Genesis, Factors, and Geochemistry of Soil Formation

Object and Subject of the Science

• The object of study of soil science is soil as a specific natural body that forms on the land surface. This is the main object of our course, and we will devote a large part of the lecture to it.
• The subject of study is the soil-forming process (or soil genesis). In other words, the subject of the science is the laws and mechanisms by which lifeless rock is transformed into that very "skin of the Earth" that sustains plants, animals, and humans (Birkeland, 1984; Weil & Brady, 2017). By studying the subject, we answer the main question: "How and why does soil become soil?"

The Place of Soil Science Among Other Sciences

Soil science is a classic example of a science that lies at the intersection of several disciplines. To understand soil, we need to combine knowledge from different fields. V. V. Dokuchaev, the founder of modern soil science, said that soil is a "mirror of the landscape," and to read it, one must simultaneously be a geologist, a botanist, a chemist, and a climatologist.

Connections of soil science with other sciences:

• With Geology: Soil forms from rocks (parent materials). The composition, structure, and properties of these rocks directly affect the properties of the future soil (Birkeland, 1984; Foth, 1990).
• With Climatology and Meteorology: Climate (temperature and moisture) is one of the main drivers of soil formation. It is climate that determines the rate and direction of processes (Weil & Brady, 2017).
• With Biology and Ecology: Soil is a habitat for a huge number of organisms (microorganisms, plants, animals). The life activity of these organisms is the main driving force behind the transformation of rock into soil (Jenny, 1941; Weil & Brady, 2017).
• With Chemistry and Physics: We actively use chemical and physical methods to describe and measure soil properties. This gives us the opportunity to move from qualitative descriptions to precise quantitative assessments (Buol et al., 2011).

In the modern world, soil science is closely integrated with geography, landscape science, as well as economics and environmental law, since it concerns basic national wealth and food security (Mukha et al., 2003; White, 2006).

A Brief Historical Excursion: How the Understanding of Soil Has Changed

Knowledge about soil has been accumulated since ancient times — since the dawn of agriculture (Mukha et al., 2003). However, as a rigorous science, soil science formed relatively recently, only about 140 years ago. Several key stages can be distinguished in its development, which radically changed our view of the subject:

1. The Agrochemistry and Agrogeology Periods (19th century):

At this time, soil was viewed either as a "storehouse" of nutrients (the agrochemical approach, associated with the names of J. Liebig) or as a product of rock weathering (the agrogeological approach). In essence, soil was not considered an independent body. To the agrochemist, it was a "nutrient substance"; to the agrogeologist, it was a "loose geological formation" (White, 2006; Mukha et al., 2003). These views were limited because they did not take into account the biological and historical nature of soil.

2. The Birth of Genetic Soil Science (late 19th – early 20th centuries):

A turning point came in 1883 with the publication of the fundamental work "Russian Chernozem" by Vasily Vasilyevich Dokuchaev. Dokuchaev made a scientific revolution by proving that soil is an independent natural-historical body that is qualitatively different from both rock and plants. He was the first to formulate the main factors of soil formation (climate, parent rock, relief, living organisms, and time) and showed that soils naturally replace each other in space (zonality). V. V. Dokuchaev is rightly considered the father of modern genetic soil science (Birkeland, 1984; Buol et al., 2011; Weil & Brady, 2017).

3. The American Period and Systematization (first half of the 20th century):

Dokuchaev's ideas were picked up and developed in the USA. Curtis F. Marbut translated the works of Dokuchaev's student K. D. Glinka and introduced the concept of the soil profile as the main object of study. He created the first multi-category soil classification system based on the soils' own properties, rather than external factors (Buol et al., 2011).

4. The Quantitative Approach and Factor Theory (mid-20th century):

The Swiss-American scientist Hans Jenny, in his famous book "Factors of Soil Formation" (1941), mathematically formalized Dokuchaev's approach. He represented soil as a function of five factors: Soil = f(Climate, Organisms, Relief, Parent Material, Time). This work laid the foundation for the transition from descriptive soil science to analytical soil science and made it possible to apply mathematical methods to study soil processes (Buol et al., 2011; Weil & Brady, 2017).

5. The Modern Stage: "Soil Taxonomy" and the Systems Approach (from the 1970s to the present):

Modern soil science has become even more precise. The classification "Soil Taxonomy" (1975), developed under the leadership of Guy D. Smith and his colleagues, is no longer just a system but a rigorous, quantitatively defined language that soil scientists around the world can speak (Buol et al., 2011; Weil & Brady, 2017). Today, we view soil not as something static but as an open, self-organizing, dynamic system that is a key element of the Earth's "critical zone" (Weil & Brady, 2017; Huang et al., 2012). At the center of our attention today is genesis — that is, the process of constant development and change of soil in time and space.

