The Soil Archives

11. The process of Podsolization is predominantly found in :

The process of Podsolization is predominantly found in :

Equatorial forest

Monsoon forest

Taiga forest

Mediterranean forest

This question was previously asked in

UPSC NDA-1 – 2023

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The correct answer is C) Taiga forest.

Podsolization is a soil-forming process that occurs in cool, humid climates, typically under coniferous forests (Taiga) or heathland vegetation. The acidic litter from coniferous trees releases organic acids which, combined with heavy rainfall, lead to the leaching (removal) of base cations, iron, and aluminum from the upper soil horizons (specifically the A and E horizons). These leached materials are then deposited in the illuvial (B) horizon, creating a distinct profile with a greyish-white or ash-coloured E horizon over a reddish-brown or black B horizon. Equatorial forests experience laterization, monsoon forests experience different leaching and deposition patterns, and Mediterranean forests are often subject to calcification or rubefaction due to dry summers and different vegetation.

Soils formed by podsolization are called Podsols. They are generally acidic and low in fertility, posing challenges for agriculture without significant amendments. The term “Podsol” comes from Russian words meaning “under ash,” referring to the characteristic greyish-white E horizon.

12. Which one of the following is a gravity transported soil?

Which one of the following is a gravity transported soil?

Alluvial

Eolian

Colluvial

Glacial

This question was previously asked in

UPSC Geoscientist – 2023

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The correct answer is Colluvial.

Colluvial soil is soil that has been transported and deposited by gravity. This occurs on slopes where material moves downwards due to processes like creep, landslides, rockfalls, and sheetwash.

Alluvial soil is transported by flowing water (rivers, streams). Eolian soil is transported by wind (e.g., loess, sand dunes). Glacial soil is transported by glaciers (e.g., till, moraines).

13. Which one of the following is the correct sequence of a typical soil p

Which one of the following is the correct sequence of a typical soil profile from top to bottom ?

Topsoil, Humus, Eluviation zone, Subsoil, Weathered parent material

Subsoil, Topsoil, Humus, Weathered parent material, Eluviation zone

Humus, Subsoil, Topsoil, Eluviation zone, Weathered parent material

Humus, Topsoil, Eluviation zone, Subsoil, Weathered parent material

This question was previously asked in

UPSC Geoscientist – 2024

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A typical soil profile is divided into horizons (layers). From top to bottom, the commonly recognized horizons are O (organic/humus), A (topsoil – mineral soil mixed with humus), E (eluviation/leaching layer below A in some soils), B (subsoil – accumulation of leached material), C (weathered parent material), and R (bedrock). Option D, starting with Humus (part of or above O), then Topsoil (A), followed by Eluviation zone (E), Subsoil (B), and finally Weathered parent material (C), represents the correct sequential arrangement of these specific layers in a typical soil profile from the surface downwards.

– Soil profile is a vertical cross-section showing soil horizons.
– Key horizons: O, A, E, B, C, R.
– Humus is organic matter, typically in O or mixed with A.
– Eluviation (E) is leaching from upper layers, Illuviation (accumulation) is in B.

The characteristics of each soil horizon (color, texture, structure, chemical composition) differ due to various soil-forming processes like weathering, leaching, accumulation of organic matter, etc.

14. Soils which reflect the composition of underlying rocks are always

Soils which reflect the composition of underlying rocks are always

young

highly evolved

mature

moderately old

This question was previously asked in

UPSC Geoscientist – 2022

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Soils develop over time through processes like weathering, decomposition, and horizon formation (pedogenesis). Young or immature soils have undergone limited pedogenic development. As a result, their properties, including mineral composition, strongly reflect the composition of the underlying parent material (bedrock or unconsolidated deposits). Highly evolved or mature soils have distinct horizons and properties that may differ significantly from the parent material due to long-term processes.

– Soil formation (pedogenesis) is a gradual process.
– Young soils are characterized by limited horizon development.
– The characteristics of young soils are strongly influenced by the parent material.
– Mature soils have well-developed horizons and properties modified by time, climate, organisms, and topography.

The degree to which a soil’s composition reflects its parent material is often used as an indicator of soil age and development stage. In highly weathered (evolved/mature) soils, many original minerals from the parent rock may have been altered or leached away, leaving behind more resistant materials or newly formed secondary minerals.

15. Which one of the following is correct?

Which one of the following is correct?

In humid tropical region, humus content is high in soil

Glacial till exhibits deep horizon

Humus accumulates in cold climate

In equatorial climates, humus content is high in soil

This question was previously asked in

UPSC Geoscientist – 2022

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– A) In humid tropical regions, high temperatures and high rainfall lead to rapid decomposition of organic matter by microbes, resulting in low humus content in the soil. (Incorrect)
– B) Glacial till is unconsolidated glacial sediment and serves as a parent material for soil development. While soils *can* develop on till, the till itself doesn’t “exhibit deep horizons”; soil horizons (A, B, C) develop *within* the soil profile over time through pedogenic processes. Glacial action often mixes material rather than creating distinct deep horizons in the till layer itself. (Incorrect)
– C) In cold climates, low temperatures significantly slow down the rate of decomposition of organic matter by microorganisms. This leads to the accumulation of undecomposed or partially decomposed organic matter, forming a thicker layer of humus (or organic horizons like O horizon) on or in the soil. (Correct)
– D) Equatorial climates are humid tropical regions with rapid decomposition, leading to low humus content. (Incorrect, same reason as A).

