ISO 6181:2023

Fertilizers and soil conditioners - Liquid methylene-urea slow release fertilizers - General requirements

This document specifies general requirements, analytical methods, sampling and preparation of test sample, marking and labelling, packaging, transport and storage for liquid methylene-urea slow release fertilizers. This document applies to pure liquid slow release fertilizers, i.e. methylene urea (MU). This document does not apply to mixtures of nitrogenous fertilizers containing liquid slow release fertilizers.

Engrais et amendements — Engrais liquides à libération lente à base de méthylène-urée — Exigences générales

General Information

• Status: Published
• Publication Date: 16-Mar-2023
• ICS: 65.080 - Fertilizers
• Technical Committee: ISO/TC 134 - Fertilizers, soil conditioners and beneficial substances
• Drafting Committee: ISO/TC 134 - Fertilizers, soil conditioners and beneficial substances
• Current Stage: 6060 - International Standard published
• Start Date: 17-Mar-2023
• Due Date: 09-Feb-2023
• Completion Date: 17-Mar-2023

Overview

ISO 6181:2023 defines general requirements for liquid methylene-urea (MU) slow release fertilizers. The standard covers product form, required analytical methods, sampling and test-sample preparation, marking and labelling, and packaging, transport and storage. ISO 6181 applies only to pure liquid methylene-urea slow release fertilizers and explicitly does not apply to mixtures of nitrogenous fertilizers that contain liquid slow release components. This standard supports consistent product quality, international trade and reliable laboratory testing for liquid MU fertilizers.

Key topics and technical requirements

ISO 6181 sets measurable product and testing requirements, including:

• Product form: liquid, transparent or coloured; visually free of solid contaminants.
• Nutrient and impurity limits:
  • Total nitrogen ≥ 24%
  • Methylene‑urea reaction products nitrogen ≥ 50% of total N
  • Ureic nitrogen ≤ 50% of total N
  • Ammonia nitrogen < 0.5%
  • Nitric nitrogen < 0.1%
  • Cyanamide nitrogen < 0.1%
  • Biuret < total N × 0.026%
  • Water‑insoluble matter ≤ 0.5%
  • Density at 20 °C ≤ 1.35 kg/l
• Analytical and test methods: specifies recognized procedures (e.g. ISO 5315 for total N, ISO 19746 for ureic N, ISO 15604 for various N forms, ISO 18643 for biuret, ISO 18645 for water‑soluble/insoluble matter, AOAC 985.19 for density).
• Sampling and sample prep: follows ISO 14820‑1 and ISO 14820‑2 procedures.
• Marking and labelling: recommends GHS conformity and requires labels to show total N, MU‑N, ureic N, density, production date, net mass and manufacturer details, plus usage instructions.
• Packaging, transport and storage: guidance to avoid sunlight, frost and extreme temperatures; warns that improper storage may cause flocculation and reduced effectiveness.

Applications and who uses this standard

ISO 6181 is practical for:

• Fertilizer manufacturers and formulators specifying quality and stability of liquid methylene‑urea products.
• Quality control and analytical testing laboratories validating fertilizer composition and impurities.
• Importers, exporters and distributors using standardized specifications for contracts and trade.
• Agricultural advisors and agronomists assessing suitability of slow release fertilizers for crops.
• Regulators and certification bodies establishing compliance benchmarks for fertilizer products.

Benefits include consistent product labelling, reliable analytical testing, minimized trade disputes and improved on‑farm performance of slow release nitrogen fertilizers.

Related standards

Relevant referenced documents include:

• ISO 5315 (total nitrogen)
• ISO 14820‑1 / ISO 14820‑2 (sampling & sample prep)
• ISO 15604 (forms of nitrogen)
• ISO 18643 / ISO 18645 (biuret and insoluble matter)
• ISO 7409 (marking and declarations)
• AOAC 985.19 (density measurement)

Keywords: ISO 6181, liquid methylene-urea, slow release fertilizers, fertilizer standards, methylene urea (MU), analytical methods, sampling, labelling, storage.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 6181
First edition
2023-03
Fertilizers and soil conditioners —
Liquid methylene-urea slow release
fertilizers — General requirements
Engrais et amendements — Engrais liquides à libération lente à base
de méthylène-urée — Exigences générales
Reference number
© 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.
ISO copyright office
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 2
4.1 Visual inspection . 2
4.2 Requirements of liquid methylene-urea slow release fertilizers . 2
5 Analytical methods . 2
5.1 Visual inspection for foreign matter . 2
5.2 Determination of the mass fraction of total nitrogen . 2
5.3 Determination of the mass fraction of ureic nitrogen . 2
5.4 Determination of the mass fraction of methylene-urea reaction products nitrogen . 2
5.5 Determination of the ammonia nitrogen . 3
5.6 Determination of the nitric nitrogen . 3
5.7 Determination of the cyanamide nitrogen . 3
5.8 Determination of the biuret content . 3
5.9 Determination of the mass fraction of water insoluble matter . 3
5.10 Determination of the density. 3
6 Sampling and preparation of test sample . 3
6.1 Sampling method . 3
6.2 Test sample preparation . 3
7 Marking and labelling . 3
8 Packaging, transport and storage .4
Bibliography . 5
iii
Foreword
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