Background Soil is naturally occurring, unconsolidated or loose material at the surface of the earth, which is capable of supporting plant and animal life. The solid phase which accounts for approximately 50 percent of the volume in a typical soil is a mixture of mineral and organic matter and gives soil its mass. The mineral matter is derived from the weathering of hard rock at the earth's surface. Organic matter is mostly composed of dead plant and animal remains. This decay in the upper layer of soil, or topsoil, is the major source of plant nutrients and other organisms.
Organic matter is what makes a soil fertile.
Soils high in organic matter do not compress as tightly allowing for more air spaces. Organic particles also hold the moisture by absorbing water. Water is held in the small air spaces Utah Agriculture in the Classroom Utah Agriculture in the Classroom between soil particles. Sand does not hold water because there is no organic matter to hold water and because the spaces between particles is large. Approximately 50 percent of the soil is made of pore space .