Soils 205- general soils

Lecture 32- soil mapping/soil survey

I.  soil mapping:  The objective of soil mapping is to identify the distribution of soil bodies on natural landscapes. 

    a.  soil mapping units:  designed for use in mapping soils on landscapes which allow for inclusions of unlike pedons and natural variability.  Presently there are five types of SMU's used in the US.

        i.  Soil consociation:  Consists of one principle pedon with allowable inclusions.  Named for the dominant soil type.

    ii.  soil complex:  Contains two or more dissimilar pedons that occur together in a characteristic pattern.  The soil types cannot be separated at the standard 1:24,000 scale.

    iii.  soil association:  Contains two or more dissimilar pedons that occur in a characteristic pattern.  The soil types can be separated at 1:24,000, but they do not meet the requirements for a consociation, so the pedons are mapped and named together.

    iv. undifferentiated soil group:  In this SMU, two or more pedons are mapped together because it is not worth the time and effort to separate them.  Usually the management potential or land use limitations are similar even if the individual soil types are dissimilar.

    v.  miscellaneous land class:  This SMU is used to indicate non-soils

II.  Soil survey:  Soil surveys are conducted to identify the distribution of SMUs across a landscape.  They are used as an inventory of natural resources and also to make land use decisions.

    a.  Intensity of soil survey:  The intensity of a soil survey will depend on the land use in the survey area and the intended use of the soil survey information.  Five levels of soil survey activities have been established by the National Co-Operative Soil Survey. 

    b.  Contents

            Soil surveys consist of maps and text.  The text contains three types of information; facts, groupings, and ratings.

        i.  Facts:  includes the basic information about the soils and landscapes in the survey area.

        Examples: horizons, textures, structure, color, drainage class, salinity, soil depth, shrink/swell, CEC, water holding capacity, etc.

        ii.  Groupings:  A grouping is a collection of soils with a similar management potential or similar properties.

        Examples:

                1.  Soil taxonomy:  Soils are grouped together based on similar characteristics.

                2.  Land capability class:  In the LCC soil mapping units are grouped together based on similar potential for agricultural land use.  Soils are divided into eight classes based on agricultural management potential and soil, site, and regional characteristics.

        LCCs

        A)  suitable for continuous cultivation

            I  =  Prime agricultural land- no limitations

            II  = Prime agricultural land- slight limitations

            III  = Agricultural land- moderate limitations

            IV  = Agricultural land- severe limitations

            LCC III and IV lands require more intensive management practices to be productive land.

        B)  permanent vegetation- forest or pasture land

            V =  slight limitations

            VI =  moderate limitations

            VII  =  severe limitations

            VIII  =  wildlands

            LCC V lands are good for pastures, while pasturing is impractical on LCC VII lands.  Class VIII lands should be left in permanent natural vegetation.

LCC V

LCC VI

LCC VII

LCC VIII

        LCC Subclasses:  capability subclasses are letters that are added to the classes to indicate limitations.

    s = soil limitation

    w = water limitation

    e = erosion limitation

    c = climate limitation

Examples:  IIIe - agricultural land with moderate limitations due to erosion

                IIIs - agricultural land with moderate limitations due to soil properties (salinty, lack of Ca, etc).

        3.  Woodland suitability:  Entirely different classification scheme.  Looks at the lands potential for the purpose of growing trees.

        4.  Wildlife habitat:  Examines protection, cover, food sources, etc.  Has groupings for wetlands (waterfowl) and uplands.

        5.  Unified and 6.  AASHO:  Engineering uses classification scheme

        7.  Range site:  Classification of the land by its potential for pasture.  Looks at how many animals the land can sustain, what management practices are needed, etc.

iii.  Ratings:  ratings are applied to individual mapping units.  Individual mapping units are examined and their potential for specific uses are rated either in terms of limitations (slight, moderate, severe) or in terms of potential (poor, fair, good).

Examples:

    1)  septic tank leach fields- important criteria

    What is the water table depth?  What is the depth to bedrock?  What is the texture of the soil?  The % slope? 

    2) roads and streets- texture, drainage, slope, organic matter, shrink-swell, etc.  Rated by limitations.

    3)  Dwellings with basements

    4)  Dwellings without basements

    5)  small commercial buildings

    For these three one needs to be concerned with the amount of organic matter, depth to water table, flooding hazard, shrink-swell, etc.  Rated by limitations.

    6)  Playgrounds and recreational areas.  These are often placed in floodplains because it is not absolutely necessary to have them open all of the time.  Other considerations:

    Soil fertility (golf course)

    soil texture (playground)

    rated by limitations

    7)  campgrounds- consider texture, dust hazard, flooding hazards, etc.

    8)  source of topsoil-  look at the potential, not the limitations.  Consider texture, organic matter content, shrink-swell, etc.