ISO/DTS 22171

Soil quality — Determination of potential cation exchange capacity (CEC) and exchangeable cations buffered at pH 7, using a molar ammonium acetate solution

Qualité du sol — Détermination de la capacité d'échange cationique (CEC) potentielle et de la teneur en cations échangeables, à l'aide d'une solution molaire d'acétate d'ammonium tamponnée à pH 7

Kakovost tal - Določanje potencialne kationske izmenjalne kapacitete (CEC) in izmenljivih kationov z uporabo pufrske raztopine amonijevega acetata s pH 7

General Information

• Status: Not Published
• ICS: 13.080.10 - Chemical characteristics of soils
• Technical Committee: ISO/TC 190/SC 3 - Chemical and physical characterization
• Drafting Committee: ISO/TC 190/SC 3/WG 14 - Physical methods
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 15-Sep-2023
• Completion Date: 15-Sep-2023
• Ref Project: oSIST ISO/DIS 22171:2023 - Soil quality - Determination of potential cation exchange capacity (CEC) and exchangeable cations buffered at pH 7, using a molar ammonium acetate solution

Standards Content (Sample)

ISO/DTS 22171
ISO/TC 190/SC 3
Date: 2022-07-11
ISO/TS 22171:2023(E)
ISO/TC 190/SC 3/WG 14
Secretariat: DIN
Date: 2023-08-31
Soil quality — Determination of potential cation exchange
capacity (CEC) and exchangeable cations buffered at pH 7, using a
molar ammonium acetate solution
Qualité du sol — DeterminationDétermination de la capacité d'échange cationique (CEC) potentielle (CEC)
et desde la teneur en cations échangeables par une, à l'aide d'une solution molaire d'acétate d'ammonium
molaire tamponnée à pH 7
DTS stage

---------------------- Page: 1 ----------------------
ISO/TS DTS 22171:2023(:(E)
© ISO 20222023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this
publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical,
including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can
be requested from either ISO at the address below or ISO'sISO’s member body in the country of the requester.
ISO Copyright Office copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Email: E-mail: [e-mail]
Website: www.iso.org
Published in Switzerland.
ii © ISO 2023 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/TS DTS 22171:2023(:(E)
Contents Page
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Reagents . 1
5 Apparatus . 3
6 Laboratory samples . 5
7 Procedure . 5
7.1 Test portion . 5
7.2 Extraction step . 5
7.3 Ammoniacal nitrogen assay by continuous flow spectrophotometry . 5
7.3.1 Apparatus set-up . 5
7.3.2 Assays . 7
7.4 Expression of results . 7
8 Test report . 8
Bibliography . 9

© ISO 2023 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO/TS DTS 22171:2023(:(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO
collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documentsdocument should be noted. This document was drafted in accordance
with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawnISO draws attention to the possibility that some of the elementsimplementation of this
document may beinvolve the subjectuse of (a) patent(s). ISO takes no position concerning the evidence,
validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of
this document, ISO had not received notice of (a) patent(s) which may be required to implement this
document. However, implementers are cautioned that this may not represent the latest information,
which may be obtained from the patent database available at www.iso.org/patents. ISO shall not be held
responsible for identifying any or all such patent rights. Details of any patent rights identified during the
development of the document will be in the Introduction and/or on the ISO list of patent declarations
received (see ).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the World
Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee Committee ISO/TC 190, Soil quality, Subcommittee
SC 3, Chemical and physical characterization.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv © ISO 2023 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/TS DTS 22171:2023(:(E)
Introduction
Cation exchange capacity (CEC) is an intrinsic property of soil defining the concentration of negatively
charged sites on soil colloids that can adsorb exchangeable cations. Cation exchange capacity can be a
good indicator of soil productivity and is useful for making recommendations of phosphorus (P),
potassium (K), and magnesium (Mg) if testing soils of different textures. Cation exchange capacity is also
used for regulatory purposes in monitoring land application of biosolids.
Cation exchange capacity is a measure of exchangeable bases and soil acidity at some specific soil pH. The
exchangeable bases and acidity neutralize negative charges arising from permanent charges due to
isomorphic substitution in clays, or pH-dependent charges from hydroxyl groups on clay and oxides or
carboxyl groups on soil organic matter. A common method for determining CEC uses 1 M ammonium
acetate at pH 7 (neutral NH4OAc) and is a standard method used for soil surveys by the Natural Resource
[6],[7[6],[7] ]
Conservation Service. . An advantage of CEC measured at a constant pH of 7 is elimination of CEC
variability due to differences in soil pH. Thus, comparisons of CEC can occur across varied soil types and
lime applications. A disadvantage of the neutral NH OAc method is that it may not provide a realistic
4
depiction of the actual CEC at the natural pH of the soil, particularly with soils having considerable pH-
dependent charge and a soil pH that is significantly different from 7. An unbuffered salt extract can be
used to determine CEC at the natural pH of soil, for example, by using a hexamminecobalt(III)-chloride
solution (see ISO 23470, References [6] and [7[6], [7].]).
The method described here determines potential cation exchange capacity (CEC) buffered at pH 7 and
exchangeable cations Ca, Mg, K, and Na. Molar ammonium acetate is added to soil to saturate exchange
+ +
sites with NH and release exchangeable cations in a leachate which are measured. The exchanged NH
4 4
is then released either with 1 M KCl or 1 M NaCl and measured to quantify the potential cation exchange
capacity at pH 7.
Ammonium acetate, due to its complexing effect, can contribute to the dissolution of part of soil
carbonates and other salts present in the soil. Calcium concentrations (or even magnesium) are thus no
longer limited to exchangeable quantities. Presence of other soluble salts such as gypsum, sodium
chloride or else would also inflate exchangeable cation quantities.
© ISO 2023 – All rights reserved v

