Structure and Soil Architecture

1.1. Texture as a Fundamental but Static Characteristic

Let's start with the most basic. Soil consists of mineral particles of various sizes: sand (2–0.05 mm), silt (0.05–0.002 mm), and clay (<0.002 mm) according to the USDA classification (Weil & Brady, 2017). Their quantitative ratio determines the soil texture.

Texture is, in essence, the soil's passport, its genetic characteristic. It changes extremely slowly, on a geological timescale, and is virtually unaffected by anthropogenic influences. Texture determines the soil's potential: its water-holding capacity, cation exchange capacity, and susceptibility to compaction. For example, we know that sandy soils will be well-drained but will retain moisture and nutrients poorly, while clayey soils will, on the contrary, have a high water-holding capacity but slow air permeability (Weil & Brady, 2017; Shukla, 2023).

However, if everything were determined only by texture, then all sandy soils would be the same, and all clayey soils would be too. But in reality, this is not the case. And here we come to the most important point.

1.2. Structure: The Organization of Particles in Space

The fact is that individual particles of sand, silt, and clay rarely exist in isolation. They combine into larger structural units — aggregates (or peds) (Marshall et al., 1996; Eash et al., 2016). This process of combination under the influence of physical, chemical, and biological factors is the formation of soil structure.

Key definition: Soil structure is the arrangement (organization) of solid particles and the associated pore space (Marshall et al., 1996). Structure answers the question of how the particles that make up the texture are packed and grouped.

Essentially, structure is the primary and most important superstructure over texture. It creates a hierarchy: large aggregates consist of smaller ones, those of even smaller ones, down to the elementary particles. This hierarchy is directly linked to the formation of pores of different sizes and, consequently, to completely different soil behavior (Eash et al., 2016; Weil & Brady, 2017).

1.3. Soil Architecture: A Modern View

In modern soil science, the concept of "structure" is often expanded to the more comprehensive term soil architecture (Weil & Brady, 2017; Shukla, 2023). Architecture is not just a description of the shape of aggregates (granular, prismatic, platy, etc.); it is a systemic representation of how the entire solid phase is arranged and, critically, how the pore space is organized.

Soil architecture includes:

1. Hierarchical organization of aggregates (from clay microdomains to macroaggregates).

2. A complex network of pores of various sizes and shapes that permeate this hierarchy.

3. Connectivity and continuity of the pore space.

4. Spatial distribution of all these elements.

An analogy can be drawn: if texture is a set of "bricks" of different sizes (sand, silt, clay), then structure is the walls made of these bricks, held together by "cement" (organic matter, iron oxides), and architecture is the whole building with its rooms (aggregates), corridors, and staircases (pores of varying connectivity), which can function as a living space or a warehouse (Weil & Brady, 2017).

Thus, moving from texture to architecture means moving from "what is there" to "how it is organized." It is this organization that predetermines water and air permeability, the ability to retain moisture and nutrients, their availability to plants, and resistance to erosion and degradation.

1.4. Why is This Important for the Plant?

For a plant, what is critically important is not so much the texture itself, but how the soil architecture provides:

• Availability of water and air in the rhizosphere (Shukla, 2023).
• Ease of root penetration and growth.
• Stability of conditions under fluctuating moisture levels (Scheffer et al., 2018).

This is precisely why two soils with the same texture but different architectures can be either a "fertile" loose chernozem or a "slumping" structureless solonetz.

Section Conclusion

We have established that texture is a fundamental but static characteristic, while soil architecture is a dynamic, hierarchically organized system that determines soil functionality. We have moved from the question "what is soil made of" to "how is it arranged." In the next section, we will take a detailed look at what soil aggregates are, how they form, and what role they play in this complex system.

2.1. Definition of an Aggregate

Definition: Aggregate (or ped) is a structural unit of soil, representing a natural cluster (union) of primary soil particles (sand, silt, clay), held together by various binding agents (Eash et al., 2016; Weil & Brady, 2017).

It is important to distinguish aggregates from clods. Clods are anthropogenic formations resulting from mechanical impact on the soil (e.g., during plowing or excavation) and lacking internal, natural structure. Aggregates, on the other hand, are products of soil formation and are separated from each other along natural planes of weakness (cracks, root channels) (Weil & Brady, 2017).

