🌿 Available iron in mineral soil — soil extract and determination, in the scopes by flame AAS, PN-R-04021

Environment PN-R-04021

Overview

WHAT THE STANDARD COVERS. The scope from the PKN catalogue card, quoted in full: "The scope of application of the methods is given. The purity of reagents, the accuracy of weighing and the interpretation of results are specified. Given are: the principles of the methods, the reagents and solutions used, the apparatus, the method of preparing the soil extract, the blank test, the performance of the determinations, the calculation of results and the final result of the determinations." The card speaks of methods in the plural but does not name them, and does not give the extraction solution.

STATUS (state of the card on 28 September 2026). The card carries the heading "Withdrawn" and the row "Date of withdrawal: 23-09-2020" — the latest withdrawal of the six standards of this series each covering a single available micronutrient (zinc and copper 2012, manganese and boron 2014, molybdenum 2018); the standard of this series on phosphorus, potassium, magnesium and manganese in organic soils (PN-R-04024:1997) carries no "Withdrawn" label in the PKN search results. There are no "Superseded by" and "Supersedes" fields. Edition: published 03-10-1994, 4 pages, PKN technical committee KT 90 (Soil Cultivation and Horticulture), ICS 13.080.10. The PKN search for "przyswajalnego" (available) (29 September 2026) shows only standards of the same series — PN-R-04016 … PN-R-04025 of 1992–1997 and two amendments to them (Az1:2002, Az1:2004) — a successor WE HAVE NOT ESTABLISHED. A regulation citing this standard as a test method WE HAVE NOT ESTABLISHED.

EXTRACT AND TECHNIQUE — ACCORDING TO A PUBLICATION OF THE NATIONAL AGRICULTURAL CHEMISTRY STATION. W. Lipiński, "Zasobność gleb Polski w mikroelementy" (Micronutrient status of Polish soils), Studia i Raporty IUNG-PIB 34(8), 2013: in the agricultural chemistry stations iron in mineral soils is determined after extraction with 1 mol/dm³ hydrochloric acid, by AAS. In the first period of micronutrient testing (1965–1983) available iron was not tested at all — Table 8 of the publication gives no method of that time for it.

CONTENT ASSESSMENT — THE TABLE FROM THE STANDARD. KSChR publication, Table 6 ("Source: PKN, 1994"), mg of iron per kg of soil — one scale for all mineral soils: low content below 700, medium 700–3800, high above 3800. In 2009–2012, according to this assessment, 21 % of the soils tested by the stations had a low content, 73 % a medium and 6 % a high content (Table 9 of the publication). Whether the stations apply this scale today — WE HAVE NOT ESTABLISHED.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17 September 2026, read on 28 September 2026). All records of number R-04021: 16 entries at 16 laboratories — the same ones that cite the standards on available zinc, copper and manganese. All in the single form "PN-R-04021:1994", so the "Laboratories" tab (records beginning with "PN-R-04021") will show all 16 — for this standard the tab and the measurement say the same. Technique at all of them: flame atomic absorption spectrometry (FAAS). AB 317 cites its own instruction IB.22 (edition 2 of 30 April 2026) next to the standard. Current scopes on the PCA website (read on 29 September 2026): all 16 entries stand in the valid issues with the same range as in the copy, and none is suspended.

CLAUSES OF THE STANDARD IN THE SCOPES. Four laboratories cite clauses 1, 2 and 4 (AB 312, AB 317, AB 921, AB 1172), and two exclude clause 3 (AB 759, AB 787) — with the FAAS technique. This looks like a standard with two methods, of which AAS is in clause 4; which method stands in clause 3 — WE HAVE NOT ESTABLISHED (the card does not name it). AB 333 excludes "clause 3.5", just as in the standards on zinc, copper and manganese.

RANGES AND CLASS LIMITS — A PLACE FOR A RESULT THAT CANNOT BE CLASSIFIED. The lower class limit (700 mg/kg) lies within the ranges of all 16 laboratories — they start from 10 to 125 mg/kg, and AB 1172 from 400. The upper limit (3800 mg/kg) lies outside the range of three: AB 277 (up to 3200), AB 779 (up to 2000) and AB 1172 (up to 1500) — for them a result within the accreditation range cannot confirm a high content. The others end from 4000 (AB 798, AB 823, AB 921) to 10 000 mg/kg (AB 284, AB 317, AB 787, AB 1186).

WHAT WE DO NOT GIVE. We did not have the text of the standard — PKN sells it (4 pages). We do not give the sample mass, the extraction conditions, the second determination method, the AAS conditions, how the blank test is performed, the formula or the precision.

Method principle

According to the card of the standard: an extract is prepared from the soil, in which iron is determined; the standard gives the principles of the methods, the blank test, the calculation of the result and its interpretation. According to the KSChR publication (2013), the mineral-soil extract is prepared with 1 mol/dm³ hydrochloric acid and iron is determined by AAS; in accreditation scopes all laboratories record flame AAS. The result in mg/kg is assessed on a single scale: low content below 700, medium 700–3800, high above 3800 mg/kg. We DO NOT GIVE the extraction and measuring conditions — we did not have the text of the standard.

Applications

• Assessment of the available-iron status of mineral soils for fertiliser advice — in accreditation scopes exclusively agricultural soil-testing stations (16 laboratories)
• One scale for all mineral soils — unlike zinc, copper and manganese, the class does not depend on the soil category

Key parameters

Standard

Standard number

PN-R-04021:1994 (wersja polska)

Title (PL)

Analiza chemiczno-rolnicza gleby — Oznaczanie zawartości przyswajalnego żelaza

Title (EN)

Agricultural chemical analysis of soil — Determination of available iron content

Step-by-step procedure

1. Status of the document

   PKN card: standard withdrawn on 23-09-2020, no successor indicated (state of the card on 28 September 2026). In the report the full designation with the year is given: PN-R-04021:1994.

2. Soil extract

   An extract (according to the KSChR publication — with 1 mol/dm³ hydrochloric acid) and a blank test are prepared from mineral soil. Sample mass and conditions NOT GIVEN.

3. Determination

   Iron in the extract is determined by the method of the standard; in accreditation scopes all laboratories record flame AAS.

4. Result

   The available-iron content is reported in mg/kg of soil.

5. Content assessment

   Low below 700, medium 700–3800, high above 3800 mg/kg. A laboratory whose range ends below 3800 mg/kg cannot confirm a high content with a result within its accreditation range.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Hydrochloric acid is corrosive — work with gloves and goggles, in a fume cupboard; its safety data sheet applies
• The spectrometer flame requires a leak-tight installation for combustible gases and the safeguards provided by the instrument manufacturer; we DO NOT GIVE the type of flame required by the standard

Frequently asked questions