Is the hydrometer method for soil particle size analysis directly comparable with a mid-infrared method for the determination of clay percentage? I am worried about the 18 samples I have analysed using the two methods and the mid-infrared method estimated an extremely high clay%. It measures twice as high clay% compared to the hydrometer method. What could cause such a major difference?
Thank you in advance for your answers.
The hydrometer method of particle size analysis calculates the physical proportions of these soil particles based on their settling rates in an aqueous solution and identifies three size classes: sand (2000 – 50 µm), silt (50 – 2.0 µm) and clay < 2.0 µm. This method uses the ASTM 152H-Type hydrometer and is based on a standard temperature of 20 oC and a particle density of 2.65 g cm-3; units are expressed as grams of soil per liter. also if you want to check your percentage samples make XRD to confirm your percentages true or false
MIRS spectroscopy generally overestimates the clay percent, if the soil has a high organic content (>5%). The magnitude of the variation would therefore depend on the organic content, the more the OC , more will be the clay content shown by MIRS. Nevertheless, the variation reported (twice in your case) still appears to be high. It is acceptable around 60-70%.
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