Aggregates are not just a random cluster of particles. They are highly organized bodies that themselves have a complex internal structure, serving as the "bricks" from which soil architecture is built (Shukla, 2023).

2.2. Hierarchy of Aggregates: From Nanometers to Centimeters

One of the key properties of aggregates is their hierarchical organization (Tisdall & Oades, 1982). This means that aggregates are built from smaller aggregates, which in turn are built from even smaller ones, down to individual clay crystals and organic molecules (see Huang, 2012, Chapter 2).

This hierarchy can be represented as follows:

1. Nano- and microaggregates (< 0.25 mm): These are the foundation of soil structure. They are formed through strong and, as a rule, long-term bonds:

• Clay domains (< 2 µm): Elementary stacks of clay plates held together by electrostatic forces (flocculation) and/or ionic bridges (Eash et al., 2016; Scheffer et al., 2018).
• Organo-mineral complexes: Associations of clay particles with colloidal organic matter (humus) and iron and aluminum oxides. These complexes are the most stable and durable elements of soil structure (Marshall et al., 1996; Weil & Brady, 2017).

2. Microaggregates (20–250 µm): Formed by binding clay domains, organo-mineral complexes, and fine silt particles. Here, polyvalent cations (Ca²⁺, Mg²⁺), humic substances, and stable microbial polysaccharides act as binding agents (see Huang, 2012, Chapter 2; Ghezzehei, 2012).

3. Macroaggregates (> 250 µm): These are the very "crumbs" and "granules" that we see in fertile soil. They consist of microaggregates glued together by "weaker" and more temporary bonds, such as:

• Fungal hyphae and root hairs, which mechanically wrap around and bind particles (Weil & Brady, 2017).
• Labile organic substances (exopolysaccharides, mucilage) released by plants and microorganisms (Shukla, 2023).
• Shrinkage-swelling and freeze-thaw cycles that "compress" particles together (Marshall et al., 1996).

This hierarchy is extremely important because different levels of aggregation respond differently to external influences. For example, macroaggregates are easily destroyed by tillage, while microaggregates and organo-mineral complexes can persist for centuries (Weil & Brady, 2017).

2.3. Shapes and Sizes of Aggregates

Depending on the conditions of soil formation, aggregates can take various forms. The main types of structure (Eash et al., 2016; Weil & Brady, 2017):

• Granular (crumb): Aggregates are approximately spherical in shape, often porous. Characteristic of topsoil under perennial grasses and in chernozems. This is an ideal structure for crop production.
• Nuts / Angular blocky: Aggregates are polyhedral with relatively flat faces. Often found in the middle part of the profile (B horizon), indicating clay accumulation processes and good drainage.
• Prismatic / Columnar: Aggregates are elongated vertically. Formed in the subsoil under the influence of shrinkage and swelling of clay minerals, especially under conditions of seasonal drying. Columnar structure with rounded tops is often associated with sodium accumulation (solonetz).
• Platy: Aggregates are flattened horizontally. Can be both a natural phenomenon (e.g., in some forest podzols) and a result of compaction by machinery.

2.4. Why are Aggregates Good?

The formation of aggregates is a key process in creating a favorable soil environment. The presence of stable aggregates is the main condition for the formation of loose, structured soil. Thanks to aggregation, soil particles cease to behave as individual sand grains or a continuous clay mass and acquire new, extremely important properties (Eash et al., 2016).

It is aggregates that create the internal heterogeneity that allows the soil to simultaneously retain moisture inside the aggregates (in fine pores) and allow excess water and air to pass between the aggregates (in large pores). The destruction of aggregates, for example during intensive tillage, leads to structural degradation, compaction, and deterioration of all physical soil properties.

Section Conclusion:

So, we have defined that aggregates are not just "clods," but fundamental, hierarchically organized structural elements of soil. They are the first and most important step in the formation of a favorable soil architecture. Their size, shape, and stability determine how the soil will function. In the next section, we will step up a level and consider soil architecture as an integrated system in which aggregates and pores are inextricably linked.

