STP1162

    Soil Survey Laboratory Methods for Characterizing Physical and Chemical Properties and Mineralogy of Soils

    Published: Jan 1993


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    Abstract

    This paper outlines the analytical methods currently used by the Soil Survey Laboratory of the National Soil Survey Center and other laboratories of the National Cooperative Soil Survey. Most of the methods were developed and tested over a period of years. Modifications of original methods have been made to facilitate automation and improve reliability.

    Physical measurements of soil samples routinely include particle size, bulk density, and water retention at 10, 33, 200, and 1500 kPa. Particle size distribution is determined by pipette and sieving. Bulk density determinations are made on equilibriated, plastic-coated clods at 10 or 33 kPa and oven dryness. Water retention measurements at 10 and 33 kPa are made on plastic-coated clods. The 200 and 1500 kPa measurements are made on prewetted, ⟨2 mm crushed samples.

    The chemical determinations include organic carbon, total nitrogen, extractable iron, aluminum, manganese, calcium, magnesium, sodium, potassium, and acidity, water-soluble cations and anions, carbonates, gypsum, cation exchange capacity, and various pH measurements. Organic carbon is by acid dichromate digestion and ferrous sulfate (FeSO4) titration. Total nitrogen is by Kjeldahl digestion. Extractable iron, aluminum, and manganese are measured in citrate dithonite and potassium chloride. Iron and aluminum are also measured in sodium, pyrophosphate, and iron, aluminum, silicon, and manganese in acid ammonium oxalate. Extractable bases are measured in a pH 7 ammonium acetate (NH4OAc) filtrate, and cation exchange capacity is measured on the soil residue from this procedure. Water-soluble cations and anions are measured in a saturation extract. Carbonates are measured by carbon dioxide (CO2) evolution. Gypsum is determined gravimetrically following its precipitation with acetone in a water extract. Exchangeable acidity is measured by barium chloride triethanolamine at pH 8.2.

    The mineralogical analyses include optical analysis of a sand or a silt fraction and X-ray diffraction and differential scanning calorimetric analysis of the clay fraction. The petrographic microscope is used to identify and count grains mounted on glass slides. X-ray diffraction analysis is made on clay films on glass slides with and without heat treatments and saturation with potassium, magnesium, and magnesium and glycerol. Differential scanning calorimetric analyses are made on samples equilibriated at 50% relative humidity.

    Keywords:

    soil analyses, soil taxonomy, particle size, bulk density, moisture retention, cation exchange capacity, extractable cations, exchangeable acidity, organic carbon, saturation extract, mineralogy


    Author Information:

    Kimble, JM
    Research soil scientist and national leader, SSIV, NSSC., SCS, and USDA,

    Knox, EG
    Research soil scientist and national leader, SSIV, NSSC., SCS, and USDA,

    Holzhey, CS
    Assistant director, NSSC., SCS, USDA, Lincoln, NE


    Paper ID: STP23868S

    Committee/Subcommittee: D18.06

    DOI: 10.1520/STP23868S


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