Topsoil is the surface layer of soil. It is usually 4 to 10 inches (10 to 25 centimeters) deep. The structure and consistency of topsoil encourage the growth of plants’ root systems. Topsoil is rich in material called organic matter, an important source of nutrients for plants and other soil organisms. Topsoil also contains bacteria and other microrganisms that are necessary for plant growth. Because fertile topsoil is required for agriculture, landscaping, and gardening, it ranks as one of our most important natural resources. Hundreds of years may be needed for topsoil to develop. For this reason, the preservation of topsoil is one of the chief goals of soil conservation. See also Conservation (Soil conservation) .
