🌿 Specific electrical conductivity of an aqueous extract of air-dried soil (fraction < 2 mm) — extraction with grade 2 water at a ratio of 1:5 (m/V) at (20 ± 1) °C, shaking for 30 min, filtration, measurement with a conductivity meter whose cell constant is checked with KCl solutions and the result corrected to 25 °C, in mS/m — an indication of the content of water-soluble electrolytes, PN-ISO 11265 (since 04-03-2026 PN-EN ISO 11265:2026-03)

Environment PN-ISO 11265

Overview

WHAT THE STANDARD COVERS. Scope from the PKN catalogue card of PN-ISO 11265:1997, in full (our translation of the Polish card text): “An instrumental method is given for the routine determination of the specific electrical conductivity in an aqueous solution of soil. It may be used for testing samples of all types of soil. The procedure applies to air-dried soil samples pretreated according to the standard PrPN-ISO 11464. It consists in extracting the soil with water at a temperature of 20 degrees C at a ratio of 1:5 (m/V) and measuring the specific electrical conductivity of the filtered extract with a conductivity meter, and the result is referred to a temperature of 25 degrees C. It is used to obtain an indication of the content of water-soluble electrolytes in the soil”. Scope from the card of the successor, PN-EN ISO 11265:2026-03, in full (our translation of the Polish card text): “This document gives an instrumental method for the routine determination of the specific electrical conductivity in an aqueous solution of soil, sewage sludge, treated biowaste and waste. The determination is carried out to obtain an indication of the content of water-soluble electrolytes in the sample. This document is applicable to air-dried samples of all types of soil, sludge, biowaste and waste”. We read the text of ISO 11265:1994 in full (the preview covers the cover, foreword, Clauses 1–10 and Annex A); of the new edition ISO 11265:2025 we have only the cover and table of contents — we do not know its content. We checked the formula for the cell constant on the image of page 2.

ACCORDING TO THE TEXT OF ISO 11265:1994 (complete). The standard was prepared by ISO/TC 190/SC 3 (chemical methods and soil characteristics); Annex A is informative. Scope (Clause 1): an instrumental method for the routine determination of the specific electrical conductivity in an aqueous extract of soil, to obtain an indication of the content of water-soluble electrolytes; for all types of air-dried soil samples. Normative references: ISO 3696 (water for laboratory use), ISO 7888 (electrical conductivity of water — also definitions of the concepts), ISO 11464 (pretreatment of samples). Principle (Clause 3): air-dried soil is extracted with water at (20 ± 1) °C at a ratio of 1:5 (m/V), the conductivity of the filtrate is measured and the result corrected to 25 °C. Reagents (Clause 4): analytical grade reagents; water with a conductivity not higher than 0,2 mS/m at 25 °C (grade 2 according to ISO 3696); potassium chloride solution c(KCl) = 0,1 mol/l — 7,456 g of KCl dried for 24 h at (220 ± 10) °C dissolved and made up to 1000 ml at 20 °C, conductivity 1290 mS/m at 25 °C; solution 0,0200 mol/l (200,0 ml of the 0,1 mol/l solution to 1000 ml), 277 mS/m at 25 °C; solution 0,0100 mol/l (100,0 ml to 1000 ml), 141 mS/m at 25 °C; KCl calibration solutions are stored in tightly sealed bottles that do not release alkali or alkaline-earth cations (plastic bottles may be suitable; plastic seals recommended, because glass welds to the bottle); commercially available conductivity standards are permitted. Apparatus (Clause 5): conductivity meter with cell, adjustable range and (automatic) temperature compensation, accuracy 1 mS/m at 20 °C, preferably with cell constant control; analytical balance with an accuracy of at least 0,01 g; thermometer with a resolution of 0,1 °C; horizontal shaking machine maintaining a 1:5 soil–water suspension, in an environment at (20 ± 1) °C (note: about 180 cycles per minute with a stroke of about 5 cm are suitable); filter paper with low ash content and high retention; 250 ml shaking bottles of borosilicate glass or polyethylene. Sample (Clause 6): fraction below 2 mm of air-dried soil pretreated according to ISO 11464. Extraction (7.1): 20,00 g of sample into the bottle, 100 ml of water at (20 ± 1) °C, bottle closed, horizontal in the shaking machine, 30 min; filtration directly through a filter paper; a blank carried out in the same way must not exceed 1 mS/m — otherwise the extraction is repeated; notes: the filtrate should just suffice for the measurements; the 1:5 ratio was chosen so that an extract can be obtained from all soils, including those rich in organic matter; extraction is carried out at (20 ± 1) °C because salt solubility depends on temperature, and after filtration the temperature of the extract may change — the measurement refers to 25 °C; the blank shows the contribution of water, glassware and filter paper; shaking should only maintain the suspension — too vigorous shaking causes excessive dispersion of clay, filtration difficulties and an erroneous result. Cell constant (7.2): measurement of the conductivity κm of the three KCl solutions according to the instrument instructions; for each solution K = κs/κm (K — cell constant in m⁻¹, κs — specific conductivity of the KCl solution, κm — measured conductivity of that solution; in print the denominator lacks the subscript “m”); the mean of the three values is the cell constant; it must not differ from the manufacturer’s value by more than 5 %; the constant is set on the conductivity meter. Measurement (7.3): conductivity of the filtrates according to the instructions, with compensation to 25 °C, to one decimal place, in mS/m. Interferences (Clause 8): contamination of the electrodes — difficult to recognize, changes the cell constant, visible when measuring the KCl solutions; air bubbles on the electrodes (e.g. when warming the extract); conductivities below 1 mS/m are disturbed by carbon dioxide and ammonia from the air — they require a special cell and are outside the scope of the standard. Repeatability (Clause 9, Table 1): two separately prepared filtrates may differ by 5 mS/m (conductivity 0–50 mS/m at 25 °C), 20 mS/m (above 50 to 200 mS/m) or 10 % (above 200 mS/m). Test report (Clause 10): reference to the standard, identification of the sample, result in whole numbers in mS/m, operations not specified in the standard or optional and other factors affecting the result. Annex A: interlaboratory trial of Wageningen Agricultural University of 1991 — 26 laboratories, five soils (two from salt-affected areas of Hungary, one from the Netherlands), means from about 31 to about 656 mS/m; repeatability limit r from about 2,4 to about 31 mS/m, reproducibility limit R from about 11,5 to about 175 mS/m (calculated according to ISO 5725:1986).

