The Soil Archives

1. Which one of the following is the largest component of the soil system

Which one of the following is the largest component of the soil system ?

Living organisms

Mineral matters

Soil solution

Soil organic matter

This question was previously asked in

UPSC CISF-AC-EXE – 2018

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The correct option is B) Mineral matters.

In a typical mineral soil composition by volume, mineral particles (sand, silt, clay) constitute the largest proportion, usually around 45-50%. Soil solution (water) and soil air each occupy roughly 20-30% of the volume, depending on moisture content. Soil organic matter makes up a much smaller percentage, typically around 5% or less in mineral soils, while living organisms are present in very small quantities compared to the total volume.

The relative proportions of these components can vary greatly depending on the soil type, location, and conditions, but mineral matter is generally the dominant component in terms of volume and mass.

2. Which one of the following is not a basic factor in soil formation?

Which one of the following is not a basic factor in soil formation?

Climate

Biological activity

Human activity (agriculture)

Time

This question was previously asked in

UPSC CBI DSP LDCE – 2023

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Human activity (agriculture) is generally considered an important factor influencing soil properties and development, but not one of the five fundamental *basic* factors of soil formation.

The five generally accepted basic factors of soil formation, often remembered by the acronym CLORPT, are: CLimate, Organisms (biological activity), Relief (topography), Parent material, and Time. While human activities like agriculture significantly modify soil, they are typically categorized as external influences or pedoturbation rather than inherent basic factors that initiate or fundamentally govern soil development from parent material.

Other human activities that impact soil include deforestation, urbanization, pollution, and irrigation. These activities can accelerate or retard soil processes, alter soil structure, composition, and fertility, but they operate upon the soil-forming processes governed by the basic factors.

3. Where does podsolization take place ?

Where does podsolization take place ?

Regions in high middle latitudes

Coastal regions in lower latitudes

Regions with hot and humid climate

Regions having arid climate

This question was previously asked in

UPSC CAPF – 2024

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Podsolization takes place primarily in regions in high middle latitudes.

Podsolization is a soil-forming process that occurs in cool, humid climates, typically under coniferous or mixed forests, on sandy parent materials. This process leads to the leaching of iron and aluminum from the surface layers and their accumulation in deeper horizons, resulting in distinctive soil profiles known as podzols or spodosols. These conditions are characteristic of many regions in high middle latitudes (e.g., Boreal forest regions).

Other soil-forming processes like laterization are associated with hot, humid climates (tropical regions), calcification with arid climates, and gleization with waterlogged conditions.

4. In which one of the following soils, the salt content is so high that

In which one of the following soils, the salt content is so high that common salt is obtained by evaporating the saline water in some areas?

Peaty soil

Alluvial soil

Laterite soil

Arid soil

This question was previously asked in

UPSC CAPF – 2021

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Arid soils are characteristic of dry regions with high evaporation. Due to capillary action, salts from lower layers are brought to the surface, leading to high salinity. In areas with saline arid soils, particularly those with shallow groundwater or proximity to saline water sources, the salt content can be so high that common salt can be obtained by evaporating the saline water collected in pans. This practice is common in Rann of Kutch, which has characteristics of arid soil.

– Arid soils are found in dry climates.
– High evaporation in arid regions leads to salt accumulation on the surface.
– Saline arid soils can be a source of common salt through evaporation.

Peaty soils are found in humid areas with waterlogged conditions and high organic matter. Alluvial soils are deposited by rivers and are generally fertile, although they can become saline in dry areas with poor drainage. Laterite soils are formed in tropical regions through intense leaching and are rich in iron and aluminum oxides, typically acidic and not saline.

5. What happens to the soil, where soil water freezes and it tends to for

What happens to the soil, where soil water freezes and it tends to form ice layers parallel with the ground surface ?

It heaves the soil upward in an uneven manner

It heaves the soil downward in an uneven manner

It heaves the soil both upward and downward in an even manner

It remains unaffected

This question was previously asked in

UPSC CAPF – 2009

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When soil water freezes and forms ice layers parallel to the ground surface, this process, known as frost heave, pushes the overlying soil upwards in an uneven manner.

Frost heave occurs when water in the soil pores freezes and expands, and further water is drawn towards the freezing front forming ice lenses. The formation and growth of these ice lenses cause the ground surface to rise.

The unevenness results from variations in soil type, moisture content, and temperature across the area. Frost heave can cause significant damage to roads, buildings, and infrastructure in areas with freezing temperatures and susceptible soils.

6. Which one of the following is an organic soil ?

Which one of the following is an organic soil ?

Aridisols

Histosols

Oxisols

Vertisols

This question was previously asked in

UPSC NDA-2 – 2023

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Organic soils are characterized by their high content of organic matter, typically formed from the accumulation and decomposition of plant remains. In the USDA soil taxonomy system, Histosols are an order of soils that are primarily composed of organic materials (often >20-30% organic carbon by weight) in the upper 80 cm, commonly found in wetland environments like bogs, marshes, and swamps.

Histosols are defined by their high organic matter content, distinguishing them from mineral soils.

Aridisols are soils of arid and semi-arid climates, typically low in organic matter. Oxisols are highly weathered soils found in tropical and subtropical regions, rich in iron and aluminum oxides. Vertisols are clay-rich soils that shrink and swell significantly with changes in moisture content. These other soil orders are classified as mineral soils.

7. Which one of the following is not a soil forming factor ?

Which one of the following is not a soil forming factor ?

Parent material

Topography

Climate

Human habitation

This question was previously asked in

UPSC NDA-2 – 2021

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The correct option is D, Human habitation.

