Soil Profile: A vertical section of the Earth's highly weathered upper surface often showing several distinct layers or horizons.
This soil profile was is located in the piedmont near Danville, Virginia. It was eroded by agriculture and has an almost indiscernible A horizon.
In technical terms topsoil is described as the "A horizon" of a soil profile. It is a porous (allows water to move through it) mixture of decomposed organic matter (called humus) and some inorganic mineral particles (mostly rock fragments).
A-Horizon - The uppermost zone in the Soil Profile, from which soluble Salts and Colloids are leached, and in which organic matter has accumulated. Generally this represents the most fertile soil layer and constitutes part of the Zone of Eluviation.
The physical constitution, particularly the structural properties, of a soil profile as exhibited by the kinds, thickness, and arrangement of the horizons in the profile, and by the texture, structure, consistence, and porosity of each horizon. 2.
deep percolation Water that moves downward through the soil profile below the root zone and cannot be used by plants.
deep percolation loss Water which percolates downward through the soil beyond the reach of plant roots.
Unsaturated Zone: portion of the soil profile which contains both air and water. Water in this zone cannot enter a well.
Vector: a carrier, typically an insect or rodent, capable of transmitting a disease.
 See also: Drainage, Soil, Organic, Table, Water
  
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