– Decomposition rate of organic matter is highly dependent on temperature and moisture.
– Cold climates slow down decomposition, promoting humus accumulation.
– Warm, humid climates accelerate decomposition, limiting humus accumulation.

Humus is stable, dark organic matter that remains after the decomposition of plant and animal residues. It is crucial for soil structure, water retention, and nutrient availability. Soils in environments like tundra or boreal forests often have significant organic horizons due to slow decomposition rates.

16. Inceptisols, Entisols, Vertisols and Mollisols are orders of which one

Inceptisols, Entisols, Vertisols and Mollisols are orders of which one of the following ?

Sugarcane

Soil

Coal

Copper

This question was previously asked in

UPSC CDS-2 – 2021

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The terms Inceptisols, Entisols, Vertisols, and Mollisols are part of the soil classification system known as USDA soil taxonomy. They represent different orders of soil.

– Soil taxonomy is a hierarchical system used to classify soils based on their properties, especially properties that can be observed and measured in the field.
– There are twelve orders in the current USDA soil taxonomy system, including those listed in the question.

– The twelve soil orders are Alfisols, Andisols, Aridisols, Entisols, Gelisols, Histosols, Inceptisols, Mollisols, Oxisols, Spodosols, Ultisols, and Vertisols.
– Each order is further divided into suborders, great groups, subgroups, families, and series.

17. Match List I with List II and select the correct answer using the code

Match List I with List II and select the correct answer using the code given below the lists :

List I (Soil type)	List II (Major characteristic)
A. Oxisols	1. Very rich in organic matter
B. Vertisols	2. Soil lacking horizons
C. Histosols	3. Very old and highly weathered
D. Entisols	4. Rich in clay content and highly basic

Code :

A-3, B-1, C-4, D-2

A-3, B-4, C-1, D-2

A-2, B-1, C-4, D-3

A-2, B-4, C-1, D-3

This question was previously asked in

UPSC CDS-2 – 2019

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The correct match is A-3, B-4, C-1, D-2.

– **Oxisols (A):** These are highly weathered soils, typically found in tropical and subtropical regions. They are characterized by subsurface horizons dominated by residual accumulations of iron and aluminum oxides and lack of weatherable minerals. They are indeed very old and highly weathered (matches 3).
– **Vertisols (B):** These are clay-rich soils that shrink and swell significantly upon drying and wetting, respectively. This shrink-swell action creates deep cracks. They are often rich in montmorillonite clay and can be highly basic (matches 4).
– **Histosols (C):** These are organic soils formed in wetlands, composed mainly of peat or muck. They contain a large amount of organic matter, usually more than 20% (matches 1).
– **Entisols (D):** These are young soils that have little or no morphological development of pedogenic horizons. They lack distinct layers characteristic of more developed soils (matches 2).

Soil classification systems like the USDA soil taxonomy categorize soils based on their properties, which reflect their formation processes and characteristics. Understanding these major soil orders helps in understanding global soil distribution and their suitability for different uses.

18. Match List I with List II and select the correct answer using the code

Match List I with List II and select the correct answer using the code given below the lists :

List I (Soil Type)	List II (Salient Characteristic)
A. Entisols	1. Soils having weakly or quickly developed horizons
B. Inceptisols	2. Weakly developed soils with no horizons
C. Histosols	3. These soils are very old and highly weathered
D. Oxisols	4. These soils have very high quantity of organic matter in the upper layers

A-2, B-1, C-4, D-3

A-2, B-4, C-1, D-3

A-3, B-4, C-1, D-2

A-3, B-1, C-4, D-2

This question was previously asked in

UPSC CDS-1 – 2022

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The correct match is A-2, B-1, C-4, D-3.

This question matches soil orders from the USDA soil taxonomy with their salient characteristics.
– Entisols (A): These are the youngest soils with little or no profile development and lack distinct horizons. They match “Weakly developed soils with no horizons” (2).
– Inceptisols (B): These soils have developed some weakly expressed horizons (incipient horizons) and are slightly more developed than Entisols but still considered young. They match “Soils having weakly or quickly developed horizons” (1).
– Histosols (C): These soils are composed primarily of organic materials, typically found in wet environments like swamps and bogs. They match “These soils have very high quantity of organic matter in the upper layers” (4).
– Oxisols (D): These are highly weathered soils found in humid tropical and subtropical regions, characterized by high concentrations of iron and aluminum oxides and deeply leached horizons. They match “These soils are very old and highly weathered” (3).

The USDA soil taxonomy is a classification system used to classify soils based on measurable soil properties. There are twelve soil orders globally. This question covers four of them, highlighting some key distinctions based on age, profile development, and composition.

19. Which one of the following with regard to Aridisol, one of the soil or

Which one of the following with regard to Aridisol, one of the soil orders, is not correct?

Lack of water for plants during most part of the year

High organic matter

Large accumulation of carbonates at depth

Absence of deep wide cracks

This question was previously asked in

UPSC CDS-1 – 2017

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Statement B is incorrect. Aridisols are soils found in arid and semi-arid climates. These environments typically have low biological productivity due to lack of water, resulting in low amounts of organic matter in the soil profiles.

Aridisols are characterized by low water availability for plants for extended periods during the year (Statement A). Due to limited leaching in dry conditions, they often show accumulation of soluble salts and carbonates in lower horizons (Statement C). They generally do not exhibit the deep, wide cracks characteristic of soils with high swelling clay content like Vertisols (Statement D).

Aridisols cover a significant portion of the Earth’s land surface, found in deserts and dry grasslands. Despite low organic matter, some Aridisols can be productive if irrigated and managed appropriately.