Adequacy of laser diffraction for soil particle size analysis

Area of Science:

• Soil Science
• Analytical Chemistry
• Geology

Background:

• Sedimentation has been the standard for particle size analysis since the early 1900s.
• Laser diffraction is emerging as an alternative, particularly in marine sediment analysis.
• Reliability of laser diffraction for diverse soil particle sizes and shapes requires evaluation.

Purpose of the Study:

• To evaluate the reliability of laser diffraction for soil particle size analysis compared to sedimentation.
• To develop a precise sampling methodology for laser diffraction analysis of soils.
• To assess the impact of sample pretreatment on laser diffraction results.

Main Methods:

• Compared laser diffraction with the sieve plummet balance sedimentation method.
• Analyzed 22 soil samples from four Australian Soil Orders.
• Developed and applied a wet riffling technique for representative sample collection.
• Utilized Lin's concordance correlation coefficient to assess method equivalence.

Main Results:

• Repeatable laser diffraction results were achieved across the manufacturer's recommended obscuration range.
• Sample pretreatment for organic carbon removal had minor, marginally significant effects on particle size distributions.
• Established empirical thresholds: <9 μm (LD) ≈ <2 μm (Sedimentation), <26 μm (LD) ≈ <20 μm (Sedimentation), <275 μm (LD) ≈ <200 μm (Sedimentation).

Conclusions:

• Laser diffraction provides reliable soil particle size distribution data.
• Consistent sample preparation is crucial for accurate and reproducible laser diffraction analysis.
• Laser diffraction is a viable and advantageous alternative to sedimentation for soil analysis.