Overview
ISO 14238:2012 specifies laboratory procedures to measure nitrogen mineralization and nitrification in soils and to assess how chemicals influence these microbial processes. The standard describes test design, soils and reagents, incubation and sampling strategies, analytical endpoints (ammonium, nitrite, nitrate), data expression (including inhibitory dose IDx) and required documentation for reliable soil quality and ecotoxicity assessments.
Key topics and requirements
- Principle: Determine rates/extent of N‑mineralization by measuring ammonium, nitrite and nitrate released from soil organic matter or an added nitrogenous substrate. Assess chemical effects by comparing treated vs control soils.
- Soil selection & characterization:
- Prefer soils consistent with test purpose; toxicity tests use low organic carbon (≈0.5–1.5% C) and low clay (sandy loam/loamy sand) to represent worst‑case bioavailability.
- Required properties: particle size distribution, water content, water‑holding capacity, pH, cation exchange capacity, organic carbon and total nitrogen (referenced ISO methods: ISO 11277, ISO 11465, ISO 11274, ISO 10390, ISO 11260, ISO 10694, ISO 11261).
- Reagents & substrates:
- Typical nitrogenous substrates: lucerne meal or horn meal (C:N ≈ 16:1) to give ~100 mg N/kg soil; ammonium salts used when testing nitrification specifically.
- Extraction: 1 mol/L KCl for N extraction; equipment includes shaker, centrifuge/filters and instruments for N analyses.
- Incubation & sampling:
- Options for bulk or individual test portions; recommended conditions for toxicity tests: (20 ± 2) °C and ~40–60% water‑holding capacity (≈0.02 MPa).
- For simple toxicity screening, measure nitrate at 0 d and 28 d to build dose–response and estimate ID25/ID50.
- Test substances & reporting: Use high‑purity or relevant technical-grade chemicals, report identifiers (IUPAC, CAS), physico‑chemical data and complete test conditions.
Applications and users
ISO 14238 is used for:
- Soil quality assessment and monitoring of microbial nitrogen cycling.
- Ecotoxicity testing to evaluate pesticide or chemical impacts on N‑mineralization and nitrification.
- Agricultural and remediation studies to assess soil fertility changes and contaminant effects.
Primary users: environmental and agricultural laboratories, ecotoxicologists, soil scientists, regulatory agencies, pesticide manufacturers and land‑management consultants.
Related standards
Key referenced ISO documents for sampling and analyses include:
For implementation, obtain ISO 14238:2012 from ISO or your national standards body.