Re: soils/laterites

>I'm organizing information to compose a FAQ entry to cover substrates.

Great.... don't forget TAG!
>[Q] Has anyone compared the use of any of the various commercial or DIYS 
>laterites with soil preparations under controlled conditions? 

not quite what you are looking for, but I have summarized soil analysis
results for a variety of soils and laterites. These were posted on the web,
but you have to be careful when retrieving because within a day or so of the
original post I put up an update after I notices an data entry error. 
I could try to find it in own my archives.

>My hypothesis is that the results should be very similar.
>I suspect that certain plant types may do better in a soil substrate
>where the soil contains humic components and probably a wider variety
>of (trace) minerals however I have absolutely no experimental data
>to support either hypothesis. The only anecdotal evidence we have is
>that a lot of people using a great variety of substrates all claim to
>have "good" results.

Another MAJOR confounder in all anecotal reports is the amount of time of
submergence AND the lenght of time that the plants were allowed to grow. Too
often I have seen reports after a week or two after planting. This is not
very relevant for a variety of reasons. In particular, it is important to
know that terrestrial soils undergo some changes after initial submergence
and that 'stabilization' occurs after a 4-6 weeks. Diana Walstand published
a great article on this subject a few years ago. She derived her results
from the literature, principally from people studying paddy rice fields. 
I believe this also covered the initial effects of organic decomposition.

> We should qualify good growth by saying it has
>two attributes: 1) vigorous growth 2) healthy leaf formation indicating
>no lack of critical nutrients. I'm not implying that substrate alone
>can satisfy all these needs but especially where we fail to provide
>all the required nutrients by artificial means, a balanced substrate 
>can help ameliorate shortages.

Another confounder is EXCESS nutrients (trace elements) which can cause
toxic effects and therefore malformed leaves or other symptoms. So, another
important detail can be the initial treatment of the water column (e.g.
water changes, use of carbon, type of plants used initially)

>[Q] Does anyone have an analysis of the elements and compounds of
>laterite? My hypothesis is that most of the constituent elements of 
>laterite participate in silica compounds and are pretty inert.

Oops. I spoke too soon. See above <g>

Neil Frank, TAG editor    Aquatic Gardeners Association    Raleigh, NC USA