationsof Chinese fir (Gunning-hamia lanceolata, (Lambert) Hooker) in Nanping, Fujian, China, werecultivated in order to show the impact of a repea...Soil properties were investigated in sites where three succeeding generationsof Chinese fir (Gunning-hamia lanceolata, (Lambert) Hooker) in Nanping, Fujian, China, werecultivated in order to show the impact of a repeated monoculture on site productivity. Compared withthe first generation (FG) stand the soil structure deteriorated in the second generation (SG) andthe third generation (TG) stands. For instance, the destruction rate of the peds increased by 55%-115% in the SG and the TG stands compared to the FG stand. Soil nutrient storage and nutrientavailability also decreased in the SG and the TG stands. For surface soils of 0-20 cm, the organicmatter content, total N and P, and available N and P decreased by 3%-20% relative to those in the FGstand. For many soil parameters, the differences between the FG stand and the SG and the TG standswere statistically significant (LSD test, P < 0.05). Furthermore, with each succeeding generation ofChinese fir, the total number of soil microbes declined, the soil enzyme activity weakened, and thesoil biological activity decreased. In order to maintain sustainable site productivity, newsilvicultural practices need to be developed for management of Chinese fir plantations.展开更多
Traditional vegetation techniques for the control of concentrated flow erosion are widely recognized, whereas only a few studies have experimentally investigated the impacts of belowground roots on the erodibility of ...Traditional vegetation techniques for the control of concentrated flow erosion are widely recognized, whereas only a few studies have experimentally investigated the impacts of belowground roots on the erodibility of topsoils in semi-arid areas. To quantify the effects of root architectures on soil erodibility and its relevant structural properties, simulated flow experiments were conducted at six-week intervals from 18 July to 20 October in 2012 in the hilly Loess Plateau. Five treatments were: 1) bare(control), 2) purple alfalfa(Medicago sativa), representing tap roots(T), 3) switchgrass(Panicum virgatum), representing fibrous roots(F), 4) purple alfalfa and switchgrass, representing both tap and fibrous roots(T + F), and 5) natural recovery(N). For each treatment, soil structural properties and root characteristics were measured at an interval of six weeks. Soil anti-scouribility was calculated. Results showed that grass planting slightly reduced soil bulk density, but increased soil aggregate content by 19.1%, 10.6%, 28.5%, and 41.2% in the treatments T, F, T + F, and N, respectively. Soil shear strength(cohesion and angle of internal friction(φ)) significantly increased after the grass was planted. As roots grew, soil cohesion increased by 115.2%–135.5%, while soil disintegration rate decreased by 39.0%–58.1% in the 21 th week compared with the recorded value in the 9th week. Meanwhile, root density and root surface area density increased by 64.0%–104.7% and 75.9%–157.1%, respectively. No significant differences in soil anti-scouribility were observed between the treatments of T and F or of T + F and N, but the treatments of T + F and N performed more effectively than T or F treatment alone in retarding concentrated flow. Soil aggregation and root surface-area density explained the observed soil anti-scouribility during concentrated flow well for the different treatments. This result proved that the restoration of natural vegetation might be the most appropriate strategy in soil reinforcement in the hilly Loess Plateau.展开更多
Soil in greenhouses is likely to suffer a gradual decline in aggregate stability. Determination of the effects of different fertiliser practices on soil aggregate stability is important for taking advantage of solar g...Soil in greenhouses is likely to suffer a gradual decline in aggregate stability. Determination of the effects of different fertiliser practices on soil aggregate stability is important for taking advantage of solar greenhouses. Soil aggregate stability and iron （Fe） and aluminium （A1） oxide contents were investigated in a 26-year long-term fertilisation experiment in greenhouse in Shenyang, China, under eight fertiliser treatments： manure （M）, fertiliser N （FN）, fertiliser N with manure （MN）, fertiliser P （FP）, fertiliser P with manure （MP）, fertiliser NP （FNP）, fertiliser NP with manure （MNP）, and control without any fertiliser （CK）. A wet sieving method was used to determine aggregate size distribution and water-stable aggregates （WSA）, mean weight diameter and geometric mean diameter as the indices of soil aggregate stability. Different fertiliser treatments had a statistically significant influence on aggregate stability and Fe and A1 oxide contents. Long-term application of inorganic fertilisers had no obvious effects on the mass proportion of aggregates. By contrast, manure application significantly increased the mass proportion of macroaggregates at the expense of microaggregates. All treatments, with the exception of FNP, significantly increased the stability of macroaggregates but decreased that of microaggregates when compared with CK. Aggregation under MP and MN was better than that under M and MNP; however, no significant differences were found among inorganic fertiliser treatments （i.e., FN, FP, and FNP）. A positive relation was found between pyrophosphate-extractable Fe and WSA （r=0.269）, but no significant relations were observed between other Fe and Al oxides and aggregate stability.展开更多
