Soil Classification _ Survey

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					Soil Classification &
• Describe the current USDA soil
  classification system
• Explain how soil surveys are prepared and
• List soil capability classes
          Soil Classification
• Soil survey
  – Depends on system of grouping soils of like
• Soil classification
  – Helps us to understand, remember, and
    communicate knowledge about soils
    History of Soil Classification
        A continual process
• 1900s – soils grouped based on soil
  forming-factors that created them
• 1938, 1949 – further systems developed
• 1960 - USDA introduced current
  classification system
• 1975 – modified this system
• 1998 – 12th soil order added
• Current system in publication:
   Soil Taxonomy: A Basic System of Soil
   Classification for Making and Interpreting
                   Soil Surveys
• Based on soil properties
• System is still evolving
• Other countries have different systems
               Soil Classes
• Hierarchical system of levels:
  – Order (12)
  – Suborder (66)
  – Great Group (>320)
  – Subgroup (>1,400)
  – Family (>8,000)
  – Series (>19,000)
  – (Phases) – not an official level
                 Soil Orders
•   Highest level,
•   Broadest group
•   12 orders
•   Based on:
    – diagnostic horizons
    – climate
                Soil Orders
•   Alfisols          •   Inceptisols
•   Andisols          •   Mollisols
•   Aridisols         •   Oxisols
•   Entisols          •   Spodosols
•   Gelisols          •   Ultisols
•   Histosols         •   Vertisols
Distribution Map of Soil Orders
• US Map:
• World Map:
• Soil Orders:
 Soil Order Maps and Descriptions
• Classification of each order:
• Posters:
• Very cold soils of tundra, cold deserts, or
  high peaks with subsoil permafrost
• Often with muck or peat surfae soil
• Mostly Alaska
• Very fragile
• Typical profile: O-A-Cf
• Uses: None safely, except wildlife
• Organic soils, usually wetlands
• Organic matter >20-30%
• Very low density
• Must be drained for use, then prone to
  subsidence and fire
• Northern Midwest and Atlantic/Gulf coastal
• Typical profile: O1-O2-O3-C
• Uses: wetlands, forest, horticulture, fuel
• Light colored, arid coarse soils, typically under
  coniferous forest
• Usually of cool humid regions, but not always
• Illuviation of iron or aluminum-humus complexes
  in B horizon
• Low base saturation, infertile
• Upper Midwest to Northeastern states
• Typical profile: A-E-Bs (or Bhs) - C
• Uses: Forest, pasture, cropland
•   Recent volcanic material
•   Dark, fertile, high CEC and OM
•   Often on volcanic slopes and high altitude
•   Pacific Northwest, Hawaii, Alaska
•   Uses: Cropland, forest
• Highly weathered tropical soils, often under
• Subsurface horizon low in weatherable minerals
  but high in aluminum or sesquioxide clays
• Low native fertility, but can be fertilized
• Hawaii and Puerto Rico
• Typical profile: A-Bo (or Bv)-C
• Uses: cropland, forest, shifting agriculture
• High in swelling clays in climates with dry
• When dry, large, deep cracks form that surface
  soil falls into, mixing the soil
• Unstable for engineering uses
• Most common in Southcentral states, especially
  Texas, some in upper plains states
• Typical profile: A-AC-C
• Uses: range and pasture, cropland
• Arid soils of cool to hot deserts and dry
• Oftlen alkaline with salted horizons
• Thin or no O or A
• High base
• Western states
• Typical profile: A-Bt-Ck or Ckm, Cy, Cz
• Uses: range, irrigated cropland
• Highly weathered soils of humid warm climates,
  often under forest
• Low base saturation (<35%), acid, leached
• Soilsoil layer with illuviated silicate clays
• Surface layer light colored, subsoil often red clay
• Productive, if properly fertilized and limed
• Southeast states mostly
• Typical profile: A-E-Bt-C
• Uses: forest, cropland
• Mostly grassland soils
• Dark, thick, high organic matter and base A
• Low to moderate rainfall
• May have illuvial or calcareous subsoil
• Highly fertile and productive
• Great Plains and Northwest states
• Typical profile: A1-A2-A3-Bw-C
• Uses: croplands, range
•   Deciduous forest soils of temperate moist climates
•   Light colored
•   Slightly to moderately acidic
•   Illuvial layer high in silicate clays
•   Medium to high saturation
•   Fertile soil
•   North central states
•   Profile: O-A-E-Bt-C
•   Uses: cropland, forest, range
• Minimal horizon development, but more than
• Often young
• May have weak B horizon by color/structure; no
• Extremely variable, widely scattered in US
• Typical profile: A-Bw-C
• Uses: Cropland, forest, range
• Lack well-developed horizons
• Young, or conditions inhibit horizon
