Soils

Q. No. 1. The black cotton soil of India has been formed due to the weathering of— (UPSC CSE Prelims, 2021)

(a) Brown forest soil

(b) Fissure volcanic rock

(d) Shale and limestone

Answer: (b)

Explanation:

● Black soil, traditionally called Regur or Black Cotton Soil, is characteristically associated with the Deccan Trap region. The Deccan Trap consists of enormous successive flows of basaltic lava erupted through fissures during the late Cretaceous–early Paleogene volcanic episode.

● Weathering of these basaltic rocks under appropriate relief and climatic conditions produced extensive clay-rich black soils over large parts of western and central India.

● Option (b), fissure volcanic rock, is correct because Deccan Trap basalt originated from extensive fissure eruptions, rather than from a single central volcanic cone.

Hence, option (b) is correct.

Q. No. 2. Assertion (A): The Regur soils of the Deccan Trap are black in colour.

Reason (R): They are rich in humus. (UPPCS Prelims, 1999)

Code:

(a) Both A and R are true, and R is the correct explanation of A

(b) Both A and R are true, but R is not the correct explanation of A

(d) A is false, but R is true

Answer: (c)

Explanation:

● The Deccan Trap contains extensive dark-coloured clayey black soils, traditionally called Regur. Hence, Assertion (A) is correct.

● Black soils are not characteristically rich in humus or organic matter. Standard Indian geography descriptions instead regard them as generally deficient in nitrogen, phosphorus and organic matter, while containing appreciable lime, iron, magnesia and potash. Hence, Reason (R) is incorrect.

● Therefore, the black colour cannot be explained by unusually high humus content.

● The precise colour of black soils varies from dark black to dark grey or brownish shades depending upon parent material, clay minerals, iron compounds, organic matter and drainage conditions. It is therefore safer in an examination to associate their colour with their mineralogical and pedogenic characteristics, rather than with humus alone.

● Black-soil fertility should also not be treated as chemically uniform. ICAR studies of black soils show considerable local variability in nutrient status and soil degradation conditions.

Hence, option (c) is correct.

Q. No. 3. Which of the following is known as “self-ploughed” soil in the country? (UP Lower Subordinate Prelims, 2009)

(a) Alluvial soil

(b) Lateritic soil

(d) Desert soil

Answer: (c)

Explanation:

● Black soil contains a high proportion of expanding clay minerals, particularly smectitic clays in many Vertisols. These clays absorb water and swell when wet, while they contract strongly when they dry.

● During the dry season, contraction creates deep, wide cracks in the soil profile. Soil material from the surface falls into these cracks; subsequent swelling and shrinking mix the soil mass. This natural churning produces the characteristic phenomenon traditionally called self-ploughing.

● The same clay-rich nature gives black soil a high water-holding capacity. Water is absorbed slowly and retained for long periods, which is particularly useful for rainfed crops through dry intervals. Deep black Vertisols are extensively used in central Indian agriculture.

● Cotton suitability arises from a combination of deep soil, clayey texture, moisture retention and appropriate chemical properties, not because black soil is rich in humus or nitrogen.

Hence, option (c) black soil is correct.

Q. No. 4. Regur soil is most widespread in— (BPSC Prelims, 2000)

(a) Maharashtra

(b) Tamil Nadu

(d) Jharkhand

Answer: (a)

Explanation:

● India's largest continuous black-soil tracts occur in the Deccan Trap region, and Maharashtra forms the geographical core of this basaltic plateau.

● Option (a), Maharashtra, is correct. Large parts of the state's plateau region are developed over basalt and carry medium to deep black soils.

● Malwa Plateau is another important black-soil region because much of it is developed over basaltic Deccan Trap lava.

Hence, option (a) is correct.

Q. No. 5. Where is black soil found in Jharkhand? (Jharkhand PCS Mains, 2016)

(a) Damodar Valley region

(b) Subarnarekha River Valley region

(d) Palamu region

Answer: (c)

Explanation:

● Jharkhand is generally associated with ancient crystalline rocks of the Chota Nagpur Plateau and widespread red and lateritic soils, but it contains an important geological exception in the Rajmahal Hills.

● The Rajmahal region contains Rajmahal Trap volcanic rocks, providing a local geological basis for darker, clay-rich soils. Pedological studies have examined soils developed from Rajmahal Trap in Sahibganj district.

● Option (c), Rajmahal Hill region, is correct. The Jharkhand Government's state geography profile explicitly records black soil in the Rajmahal area.

Hence, option (c) is correct.

Q. No. 8. With reference to alluvial soils of India, consider the following statements:

Khadar represents comparatively newer alluvium.
Bhangar generally occupies older, slightly elevated alluvial terraces.
Kankar nodules are more commonly associated with older alluvium than with annually renewed floodplain deposits.
All alluvial soils have identical texture and chemical composition.

Select the correct code given below:

(a) 1 and 2 only

(b) 1, 2 and 3 only

(d) 1, 2, 3 and 4

Answer: (b)

Explanation:

● Alluvial soil is transported soil deposited by rivers and associated floodplain processes. It dominates the Indo-Gangetic-Brahmaputra plains and occurs in river valleys and deltas elsewhere in India.

● Alluvium varies greatly in texture. Recent river deposits may range from sandy and silty to clayey.