The structure of the ＂black soil＂ in Northeast China has been greatly deteriorated by long-term intensive conventional mouldboard plow tillage （CT） practices. In this study, micro- morphological observation and im...The structure of the ＂black soil＂ in Northeast China has been greatly deteriorated by long-term intensive conventional mouldboard plow tillage （CT） practices. In this study, micro- morphological observation and image analysis of soil thin sections were conducted to evaluate the impacts of 21 years （1986-2007） of no tillage （NT） on soil structure as compared to CT in an experiment near Gongzhuling City, Jilin Province. Soil organic matter （SOM）, wet aggregate stability and saturated hydraulic conductivity （Ks） were also analyzed. Total SOM was not significantly affected by tillage systems, but fresher SOM was observed in the surface layer under NT. The aggregates under NT showed different hierarchies in the form of crumbs, and the mean weight diameter （MWD） of NT was significant higher than that of CT in the surface layer. Platy and blocky aggregates were frequently observed in the lower layers under CT practice. The compound pore structure with intertwined intra- and inter- aggregates pores under NT was well developed in a layer from 0-5 cm to 20-25 era. While under CT system, more inter-aggregate pores and fewer intra- aggregate pores were observed, and planes and channels were frequently found in the 20-25 cm layer, where maeroporosity decreased significantly and a plow pan was evident. The Ks values of NT weresignificantly lower at o-5 cm but significantly higher at 20-95 cm compared with CT, which showed the same trend with macroporosity. These results confirmed that long-term CT practice fragmented the tillage layer soil and compacted the lower layer soil and formed a plow pan. While long-term NT practice in the black soil region favored soil aggregation and a stable porous soil structure was formed, which are important to the water infiltration and prevent soil erosion.展开更多
Long-term field experiment was established in 1978 on a coastal paddy soil to determine the effect of applicationof pig manure, rice straw and chemical N fertilizer on the physical property and humus characteristics o...Long-term field experiment was established in 1978 on a coastal paddy soil to determine the effect of applicationof pig manure, rice straw and chemical N fertilizer on the physical property and humus characteristics of soil . Resultsshowed that the porosity, the microstructural coefficient, the reactivities of organic C and N, the ΔlogK value, thedegree of oxidation stability, the contents of O-alkyl C and alkyl C, and the ratio of aliphatic C to aromatic C ofhumic acid from soils received organic manure increased, whereas, the ratio of < 10 μm to >10 μm ofmicroaggregates, the humification degree of humus, the degree of organo-mineral complexation, the number-averagemolecular weight, the C/ H ratio. the contents of carboxyl and aromatic C of HAs in them decreased. These resultsindicated that the application of organic manure not only improved the physical property of the paddy soil but alsomade the HA more aliphatic in structure and younger in origin.展开更多
Inundation of the Three Gorges Reservoir has created a 30-m water-level fluctuation zone with seasonal hydrological alternations of submergence and exposure, which may greatly affect soil properties and bank stability...Inundation of the Three Gorges Reservoir has created a 30-m water-level fluctuation zone with seasonal hydrological alternations of submergence and exposure, which may greatly affect soil properties and bank stability. The aim of this study was to investigate the response of soil pore structure to seasonal water-level fluctuation in the reservoir, and particularly, the hydrological change of wetting and drying cycles. Soil pore structure was visualized with industrial X-ray computed tomography and digital image analysis techniques. The results showed that soil total porosity(? 100 ?m), total pore number, total throat number, and mean throat surface area increased significantly under wetting and drying cycles. Soil porosity, pore number and throat numberwithin each size class increased in the course of wetting and drying cycles. The coordination number, degree of anisotropy and fractal dimension were indicating an increase. In contrast, the mean shape factor, pore-throat ratio, and Euler-Poincaré number decreased due to wetting and drying cycles. These illustrated that the wetting and drying cycles made soil pore structure become more porous, continuous, heterogeneous and complex. It can thus be deduced that the water-level fluctuation would modify soil porosity, pore size distribution, and pore morphology in the Three Gorges Reservoir, which may have profound implications for soil processes, soil functions, and bank stability.展开更多
Soda residue(SR)is a type of industrial waste produced in the soda process with the ammonia-soda method.Applying SR to backfilling solves the land occupation and environmental pollution problems in coastal areas and s...Soda residue(SR)is a type of industrial waste produced in the soda process with the ammonia-soda method.Applying SR to backfilling solves the land occupation and environmental pollution problems in coastal areas and saves material costs for foundation engineering.The strength characteristics of soda residue soil(SRS)under different consolidation conditions are the key points to be solved in the engineering application of SRS.Triaxial compression tests were performed on the undisturbed SRS of Tianjin Port.The shear properties of SRS under different consolidation conditions were then discussed.Meanwhile,a structural strength model(SSM)based on Mohr-Coulomb theory was proposed.SSM reflects the influence of soil structure on undrained strength(Cu)and divides the Cu into the following two parts:friction strength(C_(uf))and original structural strength(C_(u0)).C_(uf)characterizes the magnitude of friction between soil particles,which is related to the consolidation stress.Meanwhile,C_(u0)represents the structural effect on soil strength,which is related to the soil deposition and consolidation processes.SSM was validated by the test data of undisturbed soils.Results reveal that the undisturbed soil generally had a certain C_(u0).Therefore,the SRS strength model was established by combining the experimental law of SRS with SSM.Error analysis shows that the SRS strength model can effectively predict the Cu of undisturbed SRS in Tianjin Port under different consolidation conditions.展开更多
