Explain how soil is formed ? (viil) समतल दर्पण द्वारा बने प्रतिबिम्ब के अभिलक्षण लियो। State the characteristics of the image formed by plane mini IC V Section - Q.No.4वीर्य वरीयन Long answer type question (1) उस कार्योहाइड्रेट का नाम लिखिए जिसका पाचन रुमिनेन्ट द्वारा किया 5 (7
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Answer:
Soil is the thin layer of material covering the earth’s surface and is formed from the weathering of rocks. It is made up mainly of mineral particles, organic materials, air, water and living organisms—all of which interact slowly yet constantly.
Most plants get their nutrients from the soil and they are the main source of food for humans, animals and birds. Therefore, most living things on land depend on soil for their existence.
Soil is a valuable resource that needs to be carefully managed as it is easily damaged, washed or blown away. If we understand soil and manage it properly, we will avoid destroying one of the essential building blocks of our environment and our food security.
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Soil profile showing the different layers or horizons.
The soil profile
As soils develop over time, layers (or horizons) form a soil profile.
Most soil profiles cover the earth as 2 main layers—topsoil and subsoil.
Soil horizons are the layers in the soil as you move down the soil profile. A soil profile may have soil horizons that are easy or difficult to distinguish.
Most soils exhibit 3 main horizons:
A horizon—humus-rich topsoil where nutrient, organic matter and biological activity are highest (i.e. most plant roots, earthworms, insects and micro-organisms are active). The A horizon is usually darker than other horizons because of the organic materials.
B horizon—clay-rich subsoil. This horizon is often less fertile than the topsoil but holds more moisture. It generally has a lighter colour and less biological activity than the A horizon. Texture may be heavier than the A horizon too.
C horizon—underlying weathered rock (from which the A and B horizons form).
Some soils also have an O horizon mainly consisting of plant litter which has accumulated on the soil surface.
The properties of horizons are used to distinguish between soils and determine land-use potential.
Factors affecting soil formation
Soil forms continuously, but slowly, from the gradual breakdown of rocks through weathering. Weathering can be a physical, chemical or biological process:
physical weathering—breakdown of rocks from the result of a mechanical action. Temperature changes, abrasion (when rocks collide with each other) or frost can all cause rocks to break down.