Soil Summary Class 7 NCERT Summary

Introduction

Soil is a naturally occurring substance that is valuable in sustaining life on earth.

• Humus: It is a component of soil that is formed from the dead and decayed organic matter.
• Weathering: It is the process of formation of soil by breaking down of rocks. It occurs by the action of wind, water, and climate.

Soil profile

It is a vertical section through various layers of soil. These various layers are known as horizons.

There are four types of horizons.

• A-horizon or topsoil: It is the top most soil, which is dark in colour and rich in humus. It is soft, porous, and has the ability to retain water.
• B-horizon: It is the middle next layer of the soil profile. It has lesser humus and more minerals. The layer is harder and more compact.
• C-horizon: It is the third layer made up of small lumps of rocks with cracks and crevices.
• Bedrock:  It is the lowermost hard layer and difficult to dig with a spade.

Soil Types

Soil is a mixture of rock particles and humus.

•  Soil → Rock particle + Humus

Living organisms such as microbes, earthworm, and plant roots are found in soil.

Classification of soil

(i) Sandy soil

• Sand particles are large that cannot fit together.
• Larger spaces are present between particles.
• It is light, well aerated, and dry.

(ii) Clayey soil

• Clay particles are smaller and tightly packed together.
• It has little space for air and can hold water between particles.

(iii) Loamy soil

• It is the best top soil for the growth of plants.
• It is the mixture of sand, clay, and silt.
• It contains humus and has the right water holding capacity.
• Toys, pots, and statues are made up of clayey soil.

Properties of Soil

• Percolation rate of water varies in different soil types.
  percolation rate (mL/min) = amount of water (mL)/percolation time (min)
• Percolation rate of water is highest in sandy soil and least in clayey soil.
• The soil moisture and water absorption capacity of soil also varies among different soil types.
• Loamy soil has the maximum accurate water holding capacity while sandy soil has the least.
• Climatic factors such as wind, rainfall, temperature, light, and humidity affect the soil.

Soil and crops

• The soil capacity to hold water is important for the cultivation of various crops.

Crop

• When same kinds of plants are cultivated on a large scale, it is called a crop.
  It is of two types.
  (i) Kharif crops: Crops that are sown in rainy season (June to September)
  Examples – soyabean, paddy, maize
  (ii) Rabi crops: Crops that are grown during winter season (October to March)
  Examples – wheat, gram, pea

Basic crop production practices

• Preparation of soil
• Sowing
• Adding manure and fertilizers
• Irrigation
• Protection from weeds (weeding)
• Harvesting
• Storage

Factors leading to soil pollution

Various human activities and products pollute the soil. These pollutants destroy the fertility of the soil and harm the organisms living in the soil.

Some of the important soil pollutants are given below.

• Polythene bags
• Plastic products
• Chemicals
• Pesticides

The preventive measures that can be adopted to reduce soil pollution are as follows.

• Treating the waste products before disposal
• Reducing the use of polythene bags
• Minimizing the use of products made of plastic
• Minimizing the use of pesticides
• Plastic particles and polythene bags are banned to avoid soil pollution.