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Geosciences LibreTexts

1.1: Determining Soil Physical Properties

  • Page ID
    15130
  • Learning Objectives

    Upon completion of this exercise you should be able to:

    • determine Munsell color of dry and moist soil samples
    • identify soil structure using the Field book for describing and sampling soils
    • classify soil texture using the “Feel Method”

    Purpose:

    The purpose of this exercise is to familiarize you with basic soil physical properties (color, structure, and texture) of soil samples.

    Background:

    For this exercise we will be describing basic soil properties (color, texture, and structure) in discreet hand samples. Soil color has little bearing on the function or use of soils, but provides information about soil properties and conditions. Color is most influenced by organic matter content, water content, and oxidation state. Also, soil color is the most obvious feature of a soil and one of the easiest properties to measure. We will determine soil color using a Munsell Color Chart. When using the chart to determine a soil color, soil is compared to a small color chip that is described by hue (red/yellowness), value (light/dark), and chroma (intensity of brightness) in that order. Soil color should always be determined when the soil is slightly moist.

    • Example:

     

     

    Soil structure refers to the arrangement of primary soil particles into groupings called aggregates or peds. Structure greatly influences water movement, heat transfer, aeration, and porosity in soils. Structure is characterized in terms of the shape (or type), size, and distinctness of the peds. There are four basic structural shapes, some of which are subdivided: spheroidal (granular or crumb), plate-like, blocky (angular or subangular), and prism-like (columnar or prismatic). Size includes fine, medium, or coarse, while distinctness is described as strong, moderate, or weak.

    Soil texture describes the size of soil particles within the fine earth fraction, that portion excluding gravels, cobbles and boulders. Thus, soil texture is a combination of the sand, silt, and clay fractions. There are three basic soil textural classes: sandy soils, clayey soils, and loamy soils; loams are combinations of sands, silts, and clays in nearly equal portions. The basic textural classes can be subdivided and from coarsest to finest texture are: sand, loamy sand, sandy loam, loam, silt loam, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay and clay. Texture can be further subdivided into fine and coarse factions (i.e. fine sandy loam etc.). For this exercise we will classify soil texture using the “Feel” method (see Box 4.1, page 103 in Brady and Weil) and later in the semester we will use other laboratory techniques.

    Equipment required:

    • Munsell Color Chart
    • Water spray bottle
    • Paper towels
    • Soil samples
    • Field Book for Describing and Sampling Soils (Ver. 3.0)
    • Water squirt bottle
    • Mud bucket

    Exercises:

    1. Using the Munsell Color Chart classify DRY soil color for the following samples

    A.

    B.

    C.

    D.

    E.

    2. Using the Munsell Color Chart classify MOIST soil color for the following samples:

    A.

    B.

    C.

    D.

    E.

    3. Visually inspect the soil samples to determine structure (include Type, Grade, and Size):

    A.

    B.

    C.

    D.

    E.

    4. Use the “Feel” method to determine texture for the following samples:

    A.

    B.

    C.

    D.

    E.

     

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