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Soil profile and Soil Horizon – Definition, Types, Importance

What is Soil?

  • Various scientific disciplines have provided varying definitions of the term “soil.”
  • In agriculture and horticulture, soil often refers to the medium for plant growth, typically the uppermost metre or two of material.
  • The majority of soil is composed of minerals, but it also contains organic materials (humus) and live organisms.
  • The voids between mineral grains are filled with air and water in various quantities.
  • In everyday usage, the term soil is sometimes limited to the dark topsoil in which seeds and vegetables are planted.
  • In a broader sense, civil engineers use the term soil to refer to any unconsolidated (wet-soft) material that is not bedrock.
  • According to this description, soil can be several hundred feet thick! Paleosols are ancient soils that have been buried and maintained beneath the surface, and they represent former climatic and environmental circumstances.

Soil Properties

  • Soils are porous, inorganic and organic matter-containing natural substances with a pore structure. They are generated by the interaction of the crust of the earth with atmospheric and biological factors.
  • They are dynamic earthen bodies with attributes that reflect the integrated consequences of those surface-level interactions.
  • With the passage of time, the geography of the landscape modifies these impacts.
  • Over decades, centuries, or millennia, parent materials transform into soils.
  • Soil formation occurs in layers.
  • These strata are known as horizons.
  • From building construction to other infrastructure projects, soil section properties are crucial.
  • Soils are structural and functional components of terrestrial ecosystems.
  • Through the interaction of geological, climatic, and biotic elements, numerous geological processes create soils.
  • The formation of soil is a very gradual process. It often takes thousands of years for thin soil layers to form.
  • The soil is the primary source of life for all living organisms. The physical and chemical qualities of soils have a significant impact on the distribution and growth of vegetation and life.
  • Soils are regarded as autonomous natural bodies, each with an own morphology and resulting from a unique combination of climate, living matter, parent rock components, relief, and time.
  • The morphology of each soil, as shown in its profile, results from the interaction of the genetic variables responsible for its formation.

Distribution of soil layers

  • There are variations in the vertical distribution of soils due to the duration and intensity of weathering, geomorphic conditions, and the strength of parent rocks.
  • It also differs from location to location.
  • There are also minute vertical variations within a soil mass’s section.
  • Consequently, they are known as soil horizons.
  • A soil profile is a complete segment of soil including a collection of separate horizons.
  • Horizons of soil are often arranged in layers parallel to the ground’s surface.
  • Some soils contain traces of their source rocks and the processes that formed the soil.

Importance of Soil

  • Our society values soil primarily because it serves as the basis for agriculture and forestry.
  • Obviously, soil is also a vital component of terrestrial ecosystems and is therefore essential for animals, plants, fungus, and microbes.
  • Nearly every biogeochemical cycle on Earth’s surface involves soil. Global cycling of important elements such as carbon (C), nitrogen (N), sulphur (S), and phosphorus (P) all occur in soil.
  • In the hydrologic cycle, soil facilitates the movement of precipitation from the surface to the groundwater.
  • Soil-dwelling microorganisms can also be essential components of biogeochemical cycles via decomposition and other processes such as nitrogen fixation.

Soil Forming Factors

Climate, organisms, relief, parent material, and time are the five major factors that influence the formation of soil. One may say that the local soil environment is determined by the relief, climate, and organisms, which work together to induce weathering and mixing of the soil parent material through time. As soil is produced, it frequently develops various strata, referred to technically as “horizons.” Upper horizons (designated A and O horizons) are richer in organic material and therefore essential for plant growth, whilst lower layers (such as the B and C horizons) maintain more of the bedrock’s original characteristics.

1. Climate

  • The influence of climate on soil formation includes temperature and precipitation.
  • Due to the short growing season, soils in regions with permafrost conditions tend to be shallow and poorly formed.
  • Due to limited breakdown, organic-rich surface layers are prevalent in low-lying locations.
  • In warm, tropical soils, the soils are often thicker, with considerable mineral alteration and leaching. In such climates, breakdown of organic materials and chemical weathering are accelerated.