● Khadar is the younger alluvium occurring in active floodplains and is periodically renewed by river deposition. Hence, statement 1 is correct.

● Bhangar is older alluvium occurring generally on relatively elevated terraces beyond the zone of frequent contemporary flooding. Hence, statement 2 is correct.

● Older alluvial deposits frequently contain calcareous concretions or kankar, especially in drier parts of the northern plains. Hence, statement 3 is correct.

● Alluvial soil is not uniform. Parent sediments, river source, drainage, grain size, climate and age vary enormously. Hence, statement 4 is incorrect.

Hence, option (b) is correct.

Q. No. 7. For which cultivation are Karewas famous? (67th BPSC Prelims Re-Examination, 2022)

(a) Banana

(b) Saffron

(d) Grapes

(e) None of the above / More than one of the above

Answer: (b)

Explanation:

● Karewas are elevated lacustrine–fluvio-glacial deposits of the Kashmir Valley. They consist of layers of clay, silt, sand and associated sediments accumulated when parts of the valley experienced prolonged lake deposition.

● They should not be treated as a “black soil type.” Karewas are fundamentally a geomorphic and sedimentary formation whose weathered surface supports agriculture.

● Option (b), saffron, is correct. The Kashmir Valley, especially the Pampore–Pulwama region, is famous for saffron cultivation; the Government of Jammu and Kashmir identifies saffron as an important product of Pulwama.

● Karewas are also geographically important because they preserve evidence of the Quaternary geological and climatic history of the Kashmir Valley.

Hence, option (b) is correct.

Q. No. 8. Which of the following statements regarding laterite soils of India are correct? (UPSC CSE Prelims, 2013)

They are generally red in colour.
They are rich in nitrogen and potash.
They are well-developed in Rajasthan and Uttar Pradesh.
Tapioca and cashew nuts grow well on these soils.

Select the correct code:

(a) 1, 2 and 3

(b) 2, 3 and 4

(d) 2 and 3 only

Answer: (c)

Explanation:

● Laterite soil develops under conditions of intense chemical weathering, generally associated with high temperature and heavy seasonal rainfall. Abundant rainfall causes strong downward movement of water through the soil profile, removing soluble bases and silica. This process is called laterisation.

● What remains relatively concentrated are less-soluble compounds, particularly iron and aluminium oxides. Hence laterite commonly develops reddish, reddish-brown or yellowish colours.

● Laterite soils are generally red in colour. Iron oxides dispersed through the weathered material impart the characteristic red to reddish-brown colour. Hence, statement 1 is correct.

● Laterite soils are generally poor in nitrogen and organic matter because warm and humid conditions favour rapid decomposition while heavy rainfall promotes leaching.

● Laterites are deficient in organic matter, nitrogen, phosphate and calcium, while iron and aluminium compounds remain concentrated. Hence, statement 2 is incorrect.

● Rajasthan is predominantly arid to semi-arid, where evaporation exceeds precipitation over large areas and leaching is weak. Uttar Pradesh is dominated overwhelmingly by alluvial soils of the Indo-Gangetic plain.

● Laterite soils are better associated with high-rainfall parts of the Western Ghats, Eastern Ghats and other humid peninsular and northeastern uplands. Hence, statement 3 is incorrect.

● Cashew is strongly associated with lateritic landscapes of the west coast and peninsular uplands. Tapioca/cassava can also be cultivated on such soils under suitable management.

● Laterite soils have low natural fertility but are not agriculturally useless. Manures, fertilisers and appropriate soil management can make them productive. Hence, statement 4 is correct.

Hence, option (c) is correct.

Q. No. 9. Which of the following statements is correct about laterite soil? (UPPCS Prelims, 2023)

This soil develops in areas with high temperature and heavy rainfall.
It is poor in iron oxide and aluminium.

Code:

(a) Neither 1 nor 2

(b) Both 1 and 2

(d) Only 2

Answer: (c)

Explanation:

● The defining pedogenic process is laterisation, involving intense chemical weathering and leaching under warm and humid climatic conditions.

● Heavy rainfall percolates downward through the weathered mantle. Soluble bases such as calcium and magnesium and much silica may be removed from upper parts of the profile.

● Statement 1 correctly associates laterite development with high temperature and high rainfall.

● Seasonal alternation of wet and dry conditions can further favour the development and hardening of lateritic material. Hence, statement 1 is correct.

● Statement 2 states that laterite is poor in iron oxide and aluminium. This reverses the process.

● Because iron and aluminium compounds are comparatively less mobile under many lateritic weathering environments than bases and silica, they become relatively concentrated in the weathered residue. Hence, statement 2 is incorrect.

● A useful conceptual sequence is:

Hot and wet climate → intense chemical weathering → strong leaching → removal of bases and silica → residual Fe–Al enrichment → lateritic profile.

● Leaching means the downward removal of soluble substances by percolating water.

● Laterisation is broader: it is the soil-forming process involving intensive tropical weathering, leaching and relative enrichment of iron and aluminium compounds.

Hence, option (c) is correct.

Q. No. 10. Which of the following statements is NOT true with respect to laterite soils in India? (Uttarakhand PCS Prelims, 2024)

(a) They are deficient in lime and nitrogen.

(b) They provide good building materials.

(d) They are moisture-retentive with a large clay factor.

