ASTM D4972-18
(Test Method)Standard Test Methods for pH of Soils
Standard Test Methods for pH of Soils
SIGNIFICANCE AND USE
5.1 The pH of the soil is a useful variable in determining the solubility of soil minerals, the mobility of ions in the soil, and assessing the viability of the soil-plant environment.
5.2 pH measurements are made in both test water and a calcium chloride solution because the calcium displaces some of the exchangeable aluminum. The low ionic strength counters the dilution effect on the exchange equilibrium by setting the salt concentration of the solution closer to that expected in the soil solution. The pH values obtained in the solution of calcium chloride are slightly lower than those measured in water due to the release of more aluminum ions which then hydrolyses. Therefore, both measurements are needed to fully define the character of the soil's pH.
5.3 For the purpose of these test methods, the test specimens are sieved through a 2.00 mm (No. 10) sieve. Measurements on soils or soil fractions having particle sizes larger than 2.0 mm by these test methods may be invalid. If soil or soil fractions with particles larger than 2.0 mm are used, it must be stated in the report since the results may be significantly different.
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.
SCOPE
1.1 These test methods cover the measurement of the pH of soils that will pass the 2.00 mm (No. 10) sieve. Such measurements are used in the agricultural, environmental, geotechnical, and natural resources fields. This measurement determines the degree of acidity or alkalinity in soil materials suspended in water and a 0.01 M calcium chloride solution. Measurements in both liquids are necessary to fully define the soil's pH. This variable is useful in determining the solubility of soil minerals and the mobility of ions in the soil and assessing the viability of the soil-plant environment. A more detailed discussion of the usefulness of this parameter is given in Refs (1-6)2.
1.2 Two methods for measuring the pH of soils are provided. The method to be used shall be specified by the requesting authority. When no method is specified, Method A shall be used. The pH is determined in test water and a calcium chloride solution for both methods.
1.2.1 Method A—The pH is measured using a potentiometer having a pH sensitive electrode system. This method can be used for any application and must be used when the application warrants a higher level of resolution.
1.2.2 Method B—The pH is measured using pH sensitive paper. This method can be used for any application, however, because paper typically has a lower resolution, it provides an approximate estimate of the pH of the soil and should not be used when the application requires a higher level of resolution (Note 1).
Note 1: For example, paper with a sensitivity to the nearest 1 pH unit placed into a buffer solution of 4 should indicate a pH of 4, however, it would not indicate if the pH is 4.449 or 3.449.
1.3 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 All measured and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.
1.4.1 The procedures used to specify how data are collected/recorded and calculated in the 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 variatio...
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Designation: D4972 − 18
Standard Test Methods for
1
pH of Soils
This standard is issued under the fixed designation D4972; 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* 1.4 All measured and calculated values shall conform to the
guidelines for significant digits and rounding established in
1.1 These test methods cover the measurement of the pH of
Practice D6026.
soils that will pass the 2.00 mm (No. 10) sieve. Such
1.4.1 Theproceduresusedtospecifyhowdataarecollected/
measurements are used in the agricultural, environmental,
recorded and calculated in the standard are regarded as the
geotechnical, and natural resources fields. This measurement
industry standard. In addition, they are representative of the
determines the degree of acidity or alkalinity in soil materials
significant digits that generally should be retained. The proce-
suspended in water and a 0.01 M calcium chloride solution.
dures used do not consider material variation, purpose for
Measurements in both liquids are necessary to fully define the
obtaining the data, special purpose studies, or any consider-
soil’s pH. This variable is useful in determining the solubility
ations for the user’s objectives; and it is common practice to
of soil minerals and the mobility of ions in the soil and
increase or reduce significant digits of reported data to be
assessing the viability of the soil-plant environment. A more
commensuratewiththeseconsiderations.Itisbeyondthescope
detailed discussion of the usefulness of this parameter is given
2 of these test methods to consider significant digits used in
in Refs (1-6) .
analysis methods for engineering data.
1.2 Two methods for measuring the pH of soils are pro-
1.5 This standard does not purport to address all of the
vided. The method to be used shall be specified by the
safety concerns, if any, associated with its use. It is the
requesting authority. When no method is specified, Method A
responsibility of the user of this standard to establish appro-
shall be used.The pH is determined in test water and a calcium
priate safety, health, and environmental practices and deter-
chloride solution for both methods.
mine the applicability of regulatory limitations prior to use.
