2. Origin of Soil
• SOIL FORMATION IN GEOLOGICAL CYCLE
• Primarily soils are formed from rocks through
physical and chemical weathering. If weathered rock
material remains over a parent rock then the soils
are known as Residual soils.
• If weathered material is transported and deposited
at some other location then the soils are
called Transported Soil. The transporting agency
may be water, wind, glaciers or gravity force.
• When a rock surface gets exposed to atmosphere
for an appreciable time, it disintegrates or
decomposes into small particles and thus soils are
3. Geological Cycle
• Soil is formed by geological cycle.
• The geological cycle consists of the following
• Erosion (Weathering)
5. PHYSICAL WEATHERING
• It is a mechanical process, causing disruption of
consolidated massive rocks in to smaller bits without
any corresponding chemical change. Various
weathering agents are:
• Temperature: The alternate expansion and
contraction of rocks due to variation in temperature
produce cracks. The number of cracks slowly
increases and the rock gets broken in to pieces.
This phenomenon is referred to as ‘exfoliation’. The
dark coloured rocks are subjected to fast changes in
temperature as compared with light colored rocks.
The cubical coefficient of expansion of feldspar and
quartz present in most of the rock is 1 : 2.
6. • Water: In cold region, water freezes in rock
joints and cracks. On freezing, the water
expands in volume by about 9.0 per cent with a
force of 150 tons per square foot. Due to this
tremendous pressure the rock splits and is
broken up into a loose mass of stones. The
moving water has a tremendous transport
capacity which by rolling action grinds the rocks
into pieces. A current moving at a speed of 15
cm, 30 cm, 1.2 m and 9 m / sec can carry fine
sand, gravel, stone (1 kg) and boulders of
several tons, respectively. Water through its
erosion forces removes weathered parts of
rock, thereby exposing fresh surface to
7. • Wind: Wind carrying particles in suspension
and blowing constantly over the rock at great
speed exerts a grinding action, thereby the rock
gets disintegrated. Loosely balanced rock
boulders sometimes roll down by the action of
wind and break in to pieces. At a velocity of 5
m/sec particles of 0.25 mm size are
transported, while at a velocity of 10 m/sec, the
wind can carry particles of 1mm size.
8. CHEMICAL WEATHERING
• Chemical weathering takes place mainly at the
surface of rock minerals with the disappearance
of certain minerals and the formation of
secondary products. This is called chemical
transformation. No chemical weathering is
possible without the presence of water. The
rate of chemical reaction increases with
dissolved carbon dioxide and other solute in
water, and with increases in temperature. The
principal agents of chemical weathering are
• Hydration means chemical combination of
molecules with a particular mineral. Soil forming
minerals occurring in rocks undergo hydration
when exposed to humid condition e.g.
Due to this reaction the minerals increases in
volume and become soft and more readily
• carbon dioxide dissolved in water, it forms
• The carbonic acid or carbonated water attacks
many rocks and minerals and brings them into
solution. Limestone, which is insoluble in water,
is dissolved readily by carbonated water and is
thus, removed from the parent rock.
• Oxidation means addition of oxygen is more active
in the presence of moisture and results in hydrated
oxides. Soil-forming minerals , containing iron,
manganese etc. are more subjected to oxidation,
• A rusty-looking (red) crust is formed on the surface
of the rock. The crust thickens and then slowly gets
separated from the parent rock. As process
continues, the change produced in the mineral
weakens the rock and ultimately the rock itself
crumbles to pieces.
12. • Solution :~ Some of the soluble rock mineral
are washed out from the rocks by rainfall or
percolating subsurface water, thus resulting in
decomposition of rocks an formation of soils.
13. Transportation of Soils
• The agencies responsible for the transportation
of soil particles are,
• By Water
• By Wind
• By Ice (Glacier)
• By Gravity
14. Water transported soils :
• Smooth running of water is capable of moving a
considerable volume of soil.
• Soil may be transported in the form of
suspended particles or by rolling and sliding
along the bottom of the stream.
• Particles transported by water range in size
form boulders to clay.
• Soils that are carried and deposited by water
are called alluvial soil.
16. Wind transported soils :
• Like water, wind can erode, transport and
deposit fine grained soil.
