What is Soil and Why Should We Care?
Soils perform vital functions including sustaining plant and animal life below and above the surface; regulating and partitioning water and solute flow; filtering, buffering, degrading, immobilizing, and detoxifying; storing and cycling nutrients; and providing support to structures. The living systems occurring above and below the ground surface are determined by the properties of the soil. We often ignore the soil because it is hard to observe.
Soil is a natural body comprised of solids (minerals and organic matter), liquid, and gases that occurs on the land surface, occupies space, and is characterized by one or both of the following:
horizons, or layers, that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter or the ability to support rooted plants in a natural environment.
Soil is comprised of
- Mineral matter
- Organic matter
The upper limit of soil is the boundary between soil and air, shallow water, live plants, or plant materials that have not begun to decompose. Areas are not considered to have soil if the surface is permanently covered by water too deep (typically more than 2.5 meters) for the growth of rooted plants.
The lower boundary that separates soil from the non-soil underneath is most difficult to define. Soil consists of horizons near the Earth's surface that, in contrast to the underlying parent material, have been altered by the interactions of climate, relief, and living organisms over time. Commonly, soil grades at its lower boundary to hard rock or to earthy materials virtually devoid of animals, roots, or other marks of biological activity. For purposes of classification, the lower boundary of soil is arbitrarily set at 200 cm (approximately 6 ½ feet).
Physical Properties of Soil are:
- Soil texture
- Soil structure
- Soil color
- Bulk density
Factors that Affect Soil Structure
- Kind of clay
- Amount of organic matter
- Freezing and thawing
- Wetting and drying
- Action of burrowing organisms
- Growth of root systems of plants
It is Important to remember that:
- Soil management affects soil quality
- Soils have unique physical, chemical, and biological properties important to their use
- Soils have limitations that must be understood
Concerns for life and properties include allergies, contaminants, corrosivity, crop loss, dust, erosion, flooding, frost action, gypsum dissolution, liquefaction, piping, radon, rapid runoff, salt build up, sand blowing, sedimentation, septic failure, shrink-swell, sinkholes, slope failures, soil-borne disease, subsidence, sulfidic materials, urban hydrology, and water tables.
Soil health, is defined as how well soil does what we want it to do. Healthy soil gives us clean air and water, bountiful crops and forests, productive grazing lands, diverse wildlife, and beautiful landscapes. NRCS has developed a series of web pages that include an online Soil Biology Primer, soil quality indicators and assessment, and soil quality management for major land uses. The publications section provides numerous fact and information sheets, NRCS technical notes, and posters for training and display.
The ultimate purpose of researching and assessing soil quality is not to achieve high aggregate stability, biological activity, or some other soil property. The purpose is to protect and improve long-term agricultural productivity, water quality, and habitats of all organisms, including people. We use soil characteristics as indicators of soil quality, but in the end, soil quality must be identified by how soil performs its functions.
NRCS has launched Web Soil Survey 3.0, which can be accessed at http://websoilsurvey.nrcs.usda.gov. The web-based application provides a wealth of free soils information along with soil maps, properties, and interpretations aimed at helping with land use decisions. The web site, originally launched in August 2005, continues to improve and enhance features to meet the demands of its growing customer base.