  development – sandy, wet, alluvial, steeply
• Least developed soil order
• Typical profile: A-C
• Uses: range, cropland, forest, wetlands
               Soil Classes
• Hierarchical system of levels:
  – Order (12)
  – Suborder (66)
  – Great Group (>320)
  – Subgroup (>1,400)
  – Family (>8,000)
  – Series (>19,000)
  – (Phases) – not an official level
               Soil Series
• Smaller units of soil families
• More than 19,000
• Taxonomic unit with narrowest range of
• All pedons within a series have similar soil
  profiles – polypedon
         Soil Series (cont’d)
• Named based on location where first
  identified – town, county, area
• Lowest official category in soil taxonomy –
  but is subdivided into Phases
• Phase –
  – variation of a series
  – based on some factor that affects soil
  – Examples: slope, erodibility, stoniness
             Soil Survey
• USDA developed soil classification system
  for use in soil surveys
• Classifies soils
• Provides a mapped location of soils
• Describes soil as appears in field
• Most surveying done by NRCS – Natural
  Resources Conservation Service
         Soil Survey Report
• Harford County Soil Survey, issued 1975
• Contains:
  – Taxonomy of soil
  – Soil description
  – Soil properties of each horizon
  – Suitability rating – engineering, water
    management projects, recreation, cropping,
    woodland, habitat for wildlife
     Land Capability Classes
• Indicates best long term use for the land
• Uses include:
  – Cropping, pasture, rangeland, woodland (for
    lumber), recreation, and wildlife
• Capability Classes – NCRS recognizes 8
     Land Capability Classes
• NRCS recognizes 8 land capability
• Numbered I to VIII
• Class I soils – fewest limitations
• Class VIII – most limited, unsuitable for
• Erosion hazard due to slope is main
              Class I Soils
• Few limitations
• May be heavily cropped, pastured, or
  managed for woodlands or wildlife
• Well drained and nearly level
• Fertile, easy to manage
• Crops are most profitable
• Prime & productive soils are Class I, II, III
               Class II Soils
• Suitable for all uses
• Have mild limitations
• Need moderate soil conservation when
• Can be:
  – Gently rolling, moderate erosion hazard,
    shallow soil, less than ideal tilth, slight alkali
    or saline conditions, or slightly poor drainage
                Class III Soils
• Can grow same crops as Class I and II soils, but
• Must address serious problems such as:
  – Moderately steep slopes; high erosion hazard;
  – Poor drainage; very shallow soil;
  – Droughtiness; low fertility; moderate alkali or saline
    conditions; or unstable structure
• Special conservation methods needed – limit
  number of row crops, favor closely-grown crops
• Lowest soil class safely used for all crops
                Class IV
• Marginal for cultivated crops
• Same limitations as Class III, but more
• Maybe grow closely grown crops
• Must practice careful erosion control
                 Class V
• Not suited for cultivated crops
• May be used for range, pasture,
  woodlands, and recreation
• Level soils, little erosion hazard, but …
  – Limited by: flooding, short growing season,
    rockiness, wet areas that cannot be drained
                 Class VI
• Unsuitable for cultivated crops
• May be suited for pasture, range, wildlife,
  and woodland
• Problems include:
  – Steep slopes, severe erosion hazard,
    established severe erosion, stoniness,
    shallowness, or drought
                   Class VII
•   Same problems as Class VI
•   But are more steep
•   Difficult to maintain high quality pasture
•   May be used for:
    – Range, woodlot or forest, recreation, or
      wildlife, if carefully managed
    – Slopes may be greater than 30%
                 Class VIII
• Cannot support any commercial plant
  production, even timber
• May be preserved for:
  – Recreation, wildlife, or beauty
• Examples:
  – Sandy beaches, rock outcroppings, heavily
    flooded river bottoms
   Summary of Land Capability
• Class I to III – cultivated crops
• Class IV – marginal land for cropping
• Class V to VIII – lands not suitable for
           Online Soil Data
• Geographic Information Systems (GIS)
  used to map soil data
• Integrates information on:
  – Soils, topography, land cover, land use,
    ownership, watersheds, and geology
Land Capability of United States
• 43% of U.S. soil rates Class I to III
• Rest suitable for some form of commercial
  production – grazing or woodland
• Good soils not distributed evenly through
   – Corn belt states – highest amount
   – Northern Plains and Delta states
   – West – too mountainous

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