🌿 Available boron in mineral soil — spectrophotometry with curcumin or with 1,1′-dianthrimide, PN-R-04018

Environment PN-R-04018

Overview

WHAT THE STANDARD COVERS. The scope from the PKN catalogue card, quoted in full: "Two types of methods are specified: the spectrophotometric method with curcumin and the spectrophotometric method with 1,1'-dianthrimide. The first method consists in the spectrophotometric measurement of the intensity of the orange-red colour of the curcumin–boron complex in a strongly acidic medium. The second method consists in the reaction of 1,1'-dianthrimide with boron during heating for 2-4 h at a temperature of 70-90 degrees Celsius in a sulphuric acid medium and the measurement of the intensity of the dark-blue colour of the complex." The Polish card spells the reagents inconsistently ("kurkumia" for curcumin, "dwuantrimid" next to "dwuantrymid"). The card does not give the solution with which boron is extracted from the soil.

STATUS (state of the card on 29 September 2026). The card carries the heading "Withdrawn" and the row "Date of withdrawal: 04-09-2014". There are no "Superseded by" and "Supersedes" fields. Edition: published 31-03-1993, 3 pages, PKN technical committee KT 90 (Soil Cultivation and Horticulture), ICS 13.080.10. From the same series "Agricultural chemical analysis of soil", the standards on available zinc (PN-R-04016), copper (PN-R-04017), manganese (PN-R-04019) and iron (PN-R-04021) have separate entries in this knowledge base. A successor WE HAVE NOT ESTABLISHED. The Regulation of the Minister of Agriculture and Food Economy of 27 June 1997 on the obligation to apply Polish Standards (Journal of Laws 1997 No. 83 item 535) listed "PN-93/R-04018 Agricultural chemical analysis of soil. Determination of available boron content" among the standards to be applied obligatorily (annex, division 15, class 150, item 9); in ELI the act has the status "deemed repealed", with the repeal date 01.01.2003. A regulation in force that would cite this standard WE HAVE NOT ESTABLISHED.

EXTRACT AND ASSESSMENT — 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 boron in mineral soils is determined after extraction with 1 mol/dm³ hydrochloric acid, colorimetrically; in 1965–1983 it was extracted with hot water (the Berger and Truog method) — Table 8 of the publication. Content assessment — Table 1 of the publication ("Source: PKN, 1993"), mg of boron per kg of soil, depending on the pH in 1 mol/dm³ KCl: at pH below 4.5 — low below 0.8, medium 0.8–2.6, high above 2.6; at pH 4.6–5.5 — below 1.0, 1.0–3.2, above 3.2; at pH 5.6–6.5 — below 1.3, 1.3–4.3, above 4.3; at pH above 6.5 — below 2.2, 2.2–7.2, above 7.2. The author writes that "in the case of boron and manganese the determination of additional parameters, including pH, is necessary" (our translation). In 2009–2012, according to this assessment, 74 % of the soils tested by the stations had a low content, 25 % a medium and 1 % a high content, compared with 41 %, 41 % and 18 % in 1965–1983 (Table 9 of the publication); most soils poor in boron — over 90 % — were in the Podlaskie voivodeship.

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-04018: 13 entries at 13 laboratories — regional agricultural chemistry stations. Forms: "PN-R-04018:1993" with or without clauses — 10 laboratories; "PN-93/R-04018" — 3 (AB 317, AB 789, AB 921). The "Laboratories" tab searches for records BEGINNING with "PN-R-04018" and will show 10 laboratories — checked with the tab query on the labcoda.pl production server on 29 September 2026: 10; AB 317, AB 789 and AB 921 remain outside it. Object: mineral soil — at all of them. Technique: the spectrophotometric method — at all of them. Current scopes on the PCA website (read on 29 September 2026): all 13 entries stand in the valid issues, every numerical range from the copy appears in the current document and none is suspended.

WHICH OF THE TWO METHODS. Laboratories indicate clauses of the standard. Clause 3 (or exclusion of clause 4): AB 284, AB 312, AB 779, AB 787, AB 789 — five. Clause 4 (or exclusion of clause 3): AB 277, AB 317, AB 333, AB 759, AB 921, AB 1172 — six. Without clauses: AB 827, AB 930. The card lists the methods in the order curcumin, then dianthrimide; whether clauses 3 and 4 follow this order — WE HAVE NOT ESTABLISHED, because we did not have the text of the standard. In a report the standard number alone therefore does not say by which method boron was determined.

