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Soil aggregate stability

Soil aggregate stability refers to the capacity of soil particles to form and maintain clusters, or aggregates, that resist dispersion and breakdown from disruptive forces such as water, wind, and mechanical stress, serving as a fundamental physical property that reflects overall soil health and structural integrity.^[1] These aggregates are primarily held together by binding agents including organic matter, microbial byproducts, clay minerals, and root exudates, which create a network of pores that enhance soil porosity and facilitate essential processes like water infiltration and aeration.^[2] Stable aggregates are crucial for reducing soil erodibility, preventing surface crusting, and supporting root penetration, thereby promoting sustainable plant growth and agricultural productivity.^[3] The stability of soil aggregates is influenced by a variety of environmental and management factors, including soil organic carbon content, land use practices, and climatic conditions such as precipitation intensity.^[2] For instance, conservation tillage and cover cropping enhance aggregate formation by increasing organic inputs and microbial activity, while excessive tillage or erosion can degrade stability by disrupting binding agents.^[1] In addition to structural benefits, aggregate stability plays a pivotal role in carbon sequestration, as stable macroaggregates (>0.25 mm) protect organic matter from decomposition, contributing to long-term soil fertility and mitigating greenhouse gas emissions.^[4] Poor aggregate stability, often exacerbated in arid or intensively farmed regions, leads to increased runoff, nutrient leaching, and loss of biodiversity, underscoring its importance in ecosystem resilience.^[5] Measurement of soil aggregate stability typically involves laboratory tests that simulate disruptive forces, such as wet sieving or rainfall simulation, to quantify the proportion of aggregates that remain intact.^[2] Common indices include the mean weight diameter (MWD), which assesses aggregate size distribution after slaking, and water-stable aggregate percentages, with values closer to 1 indicating high stability.^[2] These assessments are sensitive to soil texture, with finer-textured soils often exhibiting greater inherent stability due to higher clay content, though organic management practices can significantly improve stability across soil types.^[2] Overall, maintaining aggregate stability through sustainable practices is essential for addressing global challenges like soil degradation and climate change.^[3]

Fundamentals

Definition and Characteristics

Soil aggregates are secondary particles formed by the binding of primary mineral particles, such as sand, silt, and clay, into larger units that cohere more strongly to each other than to surrounding particles.^[6] These aggregates typically range in size from approximately 0.5 mm to 5 mm, though they can vary depending on soil type and environmental conditions.^[7] The formation of these units creates a structured soil matrix distinct from loose primary particles. Soil aggregates exhibit a hierarchical structure, where smaller units assemble into progressively larger ones, influencing overall soil architecture. Microaggregates, smaller than 250 μm, consist of tightly bound primary particles and are often the building blocks within larger formations, while macroaggregates, greater than 250 μm, encompass these microaggregates along with additional binding materials and void spaces.^[8] This hierarchy includes pore spaces within and between aggregates, which enhance soil porosity by providing channels for air and water movement.^[7] Key characteristics of soil aggregates include their shape, density, and internal binding agents. Shapes vary from spherical or granular forms, which promote better aeration, to more angular or blocky structures that may compact more readily.^[9] Aggregate density is generally lower than that of individual primary particles due to enclosed pores.^[10] Internal cohesion is provided by binding agents such as clay minerals, which facilitate electrostatic bonding, and organic glues like humic substances and polysaccharides that act as adhesives.^[11] Basic classification systems for soil aggregates often rely on size categories to assess distribution and function. Kemper and Rosenau's framework, a widely adopted standard, uses wet sieving with mesh sizes such as 2 mm, 1 mm, 0.5 mm, and 0.25 mm to separate aggregates into discrete classes, enabling evaluation of size-based stability and soil structure.^[12]

Importance to Soil Functioning

Soil aggregate stability plays a pivotal role in maintaining soil structure by creating pore spaces that enhance aeration, facilitate water infiltration, and allow for root penetration, thereby preventing soil compaction and supporting overall soil resiliency.^[13] Stable aggregates contribute to improved water availability for plants and reduce the risk of surface sealing, which can otherwise impede gas exchange essential for root respiration. This structural integrity is particularly vital in agricultural and natural ecosystems where compaction from machinery or foot traffic can degrade soil functionality.^[1] In nutrient cycling, stable aggregates protect organic matter from rapid decomposition, allowing microbes to gradually release essential nutrients like nitrogen and phosphorus, thereby sustaining long-term soil fertility.^[14] By enclosing organic residues within their structure, aggregates slow microbial access, promoting efficient nutrient retention and availability for plant uptake over time.^[1] This protective mechanism is crucial for maintaining productivity in diverse soil types, from croplands to rangelands. Stable aggregates significantly aid in erosion control by increasing soil resistance to detachment by water or wind, reducing particle transport and sediment loss in runoff.^[15] Soils with high aggregate stability exhibit lower erodibility, preserving topsoil layers and minimizing environmental degradation in sloped or exposed landscapes.^[16] Macroaggregates, in particular, contribute to carbon sequestration by physically isolating soil organic carbon (SOC) from decomposers, enabling long-term storage that mitigates atmospheric CO2 levels.^[17] Globally, SOC stocks in the upper 1 meter of soil are estimated at approximately 1550 Pg (as of 2025), with a substantial portion stabilized within aggregates, underscoring their role in climate regulation.^[18] Furthermore, stable aggregates foster soil biodiversity by providing microhabitats that support diverse microbial communities and facilitate soil fauna activity, such as earthworms, which enhance organic matter turnover and nutrient distribution.^[19] These habitats promote ecological interactions that bolster ecosystem resilience against disturbances. In agricultural contexts, enhanced aggregate stability improves soil tilth, leading to higher crop yields through better root development and water retention, while also reducing runoff and associated nutrient losses compared to unstable soils.^[1] For instance, fields with stable aggregates demonstrate decreased erosion-related yield reductions and improved overall farm productivity.^[16]