NEW EDITION (from the cover and table of contents of ISO 11265:2025 and the PKN card). ISO 11265:2025 is the second edition (2025-08) with a changed title “Environmental solid matrices — Determination of the specific electrical conductivity”; its table of contents has the same parts as the 1994 edition (principle, reagents, apparatus, sample, extraction, cell constant, measurement, interferences, repeatability, test report, Annex A with the interlaboratory trial), with an added clause on definitions. According to the PKN card, the scope now includes sewage sludge, treated biowaste and waste. Whether the extraction conditions or repeatability criteria have changed — we do not know.

STATUS (cards as of 02.10.2026). The card of PN-ISO 11265:1997 in the Polish version (8 pages, price group D) carries the heading “Wycofana” (withdrawn): “Date of withdrawal: 04-03-2026”, Health, Environment and Medicine Sector, KT 192 General and Soil Physics, ICS 13.080.20, “Introduces: ISO 11265:1994 [IDT], ISO 11265:1994/Cor 1:1996 [IDT]”, “Replaced by: PN-EN ISO 11265:2026-03 – English version”; the card gives the “Publication date” field as “25-08-2249” (an error on the card). The card of PN-EN ISO 11265:2026-03 in the English version (published 04-03-2026, 18 pages, price group J) does not carry the heading “Wycofana”: KT 191 Soil Chemistry, “Introduces: EN ISO 11265:2025 [IDT], ISO 11265:2025 [IDT]”, “Replaces: PN-ISO 11265:1997 – Polish version”.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, load up to 17.09.2026, read on 02.10.2026). The number 11265 appears in 10 records at 8 laboratories: AB 199 (two rows), AB 201, AB 213 (two rows), AB 300, AB 894, AB 1249, AB 1682, AB 1748. In the current scopes on the PCA website (read on 02.10.2026, issues from 19.01.2026 to 08.09.2026): “PN-ISO 11265+AC1:1997” — AB 199, AB 201, AB 213, AB 300, AB 1249; “PN-ISO 11265:1997+AC1:1997” — AB 894; “PN-ISO 11265:1997” — AB 1748; the new edition “PN-EN ISO 11265:2026-03” — only AB 1682 (scope issue of 15.05.2026). No row with this number is set in bold italics (AB 1682 has a suspension of another part of the scope). The “Laboratories” tab searches for entries STARTING WITH the entered number: “PN-ISO 11265” shows 7 laboratories and 9 items, “PN-EN ISO 11265” — 1 laboratory and 1 item (AB 1682) — checked with the tab query on the labcoda.pl production server on 02.10.2026.