RANGES AND CLASS LIMITS. Lower limits: from 0.2 mg/kg (AB 930) and 0.30 mg/kg (AB 317) to 0.6 mg/kg (AB 333) — at all of them below the lowest class limit (0.8 mg/kg). Upper: from 5.0 mg/kg (AB 317, AB 921, AB 1172) to 25 mg/kg (AB 333). The limit of high content at pH above 6.5 is 7.2 mg/kg — at the three laboratories whose range ends at 5.0 mg/kg, a result confirming a high status in an alkaline soil lies outside the accreditation range.

ALONGSIDE THIS STANDARD. Boron explicitly described as available in soil is covered, apart from this standard, only by in-house procedures of three laboratories: AB 779 (PB 09, spectrophotometric method, in a separate entry next to this standard), AB 1748 (PB-74, PB-75 and PB-79 — all with inductively coupled plasma optical emission spectrometry, ICP-OES, i.e. a technique different from the spectrophotometry of this standard) and AB 1682 ("formy przyswajalne" — available forms, ICP-OES by the Mehlich 3 method, record "Procedury badawcze" — test procedures). Boron in soil without a stated form also appears in multi-element entries with in-house procedures — with ICP-OES at AB 277 (PB 58), AB 312 (PB 30.0), AB 317 (PB.100), AB 333 (PB 52), AB 759 (PB 51), AB 798 (PB 56), AB 1186 (PB 30.0) and AB 1270 (PB-8), with ICP-OES and inductively coupled plasma mass spectrometry (ICP-MS) at AB 696 (PT-LCAW-06) and with ICP-MS at AB 1748 (PB-01); whether these are available forms, the accreditation scopes do not say. Entries with boron determined according to other standards — PN-EN 16171 with PN-ISO 11466 (AB 213) and PN-EN ISO 11885 in solutions, in mg/l (AB 213; AB 300 — with the PN-EN 12457 series) — and total boron (AB 1682) are different determinations.

WHAT WE DO NOT GIVE. We did not have the text of the standard — PKN sells it (3 pages). We do not give the sample mass, the extraction solution and conditions according to the standard, the way interfering substances are removed, the measurement wavelengths, the calibration curve, the formula or the precision.

Method principle

According to the card of the standard, boron in the soil extract is determined spectrophotometrically by one of two methods: with curcumin (orange-red complex in a strongly acidic medium) or with 1,1′-dianthrimide (dark-blue complex after 2–4 h of heating at 70–90 °C in sulphuric acid). According to the KSChR publication (2013), the mineral-soil extract is prepared with 1 mol/dm³ hydrochloric acid. The result is assessed with a table that depends on the soil pH (low, medium, high content). We DO NOT GIVE the sample mass, extraction conditions or wavelengths — we did not have the text of the standard.

Applications

• Assessment of the available-boron status of mineral soils — in the accreditation scopes of 13 regional agricultural chemistry stations
• Classification requires the soil pH (in 1 mol/dm³ KCl) — the boron class limits change with pH

Key parameters

Standard

Standard number

PN-R-04018:1993 (wersja polska)

Title (PL)

Analiza chemiczno-rolnicza gleby — Oznaczanie zawartości przyswajalnego boru

Title (EN)

Agricultural chemical analysis of soil — Determination of available boron content

Step-by-step procedure

1. Status of the document

   PKN card: standard withdrawn on 04-09-2014, no successor indicated (state of the card on 29 September 2026).

2. Soil extract

   According to the KSChR publication — 1 mol/dm³ hydrochloric acid for mineral soils. Extraction conditions according to the standard NOT GIVEN.

3. Colour reaction

   Curcumin method (strongly acidic medium) or dianthrimide method (2–4 h at 70–90 °C in sulphuric acid).

4. Spectrophotometric measurement

   Measurement of the colour intensity of the complex; in the report it is worth indicating the method — the standard number alone does not say it.

5. Content assessment

   The result in mg/kg is assessed with a table that depends on the soil pH — the pH has to be determined separately.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Sulphuric acid and heating (2–4 h at 70–90 °C) in the dianthrimide method — work in a fume cupboard, protect eyes and hands
• SUBSTANTIVE NOTE: without the soil pH the boron result cannot be classified — the class limits depend on pH

Frequently asked questions