Soil formation (pedogenesis) is a complex process influenced by several key factors. The primary soil-forming factors are generally recognized as:
1. **Parent material (A):** The geological material from which soil is formed (rock, sediment).
2. **Climate (C):** Temperature and precipitation influence weathering rates, organic decomposition, and leaching.
3. **Topography (B) (or Relief):** Slope, aspect, and elevation affect drainage, erosion, and microclimate.
4. **Organisms:** Biota, including plants, animals, fungi, bacteria, and *humans*, contribute organic matter, mix soil, and influence nutrient cycling.
5. **Time:** The duration over which soil formation processes occur.
While human activities related to habitation (agriculture, urbanization, waste disposal) significantly *impact* existing soils and can influence soil development over time (as part of the ‘Organisms’ factor), ‘human habitation’ itself is not typically listed as a fundamental, primary soil-forming factor alongside parent material, climate, topography, organisms, and time in standard pedology texts. It describes a state or land use rather than a fundamental process driver.

The CLORPT model (Climate, Organisms, Relief, Parent material, Time) is a widely used framework to describe the main factors affecting soil formation. Human activities are considered part of the ‘Organisms’ factor, but ‘human habitation’ in isolation is not a distinct primary factor in the same category as climate or parent material.

8. Statement I : The laterite soils develop in areas with high temperatur

Statement I : The laterite soils develop in areas with high temperature and high rainfall.
Statement II : Laterite soils are the result of intense leaching process.

Both the statements are individually true and Statement II is the correct explanation of Statement I

Both the statements are individually true but Statement II is not the correct explanation of Statement I

Statement I is true but Statement II is false

Statement I is false but Statement II is true

This question was previously asked in

UPSC NDA-2 – 2016

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Statement I: The laterite soils develop in areas with high temperature and high rainfall. (True)
Statement II: Laterite soils are the result of intense leaching process. (True)
Both the statements are individually true and Statement II is the correct explanation of Statement I.

– Laterite soils are characteristic of tropical and subtropical regions that experience high temperatures and heavy rainfall.
– Under these conditions, intense leaching (removal of soluble substances by percolating water) occurs. Soluble silica is removed, while oxides of iron and aluminum are left behind, leading to the formation of lateritic soils.

– Statement II explains the *process* (intense leaching) that takes place under the *conditions* described in Statement I (high temperature and high rainfall) to form laterite soils. High temperature accelerates the decomposition of organic matter and minerals, and high rainfall facilitates the downward movement and removal of soluble components.
– Laterite soils are often poor in nutrients due to intense leaching and can harden irreversibly when exposed to air.

9. Which one of the following statements is not correct?

Which one of the following statements is not correct?

Application of lime makes the soil acidic.

High acidity in soil is typical of humid climate.

Increasing soil acidity results in declining soil fertility.

Arid climate is characterized by alkaline soil.

This question was previously asked in

UPSC NDA-2 – 2015

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Let’s analyze each statement about soil acidity:
A) Application of lime (usually calcium carbonate, CaCO₃, or calcium oxide, CaO, which reacts with water to form calcium hydroxide, Ca(OH)₂) is a common agricultural practice used to *reduce* soil acidity and increase pH, making the soil more alkaline or neutral. Therefore, applying lime does not make the soil acidic; it makes it less acidic. This statement is not correct.

Lime is applied to soil to neutralize acidity (increase pH), not to make it acidic.

B) High acidity in soil is typical of humid climates where high rainfall leads to leaching of basic cations (Ca²⁺, Mg²⁺, K⁺, Na⁺) from the topsoil, leaving behind acidic ions like H⁺ and Al³⁺.
C) Increasing soil acidity can lead to declining soil fertility because essential plant nutrients (like phosphorus) become less available, and potentially toxic elements (like aluminum and manganese) become more soluble and available at low pH levels.
D) Arid climates are characterized by low rainfall, which limits the leaching of basic cations. Evaporation can also bring dissolved salts to the surface, often resulting in the accumulation of carbonates and other salts that contribute to alkalinity. Hence, arid soils are often alkaline or saline.
Since the question asks for the statement that is *not* correct, option A is the answer.

10. In the soil-forming regime, which one of the following occurs in a reg

In the soil-forming regime, which one of the following occurs in a region where evapotranspiration exceeds precipitation significantly ?

Calcification

Laterization

Podsolization

Gleization

This question was previously asked in

UPSC NDA-1 – 2023

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Soil-forming regimes are characteristic processes that occur in specific environmental conditions (primarily climate and vegetation) and lead to the development of different soil types. A region where evapotranspiration significantly exceeds precipitation is characterized by a dry climate, typical of arid or semi-arid environments.

– Calcification: Occurs in arid/semi-arid regions where precipitation is insufficient to leach soluble salts, particularly calcium carbonate, from the soil profile. Calcium accumulates in the upper horizons or forms a hardpan (caliche) due to upward capillary movement of water followed by evaporation.
– Laterization: Occurs in hot, humid climates with high rainfall, leading to intense leaching and accumulation of iron and aluminum oxides.
– Podsolization: Occurs in cool, humid climates, typically under coniferous forests, resulting in the leaching of iron, aluminum, and organic matter from upper horizons and their accumulation in lower horizons.
– Gleization: Occurs in waterlogged, anaerobic conditions, leading to the reduction of iron and characteristic grey/blue colours and mottles.

In regions where evapotranspiration exceeds precipitation, there is a net upward movement of water through capillary action in the soil profile. This water often carries dissolved minerals, including calcium. As the water evaporates at or near the surface, the dissolved minerals are left behind, leading to their accumulation. This process of calcium carbonate accumulation is known as calcification, which is characteristic of soils in dry climates.