Soils

VIVEK SRIVASTAVAM.Tech

Indian Space Research Organization

SoilSoil is the uppermost layer of Earth’s crust.

Soil is the medium in which plants grow and thus it supports the lives on earth.

The Study of Soil (Pedology)How soils are formed?

Soils are formed due to the weathering of rocks.WHAT IS SOIL?

Soil is the thin layer of loose mixture of small rock particles and rotting organic matter that covers much of the world’s

land surface.

SOIL FORMATION

Soil formation is a very long process. It begins with the weathering of rocks into small fragments. The rocks are also worn away by the agents of erosion like river, wind, sea and glacier. The sediments and tiny rock particles are then deposited by the agents of erosion. The accumulation of such sediments over the ages forms soil. Eventually, the plants that grow on the soil, shed their leaves which decay to form the topmost layer of soil called 'humus'. India is primarily an agricultural country. The success of agriculture depends upon the fertility of soils. The soils of India are classified into the following main groups depending upon the rock cover and climatic conditions.The most two important factors that determine the types of soil found in India are : i. The climate ii. The topography

•Soil is made up of mineral grains.

•Water is held between the grains in the pore spaces.

•25% of the soil is air. Oxygen is essential

•Organic matter is both coarse and fine.

•Bacteria- A thimble of soil can contain 2 billion bacteria, 30 million fungi fragments and 100,000 single cell plants and animals.

A. Parent Material – type of rock that soil is made from.B. Climate – temperature & moistureC. Living organisms – organisms (bugs & worms) and plants in the soil.D. Topography – hills and valleysE. Time or weathering – age of the soil and climate

Five factors that affect soil formation

Weatheringbreaks down rocks to create soil.

It can be caused by weather, water, or living things

EROSIONis the movement of sediment and

rock to new places.

Humus gives the topsoil a rich brown color

Leaching takes minerals carried by water to the subsoil

In a mature soil profile, there are three distinct layers(horizons) of the soil. The undisturbed rock below the soil is called the bedrock. The Ao-horizon consists of the highly decayed organic material referred to as the peat and humus. Humus gives soil horizon A a rich brown color. We see no such brown layer in the Pine Barrens.

In the A horizon, water percolates downward and carries minerals as it goes. This is called “leaching.”Leaching carries minerals down into the lower soil horizons.

The B-Horizon is called the subsoil.This horizon is where the leached minerals from horizon A end up.These leached minerals may color the subsoil. For example, the presence of iron my color the subsoil red.Horizon B-Zone of Accumulation of leached minerals

The C-horizon is called the zone of weathered bedrock. When you have a residual soil, one formed over the original bedrock, the C-horizon resembles the bedrock, but it is weathered. In a residual soil, the bedrock is below the C-horizon.Remember that the Coastal Plain does not have bedrock under the soil profile, but it has layers of sand, clay and gravel. That is because of the sea level changes over time and the rivers that flowed over it.

Soils Perform Several Vital Functions

Sustaining plant and Sustaining plant and animal life below and animal life below and above the surfaceabove the surface

Regulating and Regulating and partitioning water and partitioning water and

solute flowsolute flow

Filtering, buffering, Filtering, buffering, degrading, immobilizing, degrading, immobilizing, and detoxifyingand detoxifying

Storing and cycling Storing and cycling nutrientsnutrients

Providing support to Providing support to structuresstructures

There are five components of soil:

• 1. Rock• 2. Sand• 3. Silt• 4. Clay• 5. Humus

• Can you match each type of soil to its picture?

RockRock is solid and made of minerals

SandSand is tiny grains of worn down rock. It

doesn’t hold water or have many nutrients.

Silt

Silt is very small, broken pieces of rock. It is larger than clay, but smaller than sand. It

is powdery when dry.Sand ------------Silt---------------Clay

(larger particles) (smaller particles)

CLAYClay holds water well. It is sticky and can be

shaped when it is wet. But, it is very hard when dry.

Clay has many nutrients.

Clay is used for adobe or brick houses.

Humus

Humus is made of leaves, twigs, small animals, or other decayed substances.

Humus adds many nutrients to the soil.

Humus is in the topsoil.

Physical Features of soilSoils have many features that are used to

recognize the difference between them. They include:A. Texture – coarseness of fineness of soil

particlesB. Structure – the way in which soil particles are held togetherC. Depth of horizons – depth of each soilD. Color – darkness or lightness of soil color

The major soil types found in India

Black Soil Black soils are mainly found over the Deccan lava tract (Deccan Trap) including Maharashtra, Madhya Pradesh, Gujarat and Andhra Pradesh. These soils are found in river valley of Narmada, Tapi, Godavari and Krishna. These soils have been formed due to the weathering of the lava rocks. This is also known as the Regur soil and Cotton soil. These soils are rich in lime. iron, magnesia and alumina but lack in the phosphorus, nitrogen and organic matter.RED SOILThese soils are found in Chhotanagpur plateau, Telangana, Nilgiris, Tamil Nadu, Karnataka, Andhra Pradesh and periphery areas of Deccan Plateau. These soils have been formed due to decomposition fo underlying igneous rocks under heavy rainfall. These are suitable for the cultivation of millets, pulses. Lin-seed, tobacco etc. These soils are poor in Lime, Nitrogen and humus.

LATERITE SOILThese soils are formed under conditions of high temperature and heavy rainfall with alternate wet and dry periods. Thus its formation takes place strictly under monsoon conditions.Residual soils formed by leaching in areas of heavy rain.Leaching is a process in which the nutrients get percolated down below the soil due to heavy rainfall; thus leaving the top soil in Fertile. Also called DESILICATION..These soils are found in the north- eastern state of Meghalaya in India.It is red due to the presence of iron oxide which is formed by leaching. The soluble plant foods like potash are removed from the top soil leaving alumina and iron oxide. ALLUVIAL SOILSIt covers about 40 percent of land area of the country. They are depositional soils, transported and deposited by rivers and streams. Through a narrow corridor in Rajasthan, they extend into the plains of Gujarath. These soils are formed by the deposition of fine sediments and silt by the rivers along their banks. In India, alluvial soils are mostly found in the Great Northern Plains, the coastal plains and river deltasTypes (a)Young Khadar soils: these are newer alluvium of sandy, pale brown composition, (b) Old Bhangar soils: these consist of older alluvium

DESERT SOILThese soils cover 2 lakh sq. km areas in dry areas of Rajasthan, Gujarat, Punjab, and Haryana. These coarse soils are suitable for cultivation of jowar, bajara, cotton etc.ARID AND DESERT SOILSLarge part of arid and semi-arid region of Rajasthan and adjoining areas of Punjab and Haryana Desert soils are found in arid regions which receive very little rainfall.Saline and Alkaline Soils: These soils are found in the dry and marshy areas. These are locally known as Bhur, Rehu, Kallar. The accumulation of salts makes these soils infertile. Mountain Soils:Mountain soils are found in, as the name suggests, in mountainous regions. They are quite prone to soil erosion as a result of the top soil getting washed away due to the steep slopes of the mountains after a period of heavy rainfall. These soils are mostly thin and infertile. These include peat, meadow and forest hill soils. MARSHY SOILFound in continuously water-logged areas, or marshy areas especially in the coastal regions near the sea or near the deltas.

Natural Resources

• Made by NATURE• Cannot be replaced• Must be conserved (saved)!

Ways to Conserve Soil

• Plant trees• Plant grass• Healthy farming• Plant gardens to grow crops

• What else can you do to conserve soil?

Have a nice day!