Overview
ISO 20244:2018 specifies a rapid, field-applicable screening method for determining soil water content by refractometry. The method uses a sucrose solution that is diluted by water extracted from a soil sample; the dilution is quantified by measuring refractive index or Brix degree with a portable refractometer. This screening approach is designed for on-site geological, geotechnical and commercial applications where fast, robust water-content checks are required.
Key Topics
- Principle: mix a representative soil aliquot with a 50 % sucrose solution; water in the soil dilutes the solution and changes its refractive index. Use a correlation curve to convert refractive index (or Brix) to mass of water extracted.
- Working range and precision: suitable up to approximately 50 % moisture content. Typical precision depends on the refractometer and is generally between 0.5 % and 1 %.
- Apparatus: portable refractometer or saccharimeter (with temperature correction), portable electronic balance (a 0.1 g resolution is commonly adequate), containers, filter device and 50 % sucrose solution.
- Procedure highlights:
- Select temperature correction mode on the refractometer.
- Create a site-specific correlation curve by spiking sucrose solution with known water additions.
- Confirm instrument performance using pure water and a 50 % sucrose check solution.
- Weigh 10–30 g of soil (typical), mix with the calibrated amount of sucrose solution, filter and measure refractive index.
- Calculate water content using the correlation curve and report mass fraction percentage (rounded to the next percent).
- Limitations: results are strongly influenced by soil matrix. High clay or organic-matter content can produce significantly lower water-content values compared with standard gravimetric methods (for example, ISO 11465).
Applications
The method is targeted at situations that require fast, on-site screening rather than laboratory-grade gravimetric accuracy. Typical applications include:
- Geotechnical and geological field surveys
- Rapid site investigation for civil engineering and remediation
- Agricultural moisture checks in greenhouses and fields
- Preliminary mapping and monitoring related to greenhouse gas studies where wide-area screening is needed
Benefits include portability, speed, and minimal sample preparation, making ISO 20244:2018 useful for preliminary decision-making and large-area screening tasks.
Related Standards
- ISO 11465 (gravimetric laboratory determination of soil water content) - referenced as a comparative standard for accuracy and matrix effects
For on-site protocols, users should follow the instrument manufacturer's instructions for temperature correction, calibration, and routine quality control as described in ISO 20244:2018. The test report should reference ISO 20244:2018 and include site-specific conditions and any factors that may have influenced results.