🌿 Soil pH determination

Environmental PN-ISO 10390

Overview

STATUS (as of 02.11.2026). TWO PKN cards checked. PN-ISO 10390:1997, Polish version, published 11-12-1997, 15 pages, ICS 13.080.10, technical committee KT 191 (Soil Chemistry), "Implements: ISO 10390:1994 [EQV]" — note: EQV, i.e. EQUIVALENT, not identical to the international document. The card carries a withdrawal note dated 01-09-2022 and names the successor: PN-EN ISO 10390:2022-09 — the ENGLISH version. In the ISO catalogue the 1994 edition is withdrawn; ISO 10390:2021 is in force.

THE EDITION IN FORCE HAS A DIFFERENT TITLE AND A WIDER SUBJECT — AND IT MERGED TWO STANDARDS INTO ONE. PN-EN ISO 10390:2022-09 is entitled "Gleba, uzdatnione bioodpady oraz osady ściekowe — Oznaczanie pH" [Soil, treated biowaste and sludge — Determination of pH] (it implements EN ISO 10390:2022 [IDT] and ISO 10390:2021 [IDT]) and supersedes TWO documents at once: PN-ISO 10390:1997 and PN-EN 15933 (determination of pH in sludge and biowaste). The 1997 edition concerned soil alone — which is why this entry does not speak of sludge or biowaste. The edition in force has its own entry in this knowledge base.

IS THE WITHDRAWN EDITION STILL IN USE — MEASUREMENT ON ACCREDITATION SCOPES (22.09.2026). "PN-ISO 10390:1997" — 12 entries at 10 laboratories; "PN-EN ISO 10390:2022-09" — 140 entries at 73 laboratories. The transition to the new edition is thus mostly complete, but not entirely. MIXED FORMS also appear in the scopes, in which the prefix comes from one edition and the year from the other: "PN-ISO 10390:2022-09" (11 entries at 7 laboratories) and "PN-EN 10390:2022-09" without the ISO element (5 entries at 3 laboratories). Designations in this form DO NOT EXIST in the PKN catalogue — the catalogue returns exactly two documents for the string "10390": the 1997 edition and the 2022-09 edition.

SCOPE OF THE 1997 EDITION (from the card; ISO 10390:1994, clause 1). An instrumental method for the routine determination of pH using a glass electrode in a 1:5 (V/V) suspension of soil in water (pH-H₂O), in a solution of potassium chloride c(KCl) = 1 mol/l (pH-KCl) or in a solution of calcium chloride c(CaCl₂) = 0.01 mol/l (pH-CaCl₂). It applies to all types of air-dried soil samples, e.g. pretreated according to ISO 11464.

PROCEDURE ACCORDING TO ISO 10390:1994 (PN-ISO 10390:1997 is equivalent to this text — EQV). The laboratory sample is the fraction passing a 2 mm sieve from air-dried soil or soil dried at a temperature not higher than 40 °C; drying may change the pH, and in soils containing sulfides it may lower it substantially. A test portion of at least 5 ml is taken with a spoon of known capacity — the volume ratio allows all soils, including those of low density, to be treated in the same way — and five times its volume of water, KCl or CaCl₂ solution is added. The suspension is shaken or mixed mechanically for 5 min and left for at least 2 h but not longer than 24 h; in contaminated, recently limed and carbonate-containing soils equilibrium may not be reached within this time — then pH is measured at least twice between 2 h and 24 h and two or more values are reported. The pH meter is calibrated with at least two buffer solutions out of pH 4.00, 7.00 and 9.22 at 20 °C. The temperatures of the buffer and of the suspension shall not differ by more than 1 °C; the suspension is shaken just before measurement and measured in the settling suspension, and the reading is considered stable when it varies by not more than 0.02 pH units over 5 s. Readings are recorded to two decimal places, the result is reported to the nearest 0.1.

REPEATABILITY (clause 8). Acceptable difference between the results of two separately prepared suspensions: pH below 7.00 — 0.15; from 7.00 to 7.50 — 0.20; from 7.50 to 8.00 — 0.30; above 8.00 — 0.40. Annex A summarizes the 1990 interlaboratory trial (Wageningen Agricultural University, 30 laboratories, 5 soils).

REGULATIONS. The Regulation of the Minister of the Environment of 1.09.2016 on the method of assessing land surface contamination (Dz.U. 2016 item 1395) gives for the pH-KCl value the reference methodology “test procedure based on PN-ISO 10390” (Annex 3 point 3); pH-KCl determines there, among other things, the assignment of group II soils to subgroups II-2 and II-3 (limits 6.5 and 5.5, § 3(7)).

WHAT WE DO NOT GIVE HERE. We have not read the Polish 1997 text — the procedure is given according to ISO 10390:1994, to which PN-ISO 10390:1997 is equivalent but not identical; any deviations of the Polish edition are not described.

Method principle

A suspension of the soil sample is made up in five times its volume of water, potassium chloride solution 1 mol/l or calcium chloride solution 0.01 mol/l, and its pH is measured with a pH meter and glass electrode (ISO 10390:1994, clause 3).

The volume ratio (V/V) allows all soils to be treated in the same way — with a mass ratio the test portion would have to be adapted for soils of low density; taking the test portion with a measuring spoon is sufficiently accurate (note 1).

Applications

• Routine determination of pH-H₂O, pH-KCl or pH-CaCl₂ in all types of air-dried soil samples (clause 1)
• Assessment of land surface contamination — pH-KCl value according to the procedure based on PN-ISO 10390 and assignment to the subgroups of land group II (Dz.U. 2016 item 1395, § 3(7), Annex 3 point 3)
• Accreditation scopes citing the 1997 edition — since 01.09.2022 the document in force is PN-EN ISO 10390:2022-09

Key parameters

Standard

Standard number

PN-ISO 10390:1997 (Polish version; adopts ISO 10390:1994 [EQV])

Title (PL)

Jakość gleby — Oznaczanie pH

Title (EN)

Soil quality — Determination of pH

Step-by-step procedure

1. Laboratory sample

   Fraction passing a 2 mm square-hole sieve from air-dried soil or soil dried at a temperature not higher than 40 °C, e.g. pretreated according to ISO 11464; drying may change the pH, especially in soils containing sulfides (clause 6, note 7).

2. Suspension

   At least 5 ml of sample taken with the spoon into the bottle and five times its volume of water, KCl or CaCl₂ solution (7.1.1–7.1.2).

3. Shaking and equilibrium

   Vigorous mechanical shaking or mixing for 5 min, then at least 2 h but not longer than 24 h; in contaminated, recently limed and carbonate-containing soils — measurements at least at two times between 2 h and 24 h (7.1.3, notes 8–9).

4. Calibration

   According to the manufacturer’s manual, with at least two buffer solutions (4.4, 7.2).

5. Measurement

   Temperatures of buffer and suspension differ by not more than 1 °C; shake the suspension just before measurement and measure in the settling suspension; reading after stabilization — change of not more than 0.02 pH units over 5 s; record to two decimal places (7.3, note 12).

6. Result

   To the nearest 0.1 pH unit, stating the medium (water, KCl or CaCl₂) and any difficulties in establishing equilibrium; repeatability of two suspensions according to Table 1 (clauses 8–9).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The standard gives no safety warnings

Frequently asked questions