Overview
ISO/TS 20131-2:2018 - Soil quality - Easy laboratory assessments of soil denitrification - Part 2 specifies a standardized laboratory test to characterise the capacity of soils to reduce the greenhouse gas nitrous oxide (N2O) into dinitrogen (N2). The method quantifies transient N2O accumulation during anaerobic incubations and produces indicators (notably the maximum ratio r and an index combining level and timing of accumulation) that identify soils at risk of elevated N2O emissions.
Key topics and technical requirements
- Scope: Laboratory test on a composite of sieved field samples (typical depth 0–20 cm). Applicable year‑round except in extreme drought; results stable where no organic or lime amendments are applied.
- Sampling & preparation: Composite from ~10 sub-samples across a plot (example area ~1 000 m²) to obtain ~1 kg fresh soil; sieve to 2 mm (up to 5 mm accepted if needed); determine soil water content (SWC) per ISO 11465.
- Test principle: Measure N2O release from soil slurries under anaerobic conditions over seven days, with and without acetylene (acetylene inhibits N2O reductase). Comparison indicates soil capacity to reduce N2O.
- Materials & apparatus: pre‑evacuated vials with septa, reagent bottles (~500 ml), shaker, vacuum pump, gas chromatograph (GC) with thermal conductivity detector (TCD), Porapak Q column. Reagents include potassium nitrate (KNO3), acetylene (acetone‑free), nitrogen/argon/helium, and N2O standards.
- Procedure highlights: Six replicate bottles with 50 g sieved soil + 50 ml solution S2 (KNO3 7 mmol·L⁻¹); evacuate and refill headspace as specified; sample headspace gases for GC analysis over incubation.
- Outputs: Indicators r and index (see Annex A) that can be used to discriminate soils with low N2O‑reduction capacity and to parameterise emission models (e.g., NOE model).
Applications and users
- Who uses it: soil scientists, environmental laboratories, agronomists, greenhouse‑gas inventory compilers, land managers, researchers studying nitrogen cycling and mitigation strategies.
- Practical uses:
- Screening soils for potential high N2O emissions.
- Informing mitigation and management (fertiliser timing, drainage, organic amendments).
- Providing standardized inputs for emission models and national GHG inventories.
- Supporting research into microbial denitrification and policy decisions on agricultural emissions.
Related standards
- ISO/TS 20131-1 (Denitrifying enzyme activities) - complementary test addressing DEA.
- ISO 11465 - Determination of dry matter and water content (gravimetric).
- ISO 18400-206 - Guidance on collection/handling/storage of soil for microbiological assays.
Keywords: ISO/TS 20131-2:2018, soil quality, denitrification, N2O reduction capacity, nitrous oxide emissions, laboratory test, soil sampling, gas chromatography, acetylene inhibition.