It is precisely this understanding that we will develop throughout our module.

3.1. Inputs to the Soil System (What Enters the Soil)

1. Solar energy (Energy input):

This is the main driving factor of all processes in the soil, including its very existence. Solar energy reaches the soil surface, heats it, and creates a temperature gradient. It is the basis for plant photosynthesis and, consequently, for the input of organic matter into the soil. It is solar energy that ensures the cycle of water, nutrients, and ultimately — life in the soil (Weil & Brady, 2017; Huang et al., 2012).

2. Atmospheric precipitation (Water input):

Water is the main solvent and transport agent in the soil. It comes in the form of rain, snow, dew, and fog. Water is necessary for all chemical reactions (hydrolysis, dissolution, oxidation), for the life of plants and microorganisms, and for the movement of substances within the profile (translocation) and their removal beyond its limits (leaching) (Birkeland, 1984; Weil & Brady, 2017).

3. Atmospheric gases (Gas input):

The soil "breathes." From the atmosphere, oxygen (O₂), necessary for root respiration and aerobic microorganisms, and nitrogen (N₂), fixed by some bacteria, enter the soil. This gas exchange is critical for maintaining life in the soil and for oxidative processes (Foth, 1990; Weil & Brady, 2017).

4. Plant residues and products of organism activity (Organic input):

This is the main source of organic matter in the soil. It comes in the form of:

• Aboveground litter: leaves, branches, needles, stubble, dead grasses.
• Belowground litter: root exudates and dying roots.
• Products of the vital activity of animals and microorganisms. Microorganisms and invertebrates process this material, creating the basis for humus formation (Jenny, 1941; Weil & Brady, 2017; Huang et al., 2012).

5. Mineral material (Mineral input):

Soil receives mineral particles both from within (due to weathering of the parent rock) and from outside:

• Eolian (wind) input: dust and sand from deserts, steppes, and arable fields.
• Water input (alluvium, colluvium): suspended particles transported by surface waters and deposited on floodplains and at the foot of slopes.
• Volcanic ash (in areas of volcanism). These external inputs can dramatically affect soil properties (Birkeland, 1984; Weil & Brady, 2017).

3.2. Outputs from the Soil System (What Leaves the Soil)

1. Soil respiration (Gas output):

This is the reverse side of gas exchange. As a result of root respiration, microbial activity, and organic matter decomposition, the soil releases carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) into the atmosphere. This process is critical to the global carbon cycle and affects the greenhouse effect (Weil & Brady, 2017; Huang et al., 2012).

2. Leaching (Eluviation) (Water output with dissolved substances):

Water percolating through the soil dissolves and carries out various chemical compounds — salts, bases (calcium, magnesium, potassium), organic acids, and even fine colloidal particles. This process is called leaching or eluviation. Leached substances can enter groundwater and then rivers and oceans. This is an important channel for the loss of nutrients from the soil profile (Birkeland, 1984; Weil & Brady, 2017).

3. Surface runoff and erosion (Water and solid output):

Water that does not have time to infiltrate the soil flows over the surface, carrying away fine soil particles. This is water erosion. Wind lifts and carries away silty particles — wind erosion or deflation. This is one of the fastest and most destructive channels of soil material loss, leading to landscape degradation (Weil & Brady, 2017; Huang et al., 2012).

4. Removal with harvest and biomass (Organic and mineral output):

In anthropogenic agroecosystems, a significant part of organic and mineral substances is removed from the cycle along with agricultural crop yields. This is anthropogenic output, which especially depletes the soil if not compensated by the application of fertilizers and organic matter (Mukha et al., 2003; Weil & Brady, 2017).

5. Geological burial (Long-term output):

On a global scale, soils can be buried under a layer of new deposits (for example, during volcanic eruptions or accumulation of sediments) and, becoming part of the geological record, exit the active biological cycle for millions of years.

