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Re: Steve's nutrient method (derived from Krombholz)

Ron Wozniak asks:
> You mentioned that you use "strong MH lighting."
> Could you please specify how much? To me, strong lighting means 
> at least 3 Watts of MH or fluorescent lighting per gallon.

I use a single 250 watt MH lamps suspended about 18-20" over each of my
two larger aquariums. These are 50 & 75 gallons in capacity. See my
homepage "hall of pictures" for more specifics:

Pat Bowerman asks:
> I would like to know if the soil substrates cause a mess when a plant
> has to uprooted?

I usually just cut stem plants but uproot Crypts. Previously when I had
used a pottery clay this tended to make a small mess. Uprooting a large
plant like a full grown Amazon Sword plant can produce quite a mess
especially with vermiculite or clay. I've found that the peat/soil
combination does not create too much of a problem when uprooting Crypts.
Peat is not a problem since the particles are relatively large. Soils
tend not to have a lot of super fine clays in them but that really
depends upon the soil. Pottery clay has an extremely fine particle size
and is much more difficult to clear from the water. I've heard that
certain commercial products work well on it.

> Also, how does one know if we have a reducing substrate. Whether soil or
> laterite, how do we know if the iron is being made available to our
> plants. At what depth does this begin to occur, and at what root density
> does it cease? 

I have some data on this but its getting to late at night to dig it up.
(sorry for the pun) I think it's quite shallow and depends upon the
organic content. Aquatic plants can really control the redox potential
of a substrate and Paul has said that straight soil substrates stop
reducing iron after a few months of growth. He said manure or peat
substrates last much longer. Paul will have to answer any more
quantitative questions. My peat tanks have not been running a long time
yet. Maybe Neil Frank will favour us with a comment as a peat substrate
user! :-)

> Also, I believe that you were quoting Paul Krombholz,
> when you said that nitrates in the soil can make the iron unavailable.
> Could either of you explain this further? Should this be a concern to
> those adding plant tabs to the substrate?

Paul's comment was that these nutrients are lost by denitrification.
There is also a biochemical reaction which reduces nitrates to ammonia
but I don't know which conditions favour which reaction. I know that you
can produce a substantial amount of ammonia from nitrogenous substances
in a soil so I'm sure that not all nitrate compounds become nitrogen.
Also, other chemicals are required by the bacteria to perform
denitrification (again, I'm too tired to dig them out) but nitrates
occluded in materials such as Jobe's sticks or in clay balls are
probably much more stable. Practical experience tends to indicate these
methods of fertilization are useful. I've seen bubbles from organic
substrates (probably primarily nitrogen possibly some methane) for
months after submergence which indicates that the denitrification
process does not occur all at once.