Degraded soil aggregation arising from nitrogen(N)fertilization has been reported in many studies;however,the mechanisms have not yet been clarified.Elucidating the impact of N fertilization on soil aggregation would ...Degraded soil aggregation arising from nitrogen(N)fertilization has been reported in many studies;however,the mechanisms have not yet been clarified.Elucidating the impact of N fertilization on soil aggregation would help to improve soil structure and sustain high crop production.The objective of this study was to determine the impact of long-term N fertilization on soil aggregation and its association with binding and dispersing agents.A 12-year(2008–2019)N fertilization field experiment on a Vertisol was performed,covering a wide range of N application rates(0,360,450,540,630,and 720 kg ha-1 year-1)and including straw management(straw return and straw removal)in a wheat(Triticum aestivum L.)-maize(Zea mays L.)cropping system.Soil samples of 0–20 cm depth were collected from 12 field treatments with 3 replications in 2019.Soil aggregate stability(mean weight diameter(MWD))and contents of soil organic carbon(SOC),glomalin-related soil protein(GRSP),microbial biomass carbon(MBC),and mineral N(NH4+and NO3-)were determined.Long-term N fertilization under straw removal conditions reduced soil MWD by 12%–18%at N rates from 0 to 720 kg ha-1 compared to that under straw return(P<0.05).Soil MWD was positively associated with pH(P<0.05)and MBC(P<0.05),but negatively correlated with NH4+(P<0.05)and NO3-(P<0.05).Compared with the straw removal treatment,the straw incorporation treatment significantly improved the contents of aggregating agents(SOC,GRSP,and MBC)(P<0.001),but did not affect that of the dispersing agent(NH4+)(P>0.05);consequently,it improved soil aggregation.Overall,our results indicate that long-term N fertilization may degrade soil aggregation because of the increases in monovalent ions(H+and NH4+)and the decrease in MBC during soil acidification,especially when the applied N dose exceeded 360 kg ha-1 year-1.Our finding can minimize the negative structural impacts on Vertisol.展开更多
Soil structure is a dynamic property affected by physical, chemical, and microbiological processes. Addition of organic matter to soils and the use of different management practices have been reported to impact soil s...Soil structure is a dynamic property affected by physical, chemical, and microbiological processes. Addition of organic matter to soils and the use of different management practices have been reported to impact soil structure and crop production. Moderation in soil temperature and increases in microbial activity and soil water retention are often suggested as reasons for the rise in crop yield when organic matter is added to the soil. Less is known about the direct effect of changes in soil structure on crop production. A field experiment was conducted to study the effect of summer cover crop and in-season management system on soil structure. The experiment was a nested design with summer cover crop as the main plot and management system as the subplot. Summer cover crop treatments included cowpea （Vigna unguiculata L. Walp.） incorporated into the soil in the fall （CI）, cowpea used as mulch in the fall （CM）, sudangrass （Sorghum vulgare） incorporated into the soil in the fall （S）, and dry fallow or bare ground （B）. Management systems were organic （ORG） and conventional （CNV） systems. Lettuce （Lactuca sativa L.） and cantaloupes （Cucumis melo L.） were cultivated in rotation in the plots for three consecutive years using the same cover crops and management systems for each plot. Disturbed and undisturbed soil cores were collected at the end of the third year and used for laboratory experiments to measure physical, chemical, and hy- draulic properties. Image analysis was used to quantify soil structure properties using a scanning electron micro- scope on thin sections prepared from the undisturbed soil cores. We found that total soil carbon was correlated with porosity, saturation percentage, and pore roughness. Pore roughness was correlated with crop production in gen- eral and with marketable production in particular. We found that the higher the complexity of the pore space, the more water retained in the soil, which may increase soil water residence and reduce plant water stress.展开更多
Nitraria tangutorum Bobr.,a typical xero-halophyte,can be used for vegetation restoration and reconstruction in arid and semiarid regions affected by salinity.However,global climate change and unreasonable human activ...Nitraria tangutorum Bobr.,a typical xero-halophyte,can be used for vegetation restoration and reconstruction in arid and semiarid regions affected by salinity.However,global climate change and unreasonable human activity have exacerbated salinization in arid and semi-arid regions,which in turn has led to the growth inhibition of halophytes,including N.tangutorum.Arbuscular mycorrhizal fungi(AMF)and plant growth-promoting rhizobacteria(PGPR)have the potential to improve the salt tolerance of plants and their adaptation to saline soil environments.In this study,the effects of single and combined inoculations of AMF(Glomus mosseae)and PGPR(Bacillus amyloliquefaciens FZB42)on N.tangutorum were evaluated in severe saline soil conditions.The results indicate that AMF and PGPR alone may not adapt well to the real soil environment,and cannot ensure the effect of either growth promotion or salt-tolerance induction on N.tangutorum seedlings.However,the combination of AMF and PGPR significantly promoted mycorrhizal colonization,increased biomass accumulation,improved morphological development,enhanced photosynthetic performance,stomatal adjustment ability,and the exchange of water and gas.Co-inoculation also significantly counteracted the adverse effect of salinity on the soil structure of N.tangutorum seedlings.It is concluded that the effectiveness of microbial inoculation on the salt tolerance of N.tangutorum seedlings depends on the functional compatibility between plants and microorganisms as well as the specific combinations of AMF and PGPR.展开更多
文摘Existing strength criteria are mostly formulated to describe the mechanical properties of reconstituted soils. However, the engineering characteristics of structured soils are different from those of reconstituted soils in many aspects, especially in their strength properties, Thus, the influence of soil structure （bonding and fabric） on the mechanical properties of structured soils cannot be correctly described, By analyzing the breakage mechanism of natural soils, the structured soils can be conceptualized as binary medium materials consisting of bonded blocks and weakened bands. On this basis, a new strength criterion is pro- posed for structured soils, The expressions of the strength criterion on both meridian and deviator planes are given to describe the strength properties of structured soils on these planes. The proposed strength criterion is compared with available test data under conventional and true triaxial stress conditions in the literature. It is observed that the proposed strength criterion agrees well with the test data.
