Olympiad Test: Soil - UPSC MCQ

The uppermost fertile layer of the earth's crust is called:

         2. Humus

Humus is the organic component of soil, formed by the decomposition of leaves and other plant material by soil microorganisms. It is rich in nutrients and is crucial for soil fertility and plant growth.

The amount of water retained by soil per unit volume is called as water holding capacity. It is highest in the clayey soil.

In addition of the rock particles, the soil contains minerals, organic matter, air and water.

The decayed organic matter in the soil form humus which is black in colour.

The process of removal of top soil due to action of air, water etc. is called soil erosion.

Volcanic soils are soils in which more than half of the parent mineral matter is volcanic ash ans appear very dark in colour.

The process of breaking down big pieces of rock into smaller pieces is called weathering.

Type of soil depends upon the rock from which soil is formed. Basaltic rock forms the black soil.

The soil suited for cultivation of wheat, rice and sugarcane is called alluvial soil.

C - horizon is just above the bedrock which is made of rocks and thus weathering takes place in the C - horizon.