2. Organisms

  • Animals, plants, and microorganisms all play crucial roles in soil formation processes, organic matter production, and/or nutrient cycling. Worms, nematodes, termites, ants, gophers, and moles, among others, all contribute significantly to soil mixing and aeration by forming pores (which help store water and air).
  • Plants contribute organic matter to soil and aid in the recycling of nutrients through root absorption.
  • The sorts of trees and grasses that grow in a particular region rely on the climate, as well as the parent material and soil type.
  • With the annual loss of leaves and needles, trees tend to deposit organic matter to soil surfaces, which, over time, contributes to the formation of a thin, organic-rich A or O horizon.
  • In contrast, grasses have extensive root and surface masses that enrich the soil each fall for annuals and short-lived perennials.
  • Therefore, grassland soils have significantly thicker A horizons with higher organic matter concentrations and are more agriculturally productive than forest soils.

3. Relief (Topography and Drainage)

  • Surprisingly, the local environment can have a significant impact on the formation of soils on-site. The local topography (relief) can have significant microclimatic effects and influence soil erosion rates.
  • Compared to level regions, locations with steep slopes have more soil erosion, higher rainwater runoff, and less water infiltration, all of which contribute to poorer soil development in extremely hilly or mountainous regions.
  • In the northern hemisphere, south-facing slopes receive more direct sunshine and are therefore warmer and drier than their north-facing counterparts.
  • The cooler, wetter north-facing slopes have a more active plant community due to less evapotranspiration and, as a result, have less soil erosion and have thicker soil development due to plant rooting.
  • Soil drainage influences the accumulation and preservation of organic materials as well as the varieties of local plants. Due to the conversion of ferrous iron (Fe2+) to minerals containing ferric (Fe3+) iron, well-drained soils on hills or slopes are typically browner or redder.
  • More poorly drained soils in lowlands, alluvial plains, or upland depressions have a tendency to be greyish, greenish-grey (gleyed), or dark in colour due to iron reduction (to Fe2+) and the aggregation and preservation of organic matter in locations that tend to be anoxic.
  • Poorly drained areas tend to be lowlands into which dirt may wash and pile from adjacent uplands, resulting in A or O layers that are frequently overthickened.
  • In contrast, steeply sloping regions of highlands are susceptible to erosion and have smaller surface horizons.

4. Parent Material

  • The parent material of a soil is the substance from which the soil developed, be it river sands, shoreline deposits, glacial deposits, or different types of bedrock. In young soils, the parent material has a direct relationship with the soil type and a substantial impact.
  • As chemical, physical, and biological processes exert their influence, the parent material becomes less recognisable over time as weathering processes deepen, mix, and modify the soil.
  • Additionally, the type of parent material might influence the rate of soil growth. The transformation of highly weatherable parent materials (such as volcanic ash) into highly developed soils occurs more rapidly with highly weatherable parent materials (such as ash) than with parent materials that are quartz-rich, for example.
  • Parental materials also supply plants with nutrients and can impact soil drainage (e.g. clay is more impermeable than sand and impedes drainage).

5. Time

  • Over time, soil profiles typically become thicker (deeper), more developed, and altered. However, the rate of change is greater for soils in their formative years.
  • After tens or hundreds of thousands of years, the degree of soil change and deepening may approach equilibrium, where erosion and deepening (removals and additions) are in equilibrium.
  • Young soils ( 10,000 years) are heavily influenced by their parent material and often develop horizons and a distinct character soon. Soils of moderate age (about 10,000 to 500,000 years) are slowing in profile development and deepening, and equilibrium conditions may be approaching.
  • Old soils (>500,000 years) have typically reached their maximum horizonation and physical structure, but they may continue to undergo chemical or mineralogical changes.
  • Not usually is soil growth continuous. Geologic activities can swiftly bury soils (landslides, glacier advance, lake transgression), remove or truncate soils (rivers, shorelines), or produce soil renewal with additions of progressively deposited sediment that replenish the soil (wind or floodplain deposits).
  • Biological mixing can occasionally result in soil regression, a reversal or detour from the normal route of growth over time.

