Question

Composition of soil depends on the nature of parent rock and the quantity and type of organic materials present in it. The following components are generally found in a soil:

(1) Inorganic substances: Most of the inorganic substances, present in the soil, are derived from the parent rock.

(2) Organic material (Humus): Humus increases the productivity and water holding capacity of the soil.

(3) Soil water: It is generally present in the spaces between the soil particles. The water content of a soil has a significant effect on plant productivity.

(4) Soil air: Spaces, between the soil particles, contain air. Well aerated soils are associated with healthy roots that increase crop productivity. Soil air is important for the respiration of roots. 

(5) Living organisms: A variety of organisms are found in soil. They include micro-organisms like bacteria, fungi and algae.