基金Universidad Nacional de ColombiaUniversidade de Brasilia in Brazil for their technical and financial support。
文摘Structure is an evident determinant for macroscopic behaviors of soils.However,this is not taken into account in most constitutive models,as structure is a rather complex issue in models.For this,it is important to develop and implement simple models that can reflect this important aspect of soil behavior.This paper tried to model structured soils based on well-established concepts,such as critical state and sub-loading.Critical state is the core of the classic Cam Clay model.The sub-loading concept implies adoption of an inner(sub-loading)yield surface,according to specific hardening rules for some internal strain-like state variables.Nakai and co-workers proposed such internal variables for controlling density(p)and structure(ω),using a modified stress space,called tij.Herein,similar variables are used in the context of the better-known invariants(p and q)of the Cam Clay model.This change requires explicit adoption of a non-associated flow rule for the sub-loading surface.This is accomplished by modifying the dilatancy ratio of the Cam Clay model,as a function of the new internal variables.These modifications are described and implemented under three-dimensional(3D)conditions.The model is then applied to simulating laboratory tests under different stress paths and the results are compared to experiments reported for different types of structured soils.The good agreements show the capacity and potential of the proposed model.
基金supported by the National Key R&D Program of China(Grant No.2022YFC3901204)the Foundation for Distinguished Young Scholars of Hubei Province,China(Grant No.2021CFA096)the National Natural Science Foundation of China(Grant No.U20A20320).
文摘Evaluating the stabilized lead(Pb)-contaminated soils through sampling and laboratory testing involves costly and time-consuming processes.Therefore,this study employed a low-cost and non-destructive resistivity tool to evaluate the Pb-contaminated soils stabilized by electrolytic manganese residue(EMR)-based geopolymer(EG-OPC)from the strength and environmental benefits perspective.First,unconfined compressive strength(UCS)and leaching tests were conducted to study the stabilization effectiveness of EG-OPC.Results indicated that the UCS values of soil(5000 mg/kg of pollutants)stabilized by 20%EG-OPC were 4.87 MPa and 8.13 MPa after 7 d and 60 d of curing,respectively.After 60 d of curing,the Pb concentration in the leachate reached 44 mg/L,far lower than the control group(321 mg/L).Second,soil,pore water,and leachate resistivity(ERS,ERW,and ERL)were measured to establish fitting relationships with strength parameters and pollution risk.The good fitting results(e.g.ERS/ERW versus UCS/secant modulus(E50):correlation coefficient R2 z 0.9,ERS/ERW versus Pb contents:R2 z 0.9,and ERL versus Pb2þconcentration:R2¼0.92)and well used Archie's law(ERS versus ERW:R2>0.9)indicate that the resistivity can be used to evaluate the stabilization effectiveness.Furthermore,the microscopic results revealed two behaviors,demonstrating the reliability of resistivity:(1)with the hydration process,resistivity increases due to a denser structure and lower amounts of free water and Pb ions,and(2)the addition of Pb reduces resistivity due to its inhibition or even destructive effects on cementation and formation of hydration products.
基金support from the National Natural Science Foundation of China(No.42177299)the Guangdong Province Key Areas Research and Development Plan Project,China—Key Preparation Technology and Application of Green and Efficient Agricultural Input Controlled-Release Materials(No.2023B0202080002)。
文摘Soil aggregate stability is a fundamental measure for evaluating soil structure.While numerous tests exist for assessing soil aggregate stability,ultrasonic agitation(UA)is widely recognized for its effectiveness.Nonetheless,a significant limitation of UA is the lack of standardized methodologies and stability assessment criteria,resulting in inconsistency and incomparability across studies.Several critical factors influence the assessment of soil aggregate stability,including sample preparation(e.g.,drying,sieving,and settling duration),initial and final aggregate size classes,the definition of final energy form and its calculation,variations in instrumentation and laboratory procedures,and the absence of standardized criteria.Unlike some stability methods,UA produces a broad range of results,with dispersion energy varying significantly(0.5–13440 J g^(-1))across different soil and aggregate types due to divergent procedural settings.These settings encompass factors such as initial power and amplitude,temperature fluctuation,soil/water ratio,probe specification(diameter and insertion depth),and the choice of liquid used during the process.Furthermore,UA faces challenges related to limited reproducibility,raising doubts about its status as a standard stability assessment method.To address these issues,standardization through predefined procedures and stability criteria has the potential to transform UA into a precise and widely accepted method for both qualitative and quantitative assessments of soil stability.In this comprehensive review,we outline the challenges in standardizing UA,elucidate the factors contributing to dispersion energy variation,and offer practical recommendations to establish standardized protocols for UA in soil aggregate stability assessments.
基金supported by the National Natural Science Foundation of China(Nos.42222102,41971136,and 42171107)the Jilin Provincial Department of Science and Technology,China(No.20230508089RC)the Professional Association of the Alliance of International Science Organizations(No.ANSO-PA-2020-14).
