Soil forms the thin skin of unconsolidated mineral and organic matter on the earth’s surface and functions to maintain the ecosystems on which all life depends. Soil is dynamic, living, natural body that vital to the function of terrestrial ecosystems and represents a unique balance between the living and the dead. The perception that soil is «living», though disputed by some, results from the observation that the number of living organisms in a teaspoon of fertile soil (10g) can exceed nine billion, one and one-half times the human population of the earth. Soil form slowly, averaging 100 to 400 years per centimeter of topsoil, through the interaction of climate, topography, living organisms (microorganisms, animals, plants, and humans) and mineral parent material over time; thus the soil resource is essentially nonrenewable in human life spans ( Jenny, 1980; Lal, 1994) (From Advances in Agronomy, Volume 56, 1996, Copyright ACADEMIC PRESS,INC)