Mechanisms of Aggregate Formation

Physico-Chemical Mechanisms

Soil aggregate stability is significantly influenced by physico-chemical processes that promote particle binding through electrostatic interactions and chemical precipitation. Flocculation, a primary mechanism, arises from electrostatic attraction between negatively charged clay particles, facilitated by divalent cations such as Ca²⁺ and Mg²⁺ that bridge these charges and reduce inter-particle repulsion. This cation bridging enhances aggregate formation by overcoming the diffuse double layer around clay surfaces, with Ca²⁺ proving more effective than Mg²⁺ due to its lower hydration energy. The underlying dynamics are explained by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which posits a balance between attractive van der Waals forces and repulsive electrostatic forces; when cations compress the electrical double layer, net attraction dominates, leading to flocculation. The simplified chemical representation of this process is:

\mathrm{Ca^{2+} + 2(Clay^{-}) \to (Clay)_{2}Ca}

This flocculation is particularly pronounced in soils dominated by exchangeable Ca²⁺, contributing to the initial assembly of microaggregates (<250 μm). Cementation further stabilizes aggregates through the precipitation of inorganic binding agents that act as "glues" between particles. In calcareous soils, carbonates such as CaCO₃ precipitate and can comprise 10-20% of aggregate mass, providing structural rigidity by filling pores and linking particles. This occurs via the decomposition of calcium bicarbonate, as shown in the equation:

\mathrm{Ca(HCO_3)_2 \to CaCO_3 + CO_2 + H_2O}

In sodic soils, gypsum (CaSO₄·2H₂O) serves a similar role by supplying Ca²⁺ to displace Na⁺ and promote flocculation while precipitating as a cement. Sesquioxides, including iron (Fe) and aluminum (Al) oxides, form through hydrolysis of soluble metal ions and bind particles effectively, with Al oxides often showing greater stabilizing potential than Fe oxides due to their higher reactivity. Polyvalent cations also contribute to cementation by facilitating oxide precipitation and enhancing overall bond strength. These processes are most effective in well-aerated soils where oxidation and precipitation can proceed without interference. The type and reactivity of clay minerals play a crucial role in these mechanisms, as they determine the available surface area for cation adsorption and binding. Montmorillonite, a smectite clay, offers a high specific surface area of up to 800 m²/g, enabling extensive electrostatic interactions and flocculation sites, whereas kaolinite, with a much lower surface area (typically 10-50 m²/g), provides fewer binding opportunities and results in weaker aggregate stability. Soils rich in montmorillonite thus exhibit greater potential for physico-chemical stabilization, though excessive swelling can sometimes counteract this benefit. Soil pH modulates these interactions by influencing charge distribution on clay surfaces and the solubility of cementing agents. Optimal aggregate stability occurs at neutral pH (6-7), where dispersion is minimized due to balanced cation availability and reduced solubility of carbonates and oxides; acidic conditions (pH <6) enhance clay dispersion by increasing H⁺ competition for exchange sites, while alkaline pH (>8) promotes Na⁺ dominance and slaking in sodic environments.

Physical Mechanisms

Physical mechanisms of soil aggregate stability involve abiotic forces driven by environmental cycles and mechanical actions that promote particle cohesion without relying on biological processes. These forces include cyclic stresses from water and temperature fluctuations, as well as direct mechanical pressures, which rearrange and bind soil particles into stable aggregates. Such mechanisms are particularly prominent in regions with variable climates, where repeated stresses enhance structural integrity over time.^[20] Wetting and drying cycles exert alternate expansion and contraction on soil particles, drawing them together and increasing aggregate cohesion, especially in arid soils where these cycles are frequent. In sodic Vertisols typical of arid environments, such cycles can significantly increase the proportion of larger macroaggregates (>2000 µm) and improve mean weight diameter (MWD) after multiple iterations. Studies simulating intense drying-wetting conditions on Alfisols have shown MWD increases of up to 36% after initial cycles, with overall cohesion enhancements depending on cycle intensity and soil texture. These cycles also bolster slaking resistance, as repeated drying compresses particles, reducing breakdown upon rewetting.^[21]^[22]^[23] Shrinking and swelling processes, driven by clay mineral behavior, generate internal pressures that bind soil particles into aggregates. Smectite clays, common in many soils, expand 10-15 times their volume upon hydration due to water entering interlayer spaces, creating expansive forces that fracture and reposition particles before contraction upon drying reinforces cohesion. This cyclic pressure enhances aggregate formation by filling pores and promoting particle adhesion, particularly in clay-rich soils where swelling rates can reach 30% in macroaggregate fractions.^[24]^[25] Freezing and thawing cycles, prevalent in temperate regions with 5-10 such events annually, further contribute to aggregate stability through ice crystal formation that expands soil pores. Upon freezing, water in pores forms ice lenses that exert pressures up to several megapascals, fracturing weak bonds and displacing particles; thawing then allows reorientation and closer packing, enhancing cohesion. Wet aggregate stability typically increases after 3-6 cycles, with MWD rising before stabilizing or declining with excessive repetitions, as observed in temperate Mollisols. These cycles improve overall slaking resistance by promoting denser aggregate structures post-thaw.^[26]^[27] Tillage provides initial mechanical aggregation through direct disruption and compression. Primary tillage operations, such as plowing, mechanically mix and compact soil particles, forming transient aggregates by overcoming interparticle repulsion and promoting face-to-face clay platelet alignment. These physical actions can initiate aggregation that may later be enhanced by chemical bonds like flocculation.^[6] Across these mechanisms, quantitative improvements in aggregate stability are evident in metrics like MWD, which often increases post-cycle due to enhanced particle binding and reduced slaking susceptibility. For instance, in drying-wetting experiments, MWD rose significantly with cycle frequency, reflecting greater resistance to dispersive forces.^[23]