文摘Global climate change exerts profound effects on snow cover,with consequential impacts on microbial activities and the stability of soil organic carbon(SOC)within aggregates.Northern peatlands are significant carbon reservoirs,playing a critical role in mitigating climate change.However,the effects of snow variations on microbial-mediated SOC stability within aggregates in peatlands remain inadequately understood.Here,an in-situ field experiment manipulating snow conditions(i.e.,snow removal and snow cover)was conducted to investigate how snow variations affect soil microbial community and the associated SOC stability within soil aggregates(>2,0.25-2,and<0.25 mm)in a peatland of Northeast China.The results showed that snow removal significantly increased the SOC content and stability within aggregates.Compared to the soils with snow cover,snow removal resulted in decreased soil average temperatures in the topsoil(0-30 cm depth)and subsoil(30-60 cm depth)(by 1.48 and 1.34°C,respectively)and increased freeze-thaw cycles(by 11 cycles),consequently decreasing the stability of aggregates in the topsoil and subsoil(by 23.68%and 6.85%,respectively).Furthermore,more recalcitrant carbon and enhanced SOC stability were present in microaggregates(<0.25 mm)at two soil depths.Moreover,reductions in bacterial diversity and network stability were observed in response to snow removal.Structural equation modeling analysis demonstrated that snow removal indirectly promoted(P<0.01)SOC stability by regulating carbon to nitrogen(C:N)ratio within aggregates.Overall,our study suggested that microaggregate protection and an appropriate C:N ratio enhanced carbon sequestration in response to climate change.
文摘It has been well documented that natural normally-consolidated marine soils are generally subjected to the effects of soil structure. The interpretation of the resistance of soil structure is an important issue in the theory study and engineering practice of ocean engineering and geotechnical engineering. It is traditionally considered that the resistance of soil structure gradually disappears with increasing stress level when the applied stress is beyond the consolidation yield stress. In this study, however, it is found that this traditional interpretation of the resistance of soil structure can not explain the strength behavior of natural marine deposits with a normally-consolidated stress history. A new interpretation of the resistance of soil structure is proposed based on the strength behavior. In the preyield state, the undrained strength of natural marine deposits is composed of two components: one developed by the applied stress and the other developed by the resistance of soil structure. When the applied stress is beyond the consolidation yield stress, the strength behavior is independent of the resistance of soil structure.
基金the Major Research of the National Natural Science Foundation of China(No.90715035)HI-Tech Research and Development Program of China(Code 2007AA11Z132).
文摘Naturally deposited or residual soils exhibit more complicated behavior than remolded clays. A dual-surface damage model for structured soils is developed based on the thermodynamics framework established in our first paper. The shift stresses and the transformation between the generalized dissipative stress space and actual stress space are established following a systematic procedure. The corresponding constitutive behavior of the proposed model is determined, which reflects the internal structural configuration and damage behavior for geomaterials. Four evolution variables κj^i（i=D, R;j=V, S） and the basic parameters λ, s, v and e0 are introduced to account for the progressive loss of internal structure for natural clays. A series of fully triaxial tests and isotropic compression tests are performed for structured and reconstituted samples of Beijing and Zhengzhou natural clays. The validation of the proposed model is examined by comparing the numerical results with the experimental data.
基金financial support by Severo Ochoa Centre of Excellence (2019-2023) Grant No. CEX2018-000797-Sfunded by MCIN/AEI/10.13039/501100011033+1 种基金research projects BIA2017-84752-RPID2020-119598RB-I00
文摘The possibilities of the particle finite element method(PFEM)for modeling geotechnical problems are increasingly evident.PFEM is a numerical approach to solve large displacement and large strain continuum problems that are beyond the capabilities of classical finite element method(FEM).In PFEM,the computational domain is reconfigured for optimal solution by frequent remeshing and boundary updating.PFEM inherits many concepts,such as a Lagrangian description of continuum,from classic geomechanical FEM.This familiarity with more popular numerical methods facilitates learning and application.This work focuses on G-PFEM,a code specifically developed for the use of PFEM in geotechnical problems.The article has two purposes.The first is to give the reader an overview of the capabilities and main features of the current version of the G-PFEM and the second is to illustrate some of the newer developments of the code.G-PFEM can solve coupled hydro-mechanical static and dynamic problems involving the interaction of solid and/or deformable bodies.Realistic constitutive models for geomaterials are available,including features,such as structure and destructuration,which result in brittle response.The solutions are robust,solidly underpinned by numerical technology including mixedfield formulations,robust and mesh-independent integration of elastoplastic constitutive models and a rigorous and flexible treatment of contact interactions.The novel features presented in this work include the contact domain technique,a natural way to capture contact interactions and impose contact constraints between different continuum bodies,as well as a new simplified formulation for dynamic impact problems.The code performance is showcased by the simulation of several soil-structure interaction problems selected to highlight the novel code features:a rigid footing insertion in soft rock,pipeline insertion and subsequent lateral displacement on over-consolidated clay,screw-pile pull-out and the dynamic impact of a free-falling spherical penetrometer into clay.
基金supported by the Natural Science Foundation of China(No.41301070)the National Key Basic Research Program(973 Program) of China (No.2012CB026106)+2 种基金the West Light Program for Talent Cultivation of Chinese Academy of Sciences(toDr.ZHANG Ze)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,China Ministry of Education(to Dr.ZHANG Ze)the Scientific and Technical Projects of the Transport Department of Gansu Province,China(No.2014-03)
文摘Studies conducted over several decades have shown that the freeze-thaw cycles are a process of energy input and output in soil, which help drive the formation of soil structure, through water expansion by crystallization and the movement of water and salts by thermal gradients. However, most of these studies are published in Russian or Chinese and are less accessible to international researchers. This review brought together a wide range of studies on the effects of freezing and thawing on soil structure. The following findings are summarized： i） soil structure after freeze-thaw cycles changes considerably and the changes are due to the mechanical fragmentation of soil coarse mineral particles and the aggregation of soil fine particles; ii） the particle size of soil becomes homogeneous and the variation in soil structure weakens as the number of freeze-thaw cycles increases; iii） in the freezing process of soil, an important principle in the variation of soil particle bonding is presented as： condensation →aggregation→ crystallization; iv） the freeze-thaw cycling process has a strong effect on soil structure by changing the granulometric composition of mineral particles and structures within the soil. The freeze-thaw cycling process strengthens particle bonding, which causes an overall increase in aggregate stability of soil, showing a process from destruction to reconstruction.
