ICS 65.080  
 
Reference number
DRS 72: 2020
© RSB 2020
  
 RWANDA 
STANDARD  DRS
72
Second  edition
2020 -mm-dd
Granulated superphosphate fertilizers  — 
Specification  
   
DRS 72: 2020  
©RSB 2020  - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2020  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without  
prior written permission from R SB. 
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ePortal: www.portal.rsb.gov.rw   DRS 72: 2020  
iii                ©RSB 2020  - All rights reserved  
 Contents  Page 
1 Scope  ................................ ................................ ................................ ................................ ................ 1 
2 Normative references  ................................ ................................ ................................ ....................... 1 
3 Terms and defi nitions  ................................ ................................ ................................ ...................... 2 
4 Requirements  ................................ ................................ ................................ ................................ ...2 
4.1 General requirements ................................ ................................ ................................ ....................... 2 
4.2 Physical requirements  ................................ ................................ ................................ ..................... 2 
4.3 Chemical requirements  ................................ ................................ ................................ .................... 2 
4.4 Heavy metal contaminants  ................................ ................................ ................................ ............... 3 
5 Packaging and labelling  ................................ ................................ ................................ ................... 3 
5.1 Packaging  ................................ ................................ ................................ ................................ ......... 3 
5.2 Labelling  ................................ ................................ ................................ ................................ ........... 3 
6 Sampling  ................................ ................................ ................................ ................................ ........... 4 
Annex  A (normative)  Determination of phosphoric acid  ................................ ................................ ............ 5 
A.1 Purpose ................................ ................................ ................................ ................................ ............. 5 
A.2 Reagents and apparatus  ................................ ................................ ................................ .................. 5 
A.3 Preparation of standard solutions  ................................ ................................ ................................ ...5 
A.4 Preparation of colour development solutions ................................ ................................ ................. 6 
A.5 Procedure  ................................ ................................ ................................ ................................ ......... 6 
A.6 Calculations  ................................ ................................ ................................ ................................ ......6 
 DRS 72: 2020  
©RSB 2020  - All rights reserved                  iv 
 Foreword  
Rwanda Standard s are prepared  by Technical Committees and approved by Rwanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical committees is to prepare national standards.  Final Draft Rwanda S tandards 
adopted by Technical committ ees are ratifie d by me mbers of RSB Board of Director s for publication and 
gazettment as Rwanda Standards.  
DRS 72 was prepared by Technical Committee RSB/TC 07, Agrochemicals . 
In the preparation of this standard, reference was made to the following standard:  
1) FDARS 1482 : Granulated superphosphate fertilizers — Specification  
The assistance de rived from the above source is hereby acknowledged with thanks.  
This second edition cancels and replaces the first edition (RS  72: 2016 ), of which has been technically 
revised.  
 
 
Committee membership  
The following organizations were represented on the Technical Committee on Agrochemicals  (RSB/TC 07) in 
the preparation of this standard.  
One Acre Fund - TUBURA  
Ministry of Environment (MoE)  
University of Rwanda/College of Agriculture and Veterinary Medicine (UR/CAVM)  
University of Rwanda/College of Sciences and Technology (UR/CST)  
Rwanda Inspectorate, Competition and Consumer Protection Authority (RICA)  
Star Construction and Consultancy (SCC) Ltd  
Rwanda  Standards Board  (RSB) – Secretar iat DRS 72: 2020  
v                ©RSB 2020  - All rights reserved  
 Introduction   
A paragraph.  
 
 DRS 72: 2020  
1                ©RSB 2020  - All rights reserved  
 Granulated superphosphate fertilizers  — Specification  
1 Scope   
This Draft Rwanda  Standard specifies requirements, sampling method and test methods for granulated 
superphosphate fertilizers.  It applies for both single superphosphate and triple superphosphate.  
2 Normative references  
The following documents are referred to in the tex t 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.  
AOA C 969.02, Phosphorus (total) in fertilizers — Alkalimetric quinolinium molybdophosphate method  
AOAC 993.31, Phosphorus (available) in fertilizers — Direct extraction method  
AOAC 2006.03 , Arsenic, cadmium, cobalt, chromium, lead, molybdenum, nickel, and selenium in fertilizers — 
Microwave digestion and inductively coupled plasma -optical emission spectrometry  
EN 12048, Solid fertilizers and liming materials — Determination of moisture content — Gravimetric method 
by drying  at 1052 C 
ISO 5316, Fertilizers  — Extraction of water -soluble phosphates  
ISO 7409, Fertilizers — Marking — Presentation and declarations  
ISO 8157, Fertilizers and soil conditioners — Vocabulary  
ISO 8189, Solid fertilizers — Determination of moisture content — Gravimetric method by dryin g under 
reduced pressure  
ISO 8397, Solid fertilizers and soil conditioners — Test sieving  
ISO 14820 -1, Fertilizers and liming materials — Sampling and sample preparation — Part 1: Sampling  
ISO 14820 -2, Fertilizers and liming materials — Sampling and sample  preparation — Part 2: Sample 
preparation  
ISO 17318, Fertilizers and soil conditioners — Determination of arsenic, cadmium, chromium, lead and 
mercury contents  
  
