Understand the development of a soil profile.
Explore a layer of soil diagram to understand the layers of soil that form the
soil horizon of various soil profiles.
A soil horizon is a layer parallel to the soil
surface whose physical, chemical and biological characteristics differ from the
layers above and beneath. Horizons are defined in many cases by obvious
physical features, mainly colour and texture.
In
this article you will be able to know:
· Soil
Profile
· Layers
of Soil
· Soil
Moisture
· Types
of Soil Moisture
· Importance
Of Soil Moisture
· Measurements
Of Soil Moisture
Soil Profile Definition
Soil profile is defined as the vertical section of the soil from the ground surface downwards to where the soil meets the underlying rock.
What is Soil Profile?
The
soil is the topmost layer of the earth’s crust mainly composed of organic
minerals and rock particles that support life. A soil profile is a vertical
cross-section of the soil, made of layers running parallel to the surface.
These layers are known as soil horizons.
The
soil is arranged in layers or horizons during its formation. These layers or
horizons are known as the soil profile. It is the vertical section of the soil that is
exposed by a soil pit.
The
layers of soil can easily be identified by the soil colour and size of soil particles.
The
different layers of soil are:
· Topsoil
· Subsoil
· Parent
rock
Each
layer of soil has distinct characteristics.
Soil
profile helps in determining the
role of the soil as well.
It
helps one to differentiate the given sample of soil from other soil samples
based on factors like its colour, texture, structure, and thickness, as well as
its chemical composition.
Layers of Soil
The
soil profile is composed of a series
of horizons or layers of soil stacked one on top of the other. These layers or
horizons are represented by letters O, A, E, C, B and R.
The O-Horizon
The
O horizon is the upper layer of the topsoil which is mainly composed of organic
materials such as dried leaves, grasses, dead leaves, small rocks, twigs,
surface organisms, fallen trees, and other decomposed organic matter.
This
horizon of soil is often black brown or dark brown in colour and this is mainly
because of the presence of organic content.
The A-Horizon or Topsoil
This
layer is rich in organic material and is known as the humus layer. This layer
consists of both organic matter and other decomposed materials.
The
topsoil is soft and porous to hold enough air and water. In this layer, the
seed germination takes place and new roots are produced which grows into a new
plant.
This
layer consists of microorganisms such as earthworms, fungi, bacteria, etc.
The E-Horizon
This
layer is composed of nutrients leached from the O and A horizons. This layer is
more common in forested areas and has lower clay content.
The B-Horizon or Subsoil
It is the subsurface horizon, present just below the topsoil and above the bedrock. It is comparatively harder and more compact than topsoil. It contains less humus, soluble minerals, and organic matter. It is a site of deposition of certain minerals and metal salts such as iron oxide.
This layer holds more water than the topsoil and is lighter brown due to the presence of clay soil.
The soil of horizon-A and horizon-B is often mixed while ploughing the fields.
The C-Horizon or Saprolite
This
layer is devoid of any organic matter and is made up of broken bedrock. This
layer is also known as saprolite. The geological material present in this zone
is cemented.
The R-Horizon
It
is a compacted and cemented layer. Different types of rocks such as granite,
basalt and limestone are found here. Apart from the rocks, minerals, and
layers, soil profile
also consists of a water content, which is referred to as soil moisture.
Read: What is Remote Sensing? Understanding Remote Sensing
What Is Soil Moisture?
Water in the soil is referred to as soil moisture. Water absorption in the soil is determined by various factors. It plays a major role in soil formation.
As a
result of precipitation, water arrives at the surface. The particle size
distribution of soil determines its porous nature and causes downward movement
of water vertically which is known as infiltration.
This
penetration continues deep in the layers of soil until it reaches saturation.
Water, on reaching this barrier, cannot seep vertically further, hence it moves
sideways. Formation of puddles as a result of saturation is called surface
ponding which can be long-lasting.
Water
that is available to plants is called Root zone moisture while surface soil
moisture is the water available in the immediate upper region of soil. Moisture
content in the soil can be measured using a device known as Tensiometer.
They
are water-filled
tubes which are sealed with a porous ceramic tip towards the bottom and a gauge
at the top which is devoid of air molecules. They are penetrated into the soil
till the root level. Water passes between the tip of the device and the ambient
soil until it reaches an equilibrium and hence, tension is recorded on the
gauge.
