Soil Profit and formation

Category : 7th Class

*       Soil Profile and Formation


Soil profile is the layer of soil on the surface of the Earth. The colour of the soil is dark brown. There are three soil profiles, namely. A, horizon, B horizon and C horizon. The upper layer of soil is called/^ horizon or top soil. A horizon provides nutrition to living organism. The layer below the A horizon, is B horizon. Horizon C is below the horizon B. Some part of minerals from horizon A is transported through horizon B to horizon C. There are various kinds of insects and bacteria that live on the soil and these are essential for plants.

The organic matter (humus) is found in the soil. Soil profile looks different in the different part of the earth.


Look at the following picture of the soil profile



*         Formation of Soil

Soil is made up of rocks and minerals. Weathering is the most common cause for the formation of the soil. The rocks on the surface of the Earth are broken down into small pieces by the process of the weathering. On the basis of the size of the rocks found on the surface of the earth, soil is categorized into three types. These are sand, silt and clay.


Look at the following picture of the soil


Sand is the larger particle found in soil. It is easily available on the surface of the earth. Sandy soil contains very little humus and of low fertility. The size of the particle of the sandy soil is bigger than that of particle size of the other soil.

The size of the particle of the silt soil is smaller than sands soil and bigger than clayey soil. Silt soil can easily transported from one place to another through the movement of the air.

Look at the following picture of the silt soil

The particle size of the clayey soil is very small. The formation of clayey soil is the gradual chemical weathering of rocks.

Look at the following picture of the clayey soil






     Which one of the following is the top most layer of the soil?

(a) Horizon B

(b) Horizon C

(c) Horizon D

(d) Horizon A

(e) None of these


Answer: (d)


     Which one of the following types of soil contains least amount of humus?

(a) Sandy soil

(b) Clayey soil

(c) Loamy soil

(d) All of these

(e) None of these


Answer: (a)


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