Soil is a dynamic medium in which many chemical, physical and biological activities go on constantly. It is a result of decay and also serves as a medium for growth.

Soil is a changing and developing body. It has many characteristics that fluctuate with the seasons. It may be alternatively cold and warm or dry and moist. Biological activity is slowed or stopped if the soil becomes too cold or too dry.

Organic matter increases in soil when leaves fall or grasses die.