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PERCENT ORGANIC MATTER <br />Percent organic matter within the soil horizon indicates the amount of decomposed <br />plant material present, and also gives an indication of the amount of churning, sediment <br />deposition or scouring occurring in a soil during development. Organic matter <br />provides an important source of minerals for plant growth as well as adding structure <br />and moisture holding capability to the soil. Cook, Hyde, and Sims (1974) state that <br />topsoil should have organic matter comprising from three to twenty percent of the soil <br />makeup to be satisfactory plant growth medium. Organic matter percentage is <br />relatively variable in the soil horizons found in the SGFA. As expected, the amount of <br />organic material generally decreased with soil horizon depth. The lowest concentration <br />of organic material was found in the Fluvent(2) B horizon (1.5%). This would not be <br />unexpected given the depositional genesis of this soil type. The highest percentage of <br />organic matter was found in the Beenom-Absazokee(1) A horizon (21.1%). This <br />specific type was characterized by the presence of the Douglas fir vegetation <br />community with a deep detritus layer underneath the trees. Incorporation of large <br />amounts of organic material is a logical result following from the mesic slope position <br />of these soils and the affiliated plant community. <br />TEXTURE <br />Soil texture represents the proportions of the three major particle sizes comprising a <br />soil; sand, silt, and clay. Soils with high proportions of any single component relative <br />to the others may have detrimental characteristics related to plant growth, erosion, or <br />stability. Surface A horizons within all soil types of the SGFA were loam, sandy loam, <br />or sandy clay loam in texture. These textures aze generally suitable for plant growth <br />medium. Subsurface horizons within the SGFA soils tended towazd clay loams and <br />clays, materials less well suited for plant growth. As a general trend, the percentage of <br />chty textured material increased with depth in the soil column. Three horizons <br />exhibited clay content high enough to make them undesirable for use as a plant growth <br />medium. The Beenom-Absarokee(1) B/C horizon contained 50 percent clay, the <br />Torriorthent(3) B/C horizon contained 44 percent clay, and the Beenom-Absazokee(2) <br />B horizon contained 36 percent clay. <br />MAJOR PLANT NUTRIENTS (N, P, IQ <br />Nitrogen (N), phosphorus (P), and potassium (K) are the three most common and <br />important inorganic elements required for plant growth. Presence of these nutrients, in <br />soil in forms available to plants, is a prerequisite for revegetation. Bradshaw and <br />Chadwick (1980) determined the concentrations of many common nutrients in plants <br />and also established satisfactory concentrations in laboratory culture solutions. These <br />concentrations aze compared with the N, P, and K concentrations from the SGFA soil <br />• types below. <br />-lo- <br />