基金Project partly supported by the Natural Science Foundation of Fujian Province.
文摘A trial of interplanting and non-interplanting villous amomum (Amomum villosum Lour.) under the canopy of Chinese fir (Cunninghamia lanceolata Hook.) at age 22 was established in Sanming, Fujian of China, and a survey on soil fertility was carried out 10 years after its establishment. Compared with the control (non-interplanting), the properties of soil humus in agroforestry system were ameliorated, with a higher level of humification and resynthesis of organic detritus. The soil microbial population and enzymatic activities were both higher under the influence of villous amomum. Both the nutrient supplying and nutrient conserving capacities of the soil were improved. This agroforestry system exhibited an advantage of improved soil fertility as well as an accelerated growth of Chinese fir, it was, therefore, a sustainable management system suited for Chinese fir in South China.
基金Project supported by the National Natural Science Foundation of China (No. 30170770).
文摘Soil properties were investigated in sites where three succeeding generationsof Chinese fir (Gunning-hamia lanceolata, (Lambert) Hooker) in Nanping, Fujian, China, werecultivated in order to show the impact of a repeated monoculture on site productivity. Compared withthe first generation (FG) stand the soil structure deteriorated in the second generation (SG) andthe third generation (TG) stands. For instance, the destruction rate of the peds increased by 55%-115% in the SG and the TG stands compared to the FG stand. Soil nutrient storage and nutrientavailability also decreased in the SG and the TG stands. For surface soils of 0-20 cm, the organicmatter content, total N and P, and available N and P decreased by 3%-20% relative to those in the FGstand. For many soil parameters, the differences between the FG stand and the SG and the TG standswere statistically significant (LSD test, P < 0.05). Furthermore, with each succeeding generation ofChinese fir, the total number of soil microbes declined, the soil enzyme activity weakened, and thesoil biological activity decreased. In order to maintain sustainable site productivity, newsilvicultural practices need to be developed for management of Chinese fir plantations.
基金Strategic Priority Research Program-Climate Change:Carbon Budget and Relevant Issues of Chinese Academy of Sciences(No.XDA05060300)
文摘Traditional vegetation techniques for the control of concentrated flow erosion are widely recognized, whereas only a few studies have experimentally investigated the impacts of belowground roots on the erodibility of topsoils in semi-arid areas. To quantify the effects of root architectures on soil erodibility and its relevant structural properties, simulated flow experiments were conducted at six-week intervals from 18 July to 20 October in 2012 in the hilly Loess Plateau. Five treatments were: 1) bare(control), 2) purple alfalfa(Medicago sativa), representing tap roots(T), 3) switchgrass(Panicum virgatum), representing fibrous roots(F), 4) purple alfalfa and switchgrass, representing both tap and fibrous roots(T + F), and 5) natural recovery(N). For each treatment, soil structural properties and root characteristics were measured at an interval of six weeks. Soil anti-scouribility was calculated. Results showed that grass planting slightly reduced soil bulk density, but increased soil aggregate content by 19.1%, 10.6%, 28.5%, and 41.2% in the treatments T, F, T + F, and N, respectively. Soil shear strength(cohesion and angle of internal friction(φ)) significantly increased after the grass was planted. As roots grew, soil cohesion increased by 115.2%–135.5%, while soil disintegration rate decreased by 39.0%–58.1% in the 21 th week compared with the recorded value in the 9th week. Meanwhile, root density and root surface area density increased by 64.0%–104.7% and 75.9%–157.1%, respectively. No significant differences in soil anti-scouribility were observed between the treatments of T and F or of T + F and N, but the treatments of T + F and N performed more effectively than T or F treatment alone in retarding concentrated flow. Soil aggregation and root surface-area density explained the observed soil anti-scouribility during concentrated flow well for the different treatments. This result proved that the restoration of natural vegetation might be the most appropriate strategy in soil reinforcement in the hilly Loess Plateau.
基金supported by the National Natural Science Foundation of China(No.31171997)the Fifth Session of Geping Green Action-123 Project of Liaoning Environmental Research and Education,China(No.CEPF2012-123-1-4)the Innovative Graduate Training Program of Shenyang Agricultural University of China
文摘Soil in greenhouses is likely to suffer a gradual decline in aggregate stability. Determination of the effects of different fertiliser practices on soil aggregate stability is important for taking advantage of solar greenhouses. Soil aggregate stability and iron （Fe） and aluminium （A1） oxide contents were investigated in a 26-year long-term fertilisation experiment in greenhouse in Shenyang, China, under eight fertiliser treatments： manure （M）, fertiliser N （FN）, fertiliser N with manure （MN）, fertiliser P （FP）, fertiliser P with manure （MP）, fertiliser NP （FNP）, fertiliser NP with manure （MNP）, and control without any fertiliser （CK）. A wet sieving method was used to determine aggregate size distribution and water-stable aggregates （WSA）, mean weight diameter and geometric mean diameter as the indices of soil aggregate stability. Different fertiliser treatments had a statistically significant influence on aggregate stability and Fe and A1 oxide contents. Long-term application of inorganic fertilisers had no obvious effects on the mass proportion of aggregates. By contrast, manure application significantly increased the mass proportion of macroaggregates at the expense of microaggregates. All treatments, with the exception of FNP, significantly increased the stability of macroaggregates but decreased that of microaggregates when compared with CK. Aggregation under MP and MN was better than that under M and MNP; however, no significant differences were found among inorganic fertiliser treatments （i.e., FN, FP, and FNP）. A positive relation was found between pyrophosphate-extractable Fe and WSA （r=0.269）, but no significant relations were observed between other Fe and Al oxides and aggregate stability.
