oSIST prEN 13654-1:2025

SLOVENSKI STANDARD
01-december-2025
Izboljševalci tal in rastni substrati - Določanje dušika - 1. del: Spremenjena
Kjeldahlova metoda
Soil improvers and growing media - Determination of nitrogen - Part 1: Modified Kjeldahl
method
Bodenverbesserungsmittel und Kultursubstrate - Bestimmung von Stickstoff - Teil 1:
Modifiziertes Verfahren nach Kjeldahl
Amendements du sol et supports de culture - Détermination de l'azote - Partie 1:
Méthode de Kjeldahl modifiée
Ta slovenski standard je istoveten z: prEN 13654-1
ICS:
65.080 Gnojila Fertilizers
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2025
ICS 65.080 Will supersede EN 13654-1:2001
English Version
Soil improvers and growing media - Determination of
nitrogen - Part 1: Modified Kjeldahl method
Amendements du sol et supports de culture - Bodenverbesserungsmittel und Kultursubstrate -
Détermination de l'azote - Partie 1: Méthode de Bestimmung von Stickstoff - Teil 1: Modifiziertes
Kjeldahl modifiée Verfahren nach Kjeldahl
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 223.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
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.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 13654-1:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
4 Principle . 4
5 Reagents . 4
6 Apparatus . 4
7 Sampling . 5
8 Test sample . 5
9 Procedure . 5
9.1 Safety . 5
10 Calculation . 7
10.1 General. 7
10.2 Calculation on a dry matter basis . 7
10.3 Calculation on a volume basis . 7
11 Expression of results . 7
12 Test Report . 8
13 Validation of the method . 8
13.1 Validation in accordance with ISO 5725-2. 8
13.2 Performance characteristics. 8
Annex A (informative) Performance characteristics of the method . 9
Bibliography . 11

European foreword
This document (prEN 13654-1:2025) has been prepared by Technical Committee CEN/TC 223 “Soil
improvers and growing media”, the secretariat of which is held by NEN.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 13654-1:2001.
EN 13654-1:2001:
— Normative references have been adapted;
— The procedure has been described in more detail.
The Annex A is informative.
This document has been prepared under a standardization request addressed to CEN by the European
Commission. The Standing Committee of the EFTA States subsequently approves these requests for its
Member States.
1 Scope
This document specifies a method for the determination of nitrogen in soil improvers and growing media.
The Kjeldahl method determines ammonium-N, nitrate-N, nitrite-N and organic N content of soil
improvers and growing media. Nitrogen in N-N-linkages, N-O-linkages and some heterocyclics (especially
pyridine) is only partially determined [6], [7], [8].
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
CEN/TS 17732:2022, Soil improvers and growing media - Terminology
EN 12579:2024, Soil improvers and growing media - Sampling
prEN 13040-1:2025, Soil improvers and growing media — Sample preparation — Part 1: Sample
preparation for chemical and physical tests, determination of dry matter content, moisture content and
laboratory bulk density
3 Terms and definitions
For the purposes of this document the terms and definitions given in CEN/TS 17732:2022 apply.
4 Principle
The nitrogen content of the sample is determined using a method based on a sulfuric acid/potassium
sulfate digestion. Copper sulfate is used as the catalyst.
5 Reagents
All reagents shall be of recognized analytical grade. Use water with a specific conductivity not higher than
0,2 mS/m at 25 °C, free from the elements to be determined.
5.1 Salicylic acid/sulfuric acid, dissolve 25 g of salicylic acid (HOC H COOH) in 1 000 ml of
6 4
concentrated sulfuric acid (⍴ = 1,84 g/ml).
5.2 Potassium sulfate catalyst mixture, grind and thoroughly mix 200 g of potassium sulfate, 6 g of
copper (II) sulfate pentahydrate (This mixture may be available commercially).
5.3 Sodium thiosulfate pentahydrate, crush the crystals to form a powder that passes through a sieve
with an aperture of 0,25 mm.
5.4 Verification substances, pure substances of known nitrogen content, for example acetanilide
(C H NO), L-aspartic acid (C H NO ), or amino acids of known composition. The total content of nitrogen
8 9 4 7 4
of the calibration substance should be as similar to the sample nitrogen content as possible.
