Indian Soils - UPSC Geography Free MCQ Test with solutions

The correct answer is Option A - Black Soil

Black Soil is derived from the weathering of basalt (solidified lava) of the Deccan Traps; it is commonly called Regur or Black Cotton Soil.

It covers large parts of the Deccan Plateau, including much of Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh and portions of Karnataka and Tamil Nadu.

Physically, the soil is clayey, deep and has fine particles that make it impermeable; it swells and becomes sticky when wet and shrinks and forms wide cracks when dry, a behaviour that leads to the phenomenon called self-ploughing.

Because of its high clay content and fine texture, the soil can retain moisture for a long period, which helps rain-fed crops survive dry spells.

Chemically, black soil is rich in lime, iron, magnesia and alumina, and it contains potash; it is relatively deficient in phosphorus, nitrogen and organic matter.

Thus, the properties described correspond to Black Soil.

The correct answer is Option C - Regur Soils

Regur soils, also called black soils, develop from the weathering of basaltic (Deccan Trap) rocks.

They have a high clay content that allows them to retain moisture, swell when wet and form deep cracks on drying; these cracks aid self-aeration of the soil profile.

Chemically, these soils are typically rich in calcium carbonate, magnesium, potash and lime, and are generally deficient in phosphorus and nitrogen.

Because of their moisture-retaining capacity and nutrient profile, they are especially suitable for cotton, and also support pulses, oilseeds and cereals such as wheat, jowar and millets.

These soils are characteristically found in parts of Maharashtra, Madhya Pradesh, Gujarat, Karnataka, Andhra Pradesh and Tamil Nadu, matching the described properties.

The correct answer is Option B - Both Statement-I and Statement-II are correct and Statement-II is not the correct explanation for Statement-I

Statement I is correct: these soils have a high proportion of clay and contain clay minerals such as montmorillonite, which give them a pronounced capacity to swell when wet and to hold moisture due to very slow permeability and slow internal drainage.

Statement II is also correct: these soils are derived from basalt and are typically rich in lime (calcium carbonate), iron, magnesia (magnesium) and alumina (aluminium oxides), and often contain appreciable potash.

However, the reason for prolonged moisture retention is the soil texture and the presence of swelling clay minerals, not directly the presence of the chemical constituents listed in Statement II; therefore Statement II does not provide the correct causal explanation for Statement I.

Combining these points gives the conclusion stated in the chosen option: both statements are true, but the second statement is not the correct explanation for the first.

The correct answer is Option D - 3 only

Statement 1 is incorrect because these soils form under conditions of high temperature combined with high rainfall, where intense chemical weathering and leaching remove silica and bases; this process of laterization produces soils rich in oxides rather than developing in low-rainfall regions.

Statement 2 is incorrect because the warm, wet climate promotes rapid decomposition and removal of organic residues; hence these soils have low organic matter and are poor in nitrogen and humus.

Statement 3 is correct since the compacted, iron-rich profile of these soils allows them to be cut into bricks when moist, and they are traditionally used as a building material in many parts of the country.

Therefore, only statement 3 is correct.

The correct answer is Option A - Both Statement-I and Statement-II are correct and Statement-II is the correct explanation for Statement-I

Taiga (boreal) regions develop soils that are typically acidic owing to long-term leaching, the dominance of evergreen needle litter and the soil process called podzolization, which removes bases from the upper horizons and concentrates organic acids.

Low temperatures in these regions reduce biological activity and slow microbial breakdown of organic matter, while seasonal waterlogging above frozen layers or in poorly drained horizons creates anaerobic conditions that further slow decomposition.

Because decomposition is slowed, organic matter accumulates and produces more organic acids; combined with heavy leaching, this leads to the formation of acidic podsolic soils.

Thus, the inhibition of decomposition by low temperature and anaerobiosis is a valid and direct explanation for the observed soil acidity in taiga regions, so Statement II correctly explains Statement I.

The correct answer is Option A - 1 only

Statement 1 is correct. Alluvial soils are formed from sediments brought by rivers and deposited on plains, floodplains and deltas; they are extensive in the northern plains and river valleys and cover about 40 percent of the country's total area.

Statement 2 is incorrect. These soils are generally rich in potash and often contain appreciable lime, but they are commonly deficient in phosphorus and nitrogen. Thus the claim that they are rich in phosphorus but poor in potash is wrong.

Alluvial soils vary in texture from sandy loam to clay. Two important types are Khadar (newer, more fertile alluvium deposited by floods) and Bhangar (older alluvium often containing kankar or calcareous concretions).

The correct answer is Option C - 1, 2 and 3

Eluviation denotes the downward movement of finer and soluble soil constituents from upper horizons by percolating water; it is the process that removes materials such as clay, organic compounds and soluble salts from higher layers.

Illuviation denotes the deposition or accumulation of those materials in lower horizons that have been carried down by eluviation; thus eluviation and illuviation are complementary processes in the soil profile.

Desilication is the leaching or removal of silica from the soil profile, a process that commonly occurs under intense rainfall and acidic conditions and contributes to the development of lateritic soils enriched in iron and aluminium.

Under heavy and prolonged rainfall, bases such as calcium, magnesium, potassium and sodium are also leached downward; this is consistent with the concept of desilication removing silica along with other soluble constituents.

Therefore, each of the three given matches is factually correct, so all three statements (1, 2 and 3) are correctly matched.

The correct answer is Option C - crystalline igneous rocks in areas of low rainfall.

Red soils develop predominantly from the weathering of crystalline igneous rocks (for example, granite) where low rainfall limits intense leaching and deep chemical alteration.

The red colour results from the accumulation of iron oxides in the soil profile; when iron is more hydrated it gives a more yellow appearance, while oxidized iron produces the red colour.

