NCERT 7th Class (CBSE) Science: Soil

Question: Explain how soil pollution and soil erosion could be prevented.

Answer: 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 soil. Hence, these should be disposed off properly and if possible, their use should be avoided.
2. Industrial pollutants: Some waste products from industries and homes pollute 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, excessive use of these substances should be avoided.

Prevention of soil erosion:
Removal of the upper fertile layer of the soil (top soil) by strong wind and flowing water is known as soil erosion. Following steps can be taken to reduce soil erosion:

1. Mass awareness to reduce deforestation for industrial purposes
2. Helping local people to regenerate degrading forest
3. Planting trees

Question: Sketch the cross section of soil and label the various layers

Answer: A soil profile is a arrangement of the successive layers of the soil that would appear when we have vertical section view:

A-Horizon: Also called topsoil. Upper most layer of soil. The colour of this layer is the darkest, since it is rich in humus and minerals. It is soft, porous and hold more water than the other layers. Plants get most of the nutrients and water from this layer. It is also a home of many living organisms like rodents, snakes, moles, worms etc.

B-Horizon: Second most layer from the top. Lighter in colour. May contain little humus. Rich in minerals and serves as water reservoir.

C-Horizon: Consists of small pieces of original rock broken due to weathering. Hard and compact than the above two soils.

Bedrock: The bottom layer is the un-weathered solid rock.

Question: Why is soil regarded as our most important natural resources?

Answer: It is important as:

1. Soil itself a habitat to many organisms like Ant, Snake etc.
2. It is used for construction purposes.
3. For production of petroleum.
4. It is used to grow crops and do agriculture.
5. It is a source of many minerals.
6. It is a source of water as water seeps down into the soil.