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Charging Clay Substrate?

goldscapes

Member
Joined
21 Aug 2018
Messages
239
Location
Surrey
I have a mixed substrate made from Tesco Essentials Cat Litter, Lava Rock and ADA Malaysia. My intention is to use this as a base for a dry start prior to flooding.
The question is should I attempt to “charge” the clay substrate by soaking it with water rich in nutrients? Also would there be any benefit in adding a humus based liquid carbon source in the initial water, again to “charge” the substrate? It seems logical to me that it would be worthwhile but I’m looking for some technical expertise to back up a hunch!
Thanks for reading.
 
Answered here:

Hi all,
I think nearly all the complete substrates are calcined clays, the amount of nutrients they contain would depend upon the clay (some would be potassium rich) and how hot the calcining temperature was. Very hot temperatures will produce a harder fired product, and the heat of firing would also burn out most nutrients and any organic matter.

In some ways the initial nutrient content is a bit of a red herring, what is more important is the Cation and Anion Exchange Capacity of the clays (CEC and AEC), the capacity to retain and exchange positively (Ca++, K+) and negatively charged (NO3-, PO4-) ions.

Details here: <http://www2.nau.edu/~doetqp-p/courses/env320/lec13/Lec13.html>.

Moler clay is a calcined "diatomaceous earth" <http://en.wikipedia.org/wiki/Diatomaceous_earth>. Which means that it has both a very complex internal structure, and a reasonable CEC of about 50 meq/100g (http://www.jbhs.ccs.k12.nc.us/Facultyandstaff/withers/Supplemental Notes For APES/cation exchange capacity.pdf).

I also think that this capacity to hold onto compounds is the reason it is so difficult to remove the odour from moler clay based cat litter.

If you wanted a "complete nutrient rich substrate", you could soak the calcined media in a fertiliser solution before you sold it, but this would be a bit hit and miss. Better would be to have a small pack of Osmocote (or other "controlled release fertiliser" <http://www.springerlink.com/content/u702t10765qp7164/>) and possibly some organic matter (peat or leaf mould) included in separate packs with-in the bag. You would sprinkle these on before use (a bit like the little blue bag of salt in an old packet of crisps).

cheers Darrel
 
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