3.3. The Internal Workings of the System: Transformations and Translocations

Inputs and outputs are the external boundaries of the system. But the most interesting thing happens inside the soil itself, where these inputs are transformed. These internal processes are divided into four main types (according to the classification of R. W. Simonson, 1959) (Birkeland, 1984; Weil & Brady, 2017):

1. Transformations (Alterations): These are chemical and biological changes occurring with the material inside the soil. For example:

• Mineral weathering: the destruction of primary minerals (feldspars, micas) and the synthesis of secondary ones (clay minerals, iron and aluminum oxides).
• Humification: the transformation of plant residues into a complex complex of organic compounds — humus.

2. Translocations (Migrations): This is the physical movement of substances within the soil profile, from one horizon to another. It is carried out mainly by water (less often by living organisms) in two directions:

• Downward (eluviation): the removal of substances from the upper horizons.
• Upward (illuviation): the accumulation of substances in the lower horizons.
• Example: Fine clay particles may be washed out from the upper, eluvial horizon (A2) and deposited in the lower, illuvial (Bt), forming textural differentiation of the profile.

3.4. Visual Model: Soil as a "Reactor"

This whole complex system of inputs, outputs, and internal transformations can be presented in the form of a simple but capacious model:

This model clearly shows that soil is not an isolated warehouse but a flowing, dynamic reactor. It is the continuous flow of matter and energy that determines its state and direction of evolution. Understanding soil as an open system is the key to understanding its vulnerability: any change in the "inputs" (for example, deforestation or climate change) will inevitably lead to a change in the "outputs" and, most importantly, to a change in the soil itself.

4.1. Medium for Life and Plant Growth (Agroecological Function)

This is the oldest and most obvious function, and it is this that became the basis for the emergence of agriculture and civilization (Foth, 1990; White, 2006). Soil acts as:

• Support and substrate: plant root systems anchor in the soil, receiving mechanical support.
• Source of water and nutrients: soil accumulates and stores moisture and also contains macro- and micronutrients necessary for plants in available form.
• Medium for root respiration: soil pores contain air with oxygen necessary for root respiration and aerobic microorganisms (Foth, 1990).
• Buffer and regulator: soil moderates temperature fluctuations and chemical stresses (excess toxic compounds) due to its buffering capacity.

This function is the basis for the production of more than 95% of all human food products (Weil & Brady, 2017). We will focus on it in the following lectures of the course, but it is important to remember that it is not the only one.

4.2. Regulation of Water Regime and Filtration (Hydrological Function)

Main page: Soil water regime

Soil is a critical element of the global hydrological cycle. It performs the role of:

• Distributor: it determines which part of the precipitation will infiltrate and recharge groundwater reserves and which will flow over the surface (Weil & Brady, 2017; Birkeland, 1984).
• Reservoir: it accumulates moisture, which is then gradually consumed by plants and feeds rivers during dry periods (regulates runoff, reducing the risk of floods and droughts).
• Natural filter: as water passes through the soil profile, it is purified from suspended particles, many pathogenic microorganisms, and toxic substances due to adsorption, chemical decomposition, and biological activity (Weil & Brady, 2017; Mukha et al., 2003). This function is critically important for the formation of high-quality drinking water reserves.

4.3. Nutrient Cycling and Organic Carbon Storage (Biogeochemical Function)

Soil is the central link in the small biological cycle of matter:

• Element cycling: it serves as a site for the transformation and return to the biological cycle of elements such as carbon, nitrogen, phosphorus, and sulfur. Microorganisms decompose plant residues, mineralize organic matter, converting it into forms available to the next generation of plants (Jenny, 1941; Huang et al., 2012).
• Carbon reservoir: soil accumulates a huge amount of organic carbon — significantly more than the atmosphere and all terrestrial biomass combined (Weil & Brady, 2017; Scheffer et al., 2018). This makes soil a critical factor in regulating the greenhouse effect and global climate: carbon sequestration (locking) in soil is one of the most effective ways to mitigate climate change.

4.4. Habitat for Organisms (Biocoenotic Function)

Soil is one of the most life-rich habitats on Earth:

• Reservoir of biodiversity: one gram of fertile soil can contain up to several billion microorganisms (bacteria, fungi, actinomycetes) belonging to thousands of species (Weil & Brady, 2017; Scheffer et al., 2018).
• Habitat: soil is home not only to microorganisms but also to numerous invertebrates (worms, insects, mites, nematodes) and even some vertebrates (shrews, rodents).
• Basis of food webs: all this biota participates in the decomposition of organic matter, the creation of soil structure, and the feeding of terrestrial organisms.

This function has not only ecological but also medical significance: soil microorganisms are the source of most modern antibiotics (Weil & Brady, 2017).

