ISO 11275:2004

Overview

ISO 11275:2004 specifies a laboratory procedure - Wind's evaporation method - for the simultaneous determination of the unsaturated hydraulic conductivity and the soil water‑retention characteristic during drying (desorption). The method is designed for relatively homogeneous, undisturbed soil samples and is limited to the drying curve (not wetting). Results characterize how soil water content and matric head relate and how conductivity changes as soils dry.

Key topics and technical requirements

• Scope & limits
  • Applicable only to the drying (desorption) curve and to samples that remain non‑shrinking in the range h = 0 cm to −800 cm.
  • Conductivity determination typically spans matric heads of about −50 cm to −700 cm; water‑retention between 0 cm and −800 cm.
  • Assumes one‑dimensional flow and homogeneous hydraulic properties.
• Principle
  • Samples are wetted to near saturation, then allowed to dry from the top.
  • Tensiometers installed at different depths measure matric (pressure) head over time while the sample mass is recorded.
  • The sample is treated as compartments (one per tensiometer); water‑retention and unsaturated conductivity are derived using Wind’s evaporation analysis.
• Apparatus & test setup
  • Undisturbed sampling sleeves/rings (sample height ≤ diameter; recommended example 8 cm height × 10 cm diameter for stone‑free soils).
  • Polyamide mesh, container for controlled wetting, balance (accuracy ±0.1 %), tensiometer system (per ISO 11276), drying oven at 105 ± 2 °C.
  • Tensiometer dimensions: length < half the sample diameter; diameter < 10 % of sample height.
• Procedure essentials
  • Follow ISO 10381 series for sampling; saturate samples from the bottom to avoid air entrapment; measure height, install tensiometers, record heads and mass until air entry occurs; dry and weigh at end to compute water contents.

Applications and who uses it

• Target users: soil scientists, agronomists, hydrologists, environmental engineers, laboratory technicians, and researchers assessing soil hydraulic behaviour.
• Practical uses:
  • Deriving soil water‑retention curves and unsaturated hydraulic conductivity for modelling and irrigation scheduling.
  • Estimating plant‑available water, drainable pore space, and equivalent pore‑size distribution.
  • Supporting drainage design, pollution risk assessment, soil‑structure monitoring (compaction, tillage, amendments).
  • Supplying input data for vadose‑zone and water‑balance models.

Related standards

• ISO 10381‑1, ISO 10381‑4 (soil sampling guidance)
• ISO 11274 (water‑retention laboratory methods)
• ISO 11276 (tensiometer method)
• ISO 11461 (gravimetric soil water content with coring sleeves)

Keywords: soil quality, unsaturated hydraulic conductivity, water‑retention characteristic, Wind's evaporation method, matric head, tensiometer, laboratory method, desorption curve, soil sampling.