Answer: (d)

Explanation:

● Option (a) is correct. Intense leaching removes many soluble bases, including calcium compounds, while nitrogen and organic matter are generally low.

● Warm tropical conditions encourage rapid microbial decomposition of organic matter; heavy rainfall further promotes nutrient losses. Hence, option (a) is a correct characteristic.

● Option (b) is correct. The word laterite is derived from the Latin later, meaning brick.

● Lateritic material can be relatively soft when freshly excavated but hardens considerably on exposure and drying. Blocks of laterite have therefore traditionally been used as building material in parts of tropical India. Hence, option (b) is a correct characteristic.

● Option (c) is correct. Leaching is fundamental to laterite formation.

● Rainwater percolating through the profile removes soluble substances and bases, leaving a strongly weathered residual material. Hence, option (c) is a correct characteristic.

● Option (d) is incorrect. Laterite soils are generally described in examination geography as porous and comparatively well-drained, often with low to moderate moisture-holding capacity.

● They should not be confused with black cotton soils, whose high clay content produces very strong moisture retention and shrink–swell behaviour.

Hence, option (d) is incorrect.

● Important comparison:

Black soil → clayey → high moisture retention → swelling and cracking.

Laterite → highly weathered and leached → generally porous → comparatively poorer moisture retention.

● This is a very useful elimination pair because both are major peninsular Indian soils but their physical behaviour is substantially different.

Hence, option (d) is correct.

Q. No. 11. Which one of the following statements is not true for laterite soils? (UPPCS Prelims, 2001)

(a) They are soils of humid tropical regions.

(b) They are highly leached soils.

(d) They are rich in lime.

Answer: (d)

Explanation:

● Option (a) is correct. Laterite development is strongly associated with warm, humid tropical and monsoonal environments.

● High temperature accelerates chemical weathering, while heavy rainfall supplies water for leaching. Hence, option (a) is correct.

● Option (b) is correct. Laterites are classic highly leached soils.

● Percolating water progressively removes soluble bases and parts of the silica fraction. Hence, option (b) is correct.

● Option (c) is correct in terms of their natural fertility. They commonly have deficiencies of nitrogen, phosphorus, organic matter and bases and may be acidic.

● Nevertheless, low natural fertility does not mean cultivation is impossible. With appropriate nutrient additions and soil management, crops and plantations can be successfully grown. Hence, option (c) is correct.

● Option (d) is incorrect because lime/calcium is generally leached out, rather than becoming concentrated. Hence, option (d) is incorrect.

● The broad chemical contrast can be remembered as:

Leached away → lime/bases + soluble nutrients + much silica.

Relatively left behind → iron + aluminium compounds.

Hence, option (d) is correct.

Q. No. 12. Laterite soils are predominant in— (UPPCS Prelims, 2000)

(a) Malabar Coastal Region

(b) Coromandel Coastal Region

(d) Baghelkhand

Answer: (a)

Explanation:

● The Malabar region lies along the humid western side of southern peninsular India and experiences high temperatures together with heavy monsoonal rainfall.

● These climatic conditions strongly favour chemical weathering and leaching and therefore lateritic development.

● Option (a), Malabar Coastal Region, is correct.

● Kerala and adjoining parts of the Western Ghats contain extensive lateritic landscapes.

● Laterite distribution is controlled much more by the combination of climate + relief + drainage + duration of weathering than simply by latitude.

Hence, option (a) is correct.

Q. No. 13. Which one of the following soil types of India is rendered infertile by the presence of excess iron? (UPSC CSE Prelims, 1994)

(a) Desert sand

(b) Alluvial

(d) Lateritic

Answer: (d)

Explanation:

● Among the given options, lateritic soil is the soil characterised by strong relative enrichment of iron and aluminium oxides following intense leaching.

● Option (a), desert sand, is incorrect. Its principal limitations include aridity, poor organic matter, low moisture availability and sometimes salt/carbonate accumulation.

● Option (b), alluvial soil, is incorrect. Alluvial soils are transported river deposits and constitute some of India's most agriculturally productive soil regions.

● Option (c), podzolic soil, develops characteristically under cool, humid forest environments with pronounced eluviation and accumulation of iron/aluminium compounds in lower horizons, but it is not the intended Indian lateritic-soil answer in this question.

● Option (d), lateritic soil, is correct.

● However, the expression “rendered infertile by excess iron” is an oversimplification.

● Laterite's low fertility is more fully explained by:

– intense leaching of nutrient bases;

– deficiency of nitrogen and organic matter;

– low available phosphorus;

– acidity in many profiles;

– strong iron and aluminium oxide dominance, which can influence nutrient availability.

● Thus, iron enrichment is associated with the infertile lateritic environment but is not the sole cause of low fertility.

Hence, option (d) is correct.

Q. No. 14. With reference to laterisation, consider the following statements:

It involves intense chemical weathering.
Soluble bases and silica are substantially leached from the soil.
Iron and aluminium compounds become relatively concentrated.
It is most characteristic of cold and dry continental climates.

(a) 1 and 2 only

(b) 1, 2 and 3 only

(d) 1, 2, 3 and 4

Answer: (b)

Explanation:

● Laterisation is fundamentally an intense tropical weathering process. Hence, statement 1 is correct.

● Persistent percolation of water results in strong removal of soluble bases and significant desilication. Hence, statement 2 is correct.

