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CEC measurement units and the types of peat
I think the common term in use now is meq/100 grams. Since CEC is a
_capacity_ to hold exchangeable cations, it is defined in terms of a
monovalent ion such as H+ hence cmol/Kg is not ambiguous. Apparently
some of the history of CEC measurements do cause problems since older
methods were not very accurate. But that's not important for aquatic
plants.
It is true that there are a lot of different types of peat (just like
laterite) however the type in use in horticulture is the fine, fibrous
type classified as upland or highmoor which is derived principally from
spaghnum moss. (hence the name: Canadian Sphagnum Peat Moss, eh?) That
is the type of peat used by most of the aquarists I've talked to. I did
notice that the compressed peat plates for sale in the aquarium store
appear to be the coarse, woody type of peat, not favoured as a soil
amendment.
I found the Florida website given by Dave Gomberg to have some good
technical information so I've added that link to my substrate article
entry on peat. Thanks Dave.
If you added 2 pounds of peat to a substrate, I think you would find you
had a LOT of peat volumetrically. 2 pounds of a fine clay makes a rather
small lump which you have to add to the gravel or sand.
Another interesting point I uncovered reading about the CEC of soils is
that the clay particles in soils tend to coat coarser particles. If the
clay is left unmixed in the bottom of the substrate, I don't think it
will be nearly as effective as if you mix it well with sand and other
materials in the lower layer. You probably need only a very small amount
of clay to use it in this manner.
--
Steve Pushak teban at powersonic_bc.anti-spam.ca
Visit "Steve's Aquatic Page" http://home.infinet.net/teban/
for LOTS of pics, tips and links for aquatic gardening!!!
Aquatic Gardeners Association - technical advisor