---------------------- Page: 5 ----------------------
DRAFT INTERNATIONAL STANDARD ISO/TS 22171:2023(E)

Soil quality — Determination of potential cation exchange capacity
(CEC) and exchangeable cations buffered at pH 7, using a molar
ammonium acetate solution
1 Scope
This document specifies a method for the determination of potential cation exchange capacity (CEC) and
the content of exchangeable cations (Ca, K, Mg, Na) in soils using a molar ammonium acetate solution
buffered at pH 7 as extractant.
This document is applicable to all types of air-dry soil samples which have been prepared, for example,
according to ISO 11464.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminologicalterminology databases for use in standardization at the following
addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
— 4 Principle
Negatively charged sites on soil are saturated by ammonium ion, in leaching conditions, using a molar
ammonium acetate solution. The leaching solution can be used to determine exchangeable cations by AAS
or ICP AES measurements. An alcoholic solution is used to eliminate any remaining soluble ammonium
ion. The soil test sample is then back extracted by a molar potassium chloride or sodium chloride solution,
in order to liberate all ammonium cations fixed in the previous step. For practical reason, a single back
extraction is performed. This is generally sufficient to assess the whole CEC as the molarity of the back-
extraction solution is strong (molar solution of KCl), Ammonium cations are finally determined in the
extract by a continuous flow spectrophotometric
...

FINAL
TECHNICAL ISO/DTS
DRAFT
SPECIFICATION 22171
ISO/TC 190/SC 3
Soil quality — Determination of
Secretariat: DIN
potential cation exchange capacity
Voting begins on:
2023-09-15 (CEC) and exchangeable cations
buffered at pH 7, using a molar
Voting terminates on:
2023-11-10
ammonium acetate solution
Qualité du sol — Détermination de la capacité d'échange cationique
(CEC) potentielle et de la teneur en cations échangeables, à l'aide
d'une solution molaire d'acétate d'ammonium tamponnée à pH 7
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/DTS 22171:2023(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2023

---------------------- Page: 1 ----------------------
ISO/DTS 22171:2023(E)
FINAL
TECHNICAL ISO/DTS
DRAFT
SPECIFICATION 22171
ISO/TC 190/SC 3
Soil quality — Determination of
Secretariat: DIN
potential cation exchange capacity
Voting begins on:
(CEC) and exchangeable cations
buffered at pH 7, using a molar
Voting terminates on:
ammonium acetate solution
Qualité du sol — Détermination de la capacité d'échange cationique
(CEC) potentielle et de la teneur en cations échangeables, à l'aide
d'une solution molaire d'acétate d'ammonium tamponnée à pH 7
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
RECIPIENTS OF THIS DRAFT ARE INVITED TO
ISO copyright office
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
CP 401 • Ch. de Blandonnet 8
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
CH-1214 Vernier, Geneva
DOCUMENTATION.
Phone: [phone]
IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: [e-mail]
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/DTS 22171:2023(E)
Website: www.iso.org
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
Published in Switzerland
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
ii
  © ISO 2023 – All rights reserved
NATIONAL REGULATIONS. © ISO 2023

