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Soil profile

Soils for the most part consist of a mixture of particles of three sizes called sand, silt and clay. The most desired soil on average will contain 45% minerals, 25% water and 5% organic matter from decomposition of plants and animal material.[1]

Soil is the product of five formation factors; parent material, climate, biota, topography, and time. It is defined as any loose or unconsolidated material on the uppermost surface of the Earth that is capable of supporting life. Soils develop slowly over time and form distinctive layers or horizons. A soil has many diagnostic properties, dependent upon the quality of factors acting on the genesis of the soil. Of the many properties of soil the main ones include texture, structure and color.

Soil structure is the size, shape, and arrangement of particles into characteristic shapes or peds. When the sample is moist, a soil with strong structure will naturally break into smaller shapes of the original piece. Soils with weak structure are described as massive and the shape of broken pieces do not resemble the ped from which it was broken. Structure shape can be described as granular, blocky, prismatic, columnar, platy, and massive.

Soil texture is the proportion of sand, silt and clay particles. The particle sizes are determined by diameter; sand being 2 - 0.05 mm, silt 0.05 - 0.002 mm while clay is less than 0.002 mm. Texture can be determined through particle size analysis and the textural triangle. The textural triangle separates texture into twelve classes ranging from sand to clay.


Soil scientists study the chemical, physical, biological, and mineralogical composition of soils as it relates to plant growth. They also study the responses of various soil types to fertilizers, tillage practices, and crop rotation. Many soil scientists who work for the Federal Government conduct soil surveys, classifying and mapping soils. They provide information and recommendations to farmers and other landowners regarding the best use of land and plants to avoid or correct problems, such as erosion. They may also consult with engineers and other technical personnel working on construction projects about the effects of, and solutions to, soil problems. Because soil science is closely related to environmental science, persons trained in soil science also work to ensure environmental quality and effective land use.[2]


Sewage management systems such as leach fields around septic tanks are made useful because of the effectiveness of soil in filtering contaminants and preventing harmful migration of contaminants.

Burial of general waste at landfills and of corpses at cemeteries and other burial sites is an effective practice for prevention of disease.


  1. The Dirt on Soil Discover School
  2. Occupational Outlook Handbook, 2008-09 Edition: Agricultural and Food Scientists by the U.S. Bureau of Labor Statistics.

See Also