The substance of soil is a complex mixture of minerals, organic matter, microorganisms, water, and gases. The mineral component of soil is derived from the weathering of rocks, while the organic matter comes from plants and animals that have died and decayed. Microorganisms play a vital role in soil by decomposing organic matter and releasing nutrients into the soil. Water and gases are essential for plant growth and other soil processes.

The composition of soil varies depending on the type of rock from which it is derived, the climate, and the vegetation. Sandy soils are composed mostly of sand particles, while clay soils contain more clay particles. Loam soils are a mixture of sand, silt, and clay. Organic matter content can vary from a few percent to several percent. The pH of soil can range from very acidic to very alkaline.

Soil is a dynamic system that is constantly changing. As plants grow and die, organic matter is added to the soil. Microorganisms decompose this organic matter, releasing nutrients into the soil. Water and gases move through the soil, carrying nutrients and oxygen to plant roots. The composition of soil can also be affected by human activities, such as agriculture, construction, and mining.