Overview
ISO 13536:2024 specifies a laboratory method for determining the potential cation exchange capacity (CEC) of soils and the content of exchangeable sodium, potassium, calcium and magnesium. The method uses a barium chloride extraction solution buffered at pH = 8.1 (triethanolamine buffer) to saturate exchange sites with barium, displace barium with magnesium sulfate, and quantify excess magnesium by FAAS or ICP‑AES. The standard is applicable to all types of air‑dried soil samples and is the second edition, revising the CEC calculation and adding guidance for calcareous soils.
Key Topics
- Scope and applicability: CEC and exchangeable Na, K, Ca, Mg for air‑dried soils.
- Principle: Soil saturated with Ba2+ in a buffered BaCl2 solution; Ba2+ precipitated as BaSO4 after addition of excess MgSO4 so exchange sites are occupied by Mg2+; excess Mg2+ measured instrumentally.
- Reagents and solutions: e.g., BaCl2 (1 mol·L−1), triethanolamine solution adjusted to pH 8.1, MgSO4 (0.0200 mol·L−1), acidified lanthanum for FAAS.
- Procedure steps: sample pretreatment (ISO 11464), leaching/extraction (multiple BaCl2 buffer washes), centrifugation, collection of extracts (filtrate A for exchangeable cations, filtrate B for CEC), blank preparation, and calibration series.
- Instrumentation and calculations: magnesium quantified by FAAS (285.2 nm) or ICP‑AES; dilution and blank corrections applied; updated formula for CEC calculation included.
- Quality and limitations: warnings about barium toxicity; organic matter dissolution can underestimate potential CEC; soluble salts can cause sum of exchangeable cations to exceed CEC; special note for calcareous soils (see ISO 23470:2018).
Applications
- Soil testing and fertility assessment for agronomy and crop management
- Environmental monitoring and land‑use planning (soil quality indicators)
- Remediation projects and contaminated site assessment
- Research in soil chemistry, pedology and nutrient cycling
- Routine analytical laboratories and regulatory agencies performing standardized CEC and exchangeable cation determinations
Who uses it: analytical laboratories, agronomists, environmental consultants, soil scientists, regulators and research institutions.
Related Standards
- ISO 11464 - Pretreatment of samples for physico‑chemical analysis
- ISO 11465 - Determination of dry residue / water content
- ISO 23470:2018 - Alternative procedure for soils with low solubility of calcium carbonate minerals
Keywords: ISO 13536:2024, cation exchange capacity, CEC, barium chloride, triethanolamine buffer, exchangeable cations, soil quality, FAAS, ICP‑AES, soil testing.