Muhammad Fahad Ansari 12IEEM14

1. SOIL & ITS FORMATION
Muhammad Fahad Ansari
12IEEM14

2.  Soil is a thin layer of material on the Earth's
surface in which plants have their roots.
 It is made up of many things, such as
weathered rock and decayed plant and
animal matter.
 Soil is formed over a long period of time.
 Soil Formation takes place when many things
interact, such as air, water, plant life, animal
life, rocks, and chemicals.
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4. SOIL & ITS FORMATION
 Soil is a home for many organisms.
 Some of these organisms such as
earthworms aerate the soil and contribute to
its formation.
 All organisms that live in the soil are vital to
the energy and nutrient cycles of the Earth.
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5.  Wherever rock is exposed to changing
conditions, either at or near Earth’s surface, it
will break down, or weather into smaller and
smaller fragments.
 Therefore when the igneous, metamorphic
and sedimentary rocks of the lithosphere
weathers and disintegrates, they provide the
material needed to build soil.
 While the area of bedrock that is the source
of soil is called the soils’ parent rock.
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6.  The exposed outer layer of a rock is the most
unprotected and easily weathered layer.
 It is the outer layer that begins to change in
structure, with cracks and holes beginning to
develop.
 With time and further weathering cracks and
holes reach deeper and deeper into the
bedrock and the outer layer breaks into
smaller mineral particles.
 Finally these fragmented particles results in
the formation of soil.
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7.  The soil is a mixture of mineral particles, air,
water, bedrock and living & decaying
organisms.
 This soil formation takes hundreds of
thousand years.
 The organic activity of plants and animals can
also influence the weathering and structure of
soil and bedrock.
 Burrowing animals and plant roots
mechanically break down bedrock and aerate
the soil.
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8.  Many soil organisms aerate enough for water
and air to reach deeper into the soil.
 Water and air carry with them agents of
chemical weathering, such as carbon dioxide
and oxygen.
 When soil organisms die they again
contribute to the soil by becoming the organic
material.
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9.  With weathering processes, distinct layers of
weathered bedrock become apparent.
 These layers form what are known as the A,
B, C and R horizons in a mature soil profile.
 A soil profile is a vertical cross-section of soil
from the ground surface down to the bedrock.
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10.  The A – horizon in a soil profile is commonly
known as the topsoil.
 The B – horizon is often called the sub –
soil.
 However, the C – horizon is a layer of
partially weathered bedrock.
 The R – horizon is the bedrock.
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12. TYPES OF SOIL
There are different types of soil they are as
under:
 Loamy Soil:
 It is the ideal soil for cultivation.
 It is a very good blend of sand, decayed
vegetable and animal matter (Humus).
 This kind of soil holds moisture well, drains it
well too and is easy to work with.
 It is dark brown or black in colour.
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13. 2. Sandy Loam:
 This type of soil contains higher percentage
of sand – 50% sand and 50% humus & clay.
 Though it is not perfect, it is not that bad to
work with.
 The water drains a little faster from sandy
loam.
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14. 3. Clay Loam:
 As the name suggests, this kind of soil
contains a higher percentage of clay.
 It is difficult to work with when wet.
 But it holds plant food and moisture well and
will not need frequent watering.
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15. 4. Sandy:
 Sandy soils contain 80% or more sand.
 This kind of soil will need plenty of watering
since the sand will not retain moisture.
5. Clay:
 Soils, which contain 30% or more of clay, are
known as clay soils.
 They drain badly and become easily
waterlogged.
 When dry they do not let the roots penetrate.
 They are heavy and difficult to work with
either way, when dry or wet.
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16. SOIL EROSION & CONSERVATION
 Erosion is the removal of soil particles by the
motion of wind or water.
 Soil erosion is one of the major concerns of
modern agriculture throughout the world.
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17. The factors, which are responsible for the
erosion includes:
 Misuse of Land
 Mismanagement of arable Land
 Indiscriminate felling of trees
 Overgrazing
 Poor soil and water management
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18.  Erosion causes a decline in soil fertility, water
supply and crop yields.
 Thus it affects the productivity of the land,
which decreases the production of food, feed
and fibre.
 This adversely affects the socio – economic
conditions of the state.
 In addition erosion also causes floods, silting
up of water reservoirs, disruption of
communication systems and disturbance of
the socio economic set-up of the farming
community.
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19. Erosion is of two types:
1. Normal or Geological Erosion
 Erosion effects are not visible on the land
surface, nor is soil productivity adversely
affected.
 In quantitative terms, the amount of soil lost
is equal to the amount of soil formed.
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20. 2. Accelerated Erosion
 The effects of erosion are visible on the
ground surface.
 The rate of soil loss is greater than the rate of
soil forming.
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21. Magnitude of Erosion Problems in Pakistan
 The total area of Pakistan is 79.61 million
hectares.
 20.61 million hectares are cultivated,
 3.16 million hectares are under forest and
 11.10 million hectares are not available for
cultivation.
