🌿 Soil pH determination

Environmental PN-ISO 10390

Overview

STATUS (PKN cards as of 22.09.2026 — TWO 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.

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IS THE WITHDRAWN EDITION STILL IN USE — MEASUREMENT ON THE ACCREDITATION SCOPES (22.09.2026).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 largely, but not fully, complete. The scopes also show MIXED FORMS, 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 such a form DO NOT EXIST in the PKN catalogue — for the string "10390" the catalogue returns exactly two documents: the 1997 edition and the 2022-09 edition.

SCOPE OF THE 1997 EDITION (from the card): an instrumental method for the routine determination of pH with a glass electrode in a 1:5 (V/V) suspension of soil in water (pH-H₂O), in a potassium chloride solution c(KCl) = 1 mol/l (pH-KCl) or in a calcium chloride solution c(CaCl₂) = 0.01 mol/l (pH-CaCl₂). It applies to all types of air-dried soil samples.

Soil pH is one of the most important agrochemical parameters, affecting nutrient availability for plants, soil microorganism activity, and heavy metal mobility. Two values are determined: pH_H₂O (actual pH, in water suspension) and pH_KCl (exchangeable acidity, in 1 mol/L KCl suspension).

pH_KCl is lower than pH_H₂O by 0.5–1.5 units and better reflects soil buffering properties, as K⁺ ions displace H⁺ and Al³⁺ from the sorption complex. Agronomic soil pH classes: very acidic <4.5; acidic 4.5–5.5; slightly acidic 5.6–6.5; neutral 6.6–7.2; alkaline >7.2.

The method is simple, fast, and does not require expensive equipment, which is why it is performed en masse by Regional Chemical-Agricultural Stations (OSChR) in agricultural soil monitoring.

THE KEY OF THE TAB "PN-ISO 10390" (measurement of 23.09.2026, copy of the database of accreditation scopes): 23 entries at 17 laboratories — 12 records of the 1997 edition and 11 of the mixed form "PN-ISO 10390:2022-09". The edition in force has a separate entry in this knowledge base ("Soil pH in water, in KCl and in CaCl₂ — potentiometric method"); its key "PN-EN ISO 10390" gives 147 entries at 76 laboratories. The full scale of the core "10390" is 176 entries at 95 laboratories; besides the forms named above it includes, among others, "ISO 10390:2005" cited directly (3 times).

Method principle

The soil sample is mixed with distilled water or 1 mol/L KCl solution in a volume ratio of 1:5 (soil:liquid). The suspension is vigorously mixed for 5 minutes, left for 2 hours to equilibrate, and then pH is measured potentiometrically using a pH meter with combined glass electrode. Two-point calibration with pH 4.00 and 7.00 buffers.

Applications

• Agricultural soil monitoring (OSChR, IUNG)
• Fertilization recommendations (liming)
• Soil quality assessment according to Polish regulation
• Assessment of fertilization and cultivation impact on soil pH
• Assessment of heavy metal mobility in soil
• Environmental studies — acid rain impact

Key parameters

Standard

Standard number

PN-ISO 10390:1997 (wersja polska; wprowadza ISO 10390:1994 [EQV])

Title (PL)

Jakość gleby — Oznaczanie pH

Title (EN)

Soil quality — Determination of pH

Step-by-step procedure

1. Sample preparation

   Dry soil at room temperature. Sieve through 2 mm sieve. Measure 5 mL soil with graduated cylinder.

   ⏱ Time: 10 min

2. Suspension preparation

   To 5 mL soil add 25 mL distilled water (pH_H₂O) or 25 mL 1 mol/L KCl (pH_KCl).

   ⏱ Time: 2 min

3. Mixing

   Shake vigorously for 5 minutes on shaker (150–200 rpm) or manually.

   ⏱ Time: 5 min

4. Equilibration

   Leave suspension for 2 h (±15 min) at room temperature. Do not mix during this time.

   ⏱ Time: 2 h

5. pH meter calibration

   Calibrate pH meter with 4.00 and 7.00 buffers. Check slope (95–105% of theoretical).

   ⏱ Time: 5 min

6. pH measurement

   Immerse electrode in suspension (2 cm below surface). Wait for stabilization (±0.02 pH for 30 s). Record result.

   ⏱ Time: 2 min

7. Rinsing and repetition

   Rinse electrode with distilled water between samples. Perform duplicate every 10 samples.

   ⏱ Time: 1 min

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• KCl — harmless, standard protective measures
• Glass electrode — fragile, risk of cuts
• Gloves and safety goggles — standard equipment
• Soil may contain contaminants — use nitrile gloves
• This edition of the standard has been WITHDRAWN since 01-09-2022 — where the recipient requires a document in force, PN-EN ISO 10390:2022-09 applies
• The edition in force also covers sewage sludge and treated biowaste; this edition covers soil only
• The forms „PN-ISO 10390:1997-09" and „PN-EN 10390:2022-09" found in accreditation scopes match no document in the PKN catalogue — they mix the prefix of one edition with the year of the other

Frequently asked questions