6 Apparatus
Usual laboratory apparatus, and in particular the following:
6.1 Analytical balance, capable of weighing accurately to 1,0 mg.
6.2 Kjeldahl digestion flasks or tubes, of nominal value 50 ml, suitable for the digestion system (6.3).
NOTE Larger flasks (300 ml to 500 ml) might be necessary for bulky materials or where a larger sample mass
is used.
6.3 Digestion or mineralisation system with variable heating controls.
6.4 Sieve, 5 mm square aperture size.
6.5 Stand, capable of holding the digestion flasks or tubes.
7 Sampling
Sampling is not part of the method specified in this document. EN 12579:2024 shall be followed dealing
with soil improvers and growing media. It is important that the laboratory receives a sample that is
representative of the product under consideration. The sample should not have been damaged or
changed during transport or storage.
8 Test sample
Either prepare the test sample in accordance with prEN 13040-1:2025, Clause 10 or use the sample as
received. Choose the respective calculation procedure (Clause 10).
Losses of nitrogen can occur with samples of high ammonium-N content in alkaline situations and
particularly when these samples are dried. If the sample contains (or is suspected to contain) > 500 mg/l
NH -N fresh basis, as determined by prEN 13651:2025 [1] or prEN 13652:2025 [2], analyse the fresh
material as soon as possible.
9 Procedure
9.1 Safety
SAFETY PRECAUTIONS — Care should be taken when handling samples that may contain sharps or are
of a dusty nature.
WARNING — Digestions with sulfuric acid are potentially hazardous and laboratory coats, gloves and
safety spectacles or goggles shall be used.
The digestion shall be carried out in a well-ventilated fume cupboard with the reflux digestion on a
temperature-controlled heating apparatus. Anti-bumping granules (or roughened glass beads) may be
added both to the blank and the samples to prevent bumping and loss of solution. It is important to
maintain gentle reflux, both of the blank and the test samples, to avoid temperature fluctuations, which
can cause local superheating.
The toxicity or carcinogenicity of each reagent used in this method has not been precisely defined;
however, each chemical compound needs to be treated as a potential health hazard. From this viewpoint,
reduce exposure to these chemicals to the lowest possible level by whatever means available.
Toxic fumes are evolved by boiling sulfuric acid. Always use the concentrated acid in a fume cupboard.
9.2 Dried sample
Place a portion of the dried ground sample (Clause 8) of between 0,2 g (expected nitrogen content
≈ 0,5 %) and 1,0 g (expected nitrogen content ≈ 0,1 %) in the digestion flask (6.2). Add 20 ml of
salicylic/sulfuric acid (5.1) and swirl until the acid is thoroughly mixed with the sample. Allow the
mixture to stand for several hours (overnight). Add 0,5 g of sodium thiosulfate (5.3) through a dry funnel
with a long stem that reaches down into the bulb or the crystalline mixture (5.2) just above the acid if a
tube is used. Heat the mixture cautiously on the digestion stand (6.3) until frothing has ceased.
Heat until there are no more organic particles visible in the digestion mixture. Boil the mixture gently for
up to 5 h so that the sulfuric acid condenses about 1/3 of the way up the neck of the flask. Ensure that at
the end of the boiling process there is still liquid left.
NOTE Boiling at approximately 400 °C usually takes about 5 h, at approximately 540 °C about 3 h.
9.3 Residual moisture
The moisture in the analysed sample (9.2) is determined in accordance with prEN 13040-1:2025,
Clause 11, using 10 g of the dried sample obtained from prEN 13040-1:2025, Clause 10.
9.4 Fresh samples
Fresh solid samples shall be reduced in size to pass a 5 mm sieve or milled in the presence of dry ice (solid
carbon dioxide). Liquid samples shall be thoroughly homogenized according to prEN 13040-1:2025,
Clause 10.4. Weigh up to 20 g sample into a large Kjeldahl flask. Add sufficient salicylic/sulfuric acid (5.1)
until the acid is thoroughly mixed with the sample. Allow the mixture to stand for several hours
(overnight). Add sodium thiosulfate (5.3) (0,5 g for every 4 ml of acid used) through a dry funnel with a
long stem that reaches down into the bulb or the crystalline mixture (5.2) just above the acid if a tube is
used. Heat the mixture cautiously on the digestion stand (6.3) until frothing has ceased.
NOTE Usually 20 ml of salicylic/sulfuric acid and two tabs of the crystalline mixture (5.2) are sufficient.
Heat until there are no mor
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