Types of Soil

1. Alluvial Soil

  • It is composed of sediments carried by rivers.
  • It is sometimes referred to as “riverine soil” due to its prevalence in river basins.
  • The mixture of sand, clay, and silt that constitutes loam is known as loam.
  • Khadar alluvial soil is the annual monsoon deposition of fresh layers.
  • The Bangar alluvial soil is formed of lime nodules and is the oldest alluvial soil (kanker)
  • Rice, wheat, sugarcane, cotton, tobacco, gramme, and oilseeds thrive in this climate. In the lower Ganga-Brahmaputra Valley, it is also useful for jute farming.
  • Indus, Ganga, Brahmaputra, Punjab, Haryana, Uttar Pradesh, and Bihar West Bengal, portions of Gujarat and Rajasthan, and Assam are its origins.

2. Black Soil

  • It is generated at the origin of the underlying rocks and covers them.
  • Deccan lava tracts, which comprise portions of Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh, Rajasthan, Uttar Pradesh, and a portion of Tamil Nadu.
  • Characteristics: Fine texture and clay-like; rich in lime, iron, and magnesium; deficient in phosphorus, nitrogen, and organic matter. During the dry season, shrink and crack to promote air circulation.
  • Cotton is the predominant crop. Grams of grains, jowar, oilseed, tobacco, sugarcane, wheat, and vegetables.

3. Red Soil

  • On ancient crystalline rocks.
  • This soil is formed from crystalline and metamorphic rocks by precipitation.
  • Its high iron oxide content gives it a brownish or greyish hue.
  • Tamil Nadu, Karnataka, Andhra Pradesh, and South –east Maharashtra, as well as portions of Odisha, Chhattisgarh, Jharkhand, Bundelkhand, Meghalaya, Mizoram, Manipur, and Nagaland, are the founding states.
  • Characteristics: Low in nitrogen, phosphorus, potassium, and humus; porous with a high proportion of iron oxide; often shallow; containing modest amounts of soluble soil.
  • Suitable for nearly all types of crops, including vegetables, rice, ragi, tobacco, groundnuts, and potatoes.

4. Laterite Soil

  • Formed as a result of the weathering of rocks under high temperatures and alternating wet and dry periods. Also created through leaching (process of nutrients getting percolated down due to heavy rainfall.)
  • Highland areas of the peninsular plateau, including the summit of the Sahyadris, Eastern Ghats, Rajmahal Hills, and the eastern regions of the peninsula.
  • Low fertility as a result of high acidity and poor water retention. Additionally, leaching manure can make low-elevation soils ideal for ragi, rice, sugarcane, and paddy. Tea, cinchona, rubber, and coffee are grown at higher altitudes.

Types of Soil based on the Texture

Due to the existence of rock particles of varied sizes, the texture of the soil changes. On the basis of particle size, soil can be divided into three distinct types: clayey, loamy, and sandy.

1. Clayey Soil 

  • This sort of dirt has particles that are smaller and finer.
  • Due to the presence of smaller particles, there is less space for air between the particles.
  • Since there is limited room for air, the soil can hold more water, making it dense.
  • This sort of soil is ideal for growing wheat and gramme because it can hold substantial amounts of water.

2. Sandy Soil

  • This type of dirt has particles that are dense
  • As a result of the existence of larger particles, the particles are loosely packed, leaving huge air spaces.
  • Since there is a great deal of room for air to fill them, they are incapable of retaining water and the water quickly drains.
  • This sort of soil is ideal for growing cotton because it can hold a great deal of air.

3. Loamy Soil 

  • This soil contains both fine and coarse particles.
  • This sort of soil is capable of retaining both air and water.
  • This soil is ideal for plant growth since it has the ideal water-holding capacity and also contains humus.

What is a Soil Profile?

The soil profile is a vertical slice across the different strata of the soil. There are three horizontal layers of soil. They consist of topsoil, subsoil, and bedrock.