● Iron and aluminium oxides become residually concentrated as more mobile material is removed. Hence, statement 3 is correct.

●Laterisation is characteristic of warm, humid climates with high rainfall and intense leaching; cold and dry climates are not favourable for this process. Hence, statement 4 is incorrect.

Hence, option (b) is correct.

Q. No. 15. Consider the following pairs:

Black soil — high shrink–swell capacity
Laterite soil — intense leaching
Arid soil — accumulation of soluble salts and carbonates
Alluvial soil — exclusively residual weathering in situ

Which of the pairs given above are correctly matched?

(a) 1 and 2 only

(b) 1, 2 and 3 only

(d) 1, 2, 3 and 4

Answer: (b)

Explanation:

● Black soil commonly contains expansive clay minerals and therefore swells when wet and contracts deeply on drying. Hence, pair 1 is correct.

● Laterite soil is strongly associated with leaching under warm, high-rainfall conditions. Hence, pair 2 is correct.

● Arid soils develop under limited rainfall and high evaporation; soluble salts and calcium carbonate may therefore accumulate rather than being thoroughly leached. Hence, pair 3 is correct.

● Alluvial soil is fundamentally transported and deposited by rivers rather than being exclusively residual weathering material. Hence, pair 4 is incorrect.

Hence, option (b) is correct.

Q. No. 16. Which one of the following soils is deposited by rivers? (63rd BPSC Prelims, 2017)

(a) Red soil

(b) Black soil

(d) Laterite soil

(e) None of these/More than one of these

Answer: (c)

Explanation:

● Alluvium consists of unconsolidated sediments transported and deposited principally by running water. Rivers erode rock and soil in their upper catchments, transport material downstream, and deposit sand, silt and clay where their carrying capacity decreases.

● This distinguishes alluvial soil from a predominantly residual soil, which develops substantially in situ through weathering of underlying parent rock.

● Option (c), alluvial soil, is correct because deposition by rivers is its defining geomorphic association.

● India's greatest alluvial tract is the Indus–Ganga–Brahmaputra plain, built through long-term sedimentation by Himalayan and peninsular river systems.

● Peninsular rivers also produce important alluvial deposits, particularly in valleys and deltas. Thus, alluvium occurs in the Mahanadi, Godavari, Krishna and Kaveri deltas and locally along rivers such as the Narmada and Tapi.

Hence, option (c) is correct.

Q. No. 17. Old Kachhari clay of the Gangetic plain is called— (41st BPSC Prelims, 1996)

(a) Bhabar

(b) Bhangar

(d) Khondalite

Answer: (b)

Explanation:

● The most important classification of northern-plain alluvium is based on relative age and floodplain position.

● Bhangar represents older alluvium. It generally occurs on comparatively elevated terraces beyond the reach of normal annual floods.

● Therefore, the old alluvial deposit referred to in the question corresponds to Bhangar.

● Option (a), Bhabar, is incorrect. Bhabar is a narrow, coarse, highly permeable piedmont belt immediately south of the Shiwalik foothills. Rivers emerging from the mountains deposit pebbles and coarse material there and may temporarily disappear into the porous deposits.

● Option (b), Bhangar, is correct.

● Option (c), Khadar, is the newer alluvium deposited over active floodplains and frequently replenished by floods.

● Option (d), Khondalite, is a metamorphic rock assemblage, particularly associated with parts of the Eastern Ghats; it is not an alluvial-soil category.

● Bhangar commonly contains calcareous concretions called kankar in many parts of the northern plains.

Hence, option (b) is correct.

Q. No. 18. Match List-I with List-II and select the correct answer. (UP RO/ARO Prelims, 2021)

List-I — Soil

A. Alluvial

B. Black

C. Red

D. Desert

List-II — State

Rajasthan
Uttar Pradesh
Maharashtra
Andhra Pradesh

Code:

(a) A-1, B-4, C-3, D-2

(b) A-2, B-3, C-4, D-1

(d) A-3, B-4, C-2, D-1

Answer: (b)

Explanation:

● Alluvial soil — Uttar Pradesh (2). Uttar Pradesh lies in the extensive Indo-Gangetic alluvial plain. The state's river plains are dominated by deposits brought by the Ganga, Yamuna, Ghaghara and their tributaries. Hence, A matches 2.

● Black soil — Maharashtra (3). Maharashtra forms the core of the Deccan Trap basaltic region and contains India's most extensive continuous black-soil landscapes. Hence, B matches 3.

● Red soil — Andhra Pradesh (4). Red and red-lateritic soils are widespread over large parts of the peninsular uplands of Andhra Pradesh. Hence, C matches 4.

● Desert soil — Rajasthan (1). Western Rajasthan contains India's principal hot-arid soil belt. ICAR describes Rajasthan's soils broadly as coarse and fertility-constrained, with salinity/alkalinity important in several areas. Hence, D matches 1.

Hence, option (b) is correct.

