Soil :Introduction

What is Soil ?

Soil is the crust part of the earth. It is mainly the mixture of rock particles and humus.

Functions Of Soil:

Soil is one of the most important natural resources because

•  It supports the growth of plants by holding the roots firmly and supplying water and nutrients.
•  It is the home for many organisms.
•  Soil is essential for agriculture. Agriculture provides food, clothing and shelter for all.
•  Soil is thus an inseparable part of our life.

What do you mean by Soil Profile?

A vertical section through different layers of the soil is called the soil profile.

Diagramatic Representation of Soil profile:

                        

What are horizons?

Each layer of soil differs in feel (texture), colour, depth and chemical composition.These layers are called horizons.

What is humus?

A non living organic matter formed from remains of dead and decay  plants and animal by the activity of micro organism present in soil.

Different Layers Of Soil profile:

1. A- Horizon:

The uppermost layer, the top soil, also known as A-horizon is generally dark in color and fertile as it is rich in humus and minerals. This layer is generally soft, porous and can retain more water. This provides shelter for many living organisms such as worms, rodents, moles and beetles. The roots of small plants are embedded entirely in the topsoil.

2. B-Horizon:

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

3. C- Horizon:

 The third layer is the C-horizon which is made up of small lumps of rocks with cracks and crevices.

4. Bedrock:

 Below this layer is the bedrock, which is hard and difficult to dig with a spade. Water can be held in the tiny gaps.

What are the different types of soils found in India?

1. Late rite Soils :- This typical soil is found in those regions which receive heavy rainfall. This soil is poor in lime content and hence it is more acidic. This soil contains least moisture content.It is basically red in colour because of the presence of iron oxides. It is more popular in the coastal regions of Ratnagiri District and Malabar.      .

                                      

2.Black Soil :- It is black in colour due to presence of salt and large amount of humus . This soil becomes sticky when is wet. It does not contain adequate nitrogen but it contains sufficient phosphorous required for the growth of the plants.It is generally found in hilly areas.

                                         

3.Red and Yellow Soils : Red and yellow soils are found in areas, which receive low rainfall. They contain huge concentration of iron oxides that are responsible for giving the reddish or yellow colour.                                                                      

4.Alluvial Soils : Alluvial Soils are mainly found in the plains of northern India. These soils have low phosphorous and nitrogen content and found in the north western regions of the country 

5.Mountain Soils : Mountain soils are considered as a significant variety of soil in the Himalayan region of the country. They are mainly found in dry and cold district in the northern region of India

 

           

Learning Activity:

1) What is a a soil horizon?

a) A factor influencing how soil is formed
b) A layer of soil
c) An organism found within the soil
d) A technique used to map soils

2) Which three layers form the soil profile?

a) Air. water and soil
b) Minerals, organic matter and living organisms
c) Clay, silt and sand
d) The topsoil, subsoil and parent material

3) How does a 'sandy' soil feel like to touch?

a) Sticky
b) Gritty
c) Smooth

4) Why is organic matter (humus) an important part of soil?

a) It helps to improve water infiltration
b) It can break down organic pollutants
c) It converts nitrogen in the air into nitrates used by plants
d) It is rich in nutrients, which is important for fertility

5) Which of the following is NOT a common reason why soil maps are used?

a) To determine the land drainage capabilities of an area
b) To determine the suitability of soils for particular crops
c) To identify soils and their properties
d) To record how soils are used by people

6) Which of the following is NOT a threat commonly faced by soils?

a) Soil erosion
b) Percolation
c) Deforestation
d) Climate change