3.1. The "Aggregate – Pores – Connectivity" System

Soil architecture is essentially a dual system consisting of two inextricably linked and interpenetrating components:

1. The Solid Phase (Framework): A hierarchically organized system of aggregates, which we discussed in the previous section.

2. The Pore Space (Voids): A complex network of spaces between aggregates, within them, and between individual primary particles.

Key Idea: Soil architecture is not just aggregates or just pores. It is a single "aggregate ↔ pore" system, where the structure of the solid phase completely determines the structure of the pore space, and vice versa (Marshall et al., 1996; Weil & Brady, 2017). It is this dual system that is the environment in which plants and microorganisms live and water and air move (Shukla, 2023).

Imagine a sponge. Its solid framework (aggregates) creates a complex network of openings (pores) of different sizes. Some openings are large and connected, allowing water and air to pass through quickly. Others are small and isolated, retaining water. The sponge works precisely as an integrated system, and we cannot understand its properties by looking only at the framework or only at the pores separately. The same applies to soil.

3.2. Two Main Types of Pores: Inter- and Intra-aggregate

Our sponge analogy leads us to the most important consequence of the hierarchical organization of aggregates: the appearance of at least two fundamentally different types of pores (Ghezzehei, 2012; Eash et al., 2016).

1. Inter-aggregate pores (macropores): This is the space between aggregates. They form when individual aggregates (crumbs) adjoin each other, leaving gaps between them. These pores:

• Are mostly large (compared to other types of pores).
• Form a continuous network of channels and cracks permeating the soil.
• Serve as the main pathways for rapid water movement (infiltration, drainage) and gas exchange (oxygen into the soil, carbon dioxide out).
• Are habitats for plant roots and larger soil animals (worms, insects) (Weil & Brady, 2017).

2. Intra-aggregate pores (micropores): These are pores within the aggregates themselves. They are formed by the spaces between primary particles (sand, silt, clay) inside the structural unit. These pores:

• Are mostly small.
• Can be isolated or weakly connected to the overall pore network.
• Serve as a "reservoir" for retained water that does not drain under gravity. This water constitutes the bulk of the moisture reserves available to plants.
• Are habitats for microorganisms (bacteria, fungi) (Shukla, 2023).

3.3. Hierarchy of Pores: Macro, Meso, Micro

For ease of description and understanding of functions, soil pore space is conventionally divided into categories by size (equivalent pore diameter). The boundaries between them are conditional but reflect important physical processes.

We will use a classification that allows a clear link between pore size and function (Eash et al., 2016; Weil & Brady, 2017):

Important: The ratio of these pore types in the soil determines its hydrological properties. For example, sandy soil consists mainly of macropores, providing good aeration but low moisture storage. A well-structured clayey soil (with chernozem-like architecture) has both macropores (between aggregates) and an extensive network of meso- and micropores (within aggregates), ensuring both drainage and a large supply of available moisture. A structureless clayey soil has predominantly micropores, leading to poor drainage and aeration (Eash et al., 2016; Shukla, 2023).

3.4. Spatial Organization

Architecture is not only the size and type of pores but also their spatial arrangement. In a structured soil, we see a regular and, critically, connected distribution of pores. For example, large vertical channels left by roots or worms can cross horizons, connecting the surface with deeper layers. This vertical connectivity of macropores is a key architectural element determining infiltration rate and preventing surface runoff (Marshall et al., 1996; Scheffer et al., 2018).

Conclusion: Soil architecture is not a static set of aggregates and pores, but a complex, dynamic, hierarchical system. It determines how the soil will function: how it coexists with water and air, how it allows roots to penetrate, how it stores and provides resources. It is this system that transforms the abstract concept of "fertility" into concrete physical conditions for plant life.

Section Conclusion:

We have moved from describing individual aggregates to understanding the soil as an integral architectural system consisting of a solid framework and the pore space permeating it. We have seen that the key here is the presence of at least two types of pores (inter- and intra-aggregate) performing different functions. In the next section, we will focus in more detail on the most important element of this system – the continuity of pore space and its role in the movement of water, gases, and roots.

