Question

The top soil is darker and
A. Is drier than subsoil
B. Is richer in Na and Mg
C. Is better than subsoil
D. Contains more organic matter

Answer 1

Hint: Soil is a natural resource. It covers the earth’s surface and is rich in minerals, organic matter, etc. Soil acts as a shelter for many small microorganisms including bacteria, decomposers etc. On the basis of texture, soil can be categorized as sand, silt and clay.

Complete Answer:
The top soil is darker and contains more organic matter. Soil is a natural resource that covers earth's surface. When we dig the earth surface deep we find different layers of soil called soil profiles.
The simplest soil consists of three layers namely top soil, subsoil and bedrock.
(a) Topsoil: Topsoil is also called the A-horizon. It contains a large quantity of organic matter and soil is darker in appearance. When organisms die or when plant parts fall into the soil, they are present in this layer and get decomposed by the action of decomposers. This dead and decaying matter present in the soil is called humus. It gives dark color to soil.

(b) Subsoil: Subsoil is called B-horizon. This layer consists of soluble minerals and has an accumulation of clay. Subsoil is light brown in appearance and it has more water holding capacity than top soil due to presence of iron and clay minerals. As it is found below subsoil the organic material is less found.

(c) Bedrock: Bedrock is also known as the C-horizon. It is a layer of partially altered rock. It is found much below the depth of earth's surface. The process of weathering takes place in this layer. Weathering is the process of breaking or decomposition of rock.

Therefore, from the above explanation the correct option is (D).

Note: The study of soil is called pedology. Pedology aims at understanding characteristics of soil. Humus found in topsoil is a carbon-rich compound and it imparts dark colour to topsoil.