ISO 23400:2021

Overview

ISO 23400:2021 - "Guidelines for the determination of organic carbon and nitrogen stocks and their variations in mineral soils at field scale" - provides a standardized method to quantify soil organic carbon (soil OC) and total nitrogen (TN) stocks at plot/field scale and to detect their temporal changes. The standard applies to mineral soils only and excludes organic soils, permafrost, wetland soils and layers prone to submergence below the groundwater table. It supports reliable assessment of soil C sequestration potential and N dynamics for climate mitigation, land management and environmental monitoring.

Key technical topics and requirements

• Scope & exclusions: Focused on mineral soils at field/plot scale; explicitly excludes organic, permafrost and wetland soils.
• Site investigation strategy: Documentation of area, land use and management history, soil characterization and sampling objectives.
• Sampling design and execution:
  • Prepare a sampling plan and spatial sampling strategy to capture lateral and depth variability.
  • Collect known-volume samples (e.g., cores) from defined soil layers.
  • Use composite sampling where appropriate to represent plot-level mean values.
• Sample handling and QA:
  • Field handling, storage, transport and laboratory procedures to preserve sample integrity.
  • Safety, environmental protection and quality assurance during sampling and analysis.
• Physical and chemical determinations:
  • Measure dry mass of whole sample and dry mass of coarse fragments (>2 mm).
  • Determine fine soil mass per sampled volume (bulk density).
  • Analyze carbon and nitrogen concentrations in the fine soil fraction.
• Calculations & uncertainty:
  • Procedures to calculate OC and N stocks by layer and to aggregate to plot scale.
  • Guidance for detecting temporal changes and quantifying uncertainties (including minimum detectable differences and equivalent soil mass approaches referenced in annexes).
• Reporting: Standardized reporting formats for stocks and stock changes, including metadata required for interpretation.

Practical applications and intended users

ISO 23400:2021 is designed for:

• Soil scientists, agronomists and environmental consultants performing field-based soil C and N inventories.
• Land managers and farmers assessing soil carbon sequestration potential and nutrient management.
• Researchers monitoring long-term soil carbon and nitrogen dynamics (changes often detectable over 5–10 years).
• Carbon project developers, verifiers and policymakers needing consistent, auditable methods for carbon accounting and GHG mitigation strategies.

Applications include carbon sequestration measurement, evaluation of land-use and management impacts on soil C and N, baseline inventories for carbon markets, and environmental risk assessment for nitrogen leakage (e.g., N2O emissions, nitrate leaching).

Related standards

Normative references include ISO 16133 and ISO 18400 series (Parts 101, 105, 206) for monitoring programmes, sampling plans, sample transport/storage and handling for microbiological assessments. These referenced standards support consistent sampling and chain-of-custody practices aligned with ISO 23400:2021.