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Class seven Science Ch 9 Soil NCERT Solutions
Chapter 9: Soil
N C E R T Textbook Questions Solved
Tick the most suitable answer in questions 1 and 2.
1. In addition to the rock particles, the soil contains:
(i) Air and water
(ii) Water and plants
(iii) Minerals, organic matter, air and water
(iv) Water, air and plants
Answer: (iii) Minerals, organic matter, air and water.
2. The water holding capacity is the highest in:
(i) Sandy soil
(ii) Clayey soil
(iii) Loamy soil
(iv) A mixture of sand and loam
Answer: (ii) Clayey soil.
3. Match the items in Column I with those in Column II:
4. Explain how soil is formed.
Answer: Soil is formed through the process of weathering. Weathering is a process of physical breakdown and chemical decomposition of
rocks and minerals near or at the surface of the earth. This physical and chemical decomposition is primarily done by wind, water, and climate. As a result of these processes, large rock pieces are broken down into smaller pieces and eventually form the soil.
5. How is clayey soil useful for crops?
Answer: Following are the properties of clayey soil:
1. It has very good water holding capacity.
2. It is rich in organic matter. For growing crops, such as wheat, gram and paddy, the soil that is good at retaining water and rich in organic matter is suitable. Therefore, clayey soils having these characteristics are useful for such kind of crops.
6. List the differences between clayey soil and sandy soil.
7. Draw a cross-section of soil and label the various layers.
8. Razia conducted an experiment in the field to calculate the rate of percolation. She observed that it took 40 min for 200 mL of water to percolate through the soil sample.
Calculate the rate of percolation.
Answer: Given the amount of water = 200 ml
Percolation time = 40 min
9. Explain how soil pollution and soil erosion could be prevented.
Prevention of soil pollution:
The persistent build-up of toxic compounds in the soil is defined as soil pollution. To prevent soil pollution, its causes must be controlled.
1. Reduce the use of plastics: Plastics and polythene bags destroy the fertility of the soil. Hence, these should be disposed of properly and if possible, their use should be avoided.
2. Industrial pollutants: Some waste products from industries and homes pollute the soil. These pollutants should be treated chemically to make them harmless before they are disposed off.
3. Insecticides: Other pollutants of soil include pesticides and insecticides. Therefore, the excessive use of these substances should be avoided.
Prevention of soil erosion:
Removal of the upper fertile layer of the soil (topsoil) by strong winds and flowing water is known as soil erosion. Following steps can be taken to reduce soil erosion:
1. Create Mass awareness to reduce deforestation for industrial purposes.
2. Helping local people to regenerate the degradation of forests.
3. Planting more trees.