[USCC] Soil texture analysis lab procedure

[frank]

Craig,
Most particle size analysis for silt and clay is based on the settling 
of rock density material in water over time. Organic particles do not do 
this so will give erroneous results.

So you can remove the organic fraction (float it out, ash it, digest in 
acid) then measure the inorganic fraction . Or you can measure the 
organic particles along with the inorganic particles using a particle 
analyzer that uses a light beam into a beaker, magnetic stir bar and 
mixing. Or get an idea of size under a microscope.

Then we have the problem with measurement. Most require a size 
distribution based on weight. But you can see the problem when you have 
light woody materials along side heavy rock materials. And when 
reviewing the methods above you can see a few are based on weight and 
others comparing size. Some methods we use call for removing organic 
matter first. Some want shell material removed and other 'life' caused 
material removed to get size of the parent material.

There are some procedures based on volume of material but they are 
mostly for > 63 um size.(sand).

Frank





Craig Coker wrote:

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>Colleagues:
>
> 
>
>Can anyone recommend soil texture testing procedures other than the
>Bouyoucos Hydrometer method?  A client of mine is making up manufactured
>specialty soils from their compost plus rock fines from a nearby quarry.
>Apparently, this texture analysis procedure is giving false readings on Clay
>content in the manufactured soil sample due to the turbidity of the water
>(the finest of the rock fines) in the hydrometer, which is causing the soil
>mix to not meet the landscape architect's spec of no more than 5% clay
>content.
>
> 
>
>Many thanks!
>
>Craig
>
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>Craig Coker
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>Coker Composting & Consulting
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-- 
Frank Shields
Soil Control Lab
42 Hangar way
Watsonville, CA  95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at compostlab.com
www.compostlab.com