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Q82 (IAS/2018) Environment & Ecology › Ecology & Ecosystem Basics › Soil characteristics Official Key

With reference to agricultural soils, consider the following statements : 1. A high content of organic matter in soil drastically reduces its water holding capacity. 2. Soil does not play any role in the sulphur cycle. 3. Irrigation over a period of time can contribute to the salinization of some agricultural lands. Which of the statements given above is/are correct ?

Result
Your answer: —  Âˇ  Correct: B
Explanation

The correct answer is option B (Statement 3 only).

**Statement 1 is incorrect**: The addition of organic matter to the soil usually increases the water holding capacity of the soil.[1] In fact, for each 1-percent increase in soil organic matter, the available water holding capacity in the soil increased by 3.7 percent.[2] This is because organic matter binds soil particles into aggregates and improves the water holding capacity of soil.[3]

**Statement 2 is incorrect**: The sulphur reservoir is in the soil and sediments where it is locked in organic and inorganic deposits, and it is released by weathering of rocks, erosional runoff and decomposition of organic matter.[4] This clearly shows soil plays a crucial role in the sulphur cycle.

**Statement 3 is correct**: Intensive irrigation and excessive use of water has led to the emergence of twin environmental problems of waterlogging and soil salinity.[5] Additionally, a large tract of agricultural land has lost its fertility due to alkalisation and salinisation of soils and waterlogging.[6]

Sources
  1. [1] https://openknowledge.fao.org/3/a-a0100e.pdf
  2. [2] https://openknowledge.fao.org/3/a-a0100e.pdf
  3. [3] https://openknowledge.fao.org/3/a-a0100e.pdf
  4. [4] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > b) Sulphur Cycle > p. 21
  5. [5] INDIA PEOPLE AND ECONOMY, TEXTBOOK IN GEOGRAPHY FOR CLASS XII (NCERT 2025 ed.) > Chapter 6: Planning and Sustainable Development in Indian Context > Indira Gandhi Canal (Nahar) Command Area > p. 72
  6. [6] INDIA PEOPLE AND ECONOMY, TEXTBOOK IN GEOGRAPHY FOR CLASS XII (NCERT 2025 ed.) > Chapter 3: Land Resources and Agriculture > Degradation of Cultivable Land > p. 39
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Don’t just practise – reverse-engineer the question. This panel shows where this PYQ came from (books / web), how the examiner broke it into hidden statements, and which nearby micro-concepts you were supposed to learn from it. Treat it like an autopsy of the question: what might have triggered it, which exact lines in the book matter, and what linked ideas you should carry forward to future questions.
Q. With reference to agricultural soils, consider the following statements : 1. A high content of organic matter in soil drastically reduce…
At a glance
Origin: Books + Current Affairs Fairness: Moderate fairness Books / CA: 6.7/10 ¡ 3.3/10
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This question rewards 'First Principles' thinking over rote memorization. It combines basic physical geography (salinization) with core ecology (nutrient cycles). If you simply understand why farmers add manure (to retain moisture), Statement 1 is eliminated instantly, cracking the whole question.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
In agricultural soils, does a high content of organic matter drastically reduce the soil's water-holding capacity?
Origin: Web / Current Affairs Fairness: CA heavy Web-answerable

Web source
Presence: 5/5
"for each 1-percent increase in soil organic matter, the available water holding capacity in the soil increased by 3.7 percent."
Why this source?
  • Direct quantitative evidence that increasing organic matter raises available water-holding capacity (contradicts 'drastically reduce').
  • Shows a clear measured relationship: each 1% increase in organic matter increases available water holding capacity by 3.7%.
Web source
Presence: 5/5
"The addition of organic matter to the soil usually increases the water holding capacity of the soil. This is because the addition of organic matter increases the number of micropores and macropores in the"
Why this source?
  • States explicitly that adding organic matter usually increases water-holding capacity (opposite of a drastic reduction).
  • Provides a mechanism: organic matter increases micropores and macropores, which hold more water.
Web source
Presence: 5/5
"organic matter ... binds soil particles into aggregates and improves the water holding capacity of soil."
Why this source?
  • Notes organic matter binds particles into aggregates and improves water-holding capacity, supporting that higher organic matter enhances — not reduces — water retention.
  • Specifies this in the context of agricultural soils ('Most soils contain 2–10 percent organic matter').

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > EilUI RONMEf.IT'' /7=X x4 > p. 362
Strength: 5/5
“:EilUI RONMEf.IT'' /7=X x4 I l • Organic Fertilizers: Improves soil texture, adds organic nitrogen, and stimulates beneficial bacterial and fungi. Inorganic Fertilizer: Lowers oxygen content of the soil thereby keeping fertilizer from being taken up efficiently. • Organic Fertilizers: Improves water-holding capacity of soil.”
Why relevant

Explicitly states that organic fertilizers improve the water-holding capacity of soil (a general rule linking organic matter additions to increased water retention).

