Q1. Heavy rainfall affects soil by
(a) Increasing its acidity
(b) Increasing its alkalinity
(c) Reducing its fertility
(d) None of these
(UPSC Prelims 1980)
Answer: (c) Reducing its fertility
Explanation: Heavy rainfall can cause soil erosion, washing away nutrients, and leading to reduced fertility, especially in unprotected or sloped areas.
Q2. Gypsum is added to the soil ?
(a) To increase the alkalinity
(b) To decrease the acidity
(c) To decrease the alkalinity
(d) As an insecticide
(UPSC Prelims 1981)
Answer: (c) To decrease the alkalinity
Explanation: Gypsum (calcium sulfate) is used to neutralize alkaline soils, improving soil structure and water infiltration. It helps in reclaiming sodic soils and enhances nutrient availability for crops.
Q3. Forests help in
(a) Soil erosion
(b) Soil protection
(c) Depleting the soil of its moisture
(d) All of the above
Answer: (b) Soil protection
Explanation: Forests protect soil by preventing erosion, maintaining moisture levels, and enhancing organic content. Tree roots bind the soil, and canopy cover reduces the impact of rainfall, preserving topsoil integrity.
Q4. Massive deforestation causes
(a) Soil erosion
(b) Famine
(c) Floods
(d) None of these
(UPSC Prelims 1986)
Answer: (a) Soil erosion
Explanation: Deforestation removes the vegetative cover that holds soil in place, leading to soil erosion. It also contributes to climate change and biodiversity loss, but erosion is the most direct consequence.
Q5. Which of the following is the correct order of increasing size of the grains of soil particles ?
(A) Clay
(B) Silt
(C) Sand
(D) Gravel
(a) A, B, C, D
(b) D, C, A, B
(c) B, C, A, D
(d) C, D, B, A
(UPSC Prelims 1986)
Answer: (a) A, B, C, D
Explanation: Soil particles increase in size in the order:
- Clay (finest)
- Silt
- Sand
- Gravel (largest)
This sequence reflects particle diameter and texture.
Q6. Which of the following is the organic matter of animal and vegetable origin in the soil?
(a) Humus
(b) Vermiculite
(c) Fulminic Acid
(d) None of the above
(UPSC Prelims 1986)
Answer: (a) Humus
Explanation: Humus is the decomposed organic matter from plants and animals, found in soil. It improves soil fertility, texture, and water retention, making it vital for agriculture.