4.1. Classification of Pores by Size and Function

Pore space is a continuum, but for ease of description and understanding, we conventionally divide it into categories. There are different classifications, but we will use the most widespread and physiologically based one, which distinguishes four main groups (Eash et al., 2016; Weil & Brady, 2017; Scheffer et al., 2018):

Important: This classification is not just an academic exercise. It allows us to link pore size to their role in soil processes. For example, we can say that for good plant growth, soil must have a balance: enough macropores for aeration and drainage and a large number of meso- and micropores for moisture retention (Shukla, 2023).

4.2. Detailed Analysis of Pore Categories

Let's examine each category in more detail, particularly in the context of plant physiology.

4.3. Biopores: A Special Type of Macropore

Biopores are worth highlighting as a crucial architectural element. These are channels created by living organisms:

• Root channels: After root death, tubes reinforced by organic exudates remain.
• Earthworm burrows: Particularly important are earthworm burrows, which permeate the soil, improving drainage and aeration to depths of a meter or more (Weil & Brady, 2017).
• Insect burrows and tunnels.

Biopores are ideal macropores. They are continuous, have smooth walls, and are often enriched with organic matter. Plants actively use old root channels and worm burrows for rapid penetration deep into the profile (Eash et al., 2016).

4.4. Brief Summary of Pore Types

So, the types of pores are not just a list of categories. They are an interconnected system where each type performs its unique function. Their ratio determines the water-air regime of the soil. Soil with the "right" architecture is one that has both macropores (for rapid infiltration and respiration) and a well-developed network of meso- and micropores (for retaining a large moisture reserve). The loss of macropores (e.g., through compaction) or the destruction of aggregates containing meso- and micropores (e.g., through intensive tillage) leads to the degradation of the entire architecture and a sharp decline in soil fertility.

Section Conclusion

We have examined in detail the classification of pores by size and linked them to the functions they perform in the soil environment. We now know that "highways" (macropores) and "storehouses" (micropores) are equally important, but their joint work is impossible without connectivity. In the next section, we will move on to perhaps the most important aspect of soil architecture – pore continuity, which turns individual channels and cavities into a single, functioning transport network.

5.1. Scales of Continuity

Pore continuity manifests at different scales, from the nanoscale to the entire soil profile.

1. Micro- and mesoscale (continuity within the aggregate): This is the connectivity of micropores within the aggregate. It determines how quickly water can move inside the aggregate to a root hair or how easily gas can diffuse into the aggregate. Good internal connectivity is a condition for the "reserve" of moisture within the aggregate to be accessible to the plant (Scheffer et al., 2018; Shukla, 2023).

2. Meso- and macroscale (continuity between aggregates): This is the connectivity of meso- and macropores that form the framework of the entire architecture. This continuity provides:

• Rapid infiltration of water from the surface deep into the profile.
• Effective drainage of excess moisture.
• Gas exchange between the root zone and the atmosphere.
• Root penetration along the path of least resistance (Marshall et al., 1996; Eash et al., 2016).

5.2. How is Continuity Created?

Pore continuity does not arise by chance. It is the result of complex interactions between biological, physical, and chemical processes.

1. Biological factor (biopores): This is perhaps the most important and effective mechanism for creating continuity. Plant roots, earthworms, insects, and other soil fauna create vertical and horizontal channels. These biopores:

• Are ideally continuous: They penetrate the soil from the surface to deep layers.
• Are stable: The channel walls are reinforced with organic exudates and can persist for years even after the organism that created them has disappeared (Weil & Brady, 2017).
• Serve as "arteries": Water and air move through them tens to hundreds of times faster than through the soil matrix (Marshall et al., 1996).

2. Physical factor (shrinkage cracks): In clayey soils, especially those with high content of swelling minerals (smectites, vermiculites), wide, deep cracks form upon drying. These cracks create a powerful network of macropores that sharply increases infiltration during dry periods. However, this continuity is temporary: upon wetting, the cracks close, and connectivity drops sharply (Scheffer et al., 2018; Eash et al., 2016).

3. Aggregation factor: The very formation of aggregates creates two types of continuity. Intra-aggregate continuity (micropores) provides storage and slow movement of moisture. Inter-aggregate continuity (macropores) provides a network of "corridors" for rapid transport. It is the combination of these two networks within one system that is the key to functional architecture (Weil & Brady, 2017).

