ISO 15685:2012

Overview

ISO 15685:2012 - "Soil quality - Determination of potential nitrification and inhibition of nitrification - Rapid test by ammonium oxidation" specifies a rapid laboratory method to measure the potential rate of ammonium oxidation and the inhibition of nitrification in soils. The test is applicable to any soil containing nitrifying microorganisms and is designed as a screening tool for soil quality monitoring, waste characterization and assessing effects of cultivation, chemicals (non‑volatile), biosolid extracts and pollution on nitrification.

Key topics and technical requirements

• Principle: Ammonium-oxidizing bacteria in a buffered soil slurry (pH ~7.2) are supplied with ammonium (diammonium sulfate). Nitrite-oxidizing bacteria are inhibited with sodium chlorate so that accumulated nitrite reflects ammonium oxidation over a typical 6 h incubation.
• Measurement: Nitrite concentration is measured (e.g., automated segmented flow analysis) and converted to a rate (ng NO2‑N/g dry soil/h). Inhibition is expressed as percentage change vs control; inhibitory dose values (e.g., ID25, ID50) can be derived.
• Test conditions: Typical incubation at (25 ± 2) °C with orbital shaking; sampling commonly at 2 h and 6 h if oxidation is linear. Test medium contains a phosphate buffer, sodium chlorate (5–15 mmol/L) and ammonium source.
• Design: Replication (minimum three replicates per treatment), controls, and range‑finding for chemical concentrations (at least five concentrations in geometric progression) are required. Vehicles for poorly soluble chemicals must be controlled.
• Sample handling: Guidance on sampling, storage and characterization is referenced (ISO 10381‑6). Recommended soil descriptors include pH, organic matter, total N, particle size, water content and cation exchange capacity.
• Limitations: Volatile test substances are excluded from this standard; substances active at pH < 7.2 require pre‑exposure.

Applications and users

• Practical applications
  • Rapid screening of soil nitrifying activity for environmental monitoring and remediation assessment
  • Ecotoxicological testing of chemicals, wastes and biosolid extracts for impacts on nitrification
  • Comparative testing of polluted vs reference soils and assessment of agricultural management effects
• Who uses it
  • Environmental and agricultural laboratories
  • Soil scientists, ecotoxicologists and agronomists
  • Waste treatment facilities and regulators assessing biosolid or waste impacts on soil quality

Related standards

Relevant references and companion methods include:

• ISO 10381‑6 (soil sampling and storage)
• ISO 10390 (pH), ISO 10694 (organic carbon), ISO 11261 (total N)
• ISO 11260 (effective CEC), ISO 11277 (particle size), ISO 11465 (water content)
• ISO 14238 (nitrogen mineralization/nitrification), ISO 14256‑2 (NO2/NO3/NH4 analysis)
• EN 14735 (biosolid extract preparation)

Keywords: ISO 15685, soil quality, nitrification, ammonium oxidation, inhibition of nitrification, rapid test, biosolids, polluted soils, environmental monitoring.