基金funded by the National Science and Technology Supporting Programs of China under Grants No. 2006BAD15B01 and 2006BAD02A14
文摘The structure of the ＂black soil＂ in Northeast China has been greatly deteriorated by long-term intensive conventional mouldboard plow tillage （CT） practices. In this study, micro- morphological observation and image analysis of soil thin sections were conducted to evaluate the impacts of 21 years （1986-2007） of no tillage （NT） on soil structure as compared to CT in an experiment near Gongzhuling City, Jilin Province. Soil organic matter （SOM）, wet aggregate stability and saturated hydraulic conductivity （Ks） were also analyzed. Total SOM was not significantly affected by tillage systems, but fresher SOM was observed in the surface layer under NT. The aggregates under NT showed different hierarchies in the form of crumbs, and the mean weight diameter （MWD） of NT was significant higher than that of CT in the surface layer. Platy and blocky aggregates were frequently observed in the lower layers under CT practice. The compound pore structure with intertwined intra- and inter- aggregates pores under NT was well developed in a layer from 0-5 cm to 20-25 era. While under CT system, more inter-aggregate pores and fewer intra- aggregate pores were observed, and planes and channels were frequently found in the 20-25 cm layer, where maeroporosity decreased significantly and a plow pan was evident. The Ks values of NT weresignificantly lower at o-5 cm but significantly higher at 20-95 cm compared with CT, which showed the same trend with macroporosity. These results confirmed that long-term CT practice fragmented the tillage layer soil and compacted the lower layer soil and formed a plow pan. While long-term NT practice in the black soil region favored soil aggregation and a stable porous soil structure was formed, which are important to the water infiltration and prevent soil erosion.
文摘Long-term field experiment was established in 1978 on a coastal paddy soil to determine the effect of applicationof pig manure, rice straw and chemical N fertilizer on the physical property and humus characteristics of soil . Resultsshowed that the porosity, the microstructural coefficient, the reactivities of organic C and N, the ΔlogK value, thedegree of oxidation stability, the contents of O-alkyl C and alkyl C, and the ratio of aliphatic C to aromatic C ofhumic acid from soils received organic manure increased, whereas, the ratio of < 10 μm to >10 μm ofmicroaggregates, the humification degree of humus, the degree of organo-mineral complexation, the number-averagemolecular weight, the C/ H ratio. the contents of carboxyl and aromatic C of HAs in them decreased. These resultsindicated that the application of organic manure not only improved the physical property of the paddy soil but alsomade the HA more aliphatic in structure and younger in origin.
基金funded by the National Natural Science Foundation of China(Grant No.41771321,41771320 and 41571278)Sichuan Science and Technology Program(Grant No.2018SZ0132)
文摘Inundation of the Three Gorges Reservoir has created a 30-m water-level fluctuation zone with seasonal hydrological alternations of submergence and exposure, which may greatly affect soil properties and bank stability. The aim of this study was to investigate the response of soil pore structure to seasonal water-level fluctuation in the reservoir, and particularly, the hydrological change of wetting and drying cycles. Soil pore structure was visualized with industrial X-ray computed tomography and digital image analysis techniques. The results showed that soil total porosity(? 100 ?m), total pore number, total throat number, and mean throat surface area increased significantly under wetting and drying cycles. Soil porosity, pore number and throat numberwithin each size class increased in the course of wetting and drying cycles. The coordination number, degree of anisotropy and fractal dimension were indicating an increase. In contrast, the mean shape factor, pore-throat ratio, and Euler-Poincaré number decreased due to wetting and drying cycles. These illustrated that the wetting and drying cycles made soil pore structure become more porous, continuous, heterogeneous and complex. It can thus be deduced that the water-level fluctuation would modify soil porosity, pore size distribution, and pore morphology in the Three Gorges Reservoir, which may have profound implications for soil processes, soil functions, and bank stability.
基金the financial support from the National Natural Science Foundation of China(No.51979191)the National Key Research and Development Program of China(Nos.2016YFC0802204,2016YFC0802201)+2 种基金the National Natural Science Fund for Innovative Research Groups Science Foundation(No.51321065)the Construction Science and Technology Project of the Ministry of Transport of the People’s Republic of China(No.2014328224040)the Science and Technology Plan Project of Tianjin Port(No.2020-165)。
文摘Soda residue(SR)is a type of industrial waste produced in the soda process with the ammonia-soda method.Applying SR to backfilling solves the land occupation and environmental pollution problems in coastal areas and saves material costs for foundation engineering.The strength characteristics of soda residue soil(SRS)under different consolidation conditions are the key points to be solved in the engineering application of SRS.Triaxial compression tests were performed on the undisturbed SRS of Tianjin Port.The shear properties of SRS under different consolidation conditions were then discussed.Meanwhile,a structural strength model(SSM)based on Mohr-Coulomb theory was proposed.SSM reflects the influence of soil structure on undrained strength(Cu)and divides the Cu into the following two parts:friction strength(C_(uf))and original structural strength(C_(u0)).C_(uf)characterizes the magnitude of friction between soil particles,which is related to the consolidation stress.Meanwhile,C_(u0)represents the structural effect on soil strength,which is related to the soil deposition and consolidation processes.SSM was validated by the test data of undisturbed soils.Results reveal that the undisturbed soil generally had a certain C_(u0).Therefore,the SRS strength model was established by combining the experimental law of SRS with SSM.Error analysis shows that the SRS strength model can effectively predict the Cu of undisturbed SRS in Tianjin Port under different consolidation conditions.