4.5. Degradation and Recycling of Anthropogenic Waste (Sanitary Function)

Due to its chemical, physical, and biological properties, soil is capable of neutralizing and processing a significant amount of pollutants:

• Adsorption and immobilization: clay minerals and humus bind heavy metals and organic toxicants, preventing their migration (Weil & Brady, 2017; Huang et al., 2012).
• Biochemical destruction: microorganisms are capable of decomposing many synthetic organic compounds (some pesticides, petroleum products) into harmless components.
• Organic recycling: soil processes huge volumes of organic waste from livestock and crop production, involving them in the biological cycle.

However, this function has its limit: when permissible loads are exceeded, the buffering capacity of the soil is exhausted, and it itself becomes a source of pollution (Huang et al., 2012; Scheffer et al., 2018).

4.6. Engineering and Construction Function

Soil serves as the physical foundation for all terrestrial infrastructure:

• Foundation base: the stability of buildings, bridges, and roads depends on soil properties. Its bearing capacity, settlement, and compressibility are critical parameters for engineering calculations (Birkeland, 1984; Weil & Brady, 2017).
• Building material: soil has been used since ancient times for making adobe bricks, cob, and clay buildings, and in modern construction — as material for embankments, dams, and levees.
• Ecological construction ("green" building): soil is used as a component of green roofs, for biological wastewater treatment (filtration fields), and for the reclamation of disturbed lands (Weil & Brady, 2017).

4.7. Archive of Natural and Cultural History (Paleogeographic Function)

The soil profile accumulates information about the past landscape, climate, and even human activity:

• Paleosols (buried soils): the study of ancient soils allows reconstructing climatic changes and plant communities of past epochs (Birkeland, 1984; Buol et al., 2011). For example, the presence of red-colored soils in the modern cold tundra indicates that a hot climate existed here in the past.
• Archaeological archive: artifacts of ancient settlements, remains of tools, and seeds of cultivated plants are preserved in the soil and buried layers, making soil a valuable object for historical and archaeological research (Weil & Brady, 2017).

4.8. Aesthetic and Cultural Function

One should not forget the spiritual, aesthetic, and recreational role of soil. It is part of the natural landscape, creates the environment for gardens, parks, lawns, and determines the appearance of the area. The emotional connection with the "native land" is a cultural phenomenon that we cannot ignore (Weil & Brady, 2017; Scheffer et al., 2018). Understanding all these functions leads us to the conclusion: soil is a non-renewable resource on the scale of human life. Its degradation leads to the simultaneous destruction of all the listed functions, making the preservation of the soil cover one of the global environmental challenges of our time.

6.1. Why is it important to talk about time?

For understanding soil genesis, time is not just "another factor" but a fundamental coordinate in which all other processes unfold. As V. V. Dokuchaev figuratively remarked, time is the "age of the country" (Jenny, 1941; Mukha et al., 2003). Without time, there can be no history of development, and therefore, no soil itself as a historical body.

In soil science, two concepts of age are distinguished (Birkeland, 1984; Foth, 1990; Weil & Brady, 2017):

1. Absolute (chronological) age — is the calendar time elapsed since the beginning of soil formation (e.g., since the retreat of a glacier or the deposition of new alluvium). It is measured in years, millennia, and millions of years.

2. Relative age — is the degree of soil development expressed in morphological, physical, and chemical properties. Two soils with the same absolute age may have different relative ages due to differences in other factors (climate, parent material, relief). For example, a soil on sand in a warm, humid climate will be much more developed than a soil of the same age on dense clay in a cold, dry steppe (Birkeland, 1984; Foth, 1990).

For an agronomist, relative age is the most important, as it directly correlates with fertility and other soil properties important for agriculture.

6.2. The Scale of Soil Time: from Minutes to Millions of Years

To help you better appreciate the scales, let us imagine a time scale on which various soil processes occur. This scale will cover a vast range — from fractions of a second to hundreds of millions of years (Birkeland, 1984; Weil & Brady, 2017; Huang et al., 2012).

I. Minutes, hours, days (Instant and rapid processes)

These are processes that we can observe directly.

• Flooding and drainage: After a heavy rain, soil pores can fill with water in a matter of minutes, displacing air. This immediately affects root respiration.
• Swelling and shrinking of clays: Some clay minerals (e.g., smectites) can swell when wet and crack when dry within hours or days, destroying or creating structure (Huang et al., 2012).
• Episodic erosion: A heavy downpour can wash away a thin layer of topsoil in a single day.
• Bioturbation by insects and worms: Earthworms can mix and process the upper layers of soil within a single season (Weil & Brady, 2017; Mukha et al., 2003).