  • The soil profile is where the soil and surrounding landscape’s secrets are concealed.
  • A soil pit exposes a vertical slice of the soil, which is referred to as the soil profile.
  • A soil pit is a hole that is dug from the soil’s surface to the bedrock below.
  • Because of how soils grow, the majority of soil profiles consist of a sequence of horizons, or soil layers stacked on top of one another like cake layers.
  • These horizons can tell us a great deal about how the soil originated and what occurred nearby in the past, much like a landscape’s diary.
  • Each layer has a distinct feel (texture), hue, thickness, and chemical composition.
  • Each soil layer is known as a horizon. Horizons are produced by internal processes such as leaching or capillary movements/ascents of materials and water.
  • The soil profile is evaluated by analysing a hexagonal soil sample column.
  • A soil horizon is a layer whose physical properties vary from those of the layers above and below it.
  • Horizons are typically identified by visible physical characteristics, primarily colour and texture.
  • Since it is rich in humus and minerals, the highest horizon is often dark in colour. The humus enriches the soil and supplies nutrients for plant growth. This layer is typically soft, porous, and capable of retaining more moisture. It is known as the A-horizon or the topsoil.
  • The subsequent layer contains less humus and more minerals. This layer, which is often denser and harder, is known as the B-horizon or the middle layer.
  • The third layer is the C-horizon, which consists of minute, fractured rock fragments.

Changes To The Soil Profile

As soil ages, horizontal strata form and alterations occur. These alterations are caused by four distinct processes. Each process occurs differently at different soil depths.

  • Addition: This process occurs when items such as fallen leaves, windblown dust, or air pollution-related compounds are added to the soil.
  • Loss: This process occurs when soil materials are lost as a result of deep leaching or surface erosion.
  • Translocation: This procedure involves the movement of substances within the soil. It might occur as a result of deeper leaching into the soil or upward migration due to evaporation.
  • Transformation: In this process, elements in the soil are transformed. Decomposition of organic materials, mineral weathering to tiny particles, and chemical reactions are examples.

Soil Horizons/Layers of Soil

The soil profile consists of a sequence of horizons or soil layers layered onto one another. These vistas or strata are symbolised by letters;

  • O – horizon
  • P horizon
  • E horizon
  • A – horizon
  • B – horizon
  • C – horizon
  • D – horizon
  • R horizon
  • L horizon
Soil Horizons diagram
Soil Horizons diagram | Image Credit: Original: Wilsonbiggs Vector: EssensStrassenCC BY-SA 4.0, via Wikimedia Commons

1. The O-Horizon

  • The term for this is organic horizon.
  • The O horizon is the uppermost layer of the topsoil, which consists primarily of degraded organic debris such as dried leaves, grasses, dead leaves, small boulders, twigs, surface creatures, and fallen trees.
  • This soil horizon is typically black brown or dark brown in colour, due mostly to the presence of organic matter.
  • It develops in the upper portion of the mineral soil, where fresh or partially decomposed organic matter predominates.
  • This horizon contains over 30% organic matter if the mineral fraction contains over 50% clay, and over 20% organic matter if the mineral fraction contains less clay.
  • The organic horizons are typically present in forest soils but missing in grassland and agricultural soils.
  • There are two O-horizon subdivisions, and they are
    1. O1 
    2. O2.

a. O1 subhorizon

  • Organic horizon where the original shapes of plant and animal remains are visible to the human eye.
  • It is the uppermost layer of all horizons, and it contains newly fallen leaves and organic waste.
  • These substances may be whole or partially degraded.
  • This layer is developed in forest environments.

b. O2 subhorizon

  • Organic horizon in which it is impossible to detect the original plant or animal stuff with the naked eye.
  • This layer contains organic materials in various states of degradation.
  • This layer’s upper portion is composed of detritus, which is organic matter in the beginning stages of decomposition, such as plant and animal remains.
  • The lower layer consists of chaff, which consists of relatively degraded stuff such as the scaly, dry protective shell of cereal grains or similar plant components.

2. A – horizon

  • The uppermost soil horizon is known as the A horizon.
  • This is also known as topsoil.
  • The primary components of this stratum are the humus and mineral materials.
  • The humus layer is abundant in organic matter.
  • Due to its high water and air content, the topsoil is soft and porous.
  • This is a fertile soil layer where seed germination, root development, biological activity of microorganisms and underground animals, etc. happens.
  • This layer’s texture is soft and spongy or airy.
  • It is a dark layer where fungi, earthworms, bacteria, and other microorganisms reside.
  • The A – horizon contains three subhorizons. They constitute
    1. A1 subhorizon,
    2. A2 subhorizon 
    3. A3 subhorizon.

a. A1 subhorizon

  • The subhorizon A1 is black in colour and has a greater concentration of minerals and humus.
  • This layer is thicker in grasslands compared to forests.

b. A2 subhorizon 

  • The A2 subhorizon is the light-colored subhorizon of the A1 horizon.
  • It is mineral and humus deficient.
  • This layer is known as the subhorizon of eluviation because this is where the most leaching or eluviation occurs.

c. A3 subhorizon

  • The A3 subhorizon is the transitional layer between the A and B horizons.
  • This is a light-colored, dense layer.

