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CLASS 7-Soil


·         Soil is considered as one of the most important natural resources.

·       Soil is mixture of rock particles and humus .

·         It gives anchorage to the plants and supplies water and nutrients.

·         Soil is the native (home) for many organisms.

·         Soil is essential for agriculture which provides food, clothing and shelter for all.

Soil Profile

·         Soil is composed of many different layers.


·     Rotting dead matter in the soil is known as humus.

·         Soil is formed by the process of weathering which involves  breaking down of rocks by the action of wind, water and climate. 

·         The nature of  soil depends upon the rocks from which it has  formed and the type of vegetation that grows in it.

·         Soil profile is a vertical section through different layers of the soil .

·         Each layer differs in  chemical composition ,feel (texture), colour and depth  .

·         These layers are known  as horizons. Soil is fertile and provides nutrients to growing plants.




         A-horizon:  A-horizon layer is generally soft, porous and can retain more water.               It is known as topsoil or the A-horizon.

·         The next layer is called the B-horizon or the middle layer,Which has a lesser amount of humus but more of minerals. This layer is generally harder and more compact  .

·         The C-horizon is the third layer of soil , that is made up of small lumps of rocks with cracks and crevices.

·     Bedrock which is hard and difficult to dig with a spade. It is bottom layer of soil.

Soil types

·         Weathering of rocks results production of  small particles of various materials. which include include sand and clay.

·         The proportion  of sand and clay depends upon the rock from which the particles were formed, that is the parent rock.

·         Living organisms( bacteria, plant roots and earthworm ) are also important parts of any soil.

·         The soil is classified on the basis of the ratio of particles of various sizes.

·         If soil containing greater proportion of big particles it is called sandy soil.

·         If the ratio of fine particles is relatively higher, then it is called clayey soil.

·         If the amount of large and fine particles is   same, then the soil is called loamy.

·         Thus, the soil can be divided in categories as sandy, clayey and loamy.

Sandy Soil

·         The size of the particles in a soil has an affects on its properties.

·         Sand particles are quite large.

·         They cannot fit close together, so there are large spaces/gaps between them.

·          These spaces/gaps are filled with air.

·      Sand is well aerated  due to spaces between the particles.

·         Due to this water  can drain quickly through the spaces between the sand particles.

·          sandy soils tend to be light, well aerated and rather dry.

Clayey Soil

·         Clay particles are much smaller, pack tightly together, leaving little space for air.

·       It  can be held water in the tiny gaps between the particles of clay.

·           Clayey soils have less air.

· It are heavy as they hold more water than the sandy soils.

Loamy Soil

·       It is the best topsoil for growing plants is loam.

·             It is a mixture of sand, clay and another type of soil particle known as silt.

·         The loamy soil also contains humus in it.

·         It has the enough water holding capacity for the growth of plants.


·         Silt occurs as a deposit in riverbeds.

·         The size of the silt particles is between sand and clay.

Properties of Soil

Percolation rate of water in soil

· The property of absorption of water by soil is called     percolation . Amount of water absorbed by soil is called as percolation.

·         The amount of water absorbed by soil in a given interval of time is known ass percolation rate. And it’s formula is :-

For example, suppose that for a certain sample, it took 20 minutes for 200 mL to percolate.

Moisture in Soil

·    Moisture is measured by the quantity of water present in the soil. Even though dry soil contains a small amount of moisture. Clayey soil retains the highest amount of moisture.

Absorption of water by Soil


·         How much Soil absorbed can be found by :-

Initial volume of water in the measuring cylinder = U mL

Final volume of water in the measuring cylinder = V mL

Volume of water absorbed by the soil = (U – V) mL

Weight of water absorbed by the soil = (U – V) g

   (1 mL of water has weight equal to 1 g)

Soil and Crops

·         Different types of soils are found in different region of India.

·         In some regionss there is clayey soil, in some parts there is loamy soil while in some other parts there is sandy soil.

·         Soil is influenced by wind, rainfall, temperature, light and humidity.

·         The climatic factors and the components of soil, determine the different types of vegetation and crops that might grow in any region.

·         Clayey as well as  loamy soils are both suitable for growing cereals like wheat, and gram. This kind of soils are good at retaining water.

·         For paddy crop, soils rich in clay and organic matter and having a good  retaining capacity of  water are ideal.

·        loamy soils, which drain water easily, are good for  lentils (masoor) and other pulses.

·          Sandy or loam, which drain water easily and can hold plenty of air, are more suitable   for cotton.

·         Crops such as wheat are grown in the fine clayey soils, because they are rich in humus and are very fertile.


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