II. Years, decades (Anthropogenic and rapid natural changes)

This is the time scale in which most agronomists work.

• Accumulation of organic matter (A-horizon): Under favorable conditions (e.g., after grassing or application of large doses of organics), the formation and noticeable darkening of the surface humus horizon can occur within 10–100 years (Birkeland, 1984; Weil & Brady, 2017).
• Soil compaction: Heavy machinery and improper tillage can lead to the formation of a "plow pan" within a few years.
• Structure degradation: Intensive tillage can destroy water-stable aggregates within a few years.
• Anthropogenic salinization: Improper irrigation in arid regions can lead to salt accumulation within decades (Foth, 1990).

III. Hundreds – thousands of years (Formation of main horizons)

Over this time span, we observe the formation of a full-fledged soil profile.

• Formation of the B-horizon (Bw): Change in color and structure due to weathering and the onset of iron migration takes from several hundred to the first thousands of years (Foth, 1990; Birkeland, 1984).
• Formation of the illuvial horizon (Bt): Accumulation of clay particles washed out from the upper horizon usually requires no less than 5,000–10,000 years. For example, in the classic study of the soil chronosequence on lake terraces in Michigan (USA), a distinct illuvial horizon formed only on the terrace about 8,000 years old (Foth, 1990; Birkeland, 1984). It is this time interval that shows how slowly the textural differentiation of the profile, so valued by agronomists for its effect on the water regime, forms.
• Accumulation of carbonates in arid soils: In arid climates, the formation of carbonate horizons (Bk, K) can take from several thousand to tens of thousands of years (Birkeland, 1984).

IV. Tens – hundreds of thousands of years (Deep weathering)

This is the time scale in which the most developed and deep profiles form.

• Formation of highly weathered soils (Oxisols, Ferralsols): The formation of deep (up to 10–30 m) red-colored profiles enriched with iron and aluminum oxides (ferrallitic process), with the destruction of most primary minerals and the formation of kaolinite, goethite, and hematite, requires hundreds of thousands of years (up to 1–2 million years). Such soils are characteristic of ancient planation surfaces in the tropics (Buol et al., 2011; Weil & Brady, 2017).
• Full denudation cycle: Under natural conditions, the rate of formation of 1 cm of soil can be 0.01–0.1 mm per year. That is, the formation of a 10-centimeter layer of soil requires thousands of years, making it a practically non-renewable resource (Weil & Brady, 2017).

V. Millions of years (Geological scale)

At this time horizon, soils themselves become part of geological history.

• Burial and diagenesis: Ancient soils (paleosols) can be buried under thick layers of sediment and transformed into sedimentary rocks such as coals, bauxites, and ironstones.
• Evolution of soil-forming factors: Over millions of years, climate, plate tectonics, and atmospheric composition change, leading to a cardinal change in the types of soil formation over vast territories.

6.3. Example: Soil Formation in the Holocene (the last ~10,000 years)

The time scales are most clearly demonstrated by chronosequences — series of soils formed on surfaces of different ages under otherwise equal conditions. A classic example is the research by F. D. Hole and his colleagues in Michigan, USA (Franzmeier & Whiteside, 1963; Foth, 1990):

• Soil on the 2,250-year-old terrace: The profile consists of weakly developed A and C horizons. Humification of organics and leaching of lime from the upper part are actively occurring. This is a very young, weakly developed soil.
• Soil on the 3,000-year-old terrace: The profile already shows eluvial (E) and illuvial (Bs) horizons, in which iron and aluminum oxides accumulate. The weathering and migration of substances have noticeably progressed.
• Soil on the 8,000-year-old terrace: A fully developed profile with thick A, E, Bhs (illuvial-humus), and C horizons is observed. At this stage, significant accumulation of humus in the illuvial horizon occurs, dramatically changing soil properties.

This example clearly demonstrates that soil is not an instantaneous result but a long historical process. The soils we see today in most temperate regions formed over the last 10–15 thousand years — since the retreat of the last glacier (Weil & Brady, 2017).

6.4. Why is this important for an agronomist?

1. Understanding non-renewability: On the scale of a human life, soil is a non-renewable resource. Its recovery rate is incomparable with the rate of its destruction (erosion, degradation). Every centimeter of lost soil is the loss of hundreds and thousands of years of natural work.

