ASTM D2976-22a

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Designation: D2976 − 22 D2976 − 22a
Standard Test Method for
pH of Peat Materials
This standard is issued under the fixed designation D2976; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This test method covers the measurement of the pH of peat materials used as a growing medium. This measurement determines
the degree of acidity or alkalinity in peat materials suspended in water and a 0.01 M calcium chloride solution. Measurements in
both liquids are necessary to fully define the peat’s pH. This variable is useful in assessing the viability of the peat-plant
environment. This test method does not apply to peat that is in paper or construction materials. Test Method D4972 is used for
pH testing of soils and Test Method G51 is used for pH testing of soils for corrosion analysis (see Note 1).
NOTE 1—These three standards are being intentionally kept separate for clarity at the request of the various subcommittees.
1.2 Units—The values given in SI units are to be regarded as the standard. No other units of measurement are included in this
standard.
1.3 All measured and calculated values shall conform to the guidelines for significant digits and rounding established in Practice
D6026.
1.3.1 The procedures used to specify how data are collected/recorded and calculated, in this standard are regarded as the industry
standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not
consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives;
and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations.
It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering design.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D1193 Specification for Reagent Water
This test method is under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.22 on Media for Plant Growth.
Current edition approved Feb. 1, 2022Oct. 1, 2022. Published February 2022October 2022. Originally approved in 1971. Last previous edition approved in 20152022 as
D2976 - 15.D2976 - 22. DOI: 10.1520/D2976-22.10.1520/D2976-22A.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
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D2976 − 22a
D3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in
Engineering Design and Construction
D4753 Guide for Evaluating, Selecting, and Specifying Balances and Standard Masses for Use in Soil, Rock, and Construction
Materials Testing
D4972 Test Methods for pH of Soils
D6026 Practice for Using Significant Digits and Data Records in Geotechnical Data
G51 Test Method for Measuring pH of Soil for Use in Corrosion Testing
3. Terminology
3.1 Definitions:
3.1.1 For definitions of common technical terms used in this standard, refer to Terminology D653.
4. Summary of Test Method
4.1 Two similar test specimens are obtained from a representative sample. One specimen is mixed with test water and one is mixed
with a calcium chloride solution. They are then thoroughly stirred and both are allowed to stand for 30 min prior to testing with
a pH meter.
5. Significance and Use
5.1 The pH of peat is a useful variable in determining the solubility of minerals, the mobility of ions in the peat, and assessing
the viability of the peat-plant environment. pH measurements are made in both test water and a calcium chloride solution because
the pH readings in test water can be modified by salts, such as fertilizer material, whereas the observed pH in calcium chloride
solution is virtually independent of the initial amount of salts present in the peat. pH values obtained in a calcium chloride solution
are usually about a 0.5 to 0.8 pH unit lower than measurements in test water due to release of more hydrogen ions by cation
exchange. Both measurements are needed to fully define the character of the peat’s pH.
5.2 pH measurements are used in the agricultural, environmental, geotechnical, and natural resources fields. The pH of peat
materials is helpful when evaluating a peat as a topsoil or growing medium for plants.
NOTE 2—The quality of the result produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the
equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective
testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable
results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.
6. Interferences
6.1 A pH probe has possible interferences due to a suspension effect or sedimentation potential. This effect is the main reason Test
Method G51 cannot be used for general measurement of pH outside of that for corrosion analysis. Test Method G51 measures pH,
an aqueous parameter, without adding any aqueous phase to the soil. This lack of aqueous phase results in excessive soil
particle-pH probe contact that overestimates the activity of the hydrogen ions in solution and is therefore unacceptable for general
soil analysis.
6.2 The suspension effect can be mitigated by careful attention to inserting the probe into the aqueous phase of the slurry. The
aqueous phase consists of the partially settled suspension
7. Apparatus
7.1 pH Meter—Potentiometer equipped with an electrode system with a readability to the nearest 0.1 pH unit or better and an
accuracy of 60.1 pH unit or better. Follow the manufacturer’s instructions for the pH meter used. A silver/silver chloride electrode
system or similar is also acceptable.
7.2 Balance—Balance (Optional)—Balances shall conform to the requirements of Guide D4753. and are used when making
buffers.
D2976 − 22a
7.2.1 The balance shall have readability without estimation of 0.1 g or better. The capacity of this balance will need to exceed the
mass of the container plus peat. In general, a balance with a 0.01 g or better and a minimum capacity of 100 g is sufficient.20 g.
7.3 Specimen Mixing Container—A glass beaker or equivalent inert container with enough capacity to hold the specimen and the
test water or calcium chloride solution. Usually, a 100 mL glass beaker is large enough.
7.4 Thermometric Device—A thermometric device capable of measuring the temperature range within which the test is being
performed readable to 0.5°C or better and having an accuracy of at least 60.5°C.
7.5 Miscellaneous Items—Items such as a wash/rinse bottle (squirt bottle), trays, spatulas, plastic or glass containers to hold
reagents, and stirring rod may be useful.
8. Reagents
8.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents should conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where
such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high
purity to permit its use without lessening the accuracy of the determination.
8.2 Test Water—Type III water in accordance with Specification D1193 or distilled/deionized water with a pH between 6.5 and
7.5. De-air distilled/deionized test water by boiling for 15 min and then seal the container during cooling until it has reached room
temperature.
8.3 Buffer Solutions—Buffer solutions are commercially available and providing they meet the purity of reagents as described
above, they are an acceptable alternative to making buffer solutions. The following NIST traceable buffer solutions are typically
needed: pH of 4.0 and 7.0. When making buffer solutions, refer to Annex A1 of Test Method D4972 for
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