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Custom Soil Resource Report <br /> O horizon:An organic layer of fresh and decaying plant residue. <br /> L horizon:A layer of organic and mineral limnic materials, including <br /> coprogenous earth (sedimentary peat), diatomaceous earth, and marl. <br /> A horizon:The mineral horizon at or near the surface in which an accumulation <br /> of humified organic matter is mixed with the mineral material. Also, a plowed <br /> surface horizon, most of which was originally part of a B horizon. <br /> E horizon:The mineral horizon in which the main feature is loss of silicate clay, <br /> iron, aluminum, or some combination of these. <br /> B horizon:The mineral horizon below an A horizon. The B horizon is in part a <br /> layer of transition from the overlying A to the underlying C horizon. The B <br /> horizon also has distinctive characteristics, such as (1) accumulation of clay, <br /> sesquioxides, humus, or a combination of these; (2) prismatic or blocky <br /> structure; (3) redder or browner colors than those in the A horizon; or(4) a <br /> combination of these. <br /> C horizon:The mineral horizon or layer, excluding indurated bedrock, that is <br /> little affected by soil-forming processes and does not have the properties typical <br /> of the overlying soil material. The material of a C horizon may be either like or <br /> unlike that in which the solum formed. If the material is known to differ from that <br /> in the solum, an Arabic numeral, commonly a 2, precedes the letter C. <br /> Cr horizon:Soft, consolidated bedrock beneath the soil. <br /> R layer:Consolidated bedrock beneath the soil. The bedrock commonly <br /> underlies a C horizon, but it can be directly below an A or a B horizon. <br /> M layer:A root-limiting subsoil layer consisting of nearly continuous, horizontally <br /> oriented, human-manufactured materials. <br /> W layer:A layer of water within or beneath the soil. <br /> Humus <br /> The well decomposed, more or less stable part of the organic matter in mineral <br /> soils. <br /> Hydrologic soil groups <br /> Refers to soils grouped according to their runoff potential. The soil properties <br /> that influence this potential are those that affect the minimum rate of water <br /> infiltration on a bare soil during periods after prolonged wetting when the soil is <br /> not frozen. These properties include depth to a seasonal high water table, the <br /> infiltration rate, and depth to a layer that significantly restricts the downward <br /> movement of water. The slope and the kind of plant cover are not considered <br /> but are separate factors in predicting runoff. <br /> Igneous rock <br /> Rock that was formed by cooling and solidification of magma and that has not <br /> been changed appreciably by weathering since its formation. Major varieties <br /> include plutonic and volcanic rock(e.g., andesite, basalt, and granite). <br /> Illuviation <br /> The movement of soil material from one horizon to another in the soil profile. <br /> Generally, material is removed from an upper horizon and deposited in a lower <br /> horizon. <br /> 49 <br />