3. B – horizon

  • B – horizon refers to the stratum directly beneath the A – horizon and above the bedrock.
  • It is referred to as subsoil.
  • This layer is mineral- and clay-rich, denser or darker in colour, coarser in texture, and more compact.
  • However, it contains less organic matter, soluble minerals, and humus than other soil layers.
  • This area is also known as the zone of illuviation.
  • As a result of illuviation, the B horizon is dense, rigid, and poorly aerated.
  • While ploughing, A and B horizons are frequently mixed.
  • Three layers comprise the B horizons. They are strata
    1. B1.
    2. B2.
    3. B3.

a. Layer B1

  • This layer is a transitional layer between the A and B horizons.
  • Therefore, it resembles the A-horizon more.

b. Layer B2 

  • It is a dark-colored stratum containing the greatest quantity of leached material moved downhill by gravity water.

c. Layer B3

  • This layer is formed of massive fragments of the parent rock.

4. C – horizon

  • This stratum is composed of shattered bedrock and contains no biological material.
  • This stratum is known as saprolite as well.
  • This zone contains geological material that is cemented.
  • The C horizon is situated under the solum horizons.
  • This layer is only marginally impacted by pedogenesis.
  • If existent, clay illuviation is insignificant.
  • The lack of solum-type development (pedogenesis) is one of the distinguishing characteristics.
  • The C horizon arises either from deposits (such as loess, flood deposits, and landslides) or from the weathering of residual bedrock.
  • Leaching may fill the C horizon with carbonates brought below the solum.
  • The C horizon mimics the solum’s parent material if there is no lithologic discontinuity between the solum and C horizon and no underlying bedrock present.

5. D – horizon

  • D – horizon is the soil profile’s foundation.
  • It consists of the unweathered parent rock, also known as bedrock.
  • D horizons are not routinely distinguished, however in the Australian system, they relate to “any soil material below the solum that is unlike the solum in its general nature, is not C horizon, and cannot be assigned trustworthy horizon designation” (National Committee on Soil and Terrain, 2009, p. 151).

In addition to these levels, there are three more known layers.

6. E horizon

  • The E-horizon is the stratum where nutrients from the O-horizon and A-horizon have been washed down.
  • This region contains little clay, hence it is primarily found in forests.
  • “E”, which is an abbreviation for “eluviated,” is typically used to designate a horizon that has been severely leached of its mineral and/or organic composition, leaving a pale layer comprised primarily of silicates or silica.
  • These often exist between the A and B layers and are found only in older, well-developed soils.
  • In systems where this designation is not used, such as the Australian system, leached layers are first classed as A or B based on other features, and then the label “e” is applied.
  • Due to animal bioturbation, a stonelayer typically occurs around or at the foot of the E horizon in gravel-containing soils.

7. R horizon

  • R horizons denote the unweathered or slightly weathered bedrock layer at the soil profile’s base.
  • Unlike the layers above, the R horizons are primarily composed of continuous masses of hard rock that cannot be dug by hand.
  • If there is no lithologic discontinuity between the solum and the R horizon, then the R horizon is similar to the solum’s parent material.

8. L horizon

  • L (Limnic) horizons or layers represent mineral or organic material deposited in water by precipitation or aquatic organisms.
  • It consists of coprogenous earth (sedimentary peat), diatomaceous earth, and marl, and is typically a relic of former bodies of standing water.

Horizon Development Processes

Typically, there are four horizon development processes. They are the

  1. Additions
  2. Transformation
  3. Translocation
  4. Removal

1. Additions

  • Materials that are transferred to the site where a soil is forming can constitute additions. For instance, dust containing a high concentration of calcium carbonate could be blasted onto the forming soil to add calcium to the profile.
  • When plants die or leaves fall to the ground, they decompose, enriching the soil with organic materials.

