Edaphogenesis: what it is, stages and factors of soil formation

Edaphogenesis is defined as the process of soil formation, that is, the set of transformations that a natural system has undergone to form the soil. This process involves the interaction of factors such as climate, bedrock, topography, organisms and time, which act together to give rise to specific horizons and properties.

• Initial stage: soil formation begins with the fragmentation of the original rocks and organic remains that colonize the material. Physical disaggregation allows the entry of air and water, which activates biological and chemical processes. Minerals are altered by releasing ions that are incorporated into the soil solution, forming gels or recombining into new secondary minerals. At the same time, the remains of plants and animals undergo transformations that give rise to humus, stabilized organic matter essential in edaphogenesis. During this process, simple compounds, water and gases are also released, although the latter largely come from the atmosphere. This phase marks the initial differentiation of the soil constituents.
• Final stage: in this stage, the constituents generated in the initial phase (minerals, humus, water, gases, solutions) are reorganized and undergo mixing and differentiation processes. If they remain in place, they evolve into well-developed soil; If they are transported, they form sediments that can be edified later. The transformation here is more intense: the original minerals are physically and chemically modified, interact with the organic fraction and generate stable structural aggregates. In this phase, the mobilizations of substances that define the morphology and chemical properties of the soil predominate. In this way, edaphic horizons with their own and recognizable characteristics are consolidated.

There are five factors that influence the soil formation process: original material, climate, biological activity, time and relief. These make there such a diversity of soils.

Origin material

The parent rock determines numerous soil characteristics, mainly young soils. With respect to the surface horizons, the soil is formed by input material foreign to the underlying rocks, such as volcanic ash or salts present in rainwater. The chemical properties of the material have a great influence on the evolution of the soil. Soils formed on base-rich rocks often have illite clay or montmorillonite, a higher exchange capacity, more organic matter content, and may be more fertile. The acidic ones can give rise to soils with kaolinite clay or vermiculite and in general they are more leached and are nutritionally poor.

Climate

Climate is the most influential large-scale factor in the formation and differentiation of soils. Temperature and precipitation regulate mineral weathering, biological activity and water dynamics in the profile. Globally, soil maps often coincide with maps of climate and associated vegetation.

Time

Time acts as a cumulative factor: over hours or seasons of the year, soil properties fluctuate (temperature, humidity, pH, nutrients), but over decades or centuries the soil goes through phases of youth, maturity and senility. Paleosols show how some profiles preserve traces of past climates, even when current conditions differ. Thus, time not only allows the evolution of horizons, but also imprints memories on the soil that reflect ancient processes, modifying its morphology and composition.

Relief

The relief conditions the circulation of water, erosion and the accumulation of materials, influencing the distribution and characteristics of soils in the same environment. In high and sloping areas, erosion processes predominate, while in low or depressed areas, sediments and nutrients accumulate. Furthermore, the relief interacts with other factors such as climate and the original material, accelerating or slowing down the formation. On steep slopes the soils are young and poorly developed; In valleys and plains, they are usually deeper and fertile.

Biological factors

Soil biota plays a key role. Animals mix and transport materials, contributing to aeration and the formation of humus. Plants, through the activity of their roots and organic remains, modify the structure, pH and fertility. Vegetation protects the soil from erosion, regulates the microclimate and enriches the surface horizons. Microorganisms transform nutrients and sustain biogeochemical cycles. Human beings profoundly alter the evolution of the soil through agriculture, deforestation or contributions of organic matter. As a whole, life on the ground accelerates its transformation and defines a large part of its current characteristics.

Edaphogenetic processes are the mechanisms that, acting on the original material under the influence of formative factors (climate, relief, biota, time), generate and differentiate soil horizons. Among the main ones we can highlight:

• Humification: transformation of fresh organic matter into humus, which stabilizes nutrients and improves soil structure.
• Mineralization: Breakdown of humus and other organic compounds into simple mineral forms, releasing plant-available nutrients.
• Descaling: dissolution and loss of carbonates due to infiltration water, common in humid climates.
• Leaching: washing of nutrients and soluble salts into deeper horizons or out of the soil profile.
• Eluviation: exit or migration of fine particles (clays, oxides, organic matter) from the upper horizons.
• Iliviation: accumulation of those same particles in lower horizons (B), forming argillic, spodic horizons, etc.
• Salinization: accumulation of soluble salts in the soil, typical of arid climates or poorly drained soils.
• Laterization: strong weathering in humid tropical climates that concentrates iron and aluminum oxides.
• Podsolization: formation of acidic soils in cold and humid climates, where organic complexes drag iron and aluminum to deeper horizons.
• Gleization: reduction of iron in conditions of water saturation, causing gray and greenish colors in the profile.

• Life support: thanks to pedogenetic processes, the soil acquires physical, chemical and biological properties that allow the growth of plants and, consequently, sustain entire food chains.
• Regulation of biogeochemical cycles: the soil regulates and stores essential nutrients such as nitrogen, phosphorus, potassium, carbon, among others, acting as a reservoir that recycles matter between the biosphere, atmosphere and hydrosphere.
• Water regulation: the structure and porosity of the soil control the infiltration, storage and movement of water, influencing the recharge of aquifers and the mitigation of floods or droughts.
• Soil diversity: edaphogenesis generates a great diversity of soils globally.
• Human use: Understanding how soils form and evolve is essential for agriculture, natural resource management, conservation and environmental restoration.

How long does it take for soil to form?

The formation of soil is a very slow process. It may take more or less time to form depending on the intensity of the forming factors, since the higher the temperature, the speed will be accelerated and the greater the presence of macro, meso or micro organisms, the speed of formation will be greater.

What is the difference between edaphogenesis and pedogenesis?

Both terms are used almost synonymously, but there is a subtle difference. Edaphogenesis refers to the general process of soil formation and evolution from bedrock to the development of horizons while pedogenesis focuses more on specific and current mechanisms that act in a specific soil (leaching, humus accumulation, salinization, etc.).

What types of soils are formed with edaphogenesis?

With edaphogenesis, a great diversity of soils can be formed, including:

• Soils from arid or semi-arid areas: such as aridisols, characterized by their low organic matter and rapid water absorption.
• Fertile meadow or temperate soils: such as mollisols, rich in humus, dark and with good drainage, ideal for agriculture.
• Lateritic tropical soils or ferralsols: deep, acidic and rich in iron and aluminum oxides, with abundant tree vegetation.
• High humidity or swampy soils: such as histosols, rich in organic matter and prone to water saturation.
• Soils from cold regions: such as gelisols or cryosols, which remain frozen for much of the year.
• Young or poorly developed soils: such as entisols, formed by recent sediments and with little differentiation of horizons.
• Soils with expandable clays: such as vertisols, which crack when they dry and can make agriculture difficult.

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