Biological Mechanisms

Soil fauna, such as earthworms, ants, and termites, play a pivotal role in aggregate formation through physical manipulation and secretion of binding agents that create organo-mineral complexes. Earthworms like Lumbricus terrestris enhance stability by producing mucus-rich casts during burrowing and feeding, which bind soil particles into stable macroaggregates; studies show this activity can increase water-stable aggregates by 16–56% compared to earthworm-free controls. Ants and termites similarly contribute by excavating and reorganizing soil, incorporating organic matter to form durable organo-mineral structures that resist erosion and improve overall soil cohesion.^[28]^[29] Fungal hyphal networks, particularly from arbuscular mycorrhizal fungi (AMF), actively enmesh soil particles to stabilize aggregates, with external hyphae providing a physical framework that binds microaggregates into larger units. These networks are complemented by glomalin, a glycoprotein produced by AMF hyphae, which acts as a persistent glue; glomalin can account for up to 27% of soil organic carbon in aggregates, enhancing their resistance to slaking and dispersion. This biological enmeshment is most effective in macroaggregate formation (>250 μm), where hyphal length density correlates strongly with stability.^[30]^[31] Plant roots contribute to aggregate stability through both chemical exudates and mechanical actions. Root exudates, including polysaccharides and mucilage, serve as cementing agents that adhere soil particles, with maize root mucilage, for example, increasing aggregate stability by promoting binding in sandy soils. Roots with diameters greater than 1 mm provide mechanical entanglement, physically intertwining particles to form stable structures, particularly in the rhizosphere where exudate concentrations are highest.^[32]^[33] Microbial communities, especially bacteria, form microaggregates via biofilms and extracellular polymeric substances (EPS), which create sticky matrices that encapsulate clay and organic particles. Bacterial EPS production enhances microaggregate stability (<250 μm), with higher bacterial biomass positively correlating with aggregate mean weight diameter in various soil types. These contributions are foundational, as microaggregates serve as building blocks for larger, biologically stabilized structures.^[34]^[35] Symbiotic interactions among these biological agents amplify aggregate formation, such as the combined effects of plant roots and AMF hyphae, where roots supply carbon to fungi in exchange for enhanced hyphal binding, leading to greater macroaggregate turnover and stability. Earthworm activity further integrates these processes by incorporating root and fungal residues into casts, fostering a hierarchical aggregation that sustains soil structure over time.^[31]

External Influences on Stability

Environmental Factors

Climate influences soil aggregate stability primarily through variations in rainfall intensity and temperature regimes. High rainfall intensities exceeding 50 mm/h trigger significant erosion by promoting slaking and aggregate breakdown, as water rapidly infiltrates and disrupts soil structure, leading to increased sediment yield rates that can surge by up to 88% when intensities rise from 50 to 80 mm/h.^[36] Warmer temperatures accelerate the decomposition of organic matter, which binds aggregates, thereby reducing stability; for instance, aggregate stability declines markedly with rising water temperatures, with the content of large (>5 mm) water-stable aggregates decreasing by approximately 57% as temperatures increase from 5°C to 40°C.^[37] Soil texture and parent material also play critical roles in modulating aggregate stability across landscapes. Sandy soils exhibit lower stability compared to loamy soils due to their reduced clay content, which limits the formation of strong electrostatic bonds and organic-mineral associations essential for aggregation.^[38] In contrast, soils derived from volcanic parent materials, rich in sesquioxides like iron and aluminum oxides, demonstrate enhanced stability owing to the cementing effects of these amorphous compounds that resist breakdown.^[39] Topography further influences stability by affecting water flow dynamics. Slope gradients greater than 15% heighten erosion risk through accelerated runoff, which mechanically shears aggregates and transports fine particles, thereby diminishing overall structural integrity.^[40] Regional climatic patterns exemplify these effects distinctly. In Mediterranean climates, repeated wetting and drying cycles enhance aggregate stability by fostering crack formation and subsequent recompaction, with drought periods significantly increasing wet aggregate stability indices relative to wetter seasons.^[41] Conversely, tropical wet climates promote aggregate dispersion due to intense, frequent rain events that cause slaking and the breakdown of microaggregates into primary particles, exacerbated by low electrolyte concentrations in soil solutions.^[42] Long-term climate change projections indicate further challenges for aggregate stability. Increased drought frequency is expected to reduce soil organic carbon (SOC) levels, a key stabilizer, with models forecasting SOC declines in topsoil layers of agricultural areas by 2050, potentially reducing aggregate stability in vulnerable regions like semi-arid zones. Recent studies as of 2024 confirm that increased climate warming has severe impacts on soil organic carbon and aggregation, particularly in high-latitude regions.^[43]^[44]

