Class 7 Science
Chapter- 9
Soil Notes
Soil- The mixture of rock particles and humus is called the soil. The top layer of the earth's surface in which plants can grow, consisting of rock and mineral particles mixed with decayed organic matter and having the capability of retaining water.
Soil Profile
Formation of soil-
- Soil is formed by weathering or disintegration of parent rocks.
- Physical Weathering is degradation of rocks by physical agents like water, ice, wind, sun, etc.
- Chemical weathering is chemical decomposition of rocks.
- Biological weathering is decomposition of parent rocks by bacteria and microorganisms.
Soil Profile- Soil profile is a section through different layers of the soil, Various layers
are called horizons. A vertical section through different layers of the soil is called the soil profile. Each layer differs in feel (texture),colour, depth and chemical composition.
Humus- dead matter in the soil is called humus.
Weathering- the soil is formed by the breaking down of rocks by the action of wind, water and climate. This process is called weathering.
This layer is generally soft, porous and can retain more water. It is called the topsoil or A-horizon.
This layer is generally harder and more
compact and is called the B-horizon or B-horizon the middle layer.
The third layer is the C-horizon, C-horizon
which is made up of small lumps of
rocks with cracks and crevices.
bedrock is hard and difficult to dig with a spade.
This layer is generally harder and more
compact and is called the B-horizon or B-horizon the middle layer.
The third layer is the C-horizon, C-horizon
which is made up of small lumps of
rocks with cracks and crevices.
bedrock is hard and difficult to dig with a spade.
SOIL TYPES-
Three types of soil: clayey, loamy and sandy.
(i) Clayey Soil- The proportion of fine particles is relatively higher, then it is called clayey soil. It has an excellent water retention capacity and air circulation is sufficient. Clayey soil is used to make pots, toys and statues.
(ii) Loamy Soil- The amount of large and fine particles in the soil is called loamy. It has a good water retention capacity and air circulation is sufficient. It contains good mixture of sand, clay and humus.
(iii) Sandy Soil- Soil contains greater proportion of big particles it is called sandy soil. It has a very low water retention capacity. It is not rich in humus.
Percolation rate of water in soil-Percolation rate of water is different in different types of soil. It is highest in the sandy soil and least in the clayey soil.
Calculate the rate of percolation by using the following formula:
SOIL MOISTURE - Soil holds water in it, which is called soil moisture.
SOIL AND CROPS- Different types of soils are found in different parts of India. In some parts there is clayey soil, loamy soil while in some other parts there is sandy soil. Soil is affected by wind, rainfall, temperature, light and humidity. These
are some important climatic factors
which affect the soil profile and bring
changes in the soil structure.Different types of soils are used to cultivate different types of crops. Clayey and loamy are suitable for growing wheat, gram and paddy. Cotton is
grown in sandy loam soil.
(ii) Loamy Soil- The amount of large and fine particles in the soil is called loamy. It has a good water retention capacity and air circulation is sufficient. It contains good mixture of sand, clay and humus.
(iii) Sandy Soil- Soil contains greater proportion of big particles it is called sandy soil. It has a very low water retention capacity. It is not rich in humus.
Percolation rate of water in soil-Percolation rate of water is different in different types of soil. It is highest in the sandy soil and least in the clayey soil.
Calculate the rate of percolation by using the following formula:
SOIL MOISTURE - Soil holds water in it, which is called soil moisture.
SOIL AND CROPS- Different types of soils are found in different parts of India. In some parts there is clayey soil, loamy soil while in some other parts there is sandy soil. Soil is affected by wind, rainfall, temperature, light and humidity. These
are some important climatic factors
which affect the soil profile and bring
changes in the soil structure.Different types of soils are used to cultivate different types of crops. Clayey and loamy are suitable for growing wheat, gram and paddy. Cotton is
grown in sandy loam soil.
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