3. Introduction:-
Soil is our natural resource.
Soil is the upper-most layer of the Earth’s crust.
It is composed of various types of minerals particles-
gravel, sand ,silt, clay, inorganic salt, nitrates, sulphur,
phosphate, organic substances(humus), water, air, and
living organism.
Soil is essential for the existence of plants and
animals. It provides water and nutrient to the plants.
4. SOIL PROFILE
A soil profile is a vertical cross section of the soil.
Each layers of soil may be different from the other layers in
physical or chemical ways. The differences are developed
from the interaction of such soil-forming factors as parent
material, slope, native vegetation, weathering, and climate.
5. CHANGES TO THE SOIL PROFILE
As a soil ages, horizontal layers develop and changes result. The causes of
these changes are classified as four processes. Each process occurs differently
at various depths in the soil.
Addition—This process occurs as materials such as fallen leaves, windblown
dust, or chemicals from air pollution are added to the soil.
Loss—This process occurs when materials are lost from the soil because of
deep leaching or erosion from the surface.
Translocation—This process involves the movement of materials within the
soil. It can occur with deeper leaching into the soil or with upward
movement caused by evaporating water.
_ Transformation—In this process, materials are altered in the soil. Examples
are organic-matter decay, weathering of minerals to smaller particles, and
chemical reactions.
6. Soil Horizon
•Soil horizons are the layers in a soil profile used to classify soil types.
•Horizons based on color, texture, roots, structure, rock fragments, and
any unique characteristic worth noting.
•Master Soil Horizons are depicted by a capital letter in the order (from
top down): O, A, E, B, C, and R
7. 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 color and this is mainly because of
the presence of organic content.
8. 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.
9. E-HORIZON
The “Leaching Layer” Horizon
•Small layer between A & B horizons
•At depths of 10-15 feet
•Light in color, mainly sand & silt
•Poor mineral and clay content due to leaching
– the loss of water-retaining plant nutrients to
the water table
•Soil particles larger than in A horizon but
smaller than in B horizon
10. B-HORIZON
The “Subsoil” Horizon
•At depths of 10-30 feet
•Rich in clay and minerals like Fe & Al
•Some organic material may reach here
through leaching
•Plant roots can extend into this layer
•Red/brown in color due to oxides of Fe &
clay
11. C-HORIZON
The “Regolith” Horizon
•At depths of 30-48 feet
•Made up of large rocks or lumps
partially broken bedrock
•Least affected by weathering and
have changed the least since their
origin
•Devoid of organic matter due to it
being so far down in the soil profile
12. R-HORIZON
The “Bedrock” Horizon
•At depths of 48+ feet
•Deepest soil horizon in the soil
profile
•No rocks or boulders, only a
continuous mass of bedrock
•Colors are those of the original rock
of the area
13. Conclusion:
Soil is a major component of the Earth's ecosystem. Soil acts as an engineering
medium. It is a habitat for soil organisms and a recycling system for nutrients and
organic wastes. It is a regulator of water quality, a modifier of atmospheric
composition, and a medium for plant growth. Soils are formed by the interaction of
five soil forming factors. They are parent material, climate, biota (organisms),
topography, and time. The different influences of these factors cause different soil
horizons to form. Differences or similarities of soil horizons are used to categorize
similar soils into soil series. Soil management decisions are influenced by the
properties of each soil.
A soil profile is a vertical cross section of the soil. The differences are developed
from the interaction of such soil-forming factors as parent material, slope, native
vegetation, weathering, and climate.
As a soil ages, horizontal layers develop and changes result. The causes of these
changes are classified as four processes: addition, loss, translocation, and
transformation.
14. There are three primary soil horizons, called master horizons. They are A, B, and C.
These are part of a system for naming soil horizons in which each layer is identified
by a code: O, A, E, B, C, and R. The A horizon is often referred to as the topsoil
The B horizon is often referred to as the subsoil. The C horizon is called the substratum.
