ISO 19747:2020

INTERNATIONAL ISO
STANDARD 19747
First edition
2020-10
Fertilizers and soil conditioners —
Determination of monosilicic acid
concentrations in nonliquid fertilizer
materials
Détermination des concentrations en silicium soluble dans les
matières fertilisantes non liquides
Reference number
ISO 19747:2020(E)
©
ISO 2020

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ISO 19747:2020(E)

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ii © ISO 2020 – All rights reserved

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ISO 19747:2020(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative References . 1
3 Terms and Definitions . 1
4 Principle . 1
5 Safety . 1
6 Reagents . 2
7 Calibration standards . 3
8 Apparatus . 3
9 Procedure. 5
9.1 Sample preparation . 5
9.2 Extraction . 5
9.3 Heteropoly blue analyses . 5
9.4 Manual spectrophotometer analyses . 5
9.5 Calculations . 6
9.6 Precision . 6
9.7 Statistical analysis . 7
9.8 Ring study . 7
Annex A (Informative) Report of the international laboratories ring study . 8
Bibliography . 9
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ISO 19747:2020(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
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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
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on the ISO list of patent declarations received (see www .iso .org/ patents).
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iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 134, Fertilizers, soil conditioners and
beneficial substances.
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.
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ISO 19747:2020(E)

Introduction
[3]
Although silicon is ubiquitous in nature, making up a quarter of the earth's crust , not all forms of
[4],[5]
silicon found in soils or fertilizer products are soluble and plant-available . The form of silicon in
soils that is soluble and available for plant uptake is monosilicic acid. Worldwide, it has been estimated
that annual removal of silicon from soils during crop production can amount to 239-255 mega tons
annually, based on FAO 1998 global crop production estimates, and a conservative annual increase of
[6]
1 % through 2012. Although the first US patent on a solid Si fertilizer was issued in 1881 , fertilizer
manufacturers, governmental regulators and consumers had no means of evaluating nonliquid silicon
fertilizer materials for their monosilicic acid supplying capacity to meet and replace plant uptake needs.
[7]
The first research into the use of silicon fertilizers was reported in 1840 . Additionally, increased
plant silicon concentrations were first associated with reductions in rice (Oryza sativa L.) blast disease
[8]
(Magnaporthe grisea M.E. Barr) over a century ago in Japan . Since then, research has extended to
[9] [10]
other grasses and grains (e.g. barley (Hordeum vulgare L.) , corn (Zea mays L.) , oats (Avena sativa
[11] [12] [13] [14]
L.) , wheat (Triticum aestivum L.) , sugar cane (Saccharum officinarum L.) , pasture , turf
[15] [16]
grasses , and to dicotyledonous crops (e.g. cucumber (Cucumis sativus L.) , grapes (Vitis vinifera
[17] [18] [19] [20]
L.) , pepper (Capsicum L.) , pumpkin (Curcubita pepo L.) , soybean (Glycine max (L.) Merr.) ,
[21]
tomato (Solanum lycopersicum L.) . Beneficial effects from silicon fertility have included increased
stress tolerance (disease, insect, drought, salt, nutrient imbalance, UV-rays, low and high temperature)
[4]
and yield increases with or without stress . Other benefits from silicon supplements to soils have
[22] [23]
included CO sequestration , reductions in metals toxicity , and reduced phosphorus run-off while
2
[24]
increasing phosphorus use efficiency .
Considering the extensive research, a growing market, and the potential benefits from silicon fertility
to global agriculture; it is important that a standard method exists to enable regulation of nonliquid
silicon fertilizer materials based on their monosilicic acid supplying capacity. This is the first method
developed which correlates well with plant silicon uptake while using commonly available laboratory
equipment at a reasonable cost for the analysis. Reference the peer reviewed published version, single
[25]
lab validated AOAC method .
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INTERNATIONAL STANDARD ISO 19747:2020(E)
Fertilizers and soil conditioners — Determination of
monosilicic acid concentrations in nonliquid fertilizer
materials
1 Scope
This document establishes a method for the determination of monosilicic acid concentrations in
nonliquid fertilizer materials. Monosilicic acid is reported as silicon (Si).
This extraction method is applicable to the detection of monosilicic acid in nonliquid fertilizer products,
blended products, and beneficial substances at silicon (Si) concentrations of 2 to 84 g/kg, with a limit
of detection (LOD) of 0,6 g/kg Si, and a limit of quantification (LOQ) of 2 g/kg correlating well with
plant uptake.
This method is not applicable to liquid silicon fertilizer sources due to an expected low bias of Si
recovery and low correlation with plant uptake.
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 8157, Fertilizers and soil conditioners — Vocabulary
3 Terms and Definitions
For the purposes of this document, the terms and definitions given in ISO 8157 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
monosilicic acid
inorganic molecule that is soluble in soil solution and is the form of silicon available for plant uptake
4 Principle
Monosilicic acid (reported as Si) from nonliquid Si fertilizer sources is extracted at ambient room
temperature using a dilute Na CO -NH NO extractant. The extractant solution is analysed by manual
2 3 4 3
[26]
spectrophotometry at 660 nm using the heteropoly blue method .
5 Safety
General requirements: A minimum of standard laboratory personal protective equipment including
safety glasses, gloves, and lab coats should be worn always. Consult individual SDS for chemicals listed
and follow safety and handling conditions per individual SDS instructions.
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ISO 19747:2020(E)

