The document discusses soil mechanics, detailing the composition, functions, and layers of soil, including distinct horizons such as O, A, B, C, and R. It explains various soil types like clay, silty, sandy, loamy, chalky, and peaty, along with their characteristics and suitability for different plants. Additionally, the document highlights the importance of soil profiles in understanding soil fertility and changes due to weathering and organic decomposition.

1. MD. WAYZID BUSTANI
B.TECH
4th SEMESTER (CIVIL)
ROLL NO.:- 28601323005
ST. MARY’S TECHNICAL CAMPUS
SUB :- SOIL MECHANICS

2. Soil is the mixture of minerals, organic matter, gases,
liquids, and the myriad of organisms that together support
plant life. It is a natural body that exists as part of
the pedosphere and which performs four important
functions: it is a medium for plant growth; it is a means
of water storage, supply and purification; it is a modifier
of the atmosphere; and it is a habitat for organisms that
take part in decomposition of organic matter and the
creation of a habitat for new organisms.

3. Soil Horizons (layers): Soil is made up of distinct horizontal
layers; these layers are called horizons. They range from rich,
organic upper layers (humus and topsoil) to underlying rocky
layers ( subsoil, regolith and bedrock).

4. O Horizon - The top, organic layer of soil is dark in
colour, made up mostly of leaf litter and humus
(decomposed organic matter) that make the soil fertile
A Horizon - The layer called topsoil. Seeds germinate
and plant roots grow. It is made up of humus
(decomposed organic matter) mixed with mineral
particles. It is a soft and porous layer. It is a shelter of
living organisms like worms and rodents.
B Horizon - Also called the subsoil. It contains clay and
mineral deposits (like iron, aluminum oxides, and
calcium carbonate) that it receives from layers above it
when mineralized water drips from the soil above. This
layer is hard and compact. Roots of bigger plants
extends till this layer

5. C Horizon - Also called regolith. It
consists of slightly broken-up
bedrock (weathered parents rocks
with cracks and crevices). Plant
roots do not penetrate into this
layer; very little organic material is
found in this layer.
R Horizon - The unweathered rock
(bedrock) layer that is the last of all
the other layers. This layer is very
hard.

6. A soil horizon makes up a distinct layer of soil.
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 parent rock
material. By examining a soil profile, we can
gain valuable insight into soil fertility. As the soil
weathers and/or organic matter decomposes, the
profile of the soil changes.

8. Soil has three examples of
state: solid soil, soil with air in
the pores and soil with water
in the pores. Due to the
number of different forms of
organic and mineral
compositions, there are various
types of soil that undergoes
different environmental
pressures.

9. Clay Soil
Clay is one of the many types of soils that are distinguished as soil
in which the particles are packed tightly together with each other
with little or no air space. Because of this characteristic, clay is the
densest and heaviest type of soil.
Defining Factors:
Fine particles
Smooth when dry
Sticky when wet
Retains water
Drains poorly
Less spaces to let air pass
Rich in nutrients
Cool and dense
Ideal for crops like:
Leafy vegetables, Peas, Tomatoes, and Peppers

10. Silty Soil
Silty soil is extremely smooth and since it retains plenty of
water, it is fertile. Despite the good characteristics of this kind
of soil, it lacks nutrients compared to other types of soils. Silty
soil is ideal for agricultural use as the particles in silty soil are
miniscule.
Defining Factors:
Tiny particles
Slippery when wet
Not grainy or rocky
Extremely fertile
Retains water
Easily transported by wind and water
Good for agriculture purposes
Easily compacted
Ideal for crops like:
All vegetables and fruits

11. Sandy Soil
Sandy soils are one of the worst types of soils to grown any kind of
plants in. This is because sandy soil has one of the largest particles
and that prevents the soil from retaining water, making it hard for
the roots of plants to establish.
Defining Factors:
Large particles
Dry and gritty to touch
Easily drains water
Less water retention
Warm and airy
Even when wet, easily crumbles through the fingers
Lacks essential nutrients
Ideal for crops like:
Watermelons, Peanuts, and Peaches
Tulips, Cistus, and Hibiscus

12. Loamy Soil
Loamy soil is one of the perfect types of soil because it is a mix of
sand, clay, silt and even some humus. The pH level of loamy soil is
6, with high calcium levels. The specific composition of loamy soil
can vary, but with the right balance of additives, it can be made
ideal.
Defining Factors:
Well-drained
Fertile
Mixture of sand, silt and clay
Retains water
Retains nutrients
Strong granular structure
Soft and crumbly
Easy to work with
Well aerated
Ideal for crops like:
Tomatoes, Carrots, Parsnips, and Potatoes
Roses, Amaryllis, Marigolds, and Zinnias

13. Chalky Soil
These kinds of soils are found in limestone beds that have chalk
deposits that are deep. This is not an ideal soil for growing plants
because it can be hard to work with. Chalky soil is alkali and
causes yellow and stunted plants.
Defining Factors:
Lime rich soil
Stony
Severely dry in summers
Poor in nutrients
Warms quickly in summers
Porous
Highly alkaline
Free-draining
Ideal for plants like:
Honeysuckle, Jasminum, Rosa, and Geranium

14. Peaty Soil
The soil has a lot of organic material and is rich in water, which
makes it one of the best types of soils for plants. But the soil
needs to be drained first. Because of a high water and nutrient
content, peaty soil keeps plants healthy even in dry weather. The
acidic water content is good for controlling plant diseases and
can be used to balance the pH level of other kinds of soils.
Defining Factors:
Dark brown in color
Soft and spongy to the touch
Contains acidic water
Rich in organic matter
Retains water
Stores nutrients
Improves soil buffering
Well aerated
Found in bogs
Mixed in soil to improve structure
Ideal for plants like:
Sphagnum Moss, Ericaceous Shrubs,
and Sedges