Hi everyone,
The quantification of water-dispersible clay in soils is known to be method-dependent. In this sense, I would like to know the specific steps used by you or your laboratory.
The steps commonly used by me are detailed below:
Laboratory: Lab. of soils. Londrina, Brazil.
1) Mechanical dispersion? Yes.
1.1) Shaking intensity: 200 RPM for 1 to 16 hours.
1.2) Shaking direction: orbital horizontal
1.3) Soil:water ratio during shaking: 20 g to 100 ml.
2) Sedimentation performed in the shaking container? No.
2.1) Sieving before sedimentation? No
2.2) Soil:water ratio during sedimentation: 20 g to 1000 ml.
Hi Thadeu Rodrigues de Melo
When dealing with this type of analysis, especially for scientific purposes, it's recommended to follow a standard procedure that is citable. In Canada, I follow Carter and Gregorich (2007), which describes both the pipette and the hydrometer methods for particle size distribution analysis. A Google search for "Soil Sampling and Methods of Analysis" should give you some useful hits.
I hope this helps.
Marcos
Reference
Carter, M.R., and Gregorich, E.G. 2007. Soil Sampling and Methods of Analysis. CRC Press: Boca Raton, FL.
Basically it comes down to energy input. This comes from either the chemicals you use (activation energy) or the physical energy used shaking sonification. As the energy increases so does the amount of clay. The method you choose depends on what you want to use the data for. Find the method that best suits the purpose you want to use the data for.
The method of Carter and Gregorich (2007) as described by Marcos is appropriate
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