WHAT THE LABORATORIES TEST (items in the PCA scopes). Soil, mineral and organic soil, at AB 213 also bottom sediments — “specific electrical conductivity, conductometric method”, with ranges: (20–12 900) µS/cm and (10–10 000) µS/cm (AB 199, two rows), (50–10 000) S/cm — in the document without “µ” (AB 201), (10,0–1300) µS/cm, i.e. (1,0–130) mS/m, and for sediments (10,0–8000) µS/cm (AB 213), (7,0–16 000) µS/cm (AB 300), (15–12 800) µS/cm (AB 894), (10–50 000) µS/cm (AB 1249), (1,0–500) mS/m, i.e. (10–5000) µS/cm (AB 1682), (20–5000) µS/cm (AB 1748). Alongside pH (PN-EN ISO 10390), dry matter (PN-ISO 11465) and organic carbon.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. Units: the standard works in mS/m, laboratories give ranges in µS/cm — 1 mS/m = 10 µS/cm; a mistake shifts the result tenfold. Temperature: extraction at (20 ± 1) °C, result corrected to 25 °C — extraction in a warmer room dissolves more salt. Shaking: too vigorous shaking disperses clay, hampers filtration and changes the conductivity. Blank: above 1 mS/m the extraction must be repeated (contaminated water, glassware or filter paper). Cell: a constant differing by more than 5 % from the manufacturer’s value, contaminated electrodes and air bubbles falsify the result; below 1 mS/m the influence of CO₂ and NH₃ from the air takes the measurement outside the scope of the standard. Ratio: other soil-to-water proportions (e.g. saturated paste) give results not comparable with 1:5. Reference: PN-ISO 11265:1997 has been withdrawn since 04-03-2026 — seven of the eight laboratories still have it in their scope; the successor also covers sludge, biowaste and waste.

WHAT WE DO NOT GIVE. The content of the new edition ISO 11265:2025 (apart from the title, table of contents and the scope from the PKN card) — we do not know whether the extraction conditions, preparation of samples other than soil or the repeatability criteria have been changed.

Method principle

Air-dried soil (fraction < 2 mm) is extracted with water at a ratio of 1:5 (m/V) at (20 ± 1) °C by 30 min of shaking, filtered, and the specific electrical conductivity of the filtrate is measured with a conductivity meter whose cell constant is checked with KCl solutions, corrected to 25 °C; the result in mS/m indicates the content of water-soluble electrolytes.

Applications

• Mineral and organic soils — salinization, content of water-soluble salts, 8 laboratories
• Bottom sediments (AB 213); according to the successor PN-EN ISO 11265:2026-03 also sewage sludge, treated biowaste and waste
• Assessment of soils in agriculture, land reclamation and environmental studies

Key parameters

Standard

Standard number

PN-ISO 11265:1997 (wersja polska; ISO 11265:1994 IDT z Cor 1:1996) — wycofana 04-03-2026, zastąpiona przez PN-EN ISO 11265:2026-03 (wersja angielska; EN ISO 11265:2025 IDT, ISO 11265:2025 IDT)

Title (PL)

Jakość gleby — Oznaczanie przewodności elektrycznej właściwej (następczyni: Składniki stałe środowiska — Oznaczanie przewodności elektrycznej właściwej)

Title (EN)

Soil quality — Determination of the specific electrical conductivity (successor: Environmental solid matrices — Determination of the specific electrical conductivity)

Step-by-step procedure

1. Sample

   Fraction < 2 mm of air-dried soil pretreated according to ISO 11464. PN-ISO 11265:1997 withdrawn 04-03-2026, successor PN-EN ISO 11265:2026-03 (cards as of 02.10.2026).

2. Extraction

   20,00 g of sample + 100 ml of water at (20 ± 1) °C, 30 min horizontal shaking, filtration; blank ≤ 1 mS/m, otherwise repeat.

3. Cell constant

   Measurement of three KCl solutions, K = κs/κm, mean; agreement with the manufacturer’s value within 5 %; setting on the conductivity meter.

4. Measurement

   Conductivity of the filtrate with compensation to 25 °C, reading to one decimal place in mS/m; no bubbles on the electrodes.

5. Result

   Whole number in mS/m; two filtrates agreeing according to Table 1 (5 mS/m, 20 mS/m or 10 %); report according to Clause 10.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Test without particular hazards; drying KCl at 220 °C — heat-resistant gloves; the standard contains no safety warnings
• SUBSTANTIVE NOTE: PN-ISO 11265:1997 has been withdrawn since 04-03-2026; result in mS/m, laboratory ranges usually in µS/cm (1 mS/m = 10 µS/cm); results for soil:water ratios other than 1:5 are not comparable

Frequently asked questions