Making Interpretations Based on Soil Map Unit Information

1. Making Interpretations Based on Soil Map Unit Information FOR 4114 Spring, 2010 Dr. John M. Galbraith, CSES

2. Types of Data in SSURGO Tables • Numerical Data – Real Numbers and Integers • Some are ranges of values, some are single calculations. • Some are continuous (0 to ∞) • Some are constrained by limits (0-14 pH, 0-100%) • If not stated otherwise in the aggregation method, the representative (median) value is used. • Ordinal Classes – Numbers, Letters, Codes, Classes • These are not ranges, they are ratings • EX: Class IIw, IVe, Vis • EX: 1, 2a, 2b, 3, 4 • EX: Class A, B, C, D • EX: Poorly, moderately well, well drained

3. Examples • Clay Content >>> Low Value = 27% High Value = 35% Repr. Value = 32% • Site Index – White Oak = 85 • Available Water Supply, 0 to 150cm = 13.65 (calculated)

4. Interpretive Ratings • Examples: • Poor, Fair, Good Source of something… • EX: Source of sand • Very Low to Very High Risk of hazard… • EX: Subsidence • Very Poor to Very Good Quality for use as… • EX: Woodland wildlife habitat • Not Limited to Severely Limited for some purpose… • EX: Dwellings with basements, Slow rate treatment of wastewater • Not Hydric or Hydric • Soil is either hydric or not • Poorly Suited to Well Suited for some purpose… • EX: Mechanical planting of trees

5. Soil and Water Properties • Soil Chemical Properties – Numerical • pH = 6.4 - 7.0 (R.V. = 6.7) • Soil Erosion Factors – Numerical and Ordinal • K factor (used in RUSLE) – 0.10 • WEG (classes used in wind erosion prediction) – 2 (ordinal) • Soil Physical Properties – Numerical and Ordinal • Clay% - 27% – 35% (R.V. = 32%) • Texture – fine sandy loam • Soil Qualities and Features – Numerical and Ordinal • Depth to restrictive layer - >200 cm • Hydrologic soil group - A • Water Features – Numerical and Ordinal • Depth to water table – 50 to 100 cm • Flooding frequency class - common

6. Suitability and Limitation Ratings • Building Site Development – Ordinal Classes • Construction Materials – Ordinal Source Classes • Disaster Recovery Planning – Ordinal Classes • Land Classifications – Ordinal Classes, some Boolean • Land Management – Ordinal Classes, some Suitabilities • Military Operations – Ordinal Classes • Recreational Development – Ordinal Classes • Sanitary Facilities – Ordinal Classes • Vegetative Productivity – NumericalValues • Waste Management – Ordinal Classes • Water Management – Ordinal Classes

7. Ecological Site Assessment • Ecological Site Native Plant Community • Production (kg/ha) • Composition (%) • Growth Curve (graph)

8. Data Aggregation Methods • Dominant Soil – Component that makes up largest composition • EX: You want the most frequent (highest %) component if 2+ cmpnts. • Dominant Condition – Rating that makes up largest composition • EX: You want the majority rating if there are 2+ components • All Components – Lists all components and their rating • EX: For Soil Classification, you may want to list all components • Weighted Average – Gives the weighted average of real values • EX: The average subsoil clay% for the map unit, not just one soil • Most Limiting • EX: You want to know about the limitation that is most expensive to fix • Least Limiting • EX: You want to know whether any slightly limited soils occur out there

9. Special Conditions • No Aggregation Needed • EX: Only one value per map unit because values are assigned by map unit properties (e.g. slope%), not by individual component • Percentage Cutoff Value • EX: We only want to consider map units where the hydric soils make up 90% or more of the unit (excludes those with only hydric inclusions) • Low Value or High Value • EX: If the data is numerical and has a range of low, representative, or high, we can choose the low or the high rather than the (default) representative value.

10. Dominant Soil versus Dominant Condition • EX: Alpha, the dominant component, makes up 55%, it’s slight limitation rating or pH properties are applied to the whole map unit. • EX: Beta and Gamma have severe limits for a specific use, but the dominant Alpha component has only slight limits. If the composition of Beta + Gamma exceeds that of Alpha, the severe limit rating is applied to the whole map unit.

11. Probability Values for Rating Reasons • NOTE: Probability Values (0.00 to 1.00) are included for each Ordinal Rating • These fuzzy logic values are used to tell the user about membership in a rating class.

12. Rating Determination Charts • Section 6.18 in the National Soil Survey Handbook:http://soils.usda.gov/technical/handbook/contents/part618ex.html#ex1

13. μ 0.03 0.02 E.C. mmhos/cm 0.01 0 0.50 1.00 P Focus on Electrical Conductivity (a.k.a. salinity) • EX: Define membership in the class of soils that are < 0.3 mmhos cm-1; the basis of a slight rating for Risk of Corrosion of Uncoated Steel. • A soil component ranges from 0.00 to 0.02 cm mmhos cm-1; Is it < 0.03 or not?

14. What if there are two or more components? • EX: If a map unit is Severe for Erosion Hazard for roads/trails, and it has two major components, the component with a more erosive surface texture has a higher probability of being a member of the set of components that earn the severe rating (say 0.90 versus 0.50). • If both have the same surface texture, they would each have the same probability of being a member of the set of components that earn the severe rating (say both were 0.90 ~it depends on the texture they both have).