Soil—the thin, unconsolidated, vertically differentiated
portion of the Earth's surface—is ubiquitous and
often ignored despite its many important environmental
and life-sustaining functions. Soil is necessary
for the production of food, feed, and fiber products,
and supports buildings, roads, and playing fields. Soil
helps to safely dispose of and process biological and
industrial wastes, and it purifies and filters water that
may enter drinking water supplies. Usually, soil performs
more than one of these roles simultaneously.
Soil is in large but finite supply. It varies greatly in
chemical and physical properties both in short distances
and regionally. Some soil components cannot
be easily renewed within a human time frame; thus
the condition of soil in agriculture and the environment
is an issue of global concern. For these reasons,
an effort has been made to distinguish among the
many kinds of soils and identify those best suited for
specific uses. The concept of soil quality stems from
the desire to evaluate soils, match appropriate management
and uses for each soil, and measure changes
in soil properties.
