The associated tablular file "Soil_att" contains: the mapunit identifier, available water capacity of the soil, percent clay in the soil, the actual k-factor used in the water erosion component of the universal soil loss equation, the organic material in soil, soil permeability, cumulative thickness of all soil layers, hydrologic characteristics of the soil, quality of drainage, surface slope, liquid limit of the soil, share of a map unit having hydric soils, and the annual frequency of flooding.
The associated tabular file 'Soil_att' contains the following attributes for each soil polygon:
MUID Map unit identifier (first two characters are the state abbreviation). This attribute is used to relate this table with 'Soils250K'.
AWC Available water capacity (in inches per inch). Computed as a layer thickness weighted average, across soil layers, of a simple average of awch and awcl contained in the STATSGO layer file. Missing value indicator = -0.1
CLAY Percent of soil consisting of clay (in percent of material less than 2 millimeters in size). Computed as a layer thickness weighted average, across soil layers, of a simple average of clayh and clayl contained in the STATSGO layer file. Missing value indicator = -0.1.
KFFACT Actual k factor used in universal soil loss equation to calculate soil loss by water. Computed as a layer thickness weighted average, across soil layers, of the variable kffact contained in the STATSGO layer file. Missing value indicator = -0.1.
OM Organic material in the soil (in percent by weight). Computed as a layer thickness weighted average, across soil layers, of a simple average of omh and oml contained in the STATSGO layer file. Missing value indicator = -0.1
PERM Permeability of the soil (in inches per hour). Computed as a layer thickness weighted average, across soil layers, of a simple average of permh and perml contained in the STATSGO layer file. Missing value indicator = -0.1
THICK Depth of soil layers (in inches). Computed as the sum of the differences between laydeph and laydepl for each soil layer in the STATSGO layer file. Missing value indicator = -0.1
HYGRP A code identifying the hydrologic characteristics of the soil. The character codes defined in the STATSGO component file are converted into numeric codes.The coding transformations are A = 1 (high infiltration, deep soils, well drained to excessively drained sands and gravels), B = 2 (moderate infiltration rates, deep and moderately deep, moderately well and well drained soils with moderately coarse textures), C = 3 (slow infiltration rates, soils with layers impeding downward movement of water, or soils with moderately fine or fine textures), D = 4 (very slow infiltration rates, soils are clayey, have a high water table, or are shallow to an impervious layer), Mixture codes A/D, B/D, and C/D are assigned the value 4. Also, certain areas were selected and assigned values for hygrp based on the area type. Miscellaneous areas (denoted by M in compkind) and labeled as Dumps, and Gullied Land in compname are assigned the hygrp = 2.5 if the hydgrp value is missing. Areas denoted as Pits, Rock Outcrops, Terrace Escarpments, and Urban land with missing hydgrp are assigned a hygrp of 4. See the documentation of the SAS program "setussoils.sas" for additional details. The transformed data are averaged across components using the component percentage as weights. The missing value indicator is -0.1.
DRAIN A code identifying the quality of soil drainage. The two character code from the STATSGO component file is converted to a numeric value according to the following translation: E = 1 (excessive), SE = 2 (somewhat excessive), W = 3 (well drained), MW = 4 (moderately drained), SP = 5 (somewhat poorly drained), P = 6 (poorly drained), and VP = 7 (very poorly drained). The values are averaged across components using the component percentage as weights. The missing value indicator is -0.1.
SLOPE The slope of the map unit (in percent). Slope values contained in the STATSGO component file are averaged using the component percentage as weights. The missing value indicator is -0.1.
LL Liquid limit of soil layer (in percent moisture by weight). Computed as a layer thickness weighted average, across soil layers, of a simple average of llh and lll contained in the STATSGO layer file. Missing value indicator = -0.1.
IFHYDRIC Share of map unit with hydric soils (1 = entire map unit has hydric soils). Computed by summing the component percentage for each component designated as having hydric soils according to the variable hydric in the STATSGO component file. Missing value indicator = -0.1.
AFLDFREQ Annual flood frequency code. Flood frequency designations contained in the variable anflood in the STATSGO component file are converted to numeric codes according to the following translation: 1 = greater than 50 percent, 2 = 5 percent to 50 percent, 3 = 0 percent to 5 percent, and 4 = no flood. Translated variables are averaged across components using the component percentage as weights. The missing value indicator is -0.1.