Soil | Class 7 Science | Types of Soil | Online Classes | Session 3 - Swiflearn

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This is session 3 of the Chapter: Soil from Class 7 Science. In this Session, Trisika Mam will Introduce you the the Chapter: Soil Class 7 and will take you through the following topics:

00:00 - Introduction
10:17 - Absorption of water by soil
14:25 - Absorption of water by different soil
14:40 - Texture of soil
18:44 - Air content
25:15 - Soil erosion
27:45 - Overgrazing


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Soil
Life on earth is highly dependent upon soil. It is important in the sense that it provides anchorage
and supplies water and minerals to the plant
Layers of the soil include:
 Humus
 water
 clay
 sand
 gravel
Climatic factors effecting soil include
 Temperature
 Light
 Humidity
 Rainfall
 Wind
Humus is the rotting dead matter in soil
Weathering is the breakdown of rocks to form soil by wind, water and climate
Plastic is a non-biodegradable substance which
 Degrades soil quality
 Kills microorganisms
 Causes soil pollution
 Demanded by many people to be banned
Soil Profile
Soil profile - A vertical section through the different layers of soil is called soil profile. These
layers are the horizons.
Soil profile consists of
A horizon
 Uppermost horizon and is also called top soil
 Rich in humus and minerals which gives it a dark colour
 Soft, porous, and high water retention capacity
 Provide nutrients to growing plants and shelter to many living organisms
B horizon
 It is the middle layer
Short Notes
Class 7 Science
Soil
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 It contains less humus and more minerals
 More hard and compact layer
C horizon
 It consists of lumps of rocks
 It has cracks and crevices
Bedrock
 The lowest layer
 Hard and difficult to dig in
 Soil is the mixture of humus and rock particles
 The soil microflora also important for determining the quality soil
Types of soil
The 3 types of soil based on particle proportion include
Sandy soil
 great proportion of big particles
 Light, well aerated and usually dry
Clayey soil
 great proportion of fine particles
 Big, less aerated but hold more water
Loamy soil
 same proportion of big and fine particles
 mixture of sand, clay and silt
 contains humus and is the best soil for growing plants
 Right amount of water retention capacity
Silt occurs as a deposit in riverbeds and its particle size is between that of sand and clay.
The cultivation of different crops is dependent of different soils.
 Wheat, gram, paddy – clayey and loamy soil
 Cotton – sandy loam soil
Percolation of soil
Percolation of soil - The process in which water passes down slowly through the sol
Soil moisture – The water retained by soil. Water retention capacity of soil is an important factor
various crop cultivation.
Short Notes
Class 7 Science
Soil
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Percolation rate is measured in ml/min is given by (Amt. of water in ml/ percolation rate in min)
Percolation rate of water will vary with the type of soil – highest in sandy soil and lowest in clayey
soil
Soil erosion
Soil erosion - The removal of soil surface by wind, water or ice
 Areas devoid of vegetation has loose soil which is blown away by wind
 Most affected areas include deserts and bare lands
 It can be prevented by forestation