1.2.1 Method A—The pH is measured using a potentiometer
1.6 This international standard was developed in accor-
having a pH sensitive electrode system. This method can be
dance with internationally recognized principles on standard-
usedforanyapplicationandmustbeusedwhentheapplication
ization established in the Decision on Principles for the
warrants a higher level of resolution.
Development of International Standards, Guides and Recom-
1.2.2 Method B—The pH is measured using pH sensitive
mendations issued by the World Trade Organization Technical
paper. This method can be used for any application, however,
Barriers to Trade (TBT) Committee.
because paper typically has a lower resolution, it provides an
approximate estimate of the pH of the soil and should not be
2. Referenced Documents
used when the application requires a higher level of resolution 3
2.1 ASTM Standards:
(Note 1).
C670 Practice for Preparing Precision and Bias Statements
for Test Methods for Construction Materials
NOTE 1—For example, paper with a sensitivity to the nearest 1 pH unit
placed into a buffer solution of 4 should indicate a pH of 4, however, it
D653 Terminology Relating to Soil, Rock, and Contained
would not indicate if the pH is 4.449 or 3.449.
Fluids
1.3 Units—The values stated in SI units are to be regarded D1193 Specification for Reagent Water
D2487 Practice for Classification of Soils for Engineering
as standard. No other units of measurement are included in this
standard. Purposes (Unified Soil Classification System)
D2488 Practice for Description and Identification of Soils
(Visual-Manual Procedures)
D3740 Practice for Minimum Requirements for Agencies
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These test methods are under the jurisdiction ofASTM Committee D18 on Soil
Engaged in Testing and/or Inspection of Soil and Rock as
and Rock and is the direct responsibility of Subcommittee D18.22 on Media for
Plant Growth.
Current edition approved July 1, 2018. Published July 2018. Originally approved
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in 1989. Last previous edition approved in 2013 as D4972 – 13. DOI: 10.1520/ For referenced ASTM standards, visit the ASTM website, www.astm.org, or
D4972-18. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
2
The boldface numbers in parentheses refer to a list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this st
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D4972 − 13 D4972 − 18
Standard Test MethodMethods for
1
pH of Soils
This standard is issued under the fixed designation D4972; 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 ThisThese test method coversmethods cover the measurement of the pH of soils for uses other than for corrosion testing.
that will pass the 2.00 mm (No. 10) sieve. Such measurements are used in the agricultural, environmental, geotechnical, and natural
resources fields. This measurement determines the degree of acidity or alkalinity in soil materials suspended in water and a 0.01
M calcium chloride solution. Measurements in both liquids are necessary to fully define the soil’s pH. This variable is useful in
determining the solubility of soil minerals and the mobility of ions in the soil and assessing the viability of the soil-plant
environment. A more detailed discussion of the usefulness of this parameter is not warranted here; however, it can be found in
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many discussions of the subject. A few such discussions are given asgiven in Refs (1-6) at the end of the text.
1.2 Two methods for measuring the pH of soils are provided. The method to be used shall be specified by the requesting
authority. When no method is specified, Method A shall be used. The pH is determined in test water and a calcium chloride solution
for both methods.
1.2.1 Method A—The pH is measured using a potentiometer having a pH sensitive electrode system. This method can be used
for any application and must be used when the application warrants a higher level of resolution.
1.2.2 Method B—The pH is measured using pH sensitive paper. This method can be used for any application, however, because
paper typically has a lower resolution, it provides an approximate estimate of the pH of the soil and should not be used when the
application requires a higher level of resolution (Note 1).
NOTE 1—For example, paper with a sensitivity to the nearest 1 pH unit placed into a buffer solution of 4 should indicate a pH of 4, however, it would
not indicate if the pH is 4.449 or 3.449.
1.3 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this
standard.
1.4 All measured and calculated values shall conform to the guidelines for significant digits and rounding established in Practice
D6026.
1.4.1 The procedures used to specify how data are collected/recorded and calculated in the 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 these test methods to consider significant digits used in analysis methods for engineering data.
1.5 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.6 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
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2.1 ASTM Standards:
C670 Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials
1
ThisThese test method ismethods are under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.22 on Soil
as a Medium Media for Plant Growth.
Current edition approved Nov. 1, 2013July 1, 2018. Published November 2013July 2018. Originally approved in 1989. Last previous edition approved in 20072013 as
D4972 – 01 (2007).D4972 – 13. DOI: 10.1520/D4972-13.10.1520/D4972-18.
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The boldface numbers in parentheses refer to a list of references at the end of this standard.
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