2. Potential assessment: Knowledge of the age and degree of soil development allows one to predict its fertility, profile depth, moisture reserves, and potential yield. Young soils are often poorer in humus and nutrients.

3. Choosing a use strategy: Understanding that soil is a slowly developing system requires careful treatment. An agronomist should strive not just to "take" a harvest but to create conditions for the continuation of soil formation, maintaining the balance of organic matter and protecting the soil from erosion.

4. Paleoreconstructions: By studying soil profiles, we can learn about past climates and landscapes, which helps predict future changes. This is critically important for long-term planning under a changing climate (Birkeland, 1984).

So, soil is not just the "top layer of earth." It is the result of thousands and millions of years of continuous biochemical processes. Understanding the scales of soil time is the foundation of an agronomist's ecological thinking and the key to sustainable farming.

7.1. From a Linear Model to a Non-Linear One

In the classical understanding (especially within H. Jenny's factor model), soil formation was often represented as a linear process: a change in a factor (e.g., an increase in precipitation) leads to a proportional change in soil properties. This is a useful model for initial understanding, but it oversimplifies reality (Jenny, 1941; Birkeland, 1984).

Modern research shows that soil formation is a non-linear process. This means that:

1. Threshold effects: Changes in the soil can accumulate imperceptibly, and then, upon reaching a certain threshold, a sharp, qualitative leap occurs. For example, the long-term accumulation of calcium carbonates in the soil can lead to the sudden formation of a petrocalcic horizon (K-horizon) — a dense, cemented layer that dramatically changes the water regime of the entire soil. This is not just "more carbonates" but a qualitative change in the profile structure (Birkeland, 1984; Weil & Brady, 2017).

2. Feedback loops (Feedback loops): Processes in the soil can amplify or dampen each other. This is one of the key mechanisms of self-organization. A classic example:

• Positive feedback: Plant growth increases the input of organic matter into the soil. Organic matter improves structure, which increases water infiltration and aeration. This, in turn, stimulates further plant growth and even greater accumulation of organics. The process reinforces itself (Weil & Brady, 2017; Huang et al., 2012).
• Negative feedback: Weathering of minerals releases bases (calcium, magnesium, potassium), which neutralize the acidity created by organic acids. This slows further weathering and acidification. The process is self-limiting (Huang et al., 2012).

7.2. Soil as a Self-Organizing System

It is precisely because of threshold effects and feedback loops that soil behaves as a self-organizing system. This means that without external control, it is capable of forming ordered structures (soil horizons, aggregates) from a chaotic set of particles and processes (Weil & Brady, 2017; Huang et al., 2012).

Self-organization in soil manifests at all levels:

• At the micro-level: clay particles spontaneously aggregate into microaggregates under the influence of electrochemical forces and organic "glues" (polysaccharides, humic substances) (Huang et al., 2012).
• At the meso-level: microaggregates combine into macroaggregates (structural units — clods, nutty, prismatic structures) under the influence of plant roots, fungal mycelium, and the activity of soil fauna (Weil & Brady, 2017).
• At the macro-level: genetic horizons are formed — vertically ordered layers with different properties. This is the main result of soil self-organization as a system (Birkeland, 1984).

7.3. Constant Interaction of Components

Modern soil science views soil not as a sum of components (minerals + organics + water + air + organisms) but as their inseparable unity, where each component constantly influences all the others (Weil & Brady, 2017).

Let us consider this cycle of interactions:

1. Minerals ↔ Water: Minerals weather under the action of water, releasing nutrients. Water is retained on the surface of minerals, determining their wettability and availability to plants.

2. Minerals ↔ Organic matter: Organic acids released by microorganisms and roots accelerate the dissolution of minerals. Clay minerals and iron/aluminum oxides bind (adsorb) organic molecules, protecting them from rapid decomposition and forming organomineral complexes — the basis of structure and fertility (Huang et al., 2012).

3. Organic matter ↔ Organisms: Plant residues are food for microorganisms and soil animals. These, in turn, decompose the organics, converting them into forms available to plants (mineralization) and creating stable humus (humification).

4. Organisms ↔ Minerals: Plant roots penetrate cracks in rocks, mechanically breaking them down (physical weathering). Root exudates and organic acids dissolve minerals (chemical weathering). Microorganisms oxidize and reduce mineral compounds, changing their mobility.

This complex web of interactions makes soil not just a passive substrate but an active biogeochemical reactor that constantly processes incoming substances (Jenny, 1941; Weil & Brady, 2017).

