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Medium Erodibility 5 Noncalcareous loam antl silt loam wirh less rhan 20 percent Clay content, santly clay loam, or sandy clay <br />6 Noncalcareous loam and silt loam with more than 20 Dercent clay content, ar noncalcaraous clay loam with less than 35 percent clay content <br />Low ErotliOility 7 Silt, noncalcareouz silty clay loam with less than 35 percent clay content <br />8 Soils noI suitable for cultivation due to coarse (regments or wetness, wind erosion noI a problem <br />"I Factor: This value intlicates the relative amount of soils that can be expectetl to erode, through wind influence, in Tons-Per-Acra-Par~Yeer IT/AC/Vrl. It is related Io the wind erotlihility group number and the percent of <br />any soil aggregates greater than 0.84 mm in diameter. Values are taken form USDA-SCS, 1981 . <br />"k Faclar: this value intlicates the relative susceptibility of a surtace soils to water erosion. Values may range form .00 to .70. Higher k values indicate higher erasion susceptibility. Soils with a k factor over about 0.40 <br />era generally considered to he highly susceptible to water erosion. It should he notetl That the k factor is primarily tlerivetl from Dhysical characteristics of the soil, and does not rallect other soil erasion factors such as <br />management practices, precipitation, or length end steepness of slope. The following general arodibili[y era defined in USDA-SCS (19811. <br />Low Erotlibility: .20 or lass; Moderate Erodibility: .21-.40; High Erodibility: greater than .40 <br />"Hydrologic Group Classification of Soils: Hydrologic soil groups are used in watershed Dlanning to estimate runoff form rainfall. Soil properties are considered that influence the minimum rata of infiltration obtained for a <br />bare soils alter prolonged wetting. These properties ere: depth of seasonally high water table, intake rate end permeability after prolongetl wetting, and tlepth Io a vary slowly permeable layer. The influence of grountl <br />cover is treatetl intlepentlently -not in hydrologic sail grouping. <br />The soils have been classilied into lour groups. A through D, The indivitlual clessilications era taken from the most current ollicial soil series 'Farm 5' sheets, as summarized in USDA-SCS, 1981 antl SCS, 19e3. <br />$Iatemente in parentheses following the tlefinitions may be helpful to soil scientists wishing to place soils into hydrologic groups using the soil classification system. <br />A. FLOW runoff potentiall. Soils have high Irapidl infiltration rates even when thoroughly wetted and consist chiefly of deep to excessively tlrainad santls or gravels. Theses oils have a high rate of water <br />transmission. (includes Psamments except those in Lithic, Aquic, antl Aquotlic subgroups; soils in Grossarenic subgroups of Undults and Udalfs, antl soils in Arenic subgroups of Utlualts and Udalls except those <br />in clayey of line familiesl. <br />B. (Moderately low runoff potentiall. Soils have moderate infiltration rates when thoroughly wetted and consist chiefly of moderately deep to deep, moderately wall to well drained soils with moderately fine to <br />moderately coarse textures with moderately slow to moderately rapitl permeability. These soils have a high rata of water transmission. (Soils other than those in Groups, A, C, or DI. <br />C. (Moderately high runoff potentiall. Sails have slow infiltration rates when thoroughly wetted antl consist chiefly of soils with a layer that impetles downward movement of water, soils with moderately line to <br />fine texture, soils with slow infiltration tlua to salts or alkali, or soils with moderate water tables. These soils may ba somewhat poorly tlrainad. This category also includes well antl moderately wall tlrainetl soils <br />with slowly end very slowly permeable layers IfraB~Pans, hardpans, hard bedrock, end the like) at moderate depth (20-40 inched. Ilnclutlas soils in Albic ar Aquic subgroups; soils in Aeric subgroups of Aquents. <br />Aquepts, Aquolls, Aqualfs, and Aquulls in loamy families; soils other than those in Group D that are in line or clayey /amities except those with kaolinilic, oxidic, or halloysitic mineralogy; Humods antl Orthotls; <br />soils with Iragipans or petrocalcic horizons; soils in shallow lemilies that have permeable substrats; soils in lithic subgrouDS that have rock that is pervious or cracketl enough to allow water to penelratal. <br />D. (High runoff potentiall. Soils have very slow infiltration rates when thoroughly wetted and consist chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a claypan <br />or clay layer et or near the surface, soils with very slaw infiltration due to salts or alkali, and shallow soils over nearly impervious material. These soils have a very slow rate of water transmission (includes all <br />vertisols: all Histosols: all Aquotls; soils in Aquents, Aquepts, Aquolls, Aquolls, end Aquults except for aeric subgroups in loamy families; soils with natric horizons; soils in Lithic subgroups that have <br />impermeable substrata; and soils in shallow families that have impermeable substratal. <br />"Taxonomic inclusions are included with Foitlel. These include a mollic epipedan which is less than 20 inches thick and en argillic horizon found ai a depth less than 24 inches from the soils surface. <br />~l • <br />9-2-8 Revised 9/98 <br />