5.3. Discontinuity and its Consequences

If continuity is good, then discontinuity is bad. What disrupts pore continuity?

1. Anthropogenic impact (compaction): Traffic by heavy machinery, especially on wet soil, destroys macropores, compresses aggregates, and "seals" biopore entrances. This leads to the formation of a dense layer that sharply disrupts vertical continuity. As a result, water ponds on the surface, and roots cannot penetrate deep (Eash et al., 2016; Weil & Brady, 2017).

2. Slumping and crust formation: The destruction of aggregates on the surface and the subsequent sealing of pores create a dense crust. This crust is an almost perfect barrier to continuity, blocking the entry of water and air into the soil (Eash et al., 2016).

3. Seasonal changes: In some soils, macropore continuity is seasonal. For example, during frost periods or periods of severe waterlogging, biopores can be blocked by ice or water, and connectivity drops sharply.

5.4. Practical Significance of Continuity

Understanding pore continuity is key to answering our main question: why does the same texture give different results?

Example: Take two clayey soils. In the first (chernozem-like), aggregate hierarchy is well-developed, there are biopores from earthworms and roots, and macropores between aggregates are continuous. Water quickly penetrates deep through macropores, then slowly distributes into meso- and micropores. Roots easily grow through the channels. The soil works like a "pump," and the plant receives both water and air.

In the second (structureless clay), aggregates are absent, macropores are either very small or absent, and continuity is disrupted. Water penetrates slowly (low infiltration), and if it does penetrate, it stagnates (poor drainage). Roots suffocate from lack of oxygen and cannot grow deep due to high density. This is an example of completely different functionality with the same texture.

Conclusion for crop production: Creating and maintaining a continuous network of macropores is the main task of managing soil architecture. Practices that promote this (minimum tillage, use of cover crops, organic matter application, preservation of earthworms) are essentially investments in creating "good roads" for water, air, and roots. Practices that destroy continuity (excessive tillage, working on wet soil) are the destruction of soil infrastructure.

Section Conclusion

We have established that pore space continuity is the cornerstone of soil physics. It is what turns a set of disparate cavities into a unified transport system that determines water exchange, gas exchange, and root penetration. Disruption of continuity is essentially the disruption of connections between the different "floors" of soil architecture, leading to degradation of the entire system. In the next section, we will discuss another critical property of architecture – its stability, i.e., its ability to withstand destructive factors.

6.1. Mechanical Stability

Mechanical stability is the ability of an aggregate to resist deformation and destruction under an applied force (pressure, shear, impact) (Marshall et al., 1996; Scheffer et al., 2018). This stability is critically important during:

• Tillage: Aggregates must withstand the mechanical impact of implements without crumbling into dust.
• Machinery traffic: The soil must resist compaction and destruction under tractor wheels.
• Root growth: As roots grow, they exert pressure on aggregates; if they are too brittle, roots may destroy them, but if too strong, roots cannot penetrate.

Factors affecting mechanical stability:

1. Binding agents: This is the main factor. The strength of an aggregate is determined by how strong the bonds between its particles are. Rigid, strong bonds (e.g., cementation by iron and aluminum oxides in tropical soils, or silicon compounds) make aggregates very resistant to mechanical destruction (Eash et al., 2016; Weil & Brady, 2017).

2. Moisture: Moisture is a critical factor. Dry aggregates (especially clayey ones) can be very strong and hard. Upon wetting, their strength drops sharply because water acts as a lubricant and weakens bonds between particles (Marshall et al., 1996). This is why working on wet soil is dangerous – aggregates are easily destroyed and, upon drying, form dense clods.

3. Aggregate size: As a rule, large aggregates are less tensile strength than small ones. This is because a large aggregate has more internal stresses and defects along which failure occurs. Under mechanical impact, large aggregates break down into smaller ones – this is essentially the mechanism of their fragmentation during tillage (Eash et al., 2016).

6.2. Water Stability

Water stability is the ability of aggregates to retain their structure upon contact with water. This is perhaps the most important and informative indicator of soil structure quality, because water is the most frequent and aggressive destructive factor (Weil & Brady, 2017).