These soils are generally poor in nitrogen, phosphorus and humus; fine red and yellow loams may be fertile under irrigation and proper management, whereas coarse red soils in dry uplands are less fertile.

Regions such as parts of the Deccan Plateau, eastern and southern plateau areas and the piedmont of the Western Ghats illustrate this pattern of formation from crystalline rocks under low rainfall conditions, confirming the correctness of the option.

The correct answer is Option C - Statement I is correct, but Statement II is incorrect.

Statement I is correct because in very cold regions such as the tundra and boreal forests, low temperature and often waterlogging reduce the activity of decomposers, so the chemical breakdown and transformation of organic matter into true humus (a stable, well-decomposed organic fraction) is limited.

Statement II is incorrect: bacterial activity and general decomposer activity are low in cold climates, not high, so decomposition proceeds slowly rather than rapidly.

Because decomposition and humification are slow, organic matter may accumulate as partly decomposed material or peat, but the proportion of well-formed humus remains low; this explains why Statement I is true while Statement II is false.

The correct answer is Option D - Neither 1 nor 2

The first statement is incorrect because peaty soils form where organic matter accumulates under persistent moisture and poor drainage, not in dry regions.

Peaty soils develop in waterlogged, marshy or boggy conditions with heavy rainfall and high humidity, where decomposition is slow and dead plant matter builds up.

Such soils contain very high organic content (often as much as 40-50% of organic matter), are generally dark in colour and commonly acidic because of accumulated organic acids; they are therefore not characteristic of arid areas.

The second statement is also incorrect because saline soils arise mainly where evaporation exceeds leaching or where there is poor drainage, as in arid and semi-arid regions, in irrigated lands with inadequate drainage, and in some coastal/deltaic areas affected by seawater intrusion.

Saline soils contain excess soluble salts (salts of sodium, potassium and magnesium), reduce crop productivity, and are aggravated by high evaporation; by contrast, heavy rainfall and persistent leaching tend to remove soluble salts and therefore do not favour salinisation.

Reclamation methods commonly include improving drainage and applying gypsum where appropriate to replace sodium and leach salts from the root zone.

Because both statements are factually incorrect, the correct choice is Option D.

The correct answer is Option B - 1 and 2 only

Statement 1 is correct: Alluvial soils are depositional soils formed by material transported and deposited by rivers and streams, which build up extensive fertile plains and river valleys.

Statement 2 is correct: the sand content decreases from west to east because coarser sediments are deposited in the upper and middle reaches and near the source, while finer silt and clay settle in the lower reaches and eastern parts, making western tracts relatively more sandy and eastern tracts more clayey/loamy.

Statement 3 is incorrect as stated: these soils are generally rich in potash (and often in lime), but they are commonly deficient in nitrogen and organic matter; phosphorus may be low in some areas, but it is not correct to say they are generally poor in potash.

Therefore, only statements 1 and 2 are correct, while statement 3 is not.

The correct answer is Option B - 1 and 2 only

Rainwater leaching removes exchangeable basic cations - Ca²⁺, Mg²⁺, K⁺ and Na⁺ - from the soil profile, reducing base saturation; this leaves more H⁺ (and Al³⁺ where present) on exchange sites and therefore increases soil acidity.

Carbon dioxide produced during decomposition and root respiration dissolves in soil water to form carbonic acid (H₂CO₃), which dissociates to release H⁺ ions; this process lowers soil pH and contributes to acidity.

Lime (calcium carbonate, CaCO₃) is a neutralising amendment; it reacts with and removes H⁺ ions, thereby increasing soil pH and reducing acidity, so its addition does not cause acidity but corrects it.

Therefore, statements 1 and 2 are correct causes of soil acidity and statement 3 is not; this makes Option B the correct choice.

They are also found in the four delta regions of the south. Strips

Tea — Assam, West

Bengal, Tamil Nadu

Jute — West Bengal, Bihar,

Assam, Orissa

Rubber — Kerala, Tamil Nadu, Karnataka

Tobacco — Andhra Pradesh, Gujarat, Karnataka, Tamil Nadu

Farming - State

of alluvium occur along rivers in the plateau as well as in the mountains. Alluviums are mainly loamy, i.e. mixtures of sand and clay.

• Laterite soil is characterized by the possession of iron oxides with red colour. Nitrogen, Phosphorus and potash are not present in proper quantities so it shows low fertile texture.

• Tapioca and cashew nuts are generally grown in such soil. This soil is found loss or more in states- Odisha, Maharashtra, Andhra, Tamil Nadu, Karnataka, Meghalaya and West Bengal.

In agriculture, leaching refers to the loss of water-soluble plant nutrients from the soil, due to rain and irrigation. The rate of leaching increases with the amount of rainfall, high temperatures, and the removal of protective vegetation. In areas of extensive leaching, many plant nutrients are lost, leaving quartz and hydroxides of iron, manganese, and aluminium. This remainder forms a distinctive type of soil, called laterite.

The main objectives of the watershed management strategy of India are to restore the ecological balance by harnessing, conserving and developing degraded natural resources such as soil, vegetative cover and water.

• Red soils develop in a warm, temperate, wet climate under deciduous forests and have thin organic and mineral layers overlying a yellowish-brown leached layer resting on a red layer made of iron oxide(ferric oxide).

• Red soils generally form from iron-rich sediments. They are usually poor growing soils, low in nutrients and humus and difficult to cultivate.

• Capillary water is retained on the soil particles by surface forces. It is held so strongly that gravity cannot remove it from the soil particles.

• The molecules of capillary water are free and mobile and are present in a liquid state. Plant roots can absorb it. Capillary water is, therefore, also known as available water.