2. Transformation

  • Chemical and biological processes are responsible for the transformation of the components introduced to developing soil.
  • For instance, falling leaves and decaying plant roots can breakdown into a dark brown, nutrient-rich substance known as humus.
  • Iron and aluminium can oxidise in warm, humid environments.
  • Soil material is continuously altered in some fashion.

3. Translocation

  • It entails the flow of soil-forming elements through an evolving soil profile.
  • By moving through the soil, water translocates elements from the upper to lower regions of the profile.
  • Animals that burrow, such as earthworms, ants, etc., shift soil particles inside the profile.
  • Burrowing animals create channels through which air and water can travel, so fostering the formation of the soil.

4. Removal

  • When soil-forming components are eliminated, they are fully eliminated from the soil profile.
  • In wet conditions, dissolvable components such as calcium carbonate can be extracted from the soil profile.

Soil profile in different biomes

The profile of the soil varies between biomes. Variations can occur in various characteristics, including soil depth, horizon depth, concentration of organic matter and minerals, clay content, and colour. Let’s examine the soil profile of several biomes, such as deserts, grasslands, tropical forests, and temperate forests.

  • Desert soil: Neither O-horizon nor humus are present in desert soil. There are clay, sand, minerals, and salts in the subsoil.
  • Grassland soil: The O horizon is highly developed in grassland soil. A significant amount of organic matter is introduced annually to the grassland soil. Additionally, it features a well-developed A-horizon. By burrowing deeply into the earth, the plants’ roots will form a dense mat or sod. This sod can both reduce soil erosion and retain soil moisture.
  • Tropical rainforest soil: As a result of leaching, the topsoil of tropical rainforests is deficient in mineral nutrients and contains very little humus. This soil’s O-horizon is narrow, therefore the litter does not remain for as long. The A – horizon becomes shallower and pinker due to leaching. This soil’s B horizon is relatively deep, and the sublayers are little distinguished. Components of a B – horizon include dense clay combined with iron – aluminium compounds. In the bottom portion of the soil profile, decay occurs.
  • Temperate deciduous forest soil: Due to the slow decomposition of organic waste, there is a well-developed, dark brown O horizon in the soil of temperate deciduous forests. There are numerous sorts of mineral components in the topsoil. The A – horizon is dark and deep in colour. It is abundant in humus. The B horizon is clay-rich and contains loam. B-horizon sublayers are clearly separated. In the upper section of the B horizon, loam and silt are abundant, but the bottom region is rich in dark-brown clay. The oil in the temperate deciduous woodland has glacial origins.

What Is Soil Moisture?

  • Soil moisture refers to the water present in the soil.
  • Numerous variables influence the soil’s absorption of water.
  • It plays a crucial function in the formation of soil.
  • Due to precipitation, water is brought to the surface.
  • The particle size distribution of soil controls its porosity and produces infiltration, which is the vertical downward movement of water. This penetration continues deep into the soil layers till saturation.
  • When water reaches this barrier, it can no longer infiltrate vertically, therefore it flows laterally.
  • Surface ponding is the formation of puddles due to saturation, which can be long-lasting.
  • Root zone moisture refers to plant-accessible water, whereas surface soil moisture refers to plant-accessible water in the immediate upper region of soil.
  • The soil’s moisture content can be measured using a device called a Tensiometer.
  • They are water-filled tubes sealed at the bottom with a porous ceramic tip and at the top with a gauge devoid of air molecules.
  • They penetrate the soil to the level of the roots.
  • Water flows between the device’s tip and the surrounding soil until equilibrium is reached, at which point the gauge records the tension.
  • These measurements provide a gauge of soil moisture in that region.

Types Of Soil Moisture

The various forms of water found in soil include:

1. Gravitational Water

  • Gravitational water is water that reaches the water table of the soil as a result of gravitational force.
  • This is inaccessible to plants.

2. Hygroscopic Water

  • This water is unavailable to the plants as well.
  • It is a thin layer of water held tightly by soil particles.

