SOIL
Soil constitutes the uppermost layer of loose deposits, inhabited by living organisms. It functions as a system where energy and substance flows interact, originating from the Sun, the atmosphere, and living organisms. The depth to which living organisms, particularly plant roots, can penetrate these deposits varies from a few millimeters in arid and cold regions with dense rock formations to 4-5 meters or more in warmer, humid areas characterized by porous and permeable surface deposits. This system comprises various forms of matter and energy: mineral particles and chemical compounds from the land, radiant energy from the Sun, and water, carbon dioxide, and nitrogen from the atmosphere. Biomass releases solar energy assimilated by living organisms through photosynthesis, accumulating in hydrocarbon compounds.
Soil operates as a system due to the interaction and transformation of diverse forms of energy and substances in the earth’s crust’s surface layer through weathering. Many of these transformations exhibit cyclical or variable characteristics. For instance, the synthesis of energy-rich hydrocarbon compounds essential for plant life requires not only solar energy but also carbon dioxide from the air and water, primarily from the soil. Over time, plants decompose, enriching the soil with organic matter, which microorganisms break down, returning carbon dioxide, water, and energy to the system. The soil system, with its inherent transformations of energy and substances, is a fundamental component of the human habitat, utilized by humans to maintain nutritional balance.
SOIL PROFILE
Interactions within the soil system result in observable alterations in the soil mass. Soil sections exhibit a vertical arrangement of layers, known as soil horizons, which differ in various characteristics such as color and thickness. The number and thickness of these horizons are influenced by the relief. This sequence, encompassing all soil horizons, is referred to as a soil profile. Within the distribution area of a specific soil type, the profile structure exhibits similar features, making the soil profile the primary distinguishing characteristic of the soil type. The structure of the soil profile reflects the unique evolution of natural processes in the region to which it belongs. Typically, soil is categorized into two main horizons: the upper, active horizon, and the lower “subsoil” horizon.
In the examination of many soil profiles, a multitude of horizons is identified, commonly denoted by the Latin letters A, B, and C, starting from the surface. These horizons are often further divided into sub-horizons: A1, A2, A3, B1, B2, B3. The A horizons form in the upper part of the soil profile, while the B horizons develop in the “subsoil” layers. Horizon C comprises fragments of the underlying rock, referred to as the parent material. Occasionally, horizons O and R are also distinguished. Horizon O (or A0), consisting of forest litter covering the mineral horizons, is composed of fallen leaves. Horizon R represents compact solid rock beneath the soil. Horizons of different soils vary in their content of organic substances and clay particles, color, and other characteristics.
SOIL FORMATION
Soil formation results from the differentiation of deposits into distinct horizons within the soil profile, leading to increased complexity in its development. Initially, the characteristics of the soil are determined by the soil-forming rocks and minerals. In the absence of water, significant changes in the system do not occur; however, the introduction of water induces changes that contribute to the formation of the soil profile. Water interacts not only with the parent rock and minerals but also influences the development of organisms. Plants serve as the intermediary between the soil and the atmosphere.
The process of soil formation encompasses changes in the size of the constituent particles of weathering materials (mechanical composition), enrichment with organic matter, migration of elements in solution form (leaching), suspension (eluviation), and the accumulation of washed substances in certain horizons (illuviation).