Soil NCERT Science Class 7 Chapter 9 Summary

Soil
Upper layer of earth crust, is called soil. 
The mixture of rock particles and humus is called the soil. 

Humus
The rotting dead matter in the soil is called humus. 

Weathering
Formation of soil by break down of rocks by the action of winds, water and climate, is called weathering. 

Nature of soil depends on
The parent rock 
Vegetation grows on it. 
Wind, Climate, rainfall, temperature, light and humidity. 

Soil profile 
A vertical section through different layers of the soil is called soil profile. 
Horizon
Each layer of soil differing in texture, colour, depth, and chemical composition, is called horizon. 

A-Horizon 
It is dark in colour. 
It is rich in humus. 
Soil is fertile. 
This layer is soft and porous. 
This layer can retain more water. 
It is also called top soil. 

B-Horizon 
This layer has lesser amount of humus. 
This layer has more amount of minerals. 
This layer is harder. 
This layer is more compact. 

C-Horizon 
This layer is made up of small lumps of rocks with cracks and crevices. 

Bedrock 
The layer below C-Horizon is bedrock. 
It is hard layer. 

Types of soil 
Sandy soil 
Clayey soil 
Loamy soil 

Sandy soil 
The soil that contains greater propertion of big particles is called Sandy soil. 
The soil is loosely packed. 
Space between particles - more 
Water retaining capacity - less 
Air in soil - more 

Clayey soil
The soil that contains greater propertion of fine particles is called clayey soil. 
The soil is tightly packed. 
Space between particles - less
Water retaining capacity - more
Air in soil - less

Loamy soil
The soil that is mixture of clay, sand and silt, is called loamy soil. 
Size of particles - medium 
Space between particles - medium
Water retaining capacity - medium (good for crop) 
Air in soil - medium

Percolation rate 
Percentage of water absorbed 
Where U= Initial volume of water 
            V= Final volume of water 

Clayey soil and loamy soil are both suitable for growing crops. Because, such soil are good at retaining water. 






Comments

Post a Comment

Popular posts from this blog

Cell - Structure and Functions NCERT Science Class 8 Chapter 8 Summary Note

Image
Cell - Structure and Functions   * Cell - Structural and functional unit of life, is called cell. * Discovery of cell   - Discovered by - Robert Hooke - Used - Thin slice of cork. - Cork - Part of bark of a tree * Egg of a hen represent single cell. * Multicellular organism -Organism made of more than one cells, is called multicellular organism. - Example- Human - Multicellular organism begins life as a single cell. * Unicellular organism - Single celled organism are called unicellular organism. - Example- Amoeba * Shape of cells             Cell                                 Shape        Amoeba, WBC(White Blood Cell)     Irregular shape      Muscle cell                      Spindle shape          RBC ...
Read more

Friction NCERT Science Class 8 Chapter 12 Summary Note

Friction The force that opposes the relative motion between two surfaces in contact, is called friction.  Factors affecting friction Weight of object  Nature of surfaces in contact More the weight of object, more the friction.  More smooth surface experience less friction.  Importance of friction Friction helps in stopping object Friction helps to write, walk,  Friction helps in all activities Friction produces heat.  Harm cause by Friction Sole of shoes wear out.  Machine parts get wear out.  Friction can be increased by making surfaces rough. ( More rough means more interlocking between surfaces which means more friction )  Friction can be decreased by applying lubricant on surfaces.  Friction can be decresed by changing shape of object.  Rolling friction The force that oppose motion of rolling object, is rolling friction.  Sliding friction The force that oppose moti...
Read more

Stars and the Solar System NCERT Science Class 8 Chapter 17 Summary Note

Stars and Solar System Celestial objects The stars, the planets, the moons and many other objects in the sky are called celestial objects.  Full Moon Day  The day on which the whole disc of the moon is visible is known as full moon day.  New Moon Day On the fifteenth day after full moon day, the moon is not visible. This day is known as new moon day.  Crescent Moon  The moon whose only a small portion appears in the sky, is called crescent moon.  Phases of Moon  The various shapes of the bright part of the moon as seen during a month are called phases of moon.  The moon doesn't produce its own light.  We see the moon because, the sunlight falling on it gets reflected towards us.  The moon rotates on its axis.  The moon revolve around the Earth.  The moon has no atmosphere, no water,  Star The sun is also a star.  Sun appears larger than other stars. Because- -Stars are millions of times farther away than the sun....
Read more