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?
- A.1 and 2 only
- B.3 only
- C.1 and 3 only
- D.1, 2 and 3
Correct answer
Explanation
The correct answer is B, 3 only. Only statement 3 is correct: long-term irrigation can make farmland saline, while statements 1 and 2 reverse basic facts about soil. Statement 1 is wrong because organic matter, or humus, increases a soil's water holding capacity. Humus acts like a sponge, can hold several times its own weight in water, and improves soil structure, which is why compost and farmyard manure help soils resist drought. Statement 2 is wrong because soil is central to the sulphur cycle. Soil microbes break down organic matter and release sulphate, plants take up sulphur from the soil, and bacteria oxidise and reduce sulphur compounds there. Statement 3 is correct because irrigation water carries dissolved salts; where drainage is poor and evaporation high, the water rises, evaporates and leaves salts in the topsoil. This has created saline and alkaline (reh, kallar, usar) lands in Punjab, Haryana and western Uttar Pradesh. So options A, C and D are wrong because they include statement 1 or 2. Exam tip: humus raises water holding capacity; over-irrigation with poor drainage causes salinity, waterlogging and usar land.
Practice Questions
View allAlluvial soils vary in nature from sandy loam to clay. They are generally
- A.poor in potash and rich in phosphorus.
- B.poor in both potash and phosphorus.
- C.rich in both potash and phosphorus.
- D.rich in potash and poor in phosphorus.
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Alluvial soils, laid down by rivers, generally contain plenty of potash but lack phosphorus, and they are also often short of nitrogen and humus.
Read the full explanation →Which one among the following State capitals is closest to the Equator ?
- A.Hyderabad
- B.Bhubaneswar
- C.Panaji
- D.Mumbai
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Panaji, the capital of Goa, lies at about 15.5° N latitude, the lowest of the four cities, so it is the closest to the Equator.
Read the full explanation →Which Greek philosopher coined the term "Geography" in the 3rd century B.C.E. ?
- A.Euclid
- B.Plato
- C.Eratosthenes
- D.Clio
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Eratosthenes of Cyrene first used the word "geographia", from the Greek "geo" (earth) and "graphe" (description), so geography means a description of the Earth.
Read the full explanation →Which one of the following statements about primary waves of earthquakes is not correct ?
- A.They are similar to sound waves.
- B.They can travel only through solid materials.
- C.They travel through gaseous, liquid and solid materials.
- D.They move faster and are the first to arrive at the surface.
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This statement is false because primary waves pass through solids, liquids and gases alike. Primary or P-waves are longitudinal waves: they push and pull the rock in the same direction in which the wave travels, compressing and stretching the material just as sound waves compress air.
Read the full explanation →Which one among the following States has the longest extension in north-south direction?
- A.Jharkhand
- B.Telangana
- C.Odisha
- D.Chhattisgarh
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Chhattisgarh is a long, narrow state that stretches from about 17.8° N in Sukma district to about 24.1° N in Balrampur district, a north-south length of roughly 700 km.
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