SOIL

What is the need of soil ?

It is needed for:-

Holding the roots firmly Supplying water and nutrients

Soil formation

Temperature changes Frost Water Wind Living organisms

WEATHERINGFactors responsible for weathering

Temperature changes

Rocks expand when heated and contract when cooled.

Frost

Rainwater may become trapped in small crevices of the parent rock. In winter this water freezes to ice. The ice expands producing a lateral pressure,causing the crevices in the rock to further open up.

Water

Continual movement of rain and river water, in liquid form,causes breaking down of rock particles into finer particles.

Interesting fact!

A rock has energy in several ways. Assuming it's sitting still, a rock may have gravitational potential energy because of gravity pulling on it. It has energy stored in the chemical bonds in the molecules of the rock. Also, if the rock has some charge on it(its a possibility), it could have electrical potential energy if it was in an electric field. Then of course there is the rest energy of the rock. According to relativity(E=mc^2), the rock has some energy just by being massive.

Interesting fact!

rocks do have potential energy. Potential energy is defined as energy stored within a physical system. It is called potential because it has the potential to be converted into other forms of energy, such as kinetic energy which can do work in the process.

This means that a rock can have potential energy as simple as, a rock held at an elevation. If dropped it's potential energy is then being converted to kinetic energy.

Wind

Wind blowing across a rock surface has an abrassive affect on the rocks.

Living organisms

Weathering by living organisms is called biological weathering

Soil profile

The term used for the vertical section of soil to show the different layers or horizons of soil.

A-horison-top soil

Darkest in colour Rich in humus Very fertile Soft,porous Roots of plants are present Living organisms are present

B-horizon-sub soil

Lighter in colour Harder and more compact than the A-

horizon Rich in soluble minerals and iron oxides Remains of plants and animals are not

found Roots of tall plants reach Little organic matter found

C-horizon-parent material

Beneath c-horizon is the bed rock

Composition of soil

Rock or different types of soil Humus Soil water Soil air Soil organisms

Soil particles and soil types

Soil particles-gravel ,sand and clay Soil types-loamy, clayey and sandy

Sandy soil

Highly porous Large particles Well aerated Holds less water Dry

Clayey soil

Very little air Particles are smaller and tightly packed Holds enough water Contains humus.

Loamy soil

Different sized particles Contain humus Hold sufficient water Contain enough air

Humus

Soil water

Gravitational water

Capillary water

Soil air

For the respiration of roots and soil organisms

Soil organisms

Earthworms burrow the soil Micro-organisms release the minerals

back to the soil Some bacteria fixes nitrogen

Soil organisms

Soil colour

White Grey Yellow Red Black

Soil and crops

Clayey soil -wheat ,gram and paddy Loamy soil -Lentils and other pulses Sandy soil -cotton

Clayey soil

Wheat paddy gram

Loamy soil

Sandy soil

Cotton

Soil erosion

Deforestation

Due to over population

Over grazing

Destroys vegetation Results in barren

land

Poor farming methods

Forest fires

After fire soil is exposed to wind and water

Prevention of soil erosion

Afforestation Plant trees along the boundaries of the

field Crop rotation Proper drainage and irrigation

Afforestation

Plant trees along the boundaries

To reduce the effect of winds

Crop rotation

Proper drainage and irrigation

Terrace cropping

Reduces the steepness Checks the soil erosion

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