©RSB 2020  - All rights reserved                  2 
 3 Terms and definitions   
For the purposes of this standard, the terms and definitions given in ISO 8157 and the following apply.  
3.1 
superphosphate  
the product obtained by treating phosphate rock with sulphuric acid. It is also known as single supe rphosphate  
3.2 
concentrated superphosphate  
The product obtained by treating phosphate rock with phosphori c acid or phosphoric acid and sulphuric acid  
mixture . It is also called ‘enriched superphosphate’ or ‘triple superphosphate’.  
3.3 
available phosphorus  
the fraction of phosphorus available to plants. This is the sum of the water -soluble and citrate -soluble 
phosphorus.  
3.4 
total phosphorus  
the sum of available and citrate -insoluble phosphorus  
4 Requirements  
4.1 General requirements  
The fe rtilizer shall be homogenous, free -flowing  in the form of granules, pellets, or crystals  and free from 
foreign matter  and hard lu mps 
4.2 Physical requirements  
When test sieved in accordance with ISO 8397, the particle size for granular fertilizer shall be suc h that not 
less than 90 %, by mass of the fertilizer are particles in the size range of 1 mm to 4 mm. Not more than 5% 
shall be below 1 mm.  
4.3 Chemical requirements  
The fertilizer shall comply with the following compositional limits  in Table 1.  DRS 72: 2020  
3                ©RSB 2020  - All rights reserved  
 Table 1 — Chemical requirements  for superphosphates  
Sl. 
No.  
Characteristic  Requirement, %, by mass  Method of test  
Grade 1 Single 
Superphosphate  Grade 2 Single 
Superphosphate  Triple/ 
Concentrated 
Superphosphate  
(i) Water -soluble 
phosphate  (as P 2O5), 
min  
18.0  
14.0  
40  
ISO 5316  
(ii) Available phosphate 
(as P 2O5), min  21.5 16.5.  46.0 AOAC 969.02 / AOAC 
993.31  
(iii) Free phosphoric acid 
(as P 2O5), Max  4.0 4.0 4.0 Annex A  
(iv) Moisture, max  5.0 5.0. 4.0 EN 12048/ ISO 8189  
(v) Sulfur ( as S), min  11 11 11 ISO 15178/ EN 16032  
4.4 Heavy metal contaminants  
The heavy  metal contaminants, if present, shall not exceed the limits stipulated in Table 2.  
Table 2 — Heavy metal contaminants limits  
Sl. No.  Parameter  Limits, mg/kg  Test method  
i) Arsenic, As, max.  40 AOAC 2006.03 / ISO 17318  
ii) Cadmium, Cd, max.  30 AOAC 2006.03 / ISO 17318  
iii) Mercury, Hg, max.  0.1 AOAC 2006.03 / ISO 17318  
iv) Selenium, Se, max.  1.0 AOAC 2006.03  
v) Lead, Pb, max.  80.0 AOAC 2006.03 / ISO 17318  
vi) Nickel  120 AOAC 2006.03 / ISO 17318  
vii) Chromium, Cr Max.  500 AOAC 2006.03 / ISO 17318  
5 Packaging and labelling  
5.1 Packaging  
The fertili zer shall be packed in clean, non -defective and strong packages.  The material of which the  package  
is made shall be such as to protect the contents from moisture and also not lead to easy rupture dur ing 
handling, transportation and storage.  
5.2 Labelling  
5.2.1  Each package the fertili zer shall be legibly and indelibly marked  in accordance with ISO 7409, and 
with the following particulars:  
a) Name of the product as superphosphate fertilizer;   
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 b) type;  
c) grade   
d) name and physical address of the manufacturer/packer;  
e) minimum water -soluble phosphates stated as P2O5 content of the material;  
f) net weight of the material in th e package;  
g) content of fluorine and sulfur;  
h) manufacture and expiry or best before date;  
i) lot or batch number;  
j) handling, use and storage instructions; and  
k) warning statement similar or closely similar in meaning to the statements in 1, 2 and 3 preceded by 
the words: “WARNING”:  
 
1) do not swallow. The dust from this product may act as an irritant, avoid inhalation or contact with 
eyes and skin;  
2) this product may contain fluorine as an impurity; do not feed this product to livestock or use in 
feedstock mixtures. If top dressing pastures do not graze for 3 weeks or until rain or irrigation is 
received; and  
3) this product may contain heavy metal as impurities; its repeated use may therefore lead to 
accumulation of the same in the soil. Depending on soil characteristics, irrigation water quality, 
plant species and variety, crop uptake of heavy metals may exceed the maximum limits allowed 
in local food standards; in pasture, the offal from grazing animal may also exceed these limits ; 
therefore,  its application in accordance  to local regulation is advised.  
5.2.2  Where the fertilizer is distributed in bulk, the marking information sh all accompany the delivery note to 
the purchaser.  
6 Sampling  
Sampling and sample preparation for inspection and testing  shall be carried out in accordance with ISO 1482 0 
parts 1 and 2 . 
 DRS 72: 2020  
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 Annex  A 
(normative)  
 