The destruction of aggregates upon wetting occurs through two main mechanisms:

1. Slaking: This is the most common mechanism. When a dry aggregate is quickly immersed in water, the air trapped inside its pores cannot escape. The pressure of this air on the pore walls can exceed the aggregate's strength, and it explodes from within, breaking into many small fragments (Eash et al., 2016; Weil & Brady, 2017). This effect is especially strong in aggregates that wet quickly and unevenly.

2. Dispersion: This is destruction at the level of individual clay particles. If the soil has a lot of sodium (Na⁺), or if the concentration of salts in the soil water drops sharply, clay particles stop attracting each other (flocculating) and start repelling (dispersing). The aggregate simply "dissolves" in water, turning into a colloidal solution that clogs pores, forming a crust (Marshall et al., 1996; Scheffer et al., 2018).

Factors determining water stability:

This is a key question. The quality of soil architecture directly depends on the ability of aggregates to "withstand the impact" of water.

1. Content and quality of organic matter: This is the most important factor for most temperate soils. Organic matter (especially humus, microbial polysaccharides, and their decomposition products) acts as a glue, binding particles into strong, water-resistant aggregates. The higher the organic matter content, the higher the water stability (Eash et al., 2016; Weil & Brady, 2017). Organics also make aggregates more hydrophobic (water-repellent), slowing down water penetration and thereby reducing the slaking effect (Marshall et al., 1996).

2. Composition of exchangeable cations: Divalent cations, especially calcium (Ca²⁺), are powerful flocculating agents. They "cross-link" clay particles, making aggregates more stable in water. Conversely, monovalent sodium (Na⁺) causes dispersion and sharply reduces water stability (Eash et al., 2016; Weil & Brady, 2017). Therefore, saline or solonetzic soils with high sodium content are extremely unstable.

3. Presence of iron and aluminum oxides: In highly weathered soils (Ultisols, Oxisols), iron and aluminum oxides play the cementing role. They create very strong, water-insoluble bonds, making aggregates extremely water-stable, even with low organic matter content (Weil & Brady, 2017).

4. Wetting rate: Slow, capillary wetting allows air to escape from pores and prevents slaking. Rapid flooding (e.g., during heavy rain) is the most aggressive factor. Therefore, agronomic practices that slow down surface wetting (mulching, plant cover) increase water stability (Eash et al., 2016).

6.3. Stability as an Indicator of Architecture Quality

Structural stability is essentially an integral indicator of soil architecture health. If aggregates are easily destroyed by water or pressure, the architecture is unstable. This immediately triggers a chain of negative consequences:

• Compaction and fusion: Destroyed aggregates fill pores, the soil becomes dense and structureless.
• Reduced infiltration: Without macropores, water cannot infiltrate quickly, leading to surface runoff and erosion.
• Impaired aeration: Pores are filled with water or destroyed, roots experience oxygen deficiency.
• Difficulty in root growth: Roots find it hard to penetrate the dense, structureless mass.

Conclusion: Structural stability is not a static property but a dynamic characteristic strongly dependent on management. Practices that increase organic matter content and support biological activity (minimum tillage, organic matter application, use of cover crops) directly increase aggregate stability. Conversely, practices that destroy it (intensive tillage, working on wet soil, burning organics) lead to rapid degradation of soil architecture (Eash et al., 2016; Weil & Brady, 2017).

Section Conclusion:

We have considered stability as a critical property of architecture that determines its durability. We have distinguished between mechanical and water stability, identified the main factors (organic matter, cations, oxides) and mechanisms of destruction (slaking, dispersion). This knowledge serves as a bridge between theoretical architecture and practical soil management. In the final section, we will summarize all this and show how architecture and its stability regulate key physical processes in the soil.

7.1. Architecture as a Regulator of Water Regime

The soil water regime is perhaps the most striking example of the regulatory role of architecture.

1. Infiltration (water entry): The rate of water entry into the soil is determined by the presence and continuity of macropores on the surface and in the upper horizons (Marshall et al., 1996). If there is a network of biopores, cracks, and inter-aggregate channels, water quickly penetrates deep. If macropores are destroyed (compaction, crust), water ponds on the surface, causing runoff and erosion (Eash et al., 2016; Weil & Brady, 2017).