基金supported by the National Natural Science Foundation of China(Nos.41725004,42007007,and 41930753)the Natural Science Foundation of Jiangsu Province,China(No.BK20201104).
文摘Degraded soil aggregation arising from nitrogen(N)fertilization has been reported in many studies;however,the mechanisms have not yet been clarified.Elucidating the impact of N fertilization on soil aggregation would help to improve soil structure and sustain high crop production.The objective of this study was to determine the impact of long-term N fertilization on soil aggregation and its association with binding and dispersing agents.A 12-year(2008–2019)N fertilization field experiment on a Vertisol was performed,covering a wide range of N application rates(0,360,450,540,630,and 720 kg ha-1 year-1)and including straw management(straw return and straw removal)in a wheat(Triticum aestivum L.)-maize(Zea mays L.)cropping system.Soil samples of 0–20 cm depth were collected from 12 field treatments with 3 replications in 2019.Soil aggregate stability(mean weight diameter(MWD))and contents of soil organic carbon(SOC),glomalin-related soil protein(GRSP),microbial biomass carbon(MBC),and mineral N(NH4+and NO3-)were determined.Long-term N fertilization under straw removal conditions reduced soil MWD by 12%–18%at N rates from 0 to 720 kg ha-1 compared to that under straw return(P<0.05).Soil MWD was positively associated with pH(P<0.05)and MBC(P<0.05),but negatively correlated with NH4+(P<0.05)and NO3-(P<0.05).Compared with the straw removal treatment,the straw incorporation treatment significantly improved the contents of aggregating agents(SOC,GRSP,and MBC)(P<0.001),but did not affect that of the dispersing agent(NH4+)(P>0.05);consequently,it improved soil aggregation.Overall,our results indicate that long-term N fertilization may degrade soil aggregation because of the increases in monovalent ions(H+and NH4+)and the decrease in MBC during soil acidification,especially when the applied N dose exceeded 360 kg ha-1 year-1.Our finding can minimize the negative structural impacts on Vertisol.
文摘Soil structure is a dynamic property affected by physical, chemical, and microbiological processes. Addition of organic matter to soils and the use of different management practices have been reported to impact soil structure and crop production. Moderation in soil temperature and increases in microbial activity and soil water retention are often suggested as reasons for the rise in crop yield when organic matter is added to the soil. Less is known about the direct effect of changes in soil structure on crop production. A field experiment was conducted to study the effect of summer cover crop and in-season management system on soil structure. The experiment was a nested design with summer cover crop as the main plot and management system as the subplot. Summer cover crop treatments included cowpea （Vigna unguiculata L. Walp.） incorporated into the soil in the fall （CI）, cowpea used as mulch in the fall （CM）, sudangrass （Sorghum vulgare） incorporated into the soil in the fall （S）, and dry fallow or bare ground （B）. Management systems were organic （ORG） and conventional （CNV） systems. Lettuce （Lactuca sativa L.） and cantaloupes （Cucumis melo L.） were cultivated in rotation in the plots for three consecutive years using the same cover crops and management systems for each plot. Disturbed and undisturbed soil cores were collected at the end of the third year and used for laboratory experiments to measure physical, chemical, and hy- draulic properties. Image analysis was used to quantify soil structure properties using a scanning electron micro- scope on thin sections prepared from the undisturbed soil cores. We found that total soil carbon was correlated with porosity, saturation percentage, and pore roughness. Pore roughness was correlated with crop production in gen- eral and with marketable production in particular. We found that the higher the complexity of the pore space, the more water retained in the soil, which may increase soil water residence and reduce plant water stress.
基金the National Key Research and Development Program of China(No.2017YFE0119100)the National Natural Science Foundation of China(No.42107513)the Key Research and Development Program of Gansu(No.21YF5FA151)。
文摘Nitraria tangutorum Bobr.,a typical xero-halophyte,can be used for vegetation restoration and reconstruction in arid and semiarid regions affected by salinity.However,global climate change and unreasonable human activity have exacerbated salinization in arid and semi-arid regions,which in turn has led to the growth inhibition of halophytes,including N.tangutorum.Arbuscular mycorrhizal fungi(AMF)and plant growth-promoting rhizobacteria(PGPR)have the potential to improve the salt tolerance of plants and their adaptation to saline soil environments.In this study,the effects of single and combined inoculations of AMF(Glomus mosseae)and PGPR(Bacillus amyloliquefaciens FZB42)on N.tangutorum were evaluated in severe saline soil conditions.The results indicate that AMF and PGPR alone may not adapt well to the real soil environment,and cannot ensure the effect of either growth promotion or salt-tolerance induction on N.tangutorum seedlings.However,the combination of AMF and PGPR significantly promoted mycorrhizal colonization,increased biomass accumulation,improved morphological development,enhanced photosynthetic performance,stomatal adjustment ability,and the exchange of water and gas.Co-inoculation also significantly counteracted the adverse effect of salinity on the soil structure of N.tangutorum seedlings.It is concluded that the effectiveness of microbial inoculation on the salt tolerance of N.tangutorum seedlings depends on the functional compatibility between plants and microorganisms as well as the specific combinations of AMF and PGPR.