Management Practices

Agricultural management practices play a crucial role in maintaining or enhancing soil aggregate stability by influencing soil structure and organic matter dynamics. Conventional tillage disrupts aggregates through mechanical shearing, leading to reduced stability and increased erosion risk, whereas no-till systems preserve soil architecture by avoiding disturbance, allowing fungal hyphae and roots to bind particles more effectively. A global meta-analysis indicates that no-tillage enhances aggregate formation and associated soil organic carbon concentrations across cropland ecosystems, with studies showing increases in water-stable aggregates by approximately 7.7% in the top 0–10 cm soil layer compared to conventional tillage.^[45]^[46] Crop rotations, especially those incorporating legumes, further bolster stability by introducing organic residues that promote microbial activity and aggregate formation; for instance, legume-inclusive rotations have been found to increase macroaggregate proportions by 7–14% and overall aggregate stability by 7–9%.^[47]^[48] Soil conditioners target specific chemical imbalances to improve flocculation and reduce dispersion, thereby stabilizing aggregates. Lime application neutralizes soil acidity, facilitating calcium bridging that enhances aggregate cohesion and increases the mean weight diameter, particularly in acidic soils where surface liming elevates calcium content in smaller aggregates.^[49]^[50] In sodic soils, gypsum amends sodium-dominated exchange sites by providing soluble calcium, which displaces Na⁺ ions and reduces clay dispersion, leading to improved aggregate stability and water infiltration without significantly altering mean weight diameter in some cases.^[51]^[52] Polymers, including synthetic types like polyvinyl acetate and bio-based alternatives such as xanthan gum, act as binding agents to reinforce soil structure; bio-based polymers are preferred for their biodegradability, and their application can enhance aggregate stability through bio-aggregation, though effects vary by soil type and polymer concentration.^[53]^[54] Cover cropping and mulching provide physical protection and biological inputs that safeguard and strengthen aggregates, especially in vulnerable, erosion-prone landscapes. Cover crops, such as grasses or legumes planted between main crops, add root biomass and exudates that bind soil particles, increasing macroaggregate formation and stability while mitigating raindrop impact on bare soil.^[55] Organic mulching with crop residues or materials like straw further reduces surface sealing, promoting aggregate stability increases of 58–65% in loamy and sandy soils after two years by conserving moisture and fostering microbial decomposition.^[56]^[57] Fertilization regimes impact aggregate stability primarily through effects on soil microbial communities and organic matter quality. Excessive nitrogen inputs can suppress beneficial microbial activity, leading to aggregate destabilization over long periods, as observed in reduced stability under prolonged chemical N application.^[58] In contrast, balanced phosphorus and potassium fertilization supports root growth and enzyme activity that aid aggregate binding, with combined NPK applications promoting macroaggregate formation and improving mean weight diameter and geometric mean diameter.^[59]^[60] Restoration practices like afforestation on degraded lands progressively rebuild aggregate stability by reintroducing vegetation that enhances organic inputs and root reinforcement. Afforestation increases aggregate-associated carbon and nutrient contents, with stability peaking after 20 years in fire-affected or eroded sites due to cumulative microbial and physico-chemical bonding.^[61] In karst or semi-arid degraded areas, such efforts elevate mean weight diameter and reduce microaggregate fractions over 5–10 years, aiding overall soil recovery.^[62]^[63]

Measurement Techniques

Dry Sieving Methods

Dry sieving methods evaluate the mechanical stability of soil aggregates under dry conditions by applying physical forces to separate them into size classes, providing insights into resistance to abrasion and impact, such as those occurring during wind erosion. Soil samples are first air-dried to constant weight, typically for several days, to preserve aggregate structure without moisture-induced disruption. The air-dried soil is then gently broken to pass a 4-8 mm sieve to remove large clods while retaining natural aggregates, and a representative subsample (often 100-500 g) is placed on a stack of nested sieves with apertures ranging from 0.25 mm to 2 mm. The stack is mechanically shaken at approximately 50 oscillations per minute for 10 minutes using a sieve shaker or rotary device to simulate field mechanical stresses, allowing smaller aggregates and particles to pass through while retaining larger ones. The weight of material retained on each sieve is recorded after sieving, and the process is repeated if necessary for multiple subsamples to ensure reproducibility.^[64]^[65] Key metrics derived from the resulting aggregate size distribution include the mean weight diameter (MWD), calculated as the sum over all size classes of the mean diameter of the class multiplied by the oven-dry weight fraction of aggregates in that class:

\text{MWD} = \sum_{i=1}^{n} \overline{x_i} w_i

where \overline{x_i} is the mean diameter of the i-th size class and w_i is the proportion of the total sample weight in that class. The geometric mean diameter (GMD) is also used, computed as the antilog of the weighted average of the logarithms of the mean diameters:

\text{GMD} = \exp\left( \sum_{i=1}^{n} w_i \log \overline{x_i} \right).

