Overview
ISO 15604:2016 - Fertilizers - Determination of different forms of nitrogen in the same sample specifies analytical procedures to quantify distinct nitrogen forms (nitric/nitrate, ammoniacal/ammonium, urea and cyanamide nitrogen) in the same fertilizer sample. The method is applicable to fertilizers listed in Regulation (EC) No 2003/2003, Annex I and is designed to determine one form of nitrogen in the presence of the others using aliquots from a single prepared solution.
Key technical topics and requirements
- Scope and applicability: Applies to fertilizers containing multiple nitrogen forms, including products with calcium cyanamide.
- Principle:
- Use of Kjeldahl digestion for total soluble nitrogen (direct digestion if nitrates absent; digestion after chemical reduction if nitrates present).
- Reduction of nitrates when present using metallic iron and stannous chloride (Ulsch reduction) before Kjeldahl digestion.
- Ammonia determination follows ISO 25475 procedures.
- Determination of soluble nitrogen forms: Different aliquots of the same solution are used to determine:
- Total soluble nitrogen
- Total soluble nitrogen excluding nitrate (elimination of nitrate using ferrous sulfate in acid)
- Nitrate nitrogen by difference between appropriate digestions or by difference against ammoniacal + ureic (+ cyanamide where applicable)
- Ammoniacal nitrogen by methods in ISO 25475 or by cold distillation when other nitrogen forms are present
- Urea nitrogen by urease conversion to ammonia, by xanthydrol gravimetry, or by difference (Table-based cases)
- Cyanamide nitrogen by precipitation as a silver compound and nitrogen determination of the precipitate via Kjeldahl
- Reagents & quality: Requires analytical-grade reagents and water meeting ISO 3696 (grade 3). Specific reagents (stannous chloride, urease solution, xanthydrol, etc.) and reagent verification steps (e.g., checking reducing power of SnCl2) are prescribed.
- Apparatus: Borosilicate glass distillation apparatus with splash head; automatic distillers allowed if statistically equivalent. Sampling/preparation follows ISO 14820-2.
Practical applications and users
ISO 15604:2016 is intended for:
- Fertilizer manufacturers performing quality control and product certification
- Analytical and commercial testing laboratories analyzing fertilizer composition
- Regulatory agencies enforcing fertilizer composition per EU Regulation (EC) No 2003/2003
- Agricultural research and agronomy laboratories assessing fertilizer nitrogen forms for efficacy and environmental impact
Using ISO 15604 helps ensure consistent, traceable results for nitrate, ammoniacal, urea and cyanamide nitrogen - important for product labeling, regulatory compliance, and agronomic decision-making.
Related standards
- ISO 3696 - Water for analytical laboratory use
- ISO 14820-2 - Sampling and sample preparation
- ISO 25475 - Determination of ammoniacal nitrogen
- EN 15562 - Determination of cyanamide nitrogen
- EN 12944 series - Fertilizer terminology
Keywords: ISO 15604:2016, fertilizer nitrogen determination, Kjeldahl digestion, nitrate nitrogen, ammoniacal nitrogen, urea nitrogen, cyanamide nitrogen, fertilizer testing.