Overview
EN ISO 15685:2020 (identical to ISO 15685:2012) defines a rapid test by ammonium oxidation for assessing soil quality via the potential rate of ammonium oxidation and the inhibition of nitrification. The method targets soils that contain populations of nitrifying microorganisms and provides a screening tool to monitor soil health, evaluate wastes, and test the effects of cultivation practices, chemical substances (non‑volatile, H ≤ 1 excluded), biosolid extracts and pollution on nitrification.
Key topics and technical requirements
- Principle: Autotrophic ammonium-oxidizing bacteria in a soil slurry are exposed to ammonium sulfate in a phosphate‑buffered medium (approx. pH 7.2). Nitrite oxidation is blocked using sodium chlorate so that accumulated nitrite over a 6 h incubation reflects the potential ammonium-oxidizing activity.
- Reagents & test medium: Typical constituents include potassium phosphate buffer, sodium chlorate (5–15 mmol/l), and diammonium sulfate (~1.5 mmol/l). Stock solutions and preparation steps are specified for reproducible results.
- Apparatus: Ordinary laboratory equipment plus an orbital shaking incubator thermostatted at (25 ± 2) °C to keep slurries suspended during incubation.
- Sampling & characterization: Guidance follows ISO 10381-6. Recommended soil characterization parameters include pH, particle size, organic carbon, total nitrogen, CEC, water content and water‑holding capacity.
- Test design: At least three replicates (≈25 g moist soil each) per treatment; typical slurry volumes (e.g., 100 ml) and calculation methods for liquid addition are provided. Soils with measured ammonium-oxidizing activity between ~200–800 ng N/g dry mass/h are preferred for chemical testing.
- Scope limits: Not suitable for volatile chemicals with high Henry’s constant (H > 1).
Applications
- Rapid screening of soil nitrification potential for ecological monitoring and risk assessment.
- Testing inhibitory effects of agrochemicals, industrial chemicals and pollutants on nitrifying populations.
- Evaluating biosolids, waste samples or remediation outcomes by measuring impacts on nitrification when mixed with reference soils.
- Comparative studies of cultivation methods and land management on soil biological quality.
Who uses this standard
- Environmental laboratories and soil testing services
- Researchers in soil science, agronomy and environmental toxicology
- Waste and biosolid characterization labs
- Regulatory agencies and consultants conducting ecological risk assessments
Related standards
Normative references used with EN ISO 15685:2020 include:
Keywords: EN ISO 15685:2020, ISO 15685:2012, soil quality, nitrification, ammonium oxidation, rapid test, inhibition of nitrification, nitrifying microorganisms, biosolids, soil monitoring.