These indices quantify overall aggregate size and stability, with higher values indicating greater resistance to dry mechanical forces; for instance, MWD values exceeding 1 mm often signify well-structured soils in arid environments.^[66]^[64] These methods offer advantages such as rapid execution (typically under 30 minutes per sample), low equipment costs, and direct reflection of aggregate integrity against non-hydric breakdown processes, making them suitable for large-scale assessments in dryland agriculture. However, they overlook water-related disruption mechanisms like slaking, which can lead to overestimation of stability in humid or irrigated soils where wetting is frequent.^[67]^[2] Standardization follows USDA protocols, which specify aggregate separation into classes such as >2 mm, 1-2 mm, 0.5-1 mm, 0.25-0.5 mm, and <0.25 mm, with consistent drying and minimal pre-sieving disturbance to ensure comparability across studies. Dry sieving thus complements wet methods by focusing on arid or wind-dominated contexts for a complete stability profile.^[65]^[68]

Wet Sieving Methods

Wet sieving methods evaluate the resistance of soil aggregates to water-induced breakdown mechanisms, including slaking due to entrapped air expansion and dispersion from osmotic swelling of clay particles, which are primary drivers of soil erosion during rainfall events. These techniques are essential for assessing aggregate stability in hydrological contexts, as they replicate the slaking and dispersive forces encountered in field conditions.^[69] The standard procedure, developed by Kemper and Rosenau, begins with air-dried soil aggregates (typically 1-2 mm in diameter) pre-wetted slowly via capillary rise on filter paper or mist for 10 minutes to minimize artificial slaking from rapid immersion. The pre-wetted aggregates are then placed on a nest of sieves with mesh openings of 2, 1, 0.5, 0.25, and sometimes 0.106 mm, and oscillated vertically in shallow water (about 2-3 cm depth) at a rate of 30 cycles per minute for 15-30 minutes using a mechanical or manual apparatus. Material passing through the finest sieve is collected as dispersed fines, while residues on each sieve represent water-stable aggregates of corresponding sizes; all fractions are oven-dried and weighed to determine size distribution. This approach avoids direct immersion shocks and focuses on disruptive forces from water movement.^[69]^[2] From the resulting data, several key metrics quantify stability. The mean weight diameter (MWD) measures overall aggregate size stability, computed as the weighted average diameter:

MWD = \sum (w_i \times \bar{x}_i)

where w_i is the proportion of aggregates in size class i and \bar{x}_i is the mean diameter of that class. The percentage of water-stable aggregates (WSA) indicates the proportion of aggregates larger than a threshold size (e.g., >0.25 mm) that resist breakdown, often expressed as WSA = (mass of stable aggregates / initial mass) × 100. The dispersion ratio assesses clay dispersibility, calculated as the ratio of clay in the suspension (dispersed fines <0.25 mm) to total soil clay content, highlighting sodicity or electrolyte effects on flocculation. These metrics provide insights into both macro- and micro-scale stability.^[69]^[70]^[71] Method variants distinguish between single-sieve and multiple-sieve approaches to separate aggregate fractions. Single-sieve wet sieving uses one cutoff (e.g., 0.25 mm) to differentiate macroaggregates (>0.25 mm) from microaggregates and dispersible material, offering simplicity for routine assessments. Multiple-sieve configurations, as in the full Kemper-Rosenau setup, employ stacked sieves for a detailed distribution across size classes, enabling separation of macro- and microaggregates while capturing nuanced breakdown patterns. The choice depends on the need for granularity versus efficiency. These methods excel in mimicking rainfall-induced slaking and dispersion, yielding stability indices that correlate robustly with field erosion rates; for instance, studies report r² values exceeding 0.7 between WSA or MWD and measured soil loss under simulated or natural rainfall. However, wet sieving is labor- and time-intensive, often requiring 30-60 minutes per sample plus setup, and results are highly sensitive to initial aggregate moisture, where insufficient pre-wetting can overestimate breakdown. To adjust for non-aggregating sand content, a corrected stability index (SI) is applied:

SI = \frac{WSA - \%sand}{100 - \%sand}

where percentages are by dry weight, isolating true aggregation effects.^[69]^[2]

