UPSC CSE Prelims
Soils, Natural Vegetation & Biodiversity Previous Year Questions (PYQs)
Showing solved Previous Year Questions for Chapter: Soils, Natural Vegetation & Biodiversity
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The black cotton soil of India has been formed due to the weathering of
Detailed Explanation:
Answer: Option 2 — fissure volcanic rock
Black cotton soil (also known as Regur soil) in India is primarily formed by the weathering of basaltic lava flows from fissure volcanic eruptions. These soils are predominantly found in the Deccan Plateau region, covering parts of Maharashtra, Gujarat, Madhya Pradesh, and Karnataka, where the parent material is basaltic rock. The dark color comes from the presence of titaniferous magnetite and aluminum-rich minerals, while the high clay content gives it swelling and shrinking properties.
📝 Short Notes: Black Cotton Soil (Regur Soil)
- Parent Material: Formed from weathering of basaltic lava (Deccan Trap volcanic rocks)
- Geographical Distribution: Deccan Plateau, Malwa Plateau - mainly in Maharashtra, Gujarat, Madhya Pradesh, Karnataka, parts of Andhra Pradesh and Tamil Nadu
- Physical Properties: Deep black to dark gray color; rich in clay, lime, iron, magnesium, and aluminum but deficient in nitrogen, phosphorus, and organic matter
- Characteristic Feature: High clay content causes swelling when wet and shrinking when dry, developing deep cracks in summer
- Moisture Retention: Excellent moisture retention capacity due to high clay content, suitable for dry farming
- Major Crops: Ideal for cotton cultivation; also suitable for sugarcane, jowar, wheat, linseed, and citrus fruits
- Other Names: Regur soil, Black soil, or Tropical Black Earth
With reference to agricultural soils, consider the following statements :
- The high content of organic matter in soil drastically reduces its water holding capacity.
- Soil does not play any role in the sulphur cycle.
- Irrigation over a period of time can contribute to the salinization of some agricultural lands.
Which of the statements given above is/are correct?
Detailed Explanation:
Answer: Option 2 — 3 only
Among the three statements about agricultural soils, only statement 3 is correct. Statement 1 incorrectly claims that organic matter reduces water-holding capacity, when it actually increases it. Statement 2 incorrectly suggests soil plays no role in the sulphur cycle, when in fact soil is crucial for sulphur transformations and storage.
❌ Statement 1 – Incorrect: High organic matter content actually increases water-holding capacity of soil, not reduces it. Organic matter acts like a sponge, creating pore spaces that retain moisture effectively.
❌ Statement 2 – Incorrect: Soil plays a vital role in the sulphur cycle through microbial transformations (mineralization, immobilization) and storage of sulphur compounds like sulfates that are essential plant nutrients.
✅ Statement 3 – Correct: Prolonged irrigation, especially with poor drainage and high-salt water, causes accumulation of salts in the soil profile, leading to salinization that adversely affects crop productivity.
📝 Short Notes: Soil Properties and Agricultural Impacts
- Organic Matter Benefits: Increases water retention, improves soil structure, enhances nutrient availability, promotes microbial activity, and increases cation exchange capacity (CEC).
- Soil in Nutrient Cycles: Soil is integral to carbon, nitrogen, phosphorus, and sulphur cycles through microbial decomposition, mineralization, and nutrient transformation processes.
- Salinization Process: Occurs when irrigation water brings dissolved salts that accumulate in root zones due to evaporation and inadequate drainage, particularly in arid and semi-arid regions.
- Prevention of Salinization: Proper drainage systems, use of quality irrigation water, crop rotation with salt-tolerant species, and leaching of accumulated salts.
- Indicators of Salinization: White salt crusts on soil surface, reduced crop growth, increased soil pH, and presence of salt-tolerant weeds.
Consider the following States:
- Arunachal Pradesh
- Himachal Pradesh
- Mizoram
In which of the following states do ‘Tropical Wet Evergreen Forests’ occur?
Detailed Explanation:
Tropical Wet Evergreen Forests require high temperature (above 25°C) and high rainfall (above 200 cm annually) throughout the year.
✅ Arunachal Pradesh (Statement 1): Eastern parts receive high rainfall from monsoons and have tropical wet evergreen forests in lower elevations and foothills.
❌ Himachal Pradesh (Statement 2): Located in Western Himalayas with temperate and alpine climate; supports coniferous and temperate forests, not tropical evergreen forests.
✅ Mizoram (Statement 3): Receives heavy rainfall (200-300 cm) and has tropical wet evergreen forests covering significant areas of the state.
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Which one of the following regions of India has a combination of mangrove forest, evergreen forest and deciduous forest?
Detailed Explanation:
The Andaman and Nicobar Islands uniquely harbor all three forest types due to their diverse microclimates and varied topography.
Mangrove forests thrive in coastal brackish water zones, evergreen forests dominate the high-rainfall interior regions, and deciduous forests occur in areas with seasonal rainfall patterns.
In India, in which one of the following types of forests is teak a dominant tree species?
Detailed Explanation:
Teak (Tectona grandis) is the dominant tree species in Tropical Moist Deciduous Forests, which receive 70–200 cm annual rainfall and experience a distinct dry season (November–May) causing leaf shedding.
These forests, also called Monsoon Forests, cover largest forest area in India including regions of Madhya Pradesh, Chhattisgarh, Maharashtra, Odisha, and support species like sal, shisham, sandalwood, and bamboo alongside teak.
If you travel through the Himalayas, you are likely to see which of the following plants naturally growing there?
- Oak
- Rhododendron
- Sandalwood
Select the correct answer using the code given below.
Detailed Explanation:
✅ Statement 1 – Correct: Oak trees are commonly found in the temperate forests of the Himalayas at mid-altitudes (1500-3000 m), thriving in cool, moist conditions.
✅ Statement 2 – Correct: Rhododendron is a characteristic flowering shrub of the Himalayas, found abundantly in the alpine and sub-alpine zones with vibrant blooms.
❌ Statement 3 – Incorrect: Sandalwood grows in tropical and sub-tropical dry regions of southern and peninsular India, not in the Himalayan climate.
Which of the following statements regarding laterite soils of India are correct?
- They are generally red in colour.
- They are rich in nitrogen and potash.
- They are well-developed in Rajasthan and UP.
- Tapioca and cashew nuts grow well on these soils.
Select the correct answer using the codes given below.
Detailed Explanation:
✅ Statement 1 – Correct: Laterite soils are characterized by their distinctive rusty-red colour due to high iron oxide content formed through leaching in tropical conditions.
❌ Statement 2 – Incorrect: Laterite soils are deficient in nitrogen, potash, potassium, phosphorus, and lime, though rich in iron and aluminium oxides; humus content is also very low.
❌ Statement 3 – Incorrect: Laterite soils are well-developed in high rainfall areas of Western Ghats, Eastern Ghats (Karnataka, Kerala, Tamil Nadu, Maharashtra), Odisha, Assam, and Meghalaya — not in semi-arid Rajasthan or UP.
✅ Statement 4 – Correct: Despite low fertility, tapioca, cashew nuts, tea, coffee, and rubber grow well on laterite soils with adequate fertilization and irrigation.