How to extend

A student could combine this with basic knowledge that organic fertilizers increase soil organic matter to infer that higher organic matter tends to increase, not drastically reduce, water-holding capacity.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > Role of manures > p. 363
Strength: 5/5
“• r. Organic manures bind the sandy soil and improve its water holding capaciry. • z. They open the clayey soil and help in aerati6h better root growth. • 3. They add plant nutrients in small percentage and also add micro nutrients which are essential for plant growth. The microbial activity is increased, which helps in releasing plant nutrients available for e.g. A11 Rights Reserved. No part of this material nay be reproduced in anv ibrrl or b,v atry means, lvithout Permission in 1\'riting. rc$”
Why relevant

Says organic manures bind sandy soil and improve its water holding capacity and that they open clayey soil improving aeration—showing organic matter modifies texture and retention properties.

How to extend

Using standard facts about sandy soils having low retention and clay high retention, a student could infer organic matter raises retention in coarse soils and can change porosity in fine soils rather than drastically reducing it.

FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
Strength: 4/5
“The vegetative cover and organisms that occupy the parent materials from the beginning and also at later stages help in adding organic matter, moisture retention, nitrogen etc. Dead plants provide humus, the finely divided organic matter of the soil. Some organic acids which form during humification aid in decomposing the minerals of the soil parent materials. Intensity of bacterial activity shows up differences between soils of cold and warm climates. Humus accumulates in cold climates as bacterial growth is slow. With undecomposed organic matter because of low bacterial activity, layers of peat develop in subarctic and tundra climates. In humid tropical and equatorial climates, bacterial growth and action is intense and dead vegetation is rapidly oxidised leaving very low humus content in the soil.”
Why relevant

Notes humus (organic matter) contributes to moisture retention and other soil properties—linking organic matter directly to increased moisture-holding function.

How to extend

A student could use this rule plus general soil-water relationships to judge that more humus generally supports greater moisture retention.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > Advantages of Zero tillage > p. 356
Strength: 4/5
“• Zero tilled soils are homogenous in structure with more number of earthworms • Organic matter content increases due to less mineralization • Surface runoff is reduced due to presence of mulch”
Why relevant

States zero tillage increases organic matter and reduces surface runoff due to mulch—suggesting organic matter on surface reduces loss of water from soil.

How to extend

Combining this with a map/field knowledge of rainfall/runoff, a student could infer higher organic cover/matter helps retain water rather than drastically lowering water-holding capacity.

Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 12: How Nature Works in Harmony > Activity 12.10: Let us survey > p. 206
Strength: 3/5
“What inference do you draw from your interactions with farmers? Synthetic fertilisers and pesticides have played a vital role in improving crop production and helped countries like India become food secure. However, their long-term use can affect the environment and soil health. Overuse of synthetic fertilisers may reduce soil fertility by decreasing friendly microorganisms in soil and lowering organic matter (humus), which helps bind soil particles. Without enough humus, soil becomes prone to erosion. Also, it reduces the population of natural predators which ultimately increase the population of pests (Fig. 12.18). Heavy irrigation and repeated ploughing can also disturb soil organisms like earthworms and snails, which are important for maintaining ecological balance.”
Why relevant

Explains that humus helps bind soil particles and that lack of humus makes soil prone to erosion—implying humus stabilizes soil structure which influences water retention.

How to extend

A student could extend this by noting stable, aggregated soils (from humus) typically have better infiltration and moisture-holding characteristics versus degraded soils.

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SIMILAR QUESTIONS

IAS ¡ 2023 ¡ Q63 Relevance score: 1.89

Consider the following statements : Statement-I : The soil in tropical rain forests is rich in nutrients. Statement-II : The high temperature and moisture of tropical rain forests cause dead organic matter in the soil to decompose quickly. Which one of the following is correct in respect of the above statements?

IAS ¡ 2019 ¡ Q41 Relevance score: 1.15

Consider the following statements : 1. Agricultural soils release nitrogen oxides into environment. 2. Cattle release ammonia into environment. 3. Poultry industry releases reactive nitrogen compounds into environment. Which of the statements given above is/are correct?

CDS-I ¡ 2020 ¡ Q118 Relevance score: 0.75

Which one of the following soils is characterized by very high content of organic matter?

CDS-II ¡ 2016 ¡ Q45 Relevance score: 0.55

Which of the following statements regarding soil is/are correct? 1. Alluvial soils are rich in nitrogen content. 2. Black soils are rich in iron and lime but deficient in nitrogen. 3. Laterite soils are rich in iron and aluminium but deficient in nitrogen and potassium. Select the correct answer using the code given below.

CAPF ¡ 2025 ¡ Q103 Relevance score: 0.34

Consider the following statements: 1. The circulation of nitrogen from the inorganic compounds in the soil to form protein in plants and animals and back again is known as the nitrogen cycle. 2. The preparation of ammonia by Haber process is an endothermic reaction. 3. Urea is synthetically made by the action of ammonia and carbon dioxide under high temperature and high pressure. Which of the statements given above is/are **not** correct?