Determination of phosphoric acid  
A.1 Purpose  
This method determines the percent of phosphoric acid (P 2O5) in commercial fertilizers by colorimetry.  
A.2 Reagents and apparatus  
A.2.1  An Atomic Absorption Spectrophotometer or a suitable colorimeter.  
A.2.2  Nitric acid (HNO 3), 1.42 specific gravity  
A.2.3  Hydrochloric acid (HCl), 1.19 specific gravity  
A.2.4  Potassium phosphate, monobasic (KH 2PO 4). Primary Standard Grade, dried at 105 – 110 °C for 
several hours prior to use  
A.2.5  Ammonium molybdate [(NH 4)6MO 7O24.4H 2O], Reagent Grade  
A.2.6  p-Methylaminophenol Sulfate, Reagent grade  
A.2.7  Sodium acid sulphite (NaHSO 3), Reagent grade  
A.2.8  Cuvets, optical glass, matched, 10mm path length.  
NOTE  If available, an optical glass, automatic flow -through cuvet may be used.  
A.3 Preparation of standard solutions  
A.3.1  Phosphate Stock Solution:  Weigh 0.4394 g of dried, primary standard KH 2PO 4 into a 500 -mL 
volumetric flask. Add 30 ml of HNO 3 and 5 ml of HCl and  boil until brown fumes have been expelled. Dilute to 
volume with distilled water.  
 
A.3.2  5 ppm Working Standard:  Pipette a 5 -ml aliquot of the phosphate stock solution into a 200 -ml 
volumetric flask and dilute to volume with distilled water. This solution is equivalent to 57.2% pho sphoric acid.  
 
A.3.3  4 ppm Working Standard:  Pipette a 4 -mL aliquot of the phosphate stock solution into a 200 -mL 
volumetric flask and dilute to volume with distilled water. This solution is equivalent to 45.8% pho sphoric acid.  
 
A.3.4  Blank Working Solution:  Boil a mixture consisting of 5 ml of HCl and 30 ml of HNO 3 until brown 
fumes have been expelled, transfer to a 500 -ml volumetric flask and dilute to volume with distilled water. 
Transfer a 4 -ml aliquot to a 200 -ml volumetric flask and dilute to volume with distilled water.   
©RSB 2020  - All rights reserved                  6 
 A.4 Preparation of colour development solut ions 
A.4.1  Acid Molybdate Solution:  Pour, with stirring, a solution containing 16.62 g of ammonium molybdate 
in 156.9 ml of distilled water into a solution of 318.4 ml of HCl to which 29.6 ml of distilled wate r has been 
added.  
A.4.2  Reducing Solution:  Dissolve 1.0 g of p -methylaminophenol sulfate and 3.0 g of sodium acid sulfite 
in 100 ml distilled water.  
A.5 Procedure  
A.5.1  Weigh, to the nearest 0.1 mg, 0.50 ± 0.02 g of sample into a 500 -ml volumetric flask, adding 30 ml of 
HNO 3 and 5 ml of HCl.  
A.5.2  Boil u ntil brown fumes have been expelled, cool to room temperature and dilute to volume with 
distilled water.  
A.5.3  Transfer a 2 -ml aliquot to a 100 -ml volumetric flask and dilute to volume with distilled water.  
A.5.4  From this second dilution, transfer a 10 -ml aliquot to a 20 -ml scintillation vial and add a 2 -ml aliquot 
of acid molybdate solution and a 2 -ml aliquot of reducing solution.  
A.5.5  Allow to stand 1 hour for colo ur development. At the same time that the sample vial is prepared, a 
blank vial, a 4 ppm phosphorus vial and a 5 ppm phosphorus vial must also be prepared and allowed to 
develop colo ur along with the sample.  
A.5.6  The blank, 4 ppm phosphorus and 5 ppm phosphorus are prepared by the same procedure used for 
preparation of the sample, using 10-ml aliquots of the blank working solution, the 4 ppm phosphorus working 
standard and the 5 ppm phosphorus working standard.  
NOTE  When making determinations on fertilizers with low percentages of phosphoric acid, it is necessary to adj ust 
the sample weig ht so that the sample working dilution contains between 4 ppm and 5 ppm phosphorus.  
A.5.7  Calibrate the instrument using the blank solution, the 4 ppm phosphorus solution and the 5 ppm 
phosphorus solution, then determine the concentration of the sample sol ution.  
NOTE  When using an Atomic Absorption Spectrophotometer for colour measurements, the cuvet holder is placed 
over the burner in the light path and a Cu hollow cathode lamp is used with the instrument grating s et at a wavelength of 
640 nm.  
A.6 Calculations  
The method of calculating the  % phosphoric acid will vary according to the make and model of instrument 
used. Report the results to the nearest 0.1% P 2O5 as follows:  
% Phosphoric Acid (P 2O5)  
 DRS 72: 2020  
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 DRS 72: 2020  
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 Bibliography  
[1] ISO/IEC Directives, Part  2, Rules for the structure and drafting of International Standards , 2016  
 DRS 72: 2020  
 
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