6 Reagents
6.1 General requirements: Protect from sunlight. Store all reagents in a manner consistent with general
laboratory practices. Store in temperatures between 20 and 24 °C unless otherwise noted.
6.2 Sodium carbonate solution, 0,094 M — fill a 19 l plastic dispensing bottle with 18 l water. Add
180 g anhydrous Na CO . Stir to dissolve.
2 3
6.3 Ammonium nitrate solution, 0,20 M — fill a 19 l plastic dispensing bottle with 18 l water. Add
288 g NH NO . Stir to dissolve.
4 3
Ammonium nitrate (NH NO ): Is a strong oxidizing agent and should not be used near flames, heating
4 3
or ignition sources, combustible materials, or reducing agents to avoid the potential for combustion or
explosion hazards. NH NO shall be separated from all organic materials present within the laboratory.
4 3
Check with governmental agencies for any additional regulatory licensing requirements before
obtaining or using NH NO .
4 3
6.4 Sodium carbonate-ammonium nitrate extractant solution, 9,4 pH — add 50 ml of each solution
(6.2 and 6.3) to a plastic beaker, stir, and verify that the pH of the mixed solution is 9,4 using a pH meter.
Mixing of sodium carbonate and ammonium nitrate: Flexible vinyl gloves are to be worn when mixing
Na CO and NH NO , due to the caustic nature of this extractant. Care shall be taken to avoid eye or
2 3 4 3
skin contact. If contact is made with eyes or skin, flush immediately with clean tap water and seek
medical attention. Clean up any spills immediately.
6.5 Silicon 1000 mg/l stock solution, silicon standard — this solution, preferably 20 g/kg sodium
hydroxide, is commercially available from numerous sources. Follow specific manufacturer’s SDS for
proper storage and shelf life.
6.6 Silicon spike solution, 500 mg/l — pipette 50 ml of a stock 1000 mg/l silicon standard into a
100 ml volumetric flask. Dilute to 100 ml with water.
6.7 Ammonium Molybdate solution, 0,42 M — add 75 g ammonium molybdate [(NH ) Mo O ·
4 6 7 24
4H O] to a 1 l beaker. Add 500 ml water. Dissolve. Slowly add 100 ml concentrated (18,4 M) sulfuric acid
2
(H SO ). Cool. Transfer to a 1 l volumetric flask. Dilute to 1 l with water.
2 4
WARNING — Handling of concentrated sulfuric acid: gloves, safety goggles, face shields, and lab
coats should always be worn when handling concentrated sulfuric acid. Sulfuric acid is extremely
corrosive and dehydrating, causing severe burns. Care shall be taken to avoid eye or skin contact.
If contact is made with eyes or skin, flush immediately with clean tap water and seek immediate
medical attention. To avoid the potential for fuming and spattering of concentrated sulfuric acid
during dilution, always add sulfuric acid to water and do not add water to sulfuric acid.
6.8 Tartaric acid solution, 1,33 M — add 200 g tartaric acid (C H O )to a 1 l beaker. Add 700 ml
4 6 6
water. Stir. Transfer to a 1 l volumetric flask. Dilute to 1 l with water.
6.9 Ascorbic acid solution, 0,017 M — add 3 g ascorbic acid (C H O )to 1 l volumetric flask. Dilute to
6 8 6
1 l with water. Stopper the flask and mix by inverting 10 times. Transfer to a plastic storage bottle. Cap
tightly and refrigerate.
6.10 Intermediate silicon standard solution, 50 mg/l — dilute 5 ml of a stock 1000 mg/l silicon
standard to 100 ml in a volumetric flask. Transfer immediately to a plastic storage bottle.
6.11 Cleaning solution for glassware, dilute 4 ml/l of Nitric Acid with de-ionized water (HNO ).
3
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ISO 19747:2020(E)

6.12 Cleaning solution for flow cell, dilute 100 ml/l of HCl with de-ionized water.
7 Calibration standards
7.1 Blank: 0 mg/l Si — add 10 ml sodium carbonate–ammonium nitrate extractant solution (6.4) to a
1 l volumetric flask. Dilute to 1 l with water. Stopper the flask and mix by inverting 10 times.
7.2 Standard 1: 0,25 mg/l Si — add 10 ml sodium carbonate–ammonium nitrate extractant solution
(6.4) to a 1 L volumetric flask. Add 5 ml intermediate silicon standard solution (6.10). Dilute to 1 l with
water. Stopper the flask and mix by inverting 10 times.
7.3 Standard 2: 0,50 mg/l Si — add 10 ml sodium carbonate–ammonium nitrate extractant solution
(6.4) to a 1 l volumetric flask. Add 10 ml intermediate silicon standard solution (6.10). Dilute to 1 l with
water. Stopper the flask and mix well by inverting 10 times.
7.4 Standard 3: 1,0 mg/l Si — add 10 ml sodium carbonate–ammo
...