7.4. Soil Formation and Climate Change

Modern science pays increasing attention to how soil formation responds to global climate change. Soils are simultaneously both an indicator and a regulator of climate change (Weil & Brady, 2017; Scheffer et al., 2018).

• Soil as an indicator: Climate change (warming, changes in precipitation patterns) will inevitably lead to changes in the rate and direction of soil processes. For example, in the permafrost zone (cryolithozone), the thawing of permafrost activates the decomposition of organic matter, leading to the release of huge amounts of greenhouse gases (CO₂ and CH₄) (Scheffer et al., 2018; Huang et al., 2012).
• Soil as a regulator: Soil is the largest terrestrial reservoir of organic carbon. By managing the stocks of organic matter in the soil (through agronomic practices, reforestation), humanity can influence the concentration of CO₂ in the atmosphere. Carbon sequestration in soil is considered one of the most promising and cost-effective ways to mitigate climate change (Weil & Brady, 2017).

7.5. The Anthropogenic Factor as a New Force of Soil Formation

In the modern era, which many scientists call the Anthropocene (the age of humans), human economic activity becomes a soil-forming factor comparable in scale to natural forces (Weil & Brady, 2017; Huang et al., 2012; Richter & Tugel, 2012).

Humans affect the soil:

• Directly: tillage, application of fertilizers and amendments, irrigation, drainage, mechanical compaction, construction. This changes the physical, chemical, and biological properties of the soil.
• Indirectly: changes in vegetation cover (deforestation, plowing of steppes), climate change (greenhouse gas emissions), environmental pollution.

Modern soil formation is no longer a purely natural process but a natural-anthropogenic one. Soils created or significantly altered by humans (e.g., arable, urban, reclaimed, recultivated) are becoming a special object of study (Richter & Tugel, 2012; Mukha et al., 2003). We must understand that our impact is embedded in a complex system of feedbacks and can lead both to increased fertility (cultivation) and to degradation (erosion, salinization, depletion, pollution). Understanding soil formation as a non-linear, self-organizing process is the key to making our actions conscious and sustainable.

To summarize:

The modern view of soil formation is the view of a complex, open, non-linear, self-organizing system in which minerals, organic matter, water, air, and living organisms are in constant, dynamic interaction. This system has threshold effects, feedback loops, and the ability for self-regulation. In the modern era, humans become one of the leading factors of this system, and our task is to learn how to manage this process in such a way as to preserve and enhance soil fertility.

8.1. Soil Diagnostics and Potential Assessment

The first and most obvious application is diagnostics. Knowing the patterns of soil formation, an agronomist can use external morphological features (color, structure, horizon thickness) to determine the soil type and assess its key properties:

• Fertility: The thickness and color of the humus horizon (A) give an idea of the reserves of organic matter and potential fertility. For example, chernozems with a thick dark horizon are soils with high natural fertility, while podzolic soils with a light eluvial horizon are poor and acidic (Birkeland, 1984; Mukha et al., 2003).
• Water-physical properties: The presence and thickness of the illuvial horizon (Bt) indicates possible problems with water permeability and aeration. This is critically important for choosing a tillage and irrigation system (Weil & Brady, 2017; Foth, 1990).
• Chemical properties: The presence of a carbonate horizon (Bk, K) indicates an alkaline reaction and possible micronutrient deficiencies. Signs of salinization or alkalinity require special reclamation measures (Birkeland, 1984; Weil & Brady, 2017).
• Age and degree of development: Based on the degree of profile development (set of horizons), one can judge the age of the soil and the stage of its evolution, which helps predict its resistance to anthropogenic loads (Foth, 1990).

Thus, knowledge of genesis allows an agronomist to "read" the soil profile like a book and make the right decisions without expensive and lengthy laboratory analyses at the initial stage.

8.2. Rational Use and Choice of Agrotechnologies

Understanding the origin of the soil underlies the choice of the most effective and environmentally safe technologies for its use (Birkeland, 1984; Weil & Brady, 2017; Mukha et al., 2003).

