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Cation-Exchange Capacity (CEC-7)-San Miguel Area, Colorado, Parts of <br />Dolores, Montrose, and San Miguel Counties <br />Cation-Exchange Capacity (CEC-7) <br />' J-Bird Mine Site <br />Cation-Exchange Capacity (CEC-7)- Summary by Map Unit - San Miguel Area, Colorado, Parts of Dolores, Montrose, and <br />San Miguel Counties <br />Map unitsymbol Map unit name Rating (milliequivalents per 100 grams) Acres In AOI Percent of AOI <br />108 Wrayha stony clay 22.5 7.3 100.0% <br /> loam, 3 to 40 <br /> percent slopes <br />Totals for Area of Interest 7.3 100.0% <br />Description <br />Cation-exchange capacity (CEC-7) is the total amount of extractable cations that <br />can be held by the soil, expressed in terms of mill iequivalents per 100 grams of soil <br />at neutrality (pH 7.0) or at some other stated pH value. Soils having a low cation- <br />exchange capacity hold fewer cations and may require more frequent applications <br />of fertilizer than soils having a high cation-exchange capacity. The ability to retain <br />cations reduces the hazard of ground-water pollution. <br />For each soil layer, this attribute is actually recorded as three separate values in <br />the database. A low value and a high value indicate the range of this attribute for <br />the soil component. A "representative" value indicates the expected value of this <br />attribute for the component. For this soil property, only the representative value is <br />used. <br />Rating Options <br />Units of Measure: milliequivalents per 100 grams <br />Aggregation Method: Dominant Component <br />Aggregation is the process by which a set of component attribute values is reduced <br />to a single value that represents the map unit as a whole. <br />A map unit is typically composed of one or more "components". A component is <br />either some type of soil or some nonsoil entity, e.g., rock outcrop. For the attribute <br />being aggregated, the first step of the aggregation process is to derive one attribute <br />value for each of a map unit's components. From this set of component attributes, <br />the next step of the aggregation process derives a single value that represents the <br />map unit as a whole. Once a single value for each map unit is derived, a thematic <br />map for soil map units can be rendered. Aggregation must be done because, on <br />any soil map, map units are delineated but components are not. <br />For each of a map unit's components, a corresponding percent composition is <br />recorded. A percent composition of 60 indicates that the corresponding component <br />typically makes up approximately 60% of the map unit. Percent composition is a <br />critical factor in some, but not all, aggregation methods. <br />USDA Natural Resources Web Soil Survey 2.1 1 M4rZUUS <br />Conservation Service National Cooperative Soil Survey Page 3 of 4