Q. No. 19. Which one of the following is the most productive soil in India? (UP RO/ARO Prelims, 2014)

(a) Red soil

(b) Black soil

(d) Calcareous soil

Answer: (c)

Explanation:

Alluvial soils form the largest and most widespread soil group in India, covering about 15 lakh sq km or nearly 46% of the country’s total area. Their fertility, great depth, favourable texture, moisture availability and ease of irrigation make them highly suitable for intensive agriculture.
They are generally rich in potash, lime and phosphoric acid, but relatively deficient in nitrogen and humus.
They support major crops such as rice, wheat, sugarcane, maize, pulses, oilseeds, vegetables and jute.
Red soil can be productive with irrigation and fertilisation but is generally deficient in nitrogen, phosphorus and humus.
Black soil is highly suitable for cotton, soybean and oilseeds due to its excellent moisture-retention capacity, but is less widespread than alluvial soil.
Calcareous soil is characterised by significant calcium carbonate (CaCO₃) content and is not India's principal productive soil group.

Hence, option (c) is correct.

Q. No. 20. Choose the correct statement regarding alluvial soil. (Chhattisgarh PCS Prelims, 2020)

(a) This soil is found in about 14% of India's land surface.

(b) Phosphoric acid is found in rich quantity in this soil.

(d) This soil is not fertile.

Answer: (b)

Explanation:

Option (b) is correct: Alluvial soils generally contain appreciable amounts of potash, phosphoric acid and lime, although their nutrient status varies with location and deposition. They are among India’s most important agricultural soils.
Option (a) is incorrect: Alluvial soil covers about 15 lakh sq km, or nearly 46% of India’s total geographical area, not 14%.
Option (c) is incorrect: Reh, Thur and Chopan are terms associated with saline/alkaline (sodic) soils, particularly in parts of the northern plains, rather than names for alluvial soil as a whole. Such soils may develop within alluvial regions due to salinisation or alkalisation.
Option (d) is incorrect: Alluvial soils are generally fertile and agriculturally productive, supporting crops such as rice, wheat, sugarcane, maize, pulses and jute. However, some alluvial soils may be deficient in nitrogen, humus and, in certain areas, phosphorus.

Hence, option (b) is correct.

Q. No. 21. Which of the following types of soil has minimum water-retention capacity? (Uttarakhand PCS Prelims, 2003)

(a) Alluvial sandy soil

(b) Loamy sand soil

(d) Loamy soil

Answer: (a)

Explanation:

● Soil-water retention is strongly influenced by particle size, pore-size distribution, clay content, organic matter and soil structure.

● Sand particles are large and create relatively large macropores. Water drains rapidly under gravity through such pores.

● Therefore, a coarse sandy alluvial soil generally has relatively low water-retention capacity.

● Option (a) is correct.

● Option (b), loamy sand, contains somewhat more fine material than a strongly sandy soil and therefore usually retains somewhat more water.

● Option (c), clayey loam, has substantially greater clay content and a larger proportion of fine pores capable of retaining water.

● Option (d), loam, contains a favourable mixture of sand, silt and clay and generally combines drainage with moderate-to-good moisture storage.

Hence, option (a) is correct.

Q. No. 22. Which soil particles are present in loamy soils? (53rd–55th BPSC Prelims, 2011)

(a) Sand particles

(b) Clay particles

(d) All types of particles

Answer: (d)

Explanation:

Option (d) is correct: Loamy soil contains all three major soil particles—sand, silt and clay. Their balanced combination gives loamy soil favourable drainage, water-retention capacity, aeration and nutrient-holding ability, making it highly suitable for plant growth.
Sand particles: Largest among the three, providing good drainage and aeration but having low water-retention capacity.
Clay particles: Smallest, with high water- and nutrient-holding capacity, but relatively poor drainage and aeration.
Silt particles: Intermediate in size, with moderate water- and nutrient-holding capacity and good contribution to soil fertility.
Loamy soil: Combines the desirable properties of sand, silt and clay, providing a balance between drainage, moisture retention and aeration.

Hence, option (d) is correct.

Q. No. 23. Soils of western Rajasthan have a high content of— (UPSC CSE Prelims, 1993)

(a) Aluminium

(b) Calcium

(d) Phosphorus

Answer: (b)

Explanation:

● Western Rajasthan has an arid to semi-arid climate, with limited rainfall and strong evaporation.

● Under humid climates, percolating water leaches soluble and moderately soluble materials downward and sometimes out of the soil profile. In dry climates, leaching is much weaker.

● Consequently, calcium carbonate may accumulate within arid soil profiles, frequently forming calcareous horizons or kankar-like accumulations.

● Option (b), calcium, is correct because calcium carbonate accumulation is favoured by the weak-leaching environment.

● Desert/arid soils may also develop salinity and alkalinity where evaporation is strong and drainage is inadequate.

Hence, option (b) is correct.

Q. No. 24. Which one of the following crops enriches the nitrogen content in soil? (UPSC CSE Prelims, 1994)

(a) Potato

(b) Sorghum

(d) Pea

Answer: (d)

Explanation:

Option (d) is correct: Pea is a leguminous crop whose roots develop nodules containing symbiotic nitrogen-fixing bacteria, mainly Rhizobium. These bacteria convert atmospheric nitrogen into forms that plants can utilise, thereby increasing the availability of nitrogen in the soil.
Option (a), Potato: A non-leguminous crop that does not fix atmospheric nitrogen.
Option (b), Sorghum: A cereal crop and does not form nitrogen-fixing root nodules.
Option (c), Sunflower: An oilseed crop and does not fix atmospheric nitrogen.
Leguminous crops such as pea, gram, lentil, beans and groundnut help improve soil nitrogen status and are therefore useful in crop rotation.

Hence, option (d) is correct.

