Soil & its formation by Muhammad Fahad Ansari 12IEEM14

SOIL & ITS FORMATION

Muhammad Fahad Ansari

12IEEM14

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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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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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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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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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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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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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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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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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TYPES OF SOILThere are different types of soil they are as

under:1. 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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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Maintaining crop cover Field embankments Tillage to an appropriate depth Effective mulching Water disposal system

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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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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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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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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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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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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.