Overview
ISO 15958:2019 specifies a standardized laboratory method for the extraction of water-soluble phosphorus from fertilizers. The method is applicable to all fertilizer types, including compound fertilizers, where water-soluble phosphorus content is to be determined. The principle is simple: extraction in water by shaking under defined conditions to produce a filtrate suitable for subsequent phosphorus determination.
Key Topics
- Scope and applicability: Method applies to all fertilizers where water-soluble phosphorus is required.
- Principle: Extraction in water by shaking under specified conditions.
- Sampling and sample preparation: Sampling is not part of the method; recommended sampling and preparation are given by EN 1482 series. Grinding of the laboratory sample is recommended to improve homogeneity.
- Reagents: Distilled or demineralized water is specified as the extraction reagent.
- Apparatus: Key equipment includes:
- 500 ml graduated flask (e.g., Stohmann)
- Rotary shaker operating at 35–40 turns per minute
- Dry pleated, phosphate-free filter
- Procedure (summary):
- Weigh 5 g of laboratory sample to the nearest 0.001 g and place in a 500 ml graduated flask.
- Add 450 ml of distilled or demineralized water at 20 °C to 25 °C.
- Shake on the rotary shaker (35–40 turns/min) for 30 minutes.
- Make up to the mark with water, mix, and filter through a dry pleated phosphate-free filter.
- Test reporting: The standard lists required report elements (see below).
Applications
The ISO 15958:2019 method is intended for practical laboratory use where consistent, reproducible extraction of water-soluble phosphorus is required. Typical applications include:
- Quality control in fertilizer production to verify declared nutrient content.
- Regulatory compliance and reporting where water-soluble phosphorus must be quantified for product registration or market surveillance.
- Comparative testing and inter-laboratory studies due to the method’s standardized procedure.
This standardized extraction is intended to produce a representative aqueous extract suitable for subsequent phosphorus determination by whichever analytical technique the laboratory uses.
Related Standards
Key normative and related references cited in ISO 15958:2019:
- EN 1482-1 - Fertilizers and liming materials - Sampling (recommended sampling method)
- EN 1482-2 - Fertilizers and liming materials - Sample preparation
- EN 12944-1 / EN 12944-2 - Vocabulary for fertilizers and related terms
- Regulation (EC) No 2003/2003 - Fertilisers (referenced method in Annex IV)
- Historical: ISO 15958:2019 cancels and replaces ISO 5316:1977 (technically revised)
Test Report Essentials
The test report shall include at least:
- Identification of the sample
- Reference to the method (ISO 15958:2019)
- Test results obtained
- Dates of sampling and analysis (if known)
- Statement on fulfillment of any repeatability requirement
- Details of any optional operating parameters or incidents that could affect results
This concise, prescriptive procedure helps laboratories achieve reproducible extraction of water-soluble phosphorus and supports consistent downstream analytical determination and compliance activities.