---------------------- Page: 2 ----------------------
ISO/DTS 22171:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
5 Reagents . 1
6 Apparatus . 3
7 Laboratory samples .4
8 Procedure .4
8.1 Test portion . 4
8.2 Extraction step . 4
8.3 Ammoniacal nitrogen assay by continuous flow spectrophotometry . 5
8.3.1 Apparatus set­up . 5
8.3.2 Assays . . 6
8.4 Expression of results . 7
9 Test report . 7
Bibliography . 8
iii
© ISO 2023 – All rights reserved

---------------------- Page: 3 ----------------------
ISO/DTS 22171:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non­governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 3,
Chemical and physical characterization.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
  © ISO 2023 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/DTS 22171:2023(E)
Introduction
Cation exchange capacity (CEC) is an intrinsic property of soil defining the concentration of negatively
charged sites on soil colloids that can adsorb exchangeable cations. Cation exchange capacity can be
a good indicator of soil productivity and is useful for making recommendations of phosphorus (P),
potassium (K), and magnesium (Mg) if testing soils of different textures. Cation exchange capacity is
also used for regulatory purposes in monitoring land application of biosolids.
Cation exchange capacity is a measure of exchangeable bases and soil acidity at some specific soil pH.
The exchangeable bases and acidity neutralize negative charges arising from permanent charges due to
isomorphic substitution in clays, or pH-dependent charges from hydroxyl groups on clay and oxides or
carboxyl groups on soil organic matter. A common method for determining CEC uses 1 M ammonium
acetate at pH 7 (neutral NH OAc) and is a standard method used for soil surveys by the Natural Resource
4
[6],[7]
Conservation Service. An advantage of CEC measured at a constant pH of 7 is elimination of CEC
variability due to differences in soil pH. Thus, comparisons of CEC can occur across varied soil types and
lime applications. A disadvantage of the neutral NH OAc method is that it may not provide a realistic
4
depiction of the actual CEC at the natural pH of the soil, particularly with soils having considerable pH-
dependent charge and a soil pH that is significantly different from 7. An unbuffered salt extract can be
used to determine CEC at the natural pH of soil, for example, by using a hexamminecobalt(III)-chloride
solution (see ISO 23470, References [6] and [7]).
The method described here determines potential cation exchange capacity (CEC) buffered at pH 7 and
exchangeable cations Ca, Mg, K, and Na. Molar ammonium acetate is added to soil to saturate exchange
+
sites with NH and release exchangeable cations in a leachate which are measured. The exchanged
4
+
NH is then released either with 1 M KCl or 1 M NaCl and measured to quantify the potential cation
4
exchange capacity at pH 7.
Ammonium acetate, due to its complexing effect, can contribute to the dissolution of part of soil
carbonates and other salts present in the soil. Calcium concentrations (or even magnesium) are thus
no longer limited to exchangeable quantities. Presence of other soluble salts such as gypsum, sodium
chloride or else would also inflate exchangeable cation quantities.
v
© ISO 2023 – All rights reserved

---------------------- Page: 5 ----------------------
TECHNICAL SPECIFICATION ISO/DTS 22171:2023(E)
Soil quality — Determination of potential cation exchange
capacity (CEC) and exchangeable cations buffered at pH 7,
using a molar ammonium acetate solution
1 Scope
This document specifies a method for the determination of potential cation exchange capacity (CEC)
and the content of exchangeable cations (Ca, K, Mg, Na) in soils using a molar ammonium acetate
solution buffered at pH 7 as extractant.
This document is applicable to all types of air-dry soil samples which have been prepared, for example,
according to ISO 11464.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this d
...

SLOVENSKI STANDARD
oSIST ISO/DIS 22171:2023
01-junij-2023
Kakovost tal - Določanje potencialne kationske izmenjalne kapacitete (CEC) in
izmenljivih kationov z uporabo pufrske raztopine amonijevega acetata s pH 7
Soil quality - Determination of potential cation exchange capacity (CEC) and
exchangeable cations buffered at pH 7, using a molar ammonium acetate solution
Qualité du sol - Détermination de la capacité d'échange cationique (CEC) potentielle et
de la teneur en cations échangeables, à l'aide d'une solution molaire d'acétate
d'ammonium tamponnée à pH 7
Ta slovenski standard je istoveten z: ISO/DIS 22171
ICS:
13.080.10 Kemijske značilnosti tal Chemical characteristics of
soils
oSIST ISO/DIS 22171:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
oSIST ISO/DIS 22171:2023