Q. No. 25. When you travel in certain parts of India, you will notice red soil. What is the main reason for this colour? (UPSC CSE Prelims, 2010)

(a) Abundance of magnesium

(b) Accumulated humus

(d) Abundance of phosphates

Answer: (c)

Explanation:

● Red and yellow soils are widely associated with prolonged weathering of ancient crystalline igneous and metamorphic rocks over parts of the Peninsular Plateau.

● Their red colour is primarily associated with oxidised iron compounds, particularly ferric iron oxides distributed through the soil mass.

● Option (c), ferric oxides, is correct.

● When iron compounds occur in more hydrated forms, the soil may show yellowish colours, giving rise to the combined geographical category “red and yellow soils.”

● Do not confuse red soil with laterite. Both may look red because of iron oxides, but laterite is distinguished by far more intense leaching and advanced tropical weathering.

Hence, option (c) is correct.

Q. No. 26. The micronutrient most deficient in Indian soils among the following is— (UPPCS Special Mains, 2004)

(a) Copper

(b) Iron

(d) Zinc

Answer: (d)

Explanation:

● Plants require micronutrients such as zinc, iron, manganese, copper, boron and molybdenum in much smaller amounts than nitrogen, phosphorus and potassium, but their physiological importance is substantial.

Option (d) is correct: Zinc (Zn) is considered the most widespread micronutrient deficiency in Indian soils. ICAR assessments indicate that zinc is the most widespread micronutrient deficiency in Indian soils, affecting about 48–49% of soils, compared with 12% for iron, 5% for copper and 4% for manganese.
Zinc deficiency is particularly associated with soils having high pH, high calcium carbonate, low organic matter and intensive cultivation.
Micronutrients are required in small quantities, but they are essential for processes such as enzyme activity, chlorophyll formation, photosynthesis and plant growth.

Hence, option (d) is correct.

Q. No. 27. Karewa soils, useful for cultivation of Zafran, are found in— (64th BPSC Prelims, 2018)

(a) Kashmir Himalaya

(b) Garhwal Himalaya

(d) Eastern Himalaya

(e) None of the above/More than one of the above

Answer: (a)

Explanation:

● Karewas are thick elevated deposits of the Kashmir Valley related to its Quaternary lacustrine and fluvio-glacial history.

● They are not a standard soil order comparable with black, alluvial or laterite soil; they are primarily a geomorphic-sedimentary formation whose weathered surfaces support agriculture.

● Option (a), Kashmir Himalaya, is correct.

● Karewa surfaces are particularly famous for saffron (Zafran) cultivation around the Pampore–Pulwama area.

Hence, option (a) is correct.

Q. No. 28. Which one of the following particles has a diameter of less than 0.002 mm? (UP RO/ARO Prelims, 2016)

(a) Clay

(b) Silt

(d) None of the above

Answer: (a)

Explanation:

● Soil texture depends upon the relative proportion of sand, silt and clay in the fine-earth fraction.

Option (a) is correct: Clay is the finest major soil particle, with a diameter of less than 0.002 mm

Clay: < 0.002 mm
Silt: 0.002–0.05 mm
Sand: 0.05–2.0 mm

Because clay particles are extremely small, they have a large surface area and high capacity to retain water and nutrients, but generally have poor drainage and aeration compared with sandy soils.

Hence, option (a) is correct.

Q. No. 29. Consider the following statements regarding Usar soil: (UP BEO Prelims, 2019)

It is reclaimed by adding lime.
This soil has a pH of more than seven.
Paddy crops can be grown in this soil.

(a) 1 and 2 are correct

(b) 2 and 3 are correct

(d) Only 1 is correct

Answer: (b)

Explanation:

● Usar is a traditional north Indian term associated particularly with alkali/sodic land. Such soils commonly have high pH and excessive exchangeable sodium, which adversely affects soil aggregation, infiltration and crop growth.

● Statement 1 says Usar is reclaimed by adding lime. Lime is principally used to ameliorate acidic soils, because carbonate-containing liming materials neutralise soil acidity. Hence, statement 1 is incorrect.

● Statement 2 states that Usar soil has pH above 7. Sodic/alkali soils are alkaline; severely sodic soils of the Indo-Gangetic plain can attain substantially higher pH values. Hence, statement 2 is correct.

● Statement 3 says that paddy can be cultivated. Although unreclaimed sodic soils impose severe stress on ordinary crops, salt-/sodicity-tolerant rice varieties have been specifically developed for such environments. Hence, statement 3 is correct.

Hence, option (b) is correct.

Q. No. 30. A fertile soil suitable for growing common crops is likely to have a pH value of— (UPSC CSE Prelims, 1993)

(a) 3

(b) 4

(d) 9 to 10

Answer: (c)

Explanation:

● pH expresses the activity of hydrogen ions and indicates whether a soil is acidic, neutral or alkaline. A pH below 7 is acidic, 7 is neutral and values above 7 are alkaline.

● Most common agricultural crops perform well in a slightly acidic to near-neutral range, because many essential nutrients are comparatively available while extreme aluminium/manganese toxicity on the acidic side and micronutrient deficiencies on the alkaline side are reduced.

● Option (c), 6–7, is the best broad answer for ordinary fertile agricultural soils.