• Selection of agricultural crops: Soils formed on light sandy materials (fluvio-glacial sands) will be poor in nutrients and prone to drought — they are suitable for stress-tolerant crops (e.g., rye, lupine). Heavy clay soils, on the contrary, are rich in nutrients but poorly permeable to water — they are better suited for moisture-loving crops (rice, corn) (Mukha et al., 2003).
• Tillage system: The presence of dense illuvial horizons or a "plow pan" requires deep loosening. On soils prone to erosion (formed on loess materials), no-till and minimum tillage are preferable. Understanding how tillage affects the soil-forming process (e.g., destroys structure or accelerates humus mineralization) allows choosing minimally invasive technologies (Weil & Brady, 2017).
• Irrigation and reclamation: Knowledge of genesis helps to correctly choose the type of irrigation and drainage. For example, in soils with a carbonate horizon, it is important to avoid salinization. In soils with textural differentiation (presence of Bt), it is important to take into account the risk of perched water and waterlogging (Birkeland, 1984; Weil & Brady, 2017).

8.3. Soil Protection and Combating Degradation

Perhaps this is the most important applied significance. Understanding that soil is a slowly developing, non-renewable system on the scale of human life forces us to look anew at the problem of its protection (Weil & Brady, 2017; Huang et al., 2012; Scheffer et al., 2018).

• Combating erosion: Knowing which soils are most susceptible to erosion (light in texture, on slopes), an agronomist can plan a system of soil-protective measures: shelterbelts, buffer strips, mulching, contour plowing.
• Preventing depletion: Understanding the cycle of substances in the soil (the small biological cycle) allows competent management of nutrient flows, returning organic matter to the soil (green manures, manure, compost) and applying mineral fertilizers in balanced amounts so as not to disrupt natural processes.
• Combating salinization and alkalinization: Knowledge of the halogen soil-forming process helps develop strategies for leaching and gypsuming of saline soils, as well as preventing secondary salinization during irrigation (Mukha et al., 2003; Weil & Brady, 2017).
• Maintaining biological diversity: Understanding that soil is a habitat for a huge number of organisms stimulates the use of biological plant protection methods and organic fertilizers that support the activity of soil biota (Weil & Brady, 2017).

8.4. Reclamation of Disturbed Lands

In mining, construction, and military operations, vast areas of land are disturbed. Restoring fertility on such lands (reclamation) is essentially controlled soil formation (Huang et al., 2012; Weil & Brady, 2017). Knowledge of soil-forming factors allows accelerating this process:

• Selection of the correct parent material for backfilling.
• Creation of favorable relief.
• Application of organic matter and sowing of pioneer plants to initiate the biological cycle.
• Monitoring of time and stages of restoration.

This is a vivid example of how fundamental knowledge of genesis is transformed into applied technology.

8.5. Predicting the Consequences of Climate Change and Anthropogenic Impact

Modern soil science provides tools for predicting how soils will change under the influence of global warming and anthropogenic pressures (Weil & Brady, 2017; Huang et al., 2012). Knowledge of non-linear processes and threshold effects allows:

• Assessing the risks of soil degradation under various climatic scenarios.
• Developing adaptation strategies for agriculture (e.g., selection of drought-tolerant crops, changes in farming systems).
• Calculating the carbon balance in agroecosystems and developing measures for carbon sequestration in soils as a way to mitigate climate change.

8.6. Economic Valuation of Land

Understanding the genesis and properties of soils underlies the cadastral valuation of land, land taxation, and determination of rent (Mukha et al., 2003; White, 2006). Soil bonitation (their qualitative assessment) is impossible without detailed knowledge of their origin and evolution. It is the genetic types of soils, their texture, thickness of the humus horizon, and other properties formed during soil formation that determine their economic value.

Concluding Summary of the Lecture

We have come to the end of our first, introductory lecture. During this time, we have traveled a huge path:

1. We learned that soil science is a science of the origin, development, and properties of soil, standing at the intersection of geology, biology, chemistry, and physics.

2. We understood that soil is not just "dirt" or a "substrate" but a complex, dynamic, open, bio-inert natural body with a unique property — fertility.

3. We analyzed soil as an open system, constantly exchanging matter and energy with the environment.

4. We studied the main functions of soil: from a medium for plants and water filtration to a carbon reservoir and an archive of history.

5. We realized that genesis is a continuous process of development driven by the constant interaction of factors and processes.

6. We felt the scales of soil time: from minutes to millions of years, which makes soil a practically non-renewable resource.

7. We got acquainted with the modern view of soil formation as a non-linear, self-organizing process with thresholds and feedbacks.

8. We saw the applied significance of this knowledge for diagnostics, agriculture, nature protection, and economics.

The main conclusion of this lecture:

Soil is not a static resource but a living, developing system. Success in agriculture and environmental conservation is impossible without a deep understanding of the laws of its origin and development. Knowledge of soil genesis is not a luxury but a professional necessity for everyone who works with the land.