• Soils that are carried and deposited by wind are
called Aeolian soil.
• Large sand dunes are formed by winds. Sands
dunes are a common rather occurrence in the
desert areas of a Africa, Asia and the USA
18. Glacier deposited soils
• Glaciers are deposits of ice formed by the
compaction of snow.
• As the glaciers grow and move, they carry with
them soils varying in size form fine grained to
• Soils get mixed with the ice and are transported
far away from their original position.
• Deposits directly made by melting of glaciers
are called till.
20. Gravity deposited soils :
• Soils transported and deposited by gravity are
called colluvial soil.
• Gravity can transport material for a short
• Gravity are termed as talus.
• They include the material at the base of cliff and
23. Different types of soil
• Alluvial soil :~ Deposited by running water and
are found in river banks and river beds. They
are generally poorly graded and uniformly
• Aeolian soil :~ Deposited by wind, they are
mainly coarse grained particles and poorly
graded. They are found in desert region.
• Lacustrine soil (lake soil) :~ Soil particles
carried by flowing water and deposited in lakes
are called lake soil. These are highly
compressible and have high void ratio but shear
strength is less.
24. • Marine soil :~ Soil particles carried by flowing
water and deposited in oceans and seas are
called marine soil. Its shear strength is better
than lake soil and have high void ratio.
• Glacial soil (Drift) :~ These are the mixture of
stone pieces, silts, sands and clay which are
formed glaciers, these are generally well grade
• Colluvial soil :~ Soil is transported and
deposited by gravity are called colluvial soil.
25. • Cohesive soil :~ Soils in which the absorbed
water and particle attraction act such that it
deforms plastically at different water contents
are known as cohesive soils or clay.
• Black cotton soil :~ In its high percentage of
the clay mineral. It has very low bearing
capacity. It posses high swelling and shrinkage
• Loam :~ It is a mixture of sand, clay and silt.
26. Different types of soils found
• The state is endowed with a wide range of
macro and microclimates, physiography,
landforms, geology and vegetation that have an
influence on the genesis of soil. Soil systems
have developed over many millions of years.
The soil characteristics in a given area at a
given point of time are a function of both natural
influences and human activities. This section
deals with the different types of soils found in
• Black Soil is the most dominant soil type of
Gujarat. Three major variations recorded are:
27. Shallow black soils
• Shallow black soils have been developed from
the basaltic trap in Saurashtra and the Deccan
trap in extreme eastern part while the remaining
strips in Chhotaudepur and Saurashtra districts
have been developed from granite and gneiss
parent material. The depth of soil ranges from a
few cm to 30 cm. (Gujarat State Agricultural
Marketing Board (GSAMB) 2007). Shallow
black soils are light grey in colour and mainly
sandy clay loam in texture. The soil is poor in
28. Medium black soil
• Medium black soils have a basaltic trap parent
material. Such soils in some parts of Sabarkantha
and Panchmahals have been also developed from
the granite and gneiss parent material. These soils
vary in depth from 30 to 60 cm. They are calcareous
in nature except in the Panchmahals and
Sabarkantha districts. A layer of murum
(unconsolidated material of decomposed trap and
limestone) is found below a depth of about 40 cm,
especially in the Saurashtra region (GSAMB 2007).
The soils are silt loam to clay in texture and neutral
to alkaline in reaction. These soils are adequately
supplied with potassium and poorly supplied with
phosphorous and nitrogen.
29. Deep black soils
• The districts of Bharuch, Surat, Valsad and southern
part of Vadodara, and the Bhal region have deep
black soils. Similarly, in the Ghed tract of Junagadh
districts mostly covering the talukas of Porbandar,
Kutiyana, and Manavadar and part of the Mangrol
taluka, the deep black soils have been formed due
to the deposition of basaltic trap materials
transported by the rivers Bhadar, Minsar, Osat
Madhuvanti etc. They have faced the problem of
salinity and alkalinity. They are also impregnated
with a fairly high amount of free lime. The soils are
dark brown to very dark greyish brown in colour.
They contain 40 to 70 percent clay minerals. The
deep black soils, in general, are clay-like in texture,
poor in drainage, and neutral to alkaline in reaction.
These soils are most fertile soil in Black soils.