---------------------- Page: 2 ----------------------
oSIST ISO/DIS 22171:2023
DRAFT INTERNATIONAL STANDARD
ISO/DIS 22171
ISO/TC 190/SC 3 Secretariat: DIN
Voting begins on: Voting terminates on:
2022-02-17 2022-05-12
Soil quality — Determination of potential cation exchange
capacity (CEC) and exchangeable cations buffered at pH 7,
using a molar ammonium acetate solution
ICS: 13.080.10
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
This document is circulated as received from the committee secretariat.
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 22171:2022(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022

---------------------- Page: 3 ----------------------
oSIST ISO/DIS 22171:2023
ISO/DIS 22171:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
  © ISO 2022 – All rights reserved

---------------------- Page: 4 ----------------------
oSIST ISO/DIS 22171:2023
ISO/DIS 22171:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 1
6 Apparatus . 3
7 Laboratory samples .4
8 Procedure .4
8.1 Test portion . 4
8.2 Extraction step . 4
8.3 Ammoniacal nitrogen assay by continuous flow spectrophotometry . 5
8.3.1 Apparatus set-up . 5
8.3.2 Assays . . 5
8.4 Expression of results . 6
9 Test report . 6
Bibliography . 7
iii
© ISO 2022 – All rights reserved

---------------------- Page: 5 ----------------------
oSIST ISO/DIS 22171:2023
ISO/DIS 22171:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 3,
Chemical and physical characterization.
iv
  © ISO 2022 – All rights reserved

---------------------- Page: 6 ----------------------
oSIST ISO/DIS 22171:2023
ISO/DIS 22171:2022(E)
Introduction
Cation exchange capacity (CEC) is an intrinsic property of soil defining the concentration of negatively
charged sites on soil colloids that can adsorb exchangeable cations. Cation exchange capacity can be
a good indicator of soil productivity and is useful for making recommendations of phosphorus (P),
potassium (K), and magnesium (Mg) if testing soils of different textures. Cation exchange capacity is
also used for regulatory purposes in monitoring land application of biosolids.
Cation exchange capacity is a measure of exchangeable bases and soil acidity at some specific soil pH.
The exchangeable bases and acidity neutralize negative charges arising from permanent charges due to
isomorphic substitution in clays, or pH-dependent charges from hydroxyl groups on clay and oxides or
carboxyl groups on soil organic matter. A common method for determining CEC uses 1 M ammonium
acetate at pH 7 (neutral NH OAc) and is a standard method used for soil surveys by the Natural Resource
4
Conservation Service (Burt, 2004; Hendershot et al., 2008; Sumner and Miller, 1996). An advantage of
CEC measured at a constant pH of 7 is elimination of CEC variability due to differences in soil pH. Thus,
comparisons of CEC can occur across varied soil types and lime applications. A disadvantage of the
neutral NH OAc method is that it may not provide a realistic depiction of the actual CEC at the natural
4
pH of the soil, particularly with soils having considerable pH-dependent charge and a soil pH that is
significantly different from 7. An unbuffered salt extract can be used to determine CEC at the natural
pH of soil, for example by using a hexamine chloride solution ISO 23470, see also Burt, 2004; Sumner
and Miller, 1996; Pansu and Gautheyrou, 2006.
The method described here determines potential cation exchange capacity (CEC) buffered at pH 7 and
exchangeable cations Ca, Mg, K, and Na. Molar ammonium acetate is added to soil to saturate exchange
+
sites with NH and release exchangeable cations in a leachate which are measured. The exchanged
4
+
NH is then released either with 1 M KCl or 1 M NaCl and measured to quantify the potential cation
4
exchange capacity at pH 7.
Ammonium acetate, due to its complexing effect, can contribute to the dissolution of part of soil
carbonates and other salts present in the soil. Calcium concentrations (or even magnesium) are thus
no longer limited to exchangeable quantities. Presence of other soluble salts such as gypsum, sodium
chloride or else would also inflate exchangeable cation quantities.
v
© ISO 2022 – All rights reserved

---------------------- Page: 7 ----------------------
oSIST ISO/DIS 22171:2023

---------------------- Page: 8 ----------------------
oSIST ISO/DIS 22171:2023
DRAFT INTERNATIONAL STANDARD ISO/DIS 22171:2022(E)
Soil quality — Determination of potential cation exchange
capacity (CEC) and exchangeable cations buffered at pH 7,
using a molar ammonium acetate solution
1 Scope
This International Standard s
...