ISO 18644:2016

Overview

ISO 18644:2016 - Fertilizers and soil conditioners - Controlled‑release fertilizer - General requirements - defines the general requirements for controlled‑release fertilizers (CRFs). It covers testing methods, sampling and test‑sample preparation, marking and labelling, and package, transport and storage practices. The standard applies to products containing one or more primary nutrients (nitrogen, phosphorus and/or potassium) in a controlled‑release form, including bulk‑blended (BB) and specially processed CRFs.

Key topics and technical requirements

• Scope and classification
  • Applies to controlled‑release N, P, K and compound/BB fertilizers; products are classified by core nutrient type.
• Appearance and physical properties
  • Product shall be granules, free‑flowing, moisture‑free and free from foreign matter.
  • Particle size: 1.00 mm to 4.75 mm - at least 90%.
• Nutrient content
  • Total nutrient (N + P2O5 + K2O) mass fraction ≥ 20% (single‑nutrient fertilizers ≥ 18%).
  • Single nutrient component in multi‑element CRFs ≥ 4.0%.
• Release performance
  • Initial release rate (24 h at 25 °C or manufacturer‑specified temp) ≤ 15%.
  • Cumulative release mass fraction in 28 d ≤ 75%.
  • Cumulative release over the stated release period ≥ 75% (stated release time = time to reach 75% cumulative release at 25 °C or specified temp).
  • Marked release period must be a single value with ±20% tolerance.
• Testing and sampling
  • Prescribed test standards: ISO 5315 (total N), ISO 6598 (P), ISO 17319 (K), ISO 8397 (sieving), EN 13266 (release testing).
  • Sampling and reduction methods reference ISO 8633, ISO 7742 and ISO 7410.
• Marking & labelling
  • Use prefix “controlled‑release” or “coated controlled‑release”.
  • Package must show total nutrient content, fertilizer formula and release period; optional release curve and storage/usage instructions are recommended.
• Packaging, transport, storage
  • Avoid moisture, sunlight and damage; store in a dry, cool place.

Applications and users

ISO 18644 is intended for:

• Fertilizer manufacturers - product design, quality control and labelling compliance.
• Analytical and QC laboratories - sampling, test methods and reporting.
• Regulators and certification bodies - conformity assessment and market surveillance.
• Distributors, agronomists and large end‑users - selecting and handling CRFs to meet agronomic release expectations.

Keywords: ISO 18644, controlled‑release fertilizer, fertilizer testing, nutrient release rate, sampling and labelling, fertilizer standards, CRF storage.

Related standards

Normative references include ISO 5315, ISO 6598, ISO 7409, ISO 7410, ISO 7742, ISO 8397, ISO 8633, ISO 17319 and EN 13266 (release testing).