ISO 14256-2:2005

Overview

ISO 14256-2:2005 specifies an automated method for determining nitrate (NO3‑N), nitrite (NO2‑N) and ammonium (NH4‑N) in field‑moist soils. The method uses a 1 mol/L potassium chloride (KCl) extraction of homogenized soil and analyzes the extract with segmented flow analysis (SFA) using automated spectrophotometric detection. This part of ISO 14256 is applicable to all soil types when appropriately homogenized.

Key topics and technical requirements

• Sampling and handling
  • Protect samples from warming during sampling and transport; cool boxes recommended.
  • If analyzed within 3 days store at 4 °C; for longer storage freeze at −20 °C and control thawing time.
  • Homogenize samples to break aggregates (<5 mm) before analysis.
• Extraction
  • Use 1 mol/L KCl at a mass ratio of 1:5 (soil:extractant).
  • Extraction at 20 °C ± 2 °C for 1 hour with end‑over‑end shaking.
  • Centrifuge extracts (recommended) or allow settling; discard first 20 mL if filtered.
• Automated analysis (SFA)
  • Use segmented flow analysis systems with appropriate samplers, pumps, reaction/reduction columns and photometers.
  • Nitrate is reduced to nitrite (Cu‑Cd reduction column) and measured as nitrite; nitrite and ammonium have dedicated SFA reaction chemistries and photometric detection.
  • Reagents and calibration standards are specified (e.g., stock solutions for nitrate, nitrite, ammonium; colour reagents, Cd‑Cu reducing agent).
• Quality and timing
  • Measure extracts immediately or within 1 day; if necessary store extracts at ≤4 °C up to one week.
  • Perform blanks and calibration series; follow laboratory good practice and reagent grades (ISO 3696 reference).

Applications and users

ISO 14256-2:2005 is intended for:

• Environmental and agricultural soil testing laboratories performing routine inorganic N analysis.
• Soil scientists and agronomists monitoring soil fertility, nitrogen cycling and nutrient management.
• Regulatory and monitoring agencies assessing soil quality and environmental risk (e.g., nitrate leaching).
• Instrument manufacturers and labs implementing automated segmented flow analysis workflows.

Practical benefits include higher throughput and improved reproducibility compared to manual methods, making this standard suitable for large‑scale soil surveys, fertilizer recommendation programs and research studies.

Related standards

• ISO 14256-1: Soil quality - Part 1: Manual method (companion standard)
• ISO 3696:1987: Water for analytical laboratory use - Specification
• ISO 11465: Soil quality - Determination of dry matter and water content

Keywords: ISO 14256-2:2005, soil quality, nitrate nitrite ammonium, potassium chloride extraction, segmented flow analysis, automated soil testing, soil nitrate test.