ISO 21263:2017

INTERNATIONAL ISO
STANDARD 21263
First edition
2017-12
Slow-release fertilizers —
Determination of the release of
the nutrients — Method for coated
fertilizers
Engrais à libération lente — Détermination du mode de libération des
éléments nutritifs — Méthode applicable aux engrais enrobés
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
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ii © ISO 2017 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus . 2
6 Sampling . 2
7 Procedure. 2
7.1 Preparation of the test solution . 2
7.2 Time intervals for periodic determinations of nutrient content . 3
7.3 Determination of the nutrient content . 3
7.4 Determination of the total water-extractable nutrient content . 3
8 Expression of results . 4
9 Precision . 4
9.1 General . 4
9.2 Repeatability . 4
9.3 Reproducibility . 5
10 Test report . 5
Annex A (normative) Criteria for release conditions . 6
Annex B (informative) Accelerated test methods based on an elevated temperature .7
Bibliography . 9
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
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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
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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 on 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 the following
URL: www.iso.org/iso/foreword.html.
ISO 21263 was prepared by CEN/TC 260 as EN 13266:2001 and was adopted by Technical Committee
ISO/TC 134, Fertilizers and soil conditioners, with the following modifications:
— in Clause 1, two instances of “may” (permission) have been changed to “can” (possibility);
— in 7.2, the wording of the last sentence has been changed so that normative Annex A is cited
normatively.
iv © ISO 2017 – All rights reserved

INTERNATIONAL STANDARD ISO 21263:2017(E)
Slow-release fertilizers — Determination of the release of
the nutrients — Method for coated fertilizers
1 Scope
This document specifies a method for the determination of the slow release properties of nutrients from
coated fertilizers. pH-dependent hydrolysis and degradation by biological or microbial mechanisms are
excluded.
The specified method is only applicable to products releasing any nutrients by means of a non-biological
process (i.e. those where the nutrients are released by a physical mechanism). Microbial attack on the
coating (e.g. sulfur coated fertilizers) and the consequences thereof are not measurable by the technique
described.
This method involves a lengthy process which may not be appropriate for day to day testing purposes.
Accelerated methods can be used provided they are correlated with this document. An example of such
an accelerated method is described in Annex B. Regression analysis can also be used for this purpose.
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.
ISO 3696, Water for analytical laboratory use — Specification and test methods
EN 1482,Sampling of solid fertilizers and liming materials
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
3.1
release
transfer of a nutrient from the fertilizer to the receiving medium (water)
3.2
slow release
release under the defined conditions meeting each of the criteria set out in Annex A
3.3
initial release of a nutrient
mass fraction in percent of a nutrient released during the first 24 h after the start of the test
3.4
stated release time
time period between the start of the test and the release of a given minimum percentage of the specified
nutrient
Note 1 to entry: This may also be referred to as longevity. See Annex A.
3.5
coated fertilizer
fertilizer that is encapsulated, by covering it with a water-insoluble material, in order to reduce its
release rate in water
4 Principle
Elution of a test portion of a fertilizer with a specified volume of water. Determination of the
concentration of the nutrient(s), that have been dissolved in defined time intervals.
5 Apparatus
Ordinary laboratory apparatus and, in particular, the following.
5.1 Glass beakers, of capacity 800 ml, with a lid.
5.2 One mark volumetric flask, 500 ml capacity.
5.3 Magnetic stirrer, with a magnetic rod with a size of 25 mm, or any other suitable stirrer.
5.4 Temperature-control equipment, capable of maintaining the medium at the temperature of
(25 ± 0,5) °C.
6 Sampling
Sampling and sample preparation shall be carried out in accordance with EN 1482.
The method of sampling and of sample preparation shall be indicated in the test report. Take care to
avoid damage to, or destruction of, the coating.
Do not crush or grind the sample.
7 Procedure
7.1 Preparation of the test solution
Transfer 500 ml of water, conforming to grade 3 of ISO 3696, into a beaker (5.1). Weigh, to the nearest
0,01 g, (10 ± 0,1) g of the fertilizer, add it to the water in the beaker and record the time. Weigh the
beaker together with its contents: the sample of fertilizer, water and stirring rod. Note the total mass to
−1
the nearest 1 g. Start the stirrer (5.3) at a rotational frequency of approximately 300 min . Cover the
beaker with a lid to avoid evaporation of water and maintain the temperature at (25 ± 0,5) °C with the
temperature-control equipment (5.4).
Each time it is desired to make a nutrient determination (see 7.2), decant the solution into another
beaker (5.1), taking care to avoid any of the undissolved fertilizer being carried over. Refill the beaker
(5.1) with water (conforming to grade 3 of ISO 3696) at 25 °C so as to achieve the previously recorded
mass. Continue extraction immediately.
2 © ISO 2017 – All rights reserved

Continue the extraction procedure until more than 75 % of the n
...