Specialized Assessment Methods

Specialized assessment methods extend beyond routine sieving by incorporating dynamic, field-based, and imaging techniques to evaluate soil aggregate stability under simulated or in-situ conditions, providing insights into breakdown mechanisms like slaking and dispersion.^[72] Slaking tests assess aggregate disintegration due to rapid water entry and air entrapment, with the Le Bissonnais method being a widely adopted approach that simulates multiple breakdown pathways through pretreatments including fast wetting (to induce slaking via compressed air), slow wetting (to promote microcracking from differential swelling), stirring after prewetting (to apply mechanical stress), and immersion in ethanol (to isolate physicochemical dispersion).^[72] In this method, air-dried aggregates (typically 2-5 mm) are subjected to these treatments, followed by wet sieving to determine the mean weight diameter (MWD) of remaining fragments, yielding a stability index such as the coefficient of vulnerability (Kv = \bar{x}_0 / MWD, where \bar{x}_0 is the mean diameter of the initial aggregates), where lower Kv values indicate greater stability.^[73] Adaptations include visual scoring of slaking on a 0-3 scale, where 0 denotes fully stable aggregates and 3 indicates complete disintegration, facilitating rapid field evaluation of crusting susceptibility.^[74] Rainfall simulation offers a field-oriented evaluation by mimicking erosive forces, using portable simulators like the Cornell Rainfall Simulator to apply controlled precipitation at intensities such as 50 mm/h onto small plots or sieves containing aggregates, thereby measuring sediment yield as an indicator of stability.^[75] This technique quantifies runoff and erosion potential by collecting and weighing dislodged particles after a fixed duration (e.g., 5-10 minutes), with lower sediment yields reflecting higher aggregate resistance to raindrop impact and surface sealing.^[76] Such simulations are particularly useful for comparing management practices, as they integrate aggregate breakdown with hydrological responses in undisturbed soil.^[75] Microscopic and imaging techniques provide detailed visualization of aggregate microstructure, employing scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) for 2D chemical mapping and X-ray computed tomography (CT) for 3D internal structure analysis.^[77] SEM-EDS reveals cementing agents like Fe oxides or organic matter influencing pore walls, while CT scans quantify porosity, pore size distribution, and connectivity by segmenting grayscale images into solid and void phases, often showing anisotropic pores in stable aggregates with connected Fe-rich networks enhancing cohesion.^[77] These non-destructive methods highlight how internal voids (e.g., 20-40% porosity in macroaggregates) affect water retention and aeration, complementing macroscopic stability metrics.^[78] Emerging techniques further refine assessments, such as X-ray tomography for mapping 3D aggregate density, where radiodensity values (e.g., 1.6-1.7 g/cm³ in compacted soils) indicate compaction effects on internal solidity and void space distribution through virtual erosion simulations that peel layers to reveal structural gradients.^[78] Aggregate tensile strength tests measure the force required to fracture individual aggregates using direct tension on cores or the Brazilian splitting method, reporting values in kPa (e.g., 2.0-3.2 kPa at -100 hPa matric potential), with higher strengths correlating to better resistance against mechanical disruption in tilled soils.^[79] These approaches quantify cohesion thresholds, aiding predictions of fragmentation under load.^[80] Recent digital tools, such as the Slakes smartphone app (developed circa 2023), enable rapid quantification of slake tests through image recognition, scoring aggregate breakdown over time to assess stability in field conditions.^[81] Field methods like penetrometry offer indirect stability evaluation by inserting a cone probe to record penetration resistance, where values exceeding 2 MPa signal poor aggregate integrity and restricted root growth due to compacted, unstable structures.^[82] This portable technique links mechanical impedance to aggregate quality in situ, with no-till systems often showing elevated resistance (e.g., 1.34 Mg m⁻³ bulk density) yet sustained rooting if aggregates remain cohesive.^[82] Integration of these methods with soil organic carbon (SOC) analysis yields holistic indices, as SOC content in macroaggregates (>2 mm fractions) positively correlates with stability metrics like MWD and geometric mean diameter (GMD), while negatively affecting erodibility factors, enabling comprehensive assessments of erosion risk across land-use chronosequences.^[83] For instance, SOC enrichment boosts aggregate formation, with >0.25 mm fractions comprising 86-92% of soil mass and serving as primary carbon pools that enhance overall structural resilience.^[83]