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22.  According to one estimate wind and water
erosion affect over 76% of the country’s total
area.
 Over 36% is being eroded by water and 40%
by wind.
 About 14000 hectares go out of cultivation
due to erosion annually.
 Every year approximately one billion tonnes
of soil is being lost.
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23.  Wind erosion has led to desertification of vast
areas of Thal, Cholistan, Muzaffargarh and
Dera Ghazi Khan in Punjab.
 Thar in Sindh and vast areas of Baluchistan
where rainfall is low, summer temperatures
are high and the soil is loose and sandy.
 Water erosion is prevalent in the northern
hilly areas and the Pothohar Plateau.
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24. Mechanics of Water Erosion
 The first impact of raindrop on the soil is the
breaking up of soil clods.
 This can only occur if there is no vegetative cover.
 When raindrops fall on bare, unprotected soil, soil
clods are broken into small particles, which are
suspended in the accumulated water.
 Some of the muddy suspension flows down the
slopes in the form of runoff and part of it percolates
downwards into the soil.
 The continuous deposition of solids seals the soil
pores and the further intake of water ceases.
 Consequently more water is lost as runoff.
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27. 1. Rain drop or splash erosion
 The raindrops strike the soil surface with
great force.
 Aggregates and clods are broken into smaller
particles, which are splashed into the air, and
the surface layer of the soil is compacted and
puddle.
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29. 2. Sheet erosion
 Sheet erosion is the removal of a thin
layer of soil by water acting over the whole
surface.
 Sheet erosion damages very fertile lands
located on slopes.
 These cause great economic loss
because it results in loss of the most fertile
soil layer and diminishes soil productivity.
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30. 3. Rill erosion
 The appearance of small rivulets on
the soil surface is called rill erosion.
 This is a transitional phase between
sheet erosion and gully erosion.
 These small channels can be
smoothed out with suitable tillage
practice and proper management.
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31. 4. Gully erosion
 It is the final stage of water erosion and is
the result of constant neglect of the land.
 Gullies are active as long as their sides
are bare.
 They become inactive when they have
been stabilized by vegetation.
 Gully erosion causes much more loss
than any other form of erosion.
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32. Prevention of Water Erosion
 Previously, soil conservation referred mainly
to the prevention and control of erosion.
 Today, however, the approach is broader and
includes:
 Proper land use,
 Maintenance of soil fertility,
 Conservation of cultivated land,
 Rehabilitation of eroded land and
 Protection of land from all kinds of
degradation.
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33.  The sole objective behind the prevention
of water erosion is the conservation of soil.
 That is why the following four basic
principles are adopted for the purpose.
 Use land according to its capability.
 Retain rainwater
 Minimize runoff
 Store surplus water
 Maintain soil fertility
 Use of non – arable lands effectively
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34. Conservation of Arable Lands
 The cultivated area should be managed in
such a way that it remains productive on a
sustained basis.
 The conservation of cultivated area should
aim at reduction in the quantity and
velocity of runoff and its safe disposal.
 This can be achieved by adopting the
following practices.
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35.  Maintaining crop cover
 Field embankments
 Tillage to an appropriate depth
 Effective mulching
 Water disposal system
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36. Wind Erosion
 Wind erosion is a serious problem of dry land
regions.
 It is mainly encountered in areas where:
 Soils are loose and dry
 Soil surface is smooth and bare
 High velocity winds are frequent
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38.  The affected areas have characteristic sand
dunes, dry soil, and annual rainfall less than
150 mm and spare vegetation.
 Moving sand dunes are a great threat to the
adjacent cultivated lands, field crops,
communication, etc.
 Windstorms and dust storms not only disrupt
the means of communication but also cause
great inconvenience to human beings and
livestock.
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39. Types of Soil Movement
 There are three distinct types of soil movement,
which depend upon the size of the soil particles.
1. Suspension:
 Suspension is the movement of very fine particles,
which are less than 0.1 mm in diameter.
 The soil particles are so small that once they are
lifted into the air stream, they remain suspended in
the air for a long time by the turbulence and eddy
currents of the air and are carried for a long way.
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40. 2. Creep:
 Creep is the movement of soil particles
greater than 0.50 mm in diameter.
 These particles are not lifted in the wind
stream but are rolled along the surface of
the ground, pushed by the force of the
wind and other particles carried by the
wind.
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41. 3. Saltation:
 Saltation is the most important of all the
three types of movement.
 Particles of 0.05 – 0.5 mm diameter move
mainly by saltation.
 The particles are lifted in the wind stream
and again fall down, moving by short leaps
and bounces.
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42. Control of Wind Erosion
 The following methods are suggested as the
basis for wind erosion control.
 Improvement in the physical conditions of the
soil
 Making it more resistant to erosion
 Reduction in wind velocity
 Establishment & maintenance of barriers,
vegetative covers and residues for the
protection of soil.
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