Soil: Definitions, Functions, Formation, Soil Profiles, and Soil Development for Class 10th and 12th

Soil: Definitions, Functions, Formation, Soil Profiles, and Soil Development


Like many popular words, “soil” has numerous meanings. Whether or not it has observable soil horizons, Soil in the conventional sense is the natural environment for the growth of land plants. People value soil because it filters water, recycles waste, and supports plants that provide humans with food, fiber, drugs, and other needs. Except for bare rock, places of persistent frost or deep water, and the bare ice of glaciers, soil covers the entire surface of the earth in a continuous layer. In this way, the depth of plant roots determines the thickness of the soil.

The Russian school founded by Dokuchaiev introduced a novel understanding of soil around 1870. (Glinka, 1927). As separate natural entities, soils were thought to have distinct morphologies due to individual combinations of the climate, living things, earthy parent materials, relief, and age of landforms. A vertical slice through the many strata of each soil reveals the morphology, which reflects the combined impact of the specific genetic elements that contributed to its creation.

This idea was innovative. The soil scientist could go directly to the soil and see how all of these were expressed in concert with its morphology rather than relying solely on assumptions from the underlying rocks, the climate, or other environmental elements, either single or collectively. This idea made it possible and even important to think of all soil qualities as a whole, integrated natural body rather than as discrete traits. The impact of each trait or change in any one depends on the other characteristics in the mix. Experience has shown us that there are no useful generalizations that apply to all soils regarding any particular attribute. Depending on what is known about the formation of soil, what is experienced, and how soil reacts to management or alteration, certain characteristics are given more weight than others. However, they are separate from the taxonomy of the soil, which is based on combinations of soil properties. Both genesis research and the reactions of soils play important roles. The new idea, in short, enabled pedology.

In this text, the soil is defined as a naturally occurring body of solids (minerals and organic matter), liquid, and gases that occurs on the land surface occupies space and is distinguished by one or both of the following: horizons, or layers, that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter, or the capacity to support rooted plants in a natural environment.

The soil’s top limit is where it meets the air, shallow water, live plants, and plant materials that haven’t started to disintegrate yet. When the surface of an area is continually covered by water that is too deep (usually more than 2.5 m) for the growth of rooted plants, the area is not regarded as having soil. The locations where soil transitions to deep water, arid landscapes, rock, or ice are known as the horizontal borders of soil. Sometimes it is impossible to distinguish clearly between soil and nonsoil because the division between the two is so gradual.



Different concepts = Different definitions.

The Edaphological (concerning plant growth) is a blend of organic and inorganic materials that can support plant life

Applied science (with supporting structures) mixture of sands, gravels, and fines (very small particles) used as a foundation for the construction

Pedological (looking at soil as a distinct entity) The unconsolidated mineral or organic substance on the earth’s surface that is descended from specific parent material and exhibits the effects of time, geography, and macro-and microbes in the climate. The geosphere-biosphere-hydrosphere-atmosphere interface is where it is.

The following are some of the functions of soil:

i.Promotes the growth of higher plants

ii. The main factor determining the course of water in hydrologic systems

iii. Is nature’s mechanism for recycling nutrients

iv. Provides habitat for species.

Soil Formation

Soil-forming elements Previously, people believed that soils were static. Russian soil scientists developed the idea that soils are dynamic—that each soil evolved into the soil it is today and yet continues to change—in the late 1800s.

Five soil-forming factors that affect how soils develop were identified by the scientists. According to the theory, if all five soil-forming variables are equal, then the soil will also be equal. The term “pedogenesis” refers to the process of soil creation.

These are the five elements that shape soil:

a) Climate refers to the seasonal distribution of temperature and precipitation.

b) Plants, animals, fungi, bacteria, and other microbes are examples of biotic factors.

c) Topography: The location, aspect, and shape of slopes

d) Parent material: Alluvium and rock (wind- or water-deposited material)

e) Duration: How long has the soil been developing


The breakup of rock into increasingly smaller bits is known as weathering and is influenced by the five elements listed above. We distinguish between chemical and mechanical weathering (physical).

a) Mechanical weathering is the deterioration of rock brought on by natural phenomena including temperature changes and water freezing and thawing cycles. Since quartz is resistant to chemical weathering, it doesn’t go much smaller than these; a good example of this is quartz breaking down into tiny sand-sized particles.

b) Chemical weathering is the term used to describe how rocks deteriorate as a result of chemical processes. For instance, when combined with water, gypsum (CaSO4) and limestone (CaCO3) dissolve and form progressively smaller compounds. Micas may lose their potassium ions and change into vermiculite. To become smectite, vermiculite can further lose potassium. To become kaolinite, feldspars lose potassium. The rock in these situations weathers to a tiny or even elemental condition.

Soil Development and Soil Profiles

Horizons of soil

There are various varieties of soil, and each has a unique set of qualities. Any soil that has been thoroughly dug up will reveal layers, or horizons (O, A, E, B, C, R). A soil profile is created when the horizons are combined. Each profile describes a soil’s life as a biography. The three main layers of most soils are A, B, and C, while some soils also include an organic horizon (O).

Horizons are the individual layers that makeup soil. Depending on their location and makeup, these strata are referred to as O, A, E, B, C, and R.

O: Organic material dominates the topmost layer (humus or organic)

Primarily organic material, like decaying leaves. In certain soils, the O horizon is thin, in others, it is thick, and in still others, it is completely absent.

A – (Topsoil) Mainly composed of minerals from the original material with some organic stuff added. A suitable environment for living things like plants and animals. the mineral soil horizon that is typically at the surface or beneath an O horizon, also known as topsoil in agriculture. It is the ideal environment for plants and bacteria to develop because it has more organic carbon than the lower layers. Due to erosion or the removal of topsoil, this layer might occasionally be missing or diminished. Additionally, all surfaces created by ploughs, pastures, or other similar disturbances are referred to as A horizons.

E: If it differs from the A horizon, the E horizon is characterized by eluviation (the removal of components such as silicate clay, iron, aluminum, or organic stuff).

B: Horizon formed below an A, E, or O horizon that is characterized by the loss of the majority of the entirety of the original rock structure.

C: Hard bedrock apart, horizons or layers that aren’t significantly impacted by soil-forming processes and don’t exhibit O, A, E, or B horizon features.

R: The subordinate bedrock

A group of rocks like granite, basalt, quartzite, limestone, or sandstone that, when it is close enough to the surface to weather, serves as the parent material for various soils. Located below the C horizon, this is not soil.

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