Readings
thus obtained give a measure of soil moisture in that region.
Types of Soil Moisture
The
different types of water present in the soil include:
1. Gravitational Water
The
water that reaches the water table of the soil due to the gravitational force
is referred to as gravitational water. This is not available to the plants.
2. Hygroscopic Water
This
water is also not available to the plants. It is a thin film of water tightly held by
the soil particles.
3. Chemically Combined
Water
The
chemical compounds present in the soil particles contain water. This is known
as chemically combined water. This is also not available to the plants.
4. Capillary Water
This
water is available to the plants for absorption. This water exists between soil
particles in small capillaries.
5. Atmospheric Humidity
The
hanging roots of the epiphytes absorb the moisture in the air due to the
presence of hygroscopic hairs and spongy velamen tissues.
Importance
Of Soil Moisture Content
1. Soil
water carries food nutrients for the growth of plants
2. Soil
moisture content determines the yield of the crop in a region
3. Crucial in maintaining soil’s temperature
4. Soil moisture acts as nutrients
5. Important for soil formation
6. Moist soil is ideal for the growth of many
plants that demand a huge supply of water (Ex: Rice)
7. Soil moisture catalyses biological
activities of microbes in the soil
8. Water is a primary need for photosynthesis
in plants
Measuring Soil Moisture
The soil moisture can be measured by various
tools mentioned below:
Tensiometers
These tools measure the tension of soil
moisture. They are water-fi8lled
tubes, with a porous ceramic tip at the bottom. These are sealed and have a
vacuum gauge at the top. They are inserted in the soil to the depth of the
plant root zone.
The readings obtained in the tensiometers
indicate the availability of water in the soil.
Electrical
Resistance Blocks
These consist of two electrodes connected to
lead wires extending to the soil surface. The electrodes are embedded in the
blocks of porous material. It is used to measure soil water tension.
Time
Domain Reflectometry
(TDR)
TDR – Time Domain Reflectometry is used to
determine the soil moisture content. Steel rods are placed in the soil and
electrical signals are sent through them. The returned signals are measured to
determine soil water content.
Read: Types of Soil: Characteristics and Importance
Question For You
What
is Soil?
Soil is one of the most important naturally
occurring resources. It is the natural habitat of plants and many
microorganisms. It nourishes plants with water and essential nutrients hence
enabling their growth. Soil is the most important raw material for agriculture.
Agriculture provides food, clothing and
shelter to all entities either directly or indirectly. Hence, soil is an
inseparable part of our living.
What
is Soil Profile?
The soil profile is a vertical section of the soil that depicts all of
its horizons. The soil profile
extends from the soil surface to the rock material.
How
is Soil Formed?
Soil is mainly formed by the breakdown of
bigger rocks into smaller and fine
particles with the continuous action of wind, rain and other agents of natural
force. It takes hundreds to thousands of years for the formation of soil.
What
are the basic components of Soil?
·Air
·Water
·Minerals
Other organic matters
are the basic components of soil.
What
is the importance of Soil Profile?
The soil profile plays an important role
in maintaining the fertility of the soil and the nutrition content in the soil.
What
are the horizons of soil?
The soil profiles
are composed of a series of horizons or layers of soil, which are stacked one
above the other.
The 4 horizons of
soil are:
1. The O-Horizon.
2. The A-Horizon.
3. The B-Horizon.
4. The C-Horizon.
What
is Topsoil?
The topsoil is the
topmost layer of the soil. It is dark brown coloured soil which mainly consists
of organic matter, decomposed material and many living organisms including some
microbes, earthworms and other worms.
List
out the different types of Soil Moisture
The different types
of water present in the soil include:
1. Capillary Water.
2. Hygroscopic
Water.
3. Gravitational
Water.
4. Atmospheric
Humidity.
5. Chemically
Combined Water.
What
is humus layer in the soil?
It is also called topsoil or horizon A, which is rich in organic material. This layer consists of decomposed material and organic matter. This is the reason; the topsoil has dark brown color.
The humus makes the topsoil soft, porous to hold enough air
and water.
In this layer, the seeds germinate and roots of the plants grow.
Many living organisms like
earthworms, millipedes, and centipedes, bacteria, and fungi are found in this
layer of soil.
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