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48c <br />• Soil Permeability The c;uality of a soil layer that enables water, air, <br />or other substances to move through it. The <br />permeability of soil may be limited by the presence <br />of one nearly impermeable layer even though the <br />others are permable. <br />Soil Profile A vertical section of the soil from the surface <br />through all its horizons. Thickness as usually <br />mapped in the soil survey is to 60 inches or to <br />bedrock. <br />Soil Reaction The degree of acidity or alkalinity of a soil, <br />usually expressed as a pH value. <br />Soil Series The basic unit of soil classification being a <br />subdivision of a family and wnsisting of soils <br />which are essentially alike in all major profile <br />characteristics except to texture of the A horizon. <br />Soil Structure The combination or arrangement of primacy soil <br />particles into secondary particles, units, or <br />peels. These secondary units are characterized <br />and classified on the basis of size, shape, and <br />degree of distinctness into classes, types, and <br />grades, respectively. <br />• Soil Taxonomy The classification of soils according to their <br />natural relationships into a formal system of <br />nomenclature. <br />Soil Texture The relative proportions of sand, silt, and clay <br />sized particles in a mass of soil. <br />Subsoil The B horizon of soils with distinct profiles. In <br />soils with weak profile develognent, the subsoil <br />can be defined as the soil below the plowed soil <br />in which roots normally grow. <br />Substratum Technically, the part of the soil below where the <br />processes of soil formation are active (A and B <br />horizons); generally, the parent materials or <br />C horizon. <br />Surface Soil The upperTrost part of the soil profile which <br />generally includes the A-horizon. <br />'ibpsoil Presumably fertile soil material (or parent <br />material) that possesses desirable biological, <br />chemical, and physical properties for plant <br />establishment and growth, which is often used <br />to topdress disturbed lands. <br />• Torric A soil mositure regime defined like aridic rroisture <br />regime but used in a different category of the soil <br />taxonomy. <br />