Question 1 Define the term Paedogenesis?

Question 2 What do you mean by weathering of soil?

Question 3 How sun causes weathering of soil?

Question 4 How Water causes weathering of soil?

Question 5 How wind causes weathering of soil?

Question 6 What are the chemical methods of weathering of soil?

Question 7 What are the biological methods of weathering of soil?

Question 8 What is humus?

Question 9 How a quality of soil is judged?

Question 10 What are the three ways of weathering of soil?

Mineral Riches in the soil
The outermost layer of our earth is called crust.
The minerals found in this supply a variety to life form.These minerals will not be available to the organism if they are bound in huge rocks.
Over a long period of time,thousand and millions of years,the rocks at or near the surface of earth are broken down by various physical,chemical and biological processes.
The end product of this breaking down is fine particles of soil.

Formation of soil
1)Weathering of soil:Breaking of bigger rocks into fine smaller mineral particles.This is done in 3 ways:

Physical(Sun,water,wind etc)
Sun:It heats up rocks during the day so that they expand.At night these rocks cool down and contract.Since all parts of rock do not expand and contract at same rate,this result in the formation of cracks and ultimately the huge rock breaks up into smaller pieces.
Water:It could get into the cracks in the rocks formed due to the uneven heating by the sun.If this water later freezes,it would cause cracks to widen.
Flowing water wears away even hard rock over long period of time.Fast flowing water often carries big and small particles of rock downstream.These rocks rub against other rocks and resultant abrasion causes the rocks to wear down into smaller particles.The water then takes these particles along with it and deposit it further down its path.
Wind:Strong wind also erode rocks down.The wind also carries sand from one place to the other.

It involves a variety of chemical processes such as hydrolysis,hydration,oxidation,reduction.
It involves breaking down of complex compounds by carbonic acid present in water and by acidic substances derived from decomposition process of organic matter in soil.


Lichens,mosses and other plants live on rocks and produce acids,which accelerate the process of rock weathering.

Paedogenesis:This process involve decomposition process by bacteria and fungi by which organic materials are broken down and leads to humification and mineralization.Various organism consume organic matter and add excretory nitrogen to it.Thus addition of organic matter from dead and decomposed plants and animals is final stage in formation of soil.

Soil contains:
1)Small particles of rocks
2)Bits of decayed living organism called humus
3)Various forms of microscopic life

Type of soil is decided by average size of particles found in it.
Quality of soil is decided by amount of humus and microscopic organism found in it.Humus is a major factor in deciding the soil structure because it causes the soil to become more porous and allows water and air to penetrate deep underground.

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