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( l ) Humus .—The more or less stable fraction of the soil organic matter remaining 88 after the major portions of added plant and animal residues have decomposed. Usually it 89 is dark in color. 90 ( m ) Loam. —A soil type that contains the basic soil particles sand, silt and clay with a 91 smaller amount of clay and a roughly equivalent amount of sand and silt. An example 92 mineral composition of a loam is 40% sand, 40% silt and 20% clay. 93 ( n ) O horizon. —Organic layers of decaying plant and animal tissue containing 94 between 12-18% organic carbon excluding the root and large fiber fraction. Oi is a fibric 95 horizon, Oe is Hemic and Oa is Sapric. This horizon is typically the top horizon in a soil 96 profile when present. 97 ( o ) Silt .—Comprised of particles in the size diameter range of 0.02-0.002 mm. 98 Smaller than sand and more difficult to drain. 99 ( p ) Soil horizon .—A layer of soil, approximately parallel to the soil surface, differing 100 in properties and characteristics from adjacent layers below or above it. 101 ( q ) Soil profile .—A vertical section of the soil through all its horizons and extending 102 into the parent material. 103 ( r ) Solum .—Comprised of surface and subsoil layers that have undergone the same 104 soil-forming conditions. 108 testing with soils difficult to scope. The study of soil is interdisciplinary involving 109 chemistry, biology, physics, soil genesis and taxonomy, in addition to agricultural and 110 105 106 107 6.0 Background Information on Soil There are over 19,000 identified soils in the United States alone, making experimental

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