Minerals of soil are derived from

The soil near the surface is usually darker than the soil below it. This is because the topsoil is .....

Which one is the main source of minerals essential for man and other organisms?

The $O$ soil layer is rich in:

Select the correct statements regarding the role of soil:
$(I)$ Soil is a reservoir of essential elements.
$(II)$ Soil not only supplies minerals but also harbours nitrogen-fixing bacteria.
$(III)$ Soil acts as a matrix.
$(IV)$ Soil holds water and supplies air to the roots.

Soil is a mixture of