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Custom Soil Resource Report <br />Hillslope <br />A generic term for the steeper part of a hill between its summit and the drainage <br />line, valley flat, or depression floor at the base of a hill. <br />Horizon, soil <br />A layer of soil, approximately parallel to the surface, having distinct characteristics <br />produced by soil -forming processes. In the identification of soil horizons, an <br />uppercase letter represents the major horizons. Numbers or lowercase letters that <br />follow represent subdivisions of the major horizons. An explanation of the <br />subdivisions is given in the "Soil Survey Manual." The major horizons of mineral <br />soil are as follows: <br />O horizon: An organic layer of fresh and decaying plant residue. <br />L horizon: A layer of organic and mineral limnic materials, including coprogenous <br />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 layer <br />of transition from the overlying A to the underlying C horizon. The B horizon also <br />has distinctive characteristics, such as (1) accumulation of clay, sesquioxides, <br />humus, or a combination of these; (2) prismatic or blocky structure; (3) redder or <br />browner colors than those in the A horizon; or (4) a combination of these. <br />C horizon: The mineral horizon or layer, excluding indurated bedrock, that is little <br />affected by soil -forming processes and does not have the properties typical of the <br />overlying soil material. The material of a C horizon may be either like or unlike that <br />in which the solum formed. If the material is known to differ from that in the solum, <br />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 underlies <br />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 that <br />influence this potential are those that affect the minimum rate of water infiltration <br />on a bare soil during periods after prolonged wetting when the soil is not frozen. <br />These properties include depth to a seasonal high water table, the infiltration rate, <br />and depth to a layer that significantly restricts the downward movement of water. <br />The slope and the kind of plant cover are not considered but are separate factors <br />in predicting runoff. <br />35 <br />