● However, there is no universal optimum pH for every crop. Tea, for example, specifically favours strongly acidic soils, whereas other crops prefer neutral or mildly alkaline conditions.

Hence, option (c) is correct.

Q. No. 31. Which one of the following can be used to make acidic soil cultivable? (MPPSC Prelims, 2006)

(a) Lime

(b) Gypsum

(d) Vegetable compost

Answer: (a)

Explanation:

Option (a) is correct: Lime is commonly used to reclaim acidic soils by neutralising soil acidity and raising soil pH. It also reduces the harmful effects of excess aluminium and manganese and improves the availability of essential nutrients.
Option (b), Gypsum: Mainly used to reclaim sodic/alkali soils, not strongly acidic soils.
Option (c), Calcium: Calcium itself is an essential plant nutrient, but lime (calcium carbonate) is the standard amendment used to correct soil acidity.
Option (d), Vegetable compost: Compost improves organic matter, soil structure and nutrient availability, but it is not the primary amendment for correcting strong soil acidity.

Hence, option (a) is correct.

Q. No. 32. In India, the largest area of saline soil is found in the State of— (UPPCS Mains, 2012)

(a) Uttar Pradesh

(b) Haryana

(d) Maharashtra

Answer: (c)

Explanation:

● CSSRI's distribution table separately records saline, alkali and coastal-saline soils. Gujarat has by far the largest inland saline-soil figure among the listed states—about 1.218 million ha—and also a substantial coastal-saline area.

● Therefore, option (c), Gujarat, is correct.

● Gujarat's susceptibility reflects a combination of arid/semi-arid conditions, high evaporation, saline groundwater, irrigation-related salt accumulation and coastal influences in suitable regions.

● Uttar Pradesh, in contrast, is especially important for sodic/alkali soils, not for the largest saline-soil area.

● These three categories must therefore be distinguished:

Largest alkali/sodic area → Uttar Pradesh

Largest saline area → Gujarat

Largest total salt-affected area in the CSSRI inventory → Gujarat.

Hence, option (c) is correct.

Q. No. 33. Salinisation occurs when irrigation water accumulated in the soil evaporates, leaving behind salts and minerals. What is an effect of salinisation on irrigated land? (UPSC CSE Prelims, 2011)

(a) It greatly increases crop production.

(b) It makes some soils impermeable.

(d) It fills the air spaces in the soil with water.

Answer: (b)

Explanation:

●Secondary salinisation occurs when irrigation water containing dissolved salts accumulates in poorly drained soils. As the water evaporates or is taken up by plants, salts remain and accumulate in the root zone.

Option (a) is incorrect: Excess salts cause osmotic stress and ion toxicity, reducing crop growth and productivity.
Option (b) is correct: Prolonged salt accumulation, particularly when accompanied by sodicity (excess exchangeable sodium), can deteriorate soil structure, reduce permeability and infiltration, and make the soil difficult to cultivate.
Option (c) is incorrect: A high groundwater table can promote salinisation through capillary rise; salinisation itself does not necessarily raise the groundwater table.
Option (d) is incorrect: Filling soil pores with water is waterlogging, which may occur alongside salinisation but is a distinct process.

Hence, option (b) is correct.

Q. No. 34. Assertion (A): Saline soils in India are not appropriate for cultivation of crops.

Reason (R): Saline soils have a high proportion of salts, largely because of dry climate and poor drainage. (UP RO/ARO Prelims, 2023)

Code:

(a) Both A and R are true, but R is not the correct explanation of A.

(b) A is false but R is true.

(d) A is true but R is false.

Answer: (c)

Explanation:

● Excessive soluble salts adversely affect crop growth primarily by reducing the osmotic potential of soil water. The plant must expend more energy to obtain water, so physiological drought can occur even in moist soil.

● High concentrations of particular ions may also produce toxicity or nutrient imbalance.

● Thus, unreclaimed highly saline soils are generally unsuitable or poorly suited to ordinary crop cultivation. Hence, Assertion (A) is correct.

● Dry climates favour salinity because evaporation is high and natural leaching is weak.

● Poor drainage prevents salts introduced through weathering, groundwater or irrigation from being flushed below the root zone. Hence, Reason (R) is correct.

● These processes directly explain why salts accumulate to harmful levels. Hence, Reason (R) correctly explains Assertion (A).

Hence, option (c) is correct.

Q. No. 35. Which of the following soils is most suited for tea plantation? (UPPCS Prelims, 2002)

(a) Acidic

(b) Alkaline

(d) Regur

Answer: (a)

Explanation:

● Tea is an acid-loving crop. The Tea Research Association states that tea grows well in deep, well-drained fertile acidic soils, with an optimum soil pH broadly around 4.5–5.5.

● Option (a), acidic soil, is therefore correct.

● Drainage is crucial. Tea needs abundant moisture but does not tolerate prolonged stagnant water around the roots. Tea Research Association therefore emphasises well-drained highland soils.

Hence, option (a) is correct.

