ASTM D4972-01(2007)
(Test Method)Standard Test Method for pH of Soils
Standard Test Method for pH of Soils
SIGNIFICANCE AND USE
The pH of the soil is a useful variable in determining the solubility of soil minerals and the mobility of ions in the soil and assessing the viability of the soil-plant environment.
pH measurements are made in both 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 required to fully define the character of the soil’pH.
For the purpose of this test method the test soil must be sieved through a No. 10 sieve (2 mm sieve mesh openings). Measurements on soils or soil fractions having particle sizes larger than 2 mm by this test method may be invalid. If soil or soil fractions with particles larger than 2 mm are used, it must be stated in the report since the results may be significantly different.
All water used for this test method must be ASTM Type III or better. Type III water is defined by Specification D 1193. It is prepared by distillation, ion exchange, reverse osmosis, or a combination thereof.
SCOPE
1.1 This test method covers the measurement of the pH of soils for uses other than for corrosion testing. Such measurements are used in the agricultural, environmental, 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 many discussions of the subject. A few such discussions are given as Refs (1-6) at the end of the text.
1.2 The values given in SI units are to be regarded as the standard.
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 and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D4972 − 01(Reapproved 2007)
Standard Test Method for
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 G51 Test Method for Measuring pH of Soil for Use in
Corrosion Testing
1.1 This test method covers the measurement of the pH of
soils for uses other than for corrosion testing. Such measure-
3. Terminology
ments are used in the agricultural, environmental, and natural
3.1 Definitions:
resources fields. This measurement determines the degree of
3.1.1 For common definitions of terms used in this standard,
acidity or alkalinity in soil materials suspended in water and a
refer to Terminology D653.
0.01 M calcium chloride solution. Measurements in both
liquids are necessary to fully define the soil’s pH.This variable
4. Summary of Test Method
is useful in determining the solubility of soil minerals and the
4.1 Measurement of the pH of soils in both suspensions of
mobility of ions in the soil and assessing the viability of the
water and a calcium chloride solution are made with either a
soil-plant environment. A more detailed discussion of the
potentiometer using a pH sensitive electrode system (Method
usefulness of this parameter is not warranted here; however, it
A), or pH sensitive paper (Method B). The potentiometer is
can be found in many discussions of the subject. A few such
calibrated with buffer solutions of known pH.The pH sensitive
discussions are given as Refs (1-6) at the end of the text.
paper is a less accurate measurement and should only be used
1.2 The values given in SI units are to be regarded as the
for a rough estimate of the soil pH.The electrode must be used
standard.
forthismeasurementunlessthepHsensitivepaperisspecified.
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 5. Significance and Use
responsibility of the user of this standard to establish appro-
5.1 The pH of the soil is a useful variable in determining the
priate safety and health practices and determine the applica-
solubility of soil minerals and the mobility of ions in the soil
bility of regulatory limitations prior to use.
and assessing the viability of the soil-plant environment.
5.2 pH measurements are made in both water and a calcium
2. Referenced Documents
chloride solution because the calcium displaces some of the
2.1 ASTM Standards:
exchangeable aluminum. The low ionic strength counters the
C670 Practice for Preparing Precision and Bias Statements
dilution effect on the exchange equilibrium by setting the salt
for Test Methods for Construction Materials
concentration of the solution closer to that expected in the soil
D653 Terminology Relating to Soil, Rock, and Contained
solution. The pH values obtained in the solution of calcium
Fluids
chloride are slightly lower than those measured in water due to
D1193 Specification for Reagent Water
the release of more aluminum ions which then hydrolyses.
D3740 Practice for Minimum Requirements for Agencies
Therefore, both measurements are required to fully define the
Engaged in Testing and/or Inspection of Soil and Rock as
character of the soil’s pH.
Used in Engineering Design and Construction
5.3 For the purpose of this test method the test soil must be
sieved through a No. 10 sieve (2 mm sieve mesh openings).
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
Measurements on soils or soil fractions having particle sizes
Rock and is the direct responsibility of Subcommittee D18.22 on Soil as a Medium
larger than 2 mm by this test method may be invalid. If soil or
for Plant Growth.
soil fractions with particles larger than 2 mm are used, it must
Current edition approved Sept. 1, 2007. Published October 2007. Originally
approved in 1989. Last previous edition approved in 2001 as D4972 – 01. DOI:
be stated in the report since the results may be significantly
10.1520/D4972-01R07.
different.
The boldface numbers in parentheses refer to a list of references at the end of
the test method.
5.4 All water used for this test method must beASTM Type
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
III or better. Type III water is defined by Specification D1193.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
It is prepared by distillation, ion exchange, reverse osmosis, or
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. a combination thereof.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4972 − 01 (2007)
6. Interferences 8.5 CalciumChlorideSolution(0.01M)—Dilute20.0mLof
stock 1.0 M CaCl solution to 2 L with water. The pH of this
6.1 This test method as measured by a pH probe has
solution should be between 5 and 7.
possible interferences due to a suspension effect or sedimen-
tation potential. Users interested in a detailed discussion of the 8.6 Phosphate Buffer Solution (0.025 M)—Dissolve 3.40 g
mechanism of this effect can find it in Refs (5) and (6). of KH PO and 3.55 g of KH HPO in water and dilute to 1 L.
2 4 2 4
Dry salts2hat 130°C before use. The pH of this solution
6.2 This effect is the main reason Test Method G51 can not
should be 6.9 at 20°C. The effect of temperature is as follows:
be used for general measurement of pH outside of that for
°C pH
corrosion analysis.Test Method G51 measures pH (an aqueous
07.0
parameter) without adding any aqueous phase to the soil. This
10 6.9
results in excessive soil particle-pH probe contact that overes- 20 6.9
30 6.8
timates the activity of the hydrogen ions in solution and is
40 6.8
therefore unacceptable for general soil analysis.
9. Calibration of pH Meter
6.3 The suspension effect can be mitigated by careful
attention to 10.1.
9.1 Calibrate the pH meter using the acid potassium phtha-
late and phosphate buffer solutions. Adjustment of the pH
7. Apparatus
meter should follow the manufacturer’s direction.
7.1 Method A, pH Meter—Potentiometer equipped with
10. Procedure
glass-calomel electrode system. Follow the manufacturer’s
10.1 When making measurements with the pH electrode,
instructions for the pH meter used. A silver/silver chloride
place the electrode into the partially settled suspension to
electrode system or similar is also acceptable.
mitigate the suspension effect.
7.2 Method B, pH Paper—pH paper sensitive to a pH range
10.2 For both methods, begin with an
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.