3. Chemically Combined Water

  • The soil particles contain chemical compounds that contain water.
  • This water has been chemically mixed.
  • Likewise, this is unavailable to the plants.

4. Capillary Water

  • This water is available for absorption by the plants.
  • This water resides in tiny capillaries between dirt particles.

5. Atmospheric Humidity

  • Due to the presence of hygroscopic hairs and velamen tissues, the dangling roots of epiphytes are able to absorb moisture from the air.

Importance Of Soil Moisture Content

  • Soil water transports plant nutrients for plant growth.
  • Crop yield in a region is determined by the moisture content of the soil.
  • Important for managing soil temperature.
  • Soil moisture works as nutrients.
  • Important for the production of soil
  • Numerous plant species that require a great bit of water thrive best in moist soil (Ex: Rice).
  • Soil moisture catalyses the biological activity of soil microorganisms.
  • Water is essential to photosynthesis in plants.

Measuring Soil Moisture

The soil moisture can be measured using the following instruments:

1. Tensiometers

  • These instruments monitor soil moisture tension.
  • They consist of water-filled tubes with a porous ceramic tip.
  • This item is vacuum-sealed and topped with a vacuum gauge.
  • They are buried to the depth of the root zone of the plant.
  • The results acquired from the tensiometers reveal the soil’s water availability.

2. Electrical Resistance Blocks

  • These are comprised of two electrodes attached to lead wires that reach to the surface of the soil.
  • The electrodes are placed into the porous material blocks.
  • It is utilised to determine the soil water tension.

3. Time Domain Reflectometry (TDR)

  • The soil moisture content is determined using TDR – Time Domain Reflectometry.
  • The placement of steel rods in the soil and the transmission of electrical signals through them.
  • The returning signals are measured to estimate the moisture content of the soil.

Importance of soil Profile

  • The soil profile is one of the most fundamental topics in soil research. Understanding this notion is crucial to comprehending all of the processes that occur during soil development.
  • The soil profile is the method for identifying the various types of soil, which helps farmers determine which crops may be cultivated in a certain region.
  • A comprehensive examination of the soil profile is essential for crop husbandry because it reveals the surface and subsurface features and qualities of soil, such as depth, texture, structure, drainage conditions, and soil-moisture interactions, which directly influence plant growth.
  • The soil profile plays a crucial role in nutrient management because it provides significant insights about soil fertility.
  • Only thanks to this soil profile do we have pure groundwater. Rainwater permeates deeply into the soil and is collected, which also raises the earth’s water table.


What is a soil profile?

A soil profile is a vertical cross-section of the soil that displays the different layers or horizons in the soil. It is a useful tool for studying the properties and characteristics of the soil.

What is a soil horizon?

A soil horizon is a layer in the soil profile that has distinct characteristics and properties that differentiate it from the other layers above or below it.

How many soil horizons are typically found in a soil profile?

There are usually three to four soil horizons in a soil profile: the A horizon, the B horizon, the C horizon, and sometimes the O horizon.

What is the O horizon?

The O horizon is the topmost layer of the soil profile, made up of organic matter such as leaves, twigs, and other plant debris.

What is the A horizon?

The A horizon is the topsoil layer and is rich in organic matter, minerals, and nutrients. It is the layer where most plant roots grow.

What is the B horizon?

The B horizon is the subsoil layer and is usually less fertile than the A horizon. It is characterized by the accumulation of clay, iron, and other minerals that have leached down from the topsoil layer.

What is the C horizon?

The C horizon is the layer of weathered parent material or bedrock that underlies the subsoil layer. It is often made up of partially weathered rock fragments.

What factors determine the formation of soil horizons?

The formation of soil horizons is influenced by a variety of factors, including climate, topography, vegetation, parent material, and time.

How can soil profiles be used in agriculture?

Soil profiles can be used in agriculture to determine the soil’s nutrient and water-holding capacity, as well as to assess its suitability for certain crops.

Why is understanding soil profiles important for environmental conservation?

Understanding soil profiles is important for environmental conservation because it allows us to better manage soil resources and prevent erosion, nutrient depletion, and other forms of soil degradation that can have negative impacts on the environment.


  • Balasubramanian, A.. (2017). CHARACTERISTICS OF SOIL PROFILE. 

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