2. Redistribution of moisture (within the profile): After water has entered the soil, architecture begins to redistribute it. Through macropores, water quickly moves downward (drainage). Simultaneously, capillary forces draw water from macropores into meso- and micropores within aggregates, where it is stored as a "reserve" (Shukla, 2023). This process is ensured by the hierarchy of pores: macropores for transport, meso- and micropores for storage.

3. Availability of moisture to plants: It is architecture that determines which part of this water will be accessible to roots. Water in mesopores and large micropores is in capillary connection with roots and is easily absorbed. Water in ultramicropores is held too tightly and is unavailable (Weil & Brady, 2017). Thus, a well-structured soil with a large number of mesopores has a high supply of "active" moisture, while a structureless clay or sand has a low one.

4. Capillary rise: During dry periods, water can rise upward through the capillary network of mesopores from wetter deep layers to the root zone. This ability directly depends on the continuity of capillary pores (Scheffer et al., 2018).

7.2. Architecture as a Regulator of Gas Exchange and Aeration

For roots and most soil microorganisms, access to oxygen and removal of carbon dioxide are critically important.

1. Gas diffusion: Gas exchange between the soil and the atmosphere occurs mainly through macropores. The greater the proportion of macropores and the higher their continuity, the faster oxygen enters the root zone and the faster carbon dioxide, produced by root and microbial respiration, is removed (Marshall et al., 1996; Weil & Brady, 2017).

2. Aeration and waterlogging: If macropores are filled with water (e.g., after heavy rain), gas exchange slows down sharply. In a structureless soil with a predominance of micropores, water displaces air for a long time, creating anaerobic conditions that are harmful to most cultivated plants (Eash et al., 2016). In a structured soil, water quickly drains through macropores, and aeration is restored much faster.

7.3. Architecture as a Regulator of Thermal Regime

Soil architecture influences how the soil heats up and cools down and how heat is distributed in the profile.

1. Heat capacity and thermal conductivity: Moisture content, determined by architecture, directly affects soil heat capacity. Wet soil heats up more slowly but also cools down more slowly. Porosity and contacts between particles determine thermal conductivity: dense soil conducts heat better, loose soil worse (Scheffer et al., 2018).

2. Seasonal and daily temperature changes: Architecture influences how deeply daily and seasonal temperature fluctuations penetrate. In loose, porous soil, the temperature of the top layer fluctuates strongly, while in denser soil, fluctuations attenuate at shallower depths (Marshall et al., 1996).

3. Consequences for plants: Temperature regime is important for seed germination, root growth, and microbiological activity. Aggregated, wet soil warms up more slowly in spring but overheats more slowly during dry periods and better protects roots from overheating (Weil & Brady, 2017).

7.4. Architecture as a Regulator of Root Growth and Development

Plant roots are not just passively present in the soil; they actively interact with its architecture.

1. Root penetration: Roots grow primarily through macropores — cracks, biopores, and spaces between aggregates. A continuous network of macropores allows roots to easily and quickly penetrate deep, exploring a larger volume of soil (Weil & Brady, 2017; Eash et al., 2016).

2. Access to resources: A branched network of macropores, permeating aggregates, allows roots to reach capillary moisture stored inside aggregates. Root hairs penetrate mesopores, extracting water and nutrients.

3. Feedback: Root growth itself is a powerful factor in shaping architecture. Roots create biopores, release organic substances that bind aggregates, and thereby improve architecture for future generations of plants (Marshall et al., 1996; Weil & Brady, 2017).

7.5. Architecture as a Regulator of Degradation Resistance

Finally, architecture determines how resistant the soil is to destructive factors.

1. Resistance to erosion: Soil with a well-developed, stable structure has high water permeability and aggregate cohesion, which reduces surface runoff and particle washout. Water-stable aggregates are not washed away by rain (Eash et al., 2016).

2. Resistance to compaction: Aggregated, porous soil distributes load better and compresses less under machinery traffic. The mechanical stability of aggregates is a "safety cushion" against compaction (Weil & Brady, 2017).

3. Resilience: Soil with good architecture, even if disturbed, recovers faster due to high biological activity and the ability of aggregates to self-repair (Shukla, 2023).