ISO 18644 Fertilizers and soil conditioners — Controlled-release fertilizer — General requirements

ISO 18644:2016 sets out general requirements for controlled-release fertilizers. It was published on 7 April 2016, the same year as the companion standards for water-soluble fertilizers, sulfur-coated urea and fertilizer grade urea.

Controlled-release fertilizers depend on coatings or chemical structure to slow nutrient delivery so that a single application can serve a crop over an extended period. That proposition is only commercially meaningful if release behaviour is defined in a way both buyer and seller can test against; otherwise the term becomes marketing language rather than a specification.

The standard addresses the product-level requirements that make a release claim testable: what must be declared, how the product must be characterised, and the physical and chemical requirements that a product sold under this description has to satisfy. It is read in conjunction with the analytical method standards, in particular ISO 21263 for the determination of nutrient release from coated products.

The commercial driver is nutrient use efficiency. The argument for coated and controlled-release products is that they reduce the number of applications needed, lower leaching and volatilisation losses, and reduce the risk of root damage from a single heavy dose. Where a standard defines what 'controlled release' means, a grower can compare products on a stated release duration rather than on a description.