Re: [compost_tea] Re: Inclusion of clay in compost

From: Stephen Steyn <ssteyn_at_wcaccess.co.za>
Date: Sun, 6 Feb 2005 23:00:44 +0200

To all those who contributed to the clay story. Here's a bit more.
Thank you most kindly for your thoughts.
I asked my composter when she was teaching me to make compost "What type of=
 clay?" Should I use Kaolinite which you may know is used for porcelain, po=
ttery, roofing tiles and bricks? In fact it was first used in China to make=
 porcelain and they held the monopoly, which is why porcelain dishes are ca=
lled china. Of course subsequent discoveries were made in Georgia and the c=
olonists exported it to Cornwall where they made Wentworth pottery. It's al=
so used in paints, high quality paper, ceramics for electrical insulation a=
nd heat shielding (like the tiles on the belly of the space shuttles) and m=
others will know it from Kaopectin-type medications where it is used to lin=
e the stomach walls and inactivates diarrhoea- causing bacteria by adsorbin=
g them on the clay particle surfaces. I digress.

Many of the arguments about absorption of cations fall away if you use Kaol=
inite. Its one of the most common 1:1 clays and has a cation exchange capac=
ity (CEC) of virtually zero. Maybe its ability to adsorb bacteria as in the=
 stomach remedy is important though. Its properties are good for plates as =
it doesn't expand and contract when fired but as a soil amendment for agric=
ultural purposes its of limited value. Humus has a CEC of 150 to 250. High=
 activity clays (expanding 2:1 silicates like smectite and vermiculite, and=
 non-expanding 2:1 clays like fine-grained mica and chlorite) would be a be=
tter bet - although most of the charge on humus and low activity clays is p=
H - dependent, becoming more negative as pH rises. No I'm not a smart ass, =
I took the above from the book Nature and Properties of soils, 13th editio=
n, by Nyle Brady and R Weil, Prentice Hall Printing. Mostly pages 326 and =
360. What I'm trying to say is it seems important to define the clay you're=
 using and obviously it should be finely ground.

The argument for stability would be ok if the compost were to be applied to=
 the soil. As an extractor feedstock this would be less desirable as one wo=
uld possibly like the biota released more quickly. The argument for heat bu=
ild-up in the pile probably also has merit but as Ingham says, the pile pro=
bably has too narrow a C:N ratio to start with - the mix is too "hot". I sh=
ould of course have taken a sample from the deposit in the extractor and se=
nt it to SFI to be analysed and maybe got more clues as to its content.

Without causing trouble, how do SFI tests compare to those performed by the=
  CMC composters as outlined by Steve Diver in his interesting paper on CMC=
 compost. Has anyone compared the two?

Steve Diver also mentions Bob Baars as a European expert on CMC technology.=
 I will mail him during the week and get his thoughts on the use of clay in=
 an extractor feedstock..

Thanks for all the responses.

Steve Steyn






Received on Sun Feb 06 2005 - 18:48:25 EST

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