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Freezing-thawing impact on aggregate stability as affected by land ...
In the temperate regions, freezing-thawing leads to instability of soil aggregates. If soil aggregates enter the winter under relatively stable conditions ...
[26]
Effect of freezing and thawing processes on soil aggregate stability
Aug 6, 2025 · Wet aggregate stability generally increased when the number of freezing and thawing cycles increased from 3 to 6, but decreased after that point ...<|separator|>
[27]
[PDF] Shaping an Optimal Soil by Root–Soil Interaction
Compression resulting from water extraction by roots leads to aggregates that are denser and of greater tensile strength than those in unplanted soils [40].<|separator|>
[28]
Impact of different earthworm ecotypes on water stable aggregates ...
Feb 1, 2020 · L. terrestris only caused a significant increase in WHC (of 11%) in the upper 6.5 cm of the sandy loam soil. Linear regression indicated a ...
[29]
Nutrient spatial variability in biogenic structures of Nasutitermes ...
In soil-feeding termites, the soil organic matter is strongly modified forming organo-mineral complexes with clay. The soil organic matter ingested is further ...<|control11|><|separator|>
[30]
[PDF] What is Glomalin - USDA ARS
Glomalin, found on hyphae of arbuscular mycorrhizal fungi, coats hyphae to prevent nutrient loss and helps stabilize soil aggregates.
[31]
Contributions of interacting biological mechanisms to soil aggregate ...
The restoration of macroaggregate structure in this system was apparently driven by the direct and indirect effects of roots and external hyphae.
[32]
Influence of maize root mucilage on soil aggregate stability
This study was undertaken to determine the effects of root exudates on soil aggregate stability. Root mucilage was collected from two-month old maize plant.
[33]
Living and decaying roots as regulators of soil aggregation and ...
In addition, root exudates (e.g., root mucilage or polysaccharide exudates) can either adhere directly to mineral surfaces or function as glue-like binding ...
[34]
Microbial extracellular polymeric substances (EPS) in soil
Oct 17, 2024 · Inoculation of bacteria with high EPS production can significantly improve the stability of soil aggregates, such as Pseudomonas putida GAP ...
[35]
Importance of substrate quality and clay content on microbial ...
Mar 17, 2022 · According to Costa et al. (2018), the production of EPS is being acknowledged as a binding agent and one important driver of soil aggregation.Materials And Methods · Microbial Biomass C And Eps · Aggregate Formation And...
[36]
Effects of the Rainfall Intensity and Slope Gradient on Soil Erosion ...
Jan 17, 2023 · The cutoff value of the rainfall intensity existed between 50 mm/h and 80 mm/h. When the rainfall intensity exceeded this cutoff value, the ...Missing: destabilization | Show results with:destabilization
[37]
Effects of water temperature on soil aggregate stability between soils ...
These results indicate that soil aggregate stability and erosion resistance decrease with increasing water temperature, which may be one reason for severe soil ...
[38]
Influence of soil properties on the aggregate stability of cultivated ...
Aug 7, 2025 · Based on the correlation test results, aggregate stability is supported by clay content, pH and is indirectly related to exchanged Ca and ...
[39]
Soil Texture and Soil Structure - CTAHR
Some silicate clays are said to have a shrink-swell potential. This means that the soil minerals expand, or swell, when wet, causing the soil to become sticky ...
[40]
Influences of Slope Gradient on Soil Erosion - ResearchGate
Aug 7, 2025 · The critical slope gradient of soil erosion is dependent on grain size, soil bulk density, surface roughness, runoff length, net rain excess, and the friction ...
[41]
Seasonal soil aggregate stability variation in relation to rainfall and ...
Aug 9, 2025 · The seasonal scale of soil temperature exerted a strong influence on aggregate stability (Dimoyiannis, 2009) . This was in agreement with ...
[42]
Microaggregate Stability of Tropical Soils and its Roles ... - IntechOpen
Jul 31, 2013 · In the tropical climate, soils are subject to frequent wetting and drying cycles in the short term during the rainy season and in the long term ...
[43]
Climate change impacts on soil organic carbon stocks of ...
In this study, we applied the CarboSOIL model and global climate models to predict and analyse the effects of short- (2030), medium- (2050) and long-term (2100 ...
[44]
Global-scale no-tillage impacts on soil aggregates and associated ...
Jul 10, 2023 · The findings highlight that no-tillage may enhance the formation of soil aggregates and the associated SOC and TN concentrations in global cropland ecosystems.
[45]
Impact of no‐till, crop rotation, cover crop, and drainage on soil ...
Dec 7, 2023 · This study showed that NT practice significantly increased SOM by 5.4%, WAS by 7.7%, and bulk density by 6.7% within 0–10 cm soil profile but decreased K fs by ...
[46]
Positive effects of crop rotation on soil aggregation and associated ...
Oct 1, 2023 · Crop rotation overall improved the proportions of macroaggregates (7–14%) and aggregate stability (7–9%). Crop rotation generally increased OC ...
[47]
Different efficiencies of grain legumes in crop rotations to improve ...
Legume plants can promote C storage by enhancing the formation and stabilization of soil aggregates that protect soil organic C (SOC) from mineralization.
[48]
Lime application effects on soil aggregate properties: Use of the ...
Mar 15, 2019 · Surface liming improved soil aggregation by increasing the mean weight diameter. Smaller soil aggregates present higher percentage of calcium due to liming.
[49]
Lime‐induced loss of soil organic carbon and effect on aggregate ...
Nov 1, 1999 · Increased aggregate stability in limed soils suggested formation of new bonding involved Ca bridges.
[50]
Organic amendments and gypsum reduce dispersion and increase ...
Nov 1, 2022 · Organic amendments and gypsum effected soil dispersion and aggregation. · Gypsum can reduce dispersion but has no effect on mean weight diameter.
[51]
[PDF] Effectiveness of Gypsum in the North-central Region of the U.S.
Gypsum can reclaim sodic soils, improve soil aggregation, reduce bulk density, and reduce runoff, but special conditions are needed for these effects.
[52]
Performance of eco-friendly polymers for soil stabilization and their ...
May 23, 2023 · Contrary to synthetic polymers, most bio-based polymers are easily degradable by biological and natural processes [33].
