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Custom Soil Resource Report <br />Pedon <br />The smallest volume that can be called "a soil." A pedon is three dimensional and <br />large enough to permit study of all horizons. Its area ranges from about 10 to 100 <br />square feet (1 square meter to 10 square meters), depending on the variability of <br />the soil. <br />Percolation <br />The movement of water through the soil. <br />Perennial water (map symbol) <br />Small, natural or constructed lakes, ponds, or pits that contain water most of the <br />year. <br />Permafrost <br />Ground, soil, or rock that remains at or below 0 degrees C for at least 2 years. It <br />is defined on the basis of temperature and is not necessarily frozen. <br />pH value <br />A numerical designation of acidity and alkalinity in soil. (See Reaction, soil.) <br />Phase, soil <br />A subdivision of a soil series based on features that affect its use and <br />management, such as slope, stoniness, and flooding. <br />Piping <br />Formation of subsurface tunnels or pipelike cavities by water moving through the <br />soil. <br />Pitting <br />Pits caused by melting around ice. They form on the soil after plant cover is <br />removed. <br />Plastic limit <br />The moisture content at which a soil changes from semisolid to plastic. <br />Plasticity index <br />The numerical difference between the liquid limit and the plastic limit; the range <br />of moisture content within which the soil remains plastic. <br />Plateau (geomorphology) <br />A comparatively flat area of great extent and elevation; specifically, an extensive <br />land region that is considerably elevated (more than 100 meters) above the <br />adjacent lower lying terrain, is commonly limited on at least one side by an abrupt <br />descent, and has a flat or nearly level surface. A comparatively large part of a <br />plateau surface is near summit level. <br />44 <br />