Question

A fertile agricultural soil appears deep coloured at the surface as compared to soil one metre down. The reason for the colour of topsoil is
A. More moisture
B. Rich in organic matter
C. Rich in iron, calcium, magnesium
D. Recent formation

Answer 1

Hint: Soil fertility is a complex quality of soils that is closest to plant nutrient management. It is the part of overall soil production that deals with the availability of nutrient status, and its ability to produce nutrients out of its reserves and through external applications for crop production.

Complete answer:
The dark colour of soil is due to an accumulation of leached organic substances and organic matter which serves as a reservoir of nutrients and water in the soil, aids in reducing compacting and surface crusting, and increases water infiltration into the soil. The organic matter present in the soil is contributed by the death and decay of living organisms.
So, the right answer is Option B (Rich in organic matter).
Additional Information:-
The soil is a habitat for an immense variety of microorganisms, animals, and plant roots. A fertile soil bears healthy crops over generations with its low demand for external inputs such as fertilizers, pesticides, and energy. In fertile soil, soil organisms easily convert nutrients and organic matter into plant yields and increase the plant yield, build up organic matter, protect the plants from diseases, and make the soil highly crumbly. This soil can easily cultivate crops, has a high absorption of rainwater, and withstands capping/siltation and erosion. A fertile soil leads its filtering to clean groundwater and neutralizes acids that reach the ground surface through polluted air. A fertile soil also rapidly breaks down harmful substances such as pesticides and insecticides. A fertile soil Is an efficient reservoir for organic nutrients and carbon dioxide. Thus it prevents over-fertilization of rivers, lakes, and seas and contributes to reducing global warming.

Note: The most important natural soil functions are: production function(yields that suit local conditions), transformation function (Nutrients are efficiently turned in condition). It should have high fertility and should absorb water and reduce erosion.