🌱 Water-soluble phosphorus — extraction from fertilizers — PN-EN 15958

Physicochemistry PN-EN 15958

Overview

WHAT THIS TEST IS — SCOPE FROM THE PKN CARD (Polish version), IN FULL: "W niniejszej Normie Europejskiej określono metodę ekstrakcji fosforu rozpuszczalnego w wodzie. Metoda ma zastosowanie do wszystkich nawozów, łącznie z nawozami wieloskładnikowymi, w których oznacza się fosfor rozpuszczalny w wodzie" [This European Standard specifies a method for the extraction of water-soluble phosphorus. The method is applicable to all fertilizers, including compound fertilizers, in which water-soluble phosphorus is determined]. Unlike PN-EN 15956 and PN-EN 15957, the scope does not refer to Regulation (EC) No 2003/2003 — it covers every fertilizer in which water-soluble phosphorus is determined. The regulation appears only in the bibliography (Annex IV, method 3.1.6).

PRINCIPLE (clause 4): extraction in water by shaking under specified conditions. The phosphorus in the extract is determined separately — in accreditation scopes PN-EN 15959 stands with this standard in all 16 entries (a separate entry in this database).

PROCEDURE — THE WHOLE EXTRACTION (clauses 5–8): • sample according to EN 1482-2; the standard recommends grinding the laboratory sample for the sake of homogeneity; • 5 g of sample, weighed to the nearest 0.001 g, into a 500 ml volumetric flask (e.g. a Stohmann flask); • 450 ml of water at a temperature of 20 °C to 25 °C; • 30 min of shaking in a rotary shaker (35 to 40 revolutions per minute); • make up to the mark with water, mix thoroughly by shaking and filter through a dry phosphate-free pleated filter. The test report has to state, among other things, whether the repeatability limit requirement was met.

WHAT DECIDES COMPARABILITY: the water temperature (20–25 °C), the time (30 min) and the manner of shaking (rotary shaker, 35–40 rpm). These are conventional conditions — "water-soluble" phosphorus is the phosphorus extracted under exactly these conditions.

EDITIONS (state of the PKN card on 25.09.2026). PN-EN 15958:2011 — Polish version, publication 11-06-2015, 10 pages, KT 156 Fertilizers, introduces EN 15958:2011 [IDT], without the "Wycofana" [Withdrawn] header; the catalogue also has the English version. EN 15958:2011 replaced CEN/TS 15958:2009 (the specification adopted as a standard, editorial changes). At the publisher (the CEN catalogue run by iTeh, read on 25.09.2026): published 23-11-2011; stage 90.93 — decision to confirm after the systematic review (enquiry from 20-06-2023, closing 23-09-2026).

HOW ACCREDITATION SCOPES CITE THE STANDARD. Measurement of 25.09.2026 on the database of PL accreditation scopes (1310 laboratories with entries): 16 entries at 16 laboratories; notation "PN-EN 15958:2011" (15) and once in one field with "PN-EN 15959:2011". The subject of the test is "Nawozy mineralne (nieorganiczne)" [Mineral (inorganic) fertilizers] (14); the methodology most often "Zawartość fosforu rozpuszczalnego w wodzie" [Content of water-soluble phosphorus] (11); the technique "Metoda wagowa" [Gravimetric method] (14). In the same entries: PN-EN 15959 in all 16 (12 × the 2024-05 edition, 4 × the withdrawn 2011 edition, including once in one field together with PN-EN 15958), PN-EN 15956:2011 and PN-EN 15957:2011 (2 each), PN-C-87015:1988 clause 6 (1). The declared ranges (in % P₂O₅ or % P) have lower limits from 0.2 % to 5.0 %, and upper ones from 23.6 % to 60 %.

THE KEY OF THE "LABORATORIES" TAB: "PN-EN 15958" — 16 laboratories and 16 entries, without foreign entries.

WHAT WE DO NOT GIVE. We had the text of EN 15958:2011 made available by the publisher: the foreword, clauses 1–9 and the bibliography — the whole content of the standard. Nothing in the standard needs supplementing; for the determination of phosphorus in the filtrate we refer to the entry on PN-EN 15959.

Method principle

5 g of fertilizer is shaken for 30 min with 450 ml of water (20–25 °C) in a 500 ml volumetric flask in a rotary shaker (35–40 rpm), made up to the mark and filtered through a phosphate-free filter. The phosphorus in the filtrate is determined according to PN-EN 15959.

Applications

• Fertilizers, including compound ones, for which water-soluble phosphorus is declared (e.g. superphosphates, NPK fertilizers)
• One of the three forms of phosphorus declared in fertilizers — next to the form soluble in neutral ammonium citrate (PN-EN 15957) and the form soluble in mineral acids (PN-EN 15956)
• The first stage of the "extraction + determination" pair: PN-EN 15958 with PN-EN 15959

Key parameters

Standard

Standard number

PN-EN 15958:2011 (wersja polska z 2015 r.; w katalogu PKN także wersja angielska; wprowadza EN 15958:2011 [IDT])

Title (PL)

Nawozy — Ekstrakcja fosforu rozpuszczalnego w wodzie

Title (EN)

Fertilizers — Extraction of water soluble phosphorus

Step-by-step procedure

1. Sample

   According to EN 1482-2; grind the laboratory sample (recommendation for the sake of homogeneity).

2. Test portion

   5 g ± 0.001 g into a 500 ml volumetric flask.

3. Extraction

   Add 450 ml of water at a temperature of 20–25 °C and shake in a rotary shaker.

   ⏱ Time: 30 min • 🌡 Temperature: 20–25 °C

4. Making up and filtration

   Make up to the mark with water, mix thoroughly by shaking, filter through a dry pleated filter.

5. Determination

   Phosphorus in the filtrate — according to PN-EN 15959; the test report includes, among other things, information on the repeatability limit.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Fertilizer dust during grinding and weighing — dust mask
• Rotary shaker — flasks well closed and fastened

Frequently asked questions