[53]
Review on biopolymer-based soil treatment (BPST) technology in ...
Biopolymers enhance the stability and surface erosion resistance of slopes and dam structures via multiple interactions, including bio-aggregation, bio-crusting ...
[54]
Using Cover Crops to Improve Soil and Water Quality - Ohioline
May 15, 2017 · Cover crops increase SOM, macroporosity, soil permeability, mean aggregate size and aggregate stability (macroaggregates vs. microaggregates) ...
[55]
Agri‐Mat Mulching Improves Aggregate Stability and Soil Pore ...
Jan 5, 2025 · In the loam soil, the 100% AG treatment increased the stability of the aggregates by 58% and by 65% in the sandy loam soil after two years. The ...
[56]
Effects of organic mulching on soil aggregate stability ... - SpringerLink
Oct 19, 2021 · Organic mulching is effective for improving soil quality and aggregate stability. This study evaluated how soil binding agents changed aggregate ...<|separator|>
[57]
Influence of long-term fertilization on soil aggregates stability and ...
Jun 7, 2023 · Long-term application of chemical fertilizer could reduce the soil aggregates stability, storage and activity of SOC in macro-aggregates.
[58]
Impacts of nitrogen (N), phosphorus (P), and potassium (K) fertilizers ...
Both NPK and NPKS treatments improved the soil structural stability (mean weight diameter and geometric mean diameter) by promoting the formation of ...Abstract · Introduction · Maize Yield Affected By...
[59]
Dynamics of soil aggregate stability as induced by potassium in a ...
They found that an increase in PAR and CROSS as influenced by potassium application resulted in greater stability of soil aggregates compared to the control ...
[60]
Effects of rehabilitation through afforestation on soil aggregate ...
Oct 15, 2020 · Soil aggregates have the greatest stability after 20 years afforestation of forest fire trace land. · The maximum C was accumulated in the ...
[61]
Afforestation Influences Soil Aggregate Stability by Regulating ...
The afforestation restoration increased the content of soil aggregate-related SOC, TN, and TP, and increased with the decrease in the aggregate particle size.
[62]
Effects of Afforestation on Soil Aggregate Stability, Carbon, and ...
It causes a loss in soil nutrients and a decline in land productivity, which severely limits the growth of the regional ecology and social economy [15].
[63]
[PDF] SOIL AGGREGATE DISTRIBUTION BY DRY SIEVING
Dry sieving provides an indirect measure of field aggregate size distribution that can be expressed as mean weight diameter (MWDds) (van Bavel, 1949), or as a.
[64]
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### Summary of Dry Sieving Method for Soil Aggregate Stability
[65]
[PDF] 2.6 Aggregate Stability and Size Distribution
Soil aggregate stability indexes and crop yields. Soil Sci. 91:138-146. Díaz-Zorita, M., J.H. Grove, and E. Perfect. 2000. Sampling and sieving procedures ...
[66]
The Impact of Field Moisture Content on Size Distribution and Stability
The dry sieving method offers an indirect measure of aggregate size distribution, subject to forces such as abrasion and impact among soil aggregates [8]. In ...
[67]
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### Dry Sieving Procedure for Soil Aggregates Summary
[68]
https - DOI
No information is available for this page. · Learn why
[69]
[PDF] Factors affecting clay dispersion and aggregate stability of arid zone ...
It is apparent from the values in Table 2 that the clay dispersion index correlated with more factors and to a greater degree than did the aggregate stability ...
[70]
[PDF] Evaluation of aggregate stability methods for soil health
Sep 18, 2022 · Liu, A., Ma, B.L., Bomke, A.A., 2005. Effects of cover crops on soil aggregate stability, total organic carbon, and polysaccharides. Soil Sci.
[71]
Aggregate stability and assessment of soil crustability and erodibility ...
The relations between aggregate breakdown, crusting and water erosion are analysed, and existing methods for the assessment of aggregate stability are reviewed.
[72]
[PDF] Comparison of two methods for aggregate stability measurement
The aim of this paper is to compare two aggregate stability measurement methods on a set of reclaimed dumpsite soils. Method proposed by Le Bissonnias (1996) is ...
[73]
Macro-aggregate stability (Le Bissonnais) test: slaking stability index...
This study introduced and optimized the Sonication and Laser Diffractometry technique (SLD) for evaluating the stability of soil aggregates, drawing comparisons ...
[74]
Comparing Aggregate Stability Methods - Soil Health Institute
Oct 13, 2022 · We compared four common methods of measuring aggregate stability: water stable aggregates using the Cornell Rainfall Simulator, wet sieved water stable ...
[75]
Evaluation of methods for determining soil aggregate stability
This paper explores the effects of various approaches for the measurement of aggregate stability, and reports on the mechanisms responsible for the breakdown.
[76]
Characterization of the pore structure and cementing substances of ...
Dec 14, 2016 · In this research, we suggest a data fusion workflow to characterize the pore and chemical structure within aggregates from CT scans and SEM–EDS.Missing: internal | Show results with:internal
[77]
Characterization of soil aggregate structure by virtual erosion of X ...
Aggregate porosity, pore size distribution and pore structure can be studied using X-ray CT complimenting other methods such as soil saturated hydraulic ...Missing: scans | Show results with:scans
[78]
Tensile strength of soil cores in relation to aggregate ... - ScienceDirect
The direct tensile strength results showed that the PAC soil had significantly higher tensile strength than the REF soil (e.g. 3.2 and 2.0 kPa, respectively at ...
[79]
Methodology for determination of tensile strength of soil aggregates
Tensile strength of soil aggregates can be calculated from their crushing forces provided that the aggregate diameters are known. Three simple types of ...
[80]
Soil Bulk Density and Penetration Resistance under Different Tillage ...
Penetrometer values greater than 2 MPa are generally reported to produce a significant root growth reduction (Atwell, 1993). However, in well-structured soils ...
[81]
Soil organic carbon and soil aggregate stability associated with ...
Sep 1, 2021 · Therefore, the stability of soil aggregates is an important index to evaluate the risk of soil erosion. SOC is the key cementing material for ...