ASTM D4972-95a

NOTICE: This standard has either been superseded and replaced by a new version or
withdrawn.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: D 4972 – 95a
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
1
pH of Soils
This standard is issued under the fixed designation D 4972; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope calibrated with buffer solutions of known pH. The pH sensitive
paper is a less accurate measurement and should only be used
1.1 This test method covers the measurement of the pH of
for a rough estimate of the soil pH. The electrode must be used
soils for uses other than for corrosion testing. Such measure-
for this measurement unless the pH sensitive paper is specified.
ments are used in the agricultural, environmental, and natural
resources fields. This measurement determines the degree of
4. Significance and Use
acidity or alkalinity in soil materials suspended in water and a
4.1 The pH of the soil is a useful variable in determining the
0.01 M calcium chloride solution. Measurements in both
solubility of soil minerals and the mobility of ions in the soil
liquids are necessary to fully define the soil’s pH. This variable
and assessing the viability of the soil-plant environment.
is useful in determining the solubility of soil minerals and the
4.2 pH measurements are made in both water and a calcium
mobility of ions in the soil and assessing the viability of the
chloride solution because the calcium displaces some of the
soil-plant environment. A more detailed discussion of the
exchangeable aluminum. The low ionic strength counters the
usefulness of this parameter is not warranted here; however, it
dilution effect on the exchange equilibrium by setting the salt
can be found in many discussions of the subject. A few such
2 concentration of the solution closer to that expected in the soil
discussions are given as Refs (1-6) at the end of the text.
solution. The pH values obtained in the solution of calcium
1.2 The values given in SI units are to be regarded as the
chloride are slightly lower than those measured in water due to
standard.
the release of more aluminum ions which then hydrolyses.
1.3 This standard does not purport to address all of the
Therefore, both measurements are required to fully define the
safety concerns, if any, associated with its use. It is the
character of the soil’s pH.
responsibility of the user of this standard to establish appro-
4.3 For the purpose of this test method the test soil must be
priate safety and health practices and determine the applica-
sieved through a No. 10 sieve (2 mm sieve mesh openings).
bility of regulatory limitations prior to use.
Measurements on soils or soil fractions having particle sizes
2. Referenced Documents 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
2.1 ASTM Standards:
be stated in the report since the results may be significantly
C 670 Practice for Preparing Precision and Bias Statements
3
different.
for Test Methods for Construction Materials
4
4.4 All water used for this test method must be ASTM Type
D 1193 Specification for Reagent Water
III or better. Type III water is defined by Specification D 1193.
G 51 Test Method for pH of Soil for Use in Corrosion
5
It is prepared by distillation, ion exchange, reverse osmosis, or
Testing
a combination thereof.
3. Summary of Test Method
5. Interferences
3.1 Measurement of the pH of soils in both suspensions of
5.1 This test method as measured by a pH probe has
water and a calcium chloride solution are made with either a
possible interferences due to a suspension effect or sedimen-
potentiometer using a pH sensitive electrode system (Method
tation potential. Users interested in a detailed discussion of the
A), or pH sensitive paper (Method B). The potentiometer is
mechanism of this effect can find it in Refs (5) and (6).
5.2 This effect is the main reason Test Method G 51 can not
1
This test method is under the jurisdiction of ASTM Committee D-18 on Soil
be used for general measurement of pH outside of that for
and Rock and is the direct responsibility of Subcommittee D18.22 on Soil as a
corrosion analysis. Test Method G 51 measures pH (an aque-
Medium for Plant Growth.
ous parameter) without adding any aqueous phase to the soil.
Current edition approved July 15, 1995. Published August 1995. Originally
This results in excessive soil particle-pH probe contact that
published as D 4972 – 89. Last previous edition D 4972 – 95.
2
The boldface numbers in parentheses refer to a list of referenc
...