Overview
ISO 11465:1993 defines a standard gravimetric procedure for determining soil dry matter and water content on a mass basis. The method is applicable to all soil types and covers different procedures for air-dried (e.g. pretreated per ISO 11464) and field‑moist samples. The principle is simple: dry a measured soil amount to constant mass and calculate dry matter and water content from the mass difference.
Key procedural points specified in the standard include:
- Oven drying at 105 °C ± 5 °C until constant mass is reached.
- Definition of constant mass: successive weighings 4 h apart differing by no more than 0.1% (m/m) of the last mass.
- Use of a desiccator (cooling at least 45 min) and an analytical balance (accuracy ≈10 mg).
- Container capacity guidance: 25–100 ml for air‑dried samples; ≥100 ml for field‑moist samples.
Key Topics
- Scope and applicability: Method applies to all soil samples; different handling for air‑dried vs. field‑moist samples.
- Apparatus & sampling: Oven with forced‑air ventilation, desiccator, moisture‑proof containers and a precision balance.
- Procedure highlights:
- Weigh containers before and after filling with the sampled soil.
- Dry container and sample together (including the lid) to constant mass at 105 °C.
- Cool in desiccator and reweigh immediately to compute mass losses.
- Special cases:
- High‑organic soils (e.g., peat) may require drying at 50 °C or vacuum drying to avoid decomposition.
- Some minerals (e.g., gypsum) may lose structural water at 105 °C; report such characteristics when relevant.
- Accuracy & repeatability: Results reported to 0.1% (m/m) accuracy; the standard includes repeatability criteria for duplicate determinations.
Applications
This gravimetric method is frequently used by:
- Soil testing laboratories for routine moisture/dry‑matter determinations.
- Environmental and agricultural QA/QC to assess soil water status and mass‑based dry content.
- Research where a reliable, traceable oven‑dry reference is required for soil physical or chemical analyses.
Practical benefits:
- Simple, reproducible technique requiring basic laboratory equipment.
- Direct mass‑based results that integrate naturally into further calculations (e.g., mass‑based nutrient concentrations).
- Clear procedural controls (temperature, cooling, weighing) that support quality assurance and interlaboratory comparison.
Related Standards
- ISO 11461 - for soil water content on a volume basis (gravimetric reference).
- ISO 11464 - for pretreatment of soil samples prior to physico‑chemical analyses.
When reporting results, ISO 11465 recommends documenting sample identification, the method reference, results (wdm or wH,o), soil characteristics (e.g., presence of gravel, gypsum), and any deviations or optional details that may affect outcomes.
Keywords: ISO 11465, soil quality, gravimetric method, dry matter, water content, oven drying, field‑moist, air‑dried, desiccator, analytical balance.
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