Q. No. 36. Which one of the following types of erosion is responsible for the formation of Chambal Ravines? (UPSC CSE Prelims, 1994)

(a) Splash

(b) Sheet

(d) Gully

Answer: (d)

Explanation:

Option (d) is correct: The Chambal Ravines are primarily formed by gully erosion, where concentrated surface runoff cuts deep channels into the easily erodible alluvial soils.
Small rills progressively enlarge and merge into deeper gullies, resulting in extensive ravine and badland topography.
Ravines are larger, deeply dissected erosional landforms that develop through prolonged gully and stream erosion.
Option (a), Splash erosion: Raindrops detach and displace soil particles but do not produce the deep channels characteristic of Chambal ravines.
Option (b), Sheet erosion: Removes a relatively uniform thin layer of soil from the surface.
Option (c), Rill erosion: Produces small, shallow channels that may develop into gullies if erosion continues.

Hence, option (d) is correct.

Q. No. 37. Which one of the following areas in India has a critical problem of soil erosion? (UPPCS Prelims, 2004)

(a) Malwa Plateau

(b) Foothill areas of the Shivalik ranges

(d) Meghalaya Plateau

Answer: (b)

Explanation:

● The Shivaliks are the youngest and outermost Himalayan ranges. They consist extensively of relatively weak, unconsolidated to poorly consolidated sedimentary material.

● Their steep slopes, strong relief, seasonally intense monsoon rainfall, rapid runoff and human disturbance make sections of the Shivalik foothills highly susceptible to erosion.

● Option (b), Shivalik foothills, is therefore correct.

● Soil erosion is especially severe where several erosivity factors coincide:

steep slope + erodible material + intense rainfall + sparse/removed vegetation + concentrated runoff.

● This can be conceptually expressed through the logic of the Universal Soil Loss Equation (USLE). Soil loss depends upon rainfall erosivity, soil erodibility, slope length and steepness, vegetation/management cover and conservation practices.

● Other important Indian erosion regions include the Chambal–Yamuna badlands, Chota Nagpur Plateau, parts of Maharashtra's black-soil region and wind-eroded Rajasthan–Gujarat–Haryana drylands.

Hence, option (b) is correct.

Q. No. 38. Identify the correct order of the process of soil erosion. (UPSC CSE Prelims, 2001)

(a) Splash erosion → Sheet erosion → Rill erosion → Gully erosion

(b) Sheet erosion → Splash erosion → Gully erosion → Rill erosion

(d) Gully erosion → Rill erosion → Sheet erosion → Splash erosion

Answer: (a)

Explanation:

● Splash erosion represents initial detachment. Raindrop impact breaks soil aggregates and throws fine particles away from the point of impact. Bare soil is especially susceptible. Hence, splash erosion forms the first element in the conventional sequence.

● Once rainfall exceeds infiltration and runoff begins moving downslope over a broad surface, fine detached material can be removed relatively uniformly. This is sheet erosion. Hence, sheet erosion follows splash erosion in the conventional progression.

● As runoff becomes concentrated along minor irregularities and depressions, it cuts numerous shallow channels known as rills. Rills are generally shallow enough to be removed by routine tillage. Hence, rill erosion follows sheet erosion.

● Continued concentration and enlargement can produce deep channels that normal cultivation cannot erase. This is gully erosion. Hence, gully erosion represents the most advanced stage among the four listed.

● The conventional sequence is therefore:

Splash → Sheet → Rill → Gully

Hence, option (a) is correct.

Q. No. 39. The rotation of crops is essential for— (Uttarakhand PCS Prelims, 2010)

(a) Increasing protein content in plants

(b) Getting different crops

(d) Maintaining soil moisture

Answer: (c)

Explanation:

● Crop rotation means growing different crops in a planned sequence on the same field over successive seasons or years.

● Repeated cultivation of the same crop can continuously draw upon similar nutrient pools and may encourage crop-specific weeds, pests and diseases.

● Proper rotation distributes nutrient demand more efficiently and may improve organic-matter cycling and soil structure.

● Where the rotation contains legumes, symbiotic nitrogen fixation can add biologically fixed nitrogen to the farming system.

● Option (c), increasing/maintaining soil fertility, is the best answer.

● Crop rotation can also reduce erosion because differing root systems and seasonal ground cover prevent prolonged periods of completely exposed soil.

Hence, option (c) is correct.

Q. No. 40. In India, the problem of soil erosion is associated with which of the following? (UPSC CSE Prelims, 2014)

Terrace cultivation
Deforestation
Tropical climate

(a) 1 and 2 only

(b) 2 only

(d) 1, 2 and 3

Answer: (b)

Explanation:

● Terrace cultivation is specifically intended to reduce erosion on slopes by decreasing slope length and runoff velocity. Hence, statement 1 is incorrect.

● Deforestation removes the protective canopy, litter and root network. Without vegetation, raindrops strike the soil directly, surface runoff may increase, and roots no longer reinforce soil aggregates and slopes. Hence, statement 2 is correct.

● “Tropical climate” is too broad to be considered a direct cause in itself.

● Certain tropical environments certainly have high rainfall erosivity, especially where intense rainfall occurs on exposed slopes. But tropical forests with intact protective vegetation can have relatively low soil loss despite intense rainfall. It is therefore the interaction of rainfall intensity, slope, soil, cover and land management—not simply the label “tropical climate”—that determines accelerated erosion. Hence, statement 3 is incorrect.

● This question highlights the difference between natural erosivity and accelerated anthropogenic erosion.

● Natural erosion continuously shapes landscapes.

● Accelerated erosion occurs when vegetation removal, overgrazing, inappropriate tillage, road construction or other disturbances increase soil loss beyond normal pedogenic replacement.

Hence, option (b) is correct.