[APD] RE: N from the substrate

["Thomas Barr" <tcbiii at earthlink_net>]

Steve, I am trying to consider what advantage adding fert's to the
substrate provide.
There's no way to measure the life of these sources till the plant is
already deficient.

Osomcoat and other house plant fert's have NH4, if you uproot or disturb
the substrate, and you have decent amount of lighting, that is a recipe for
algae and green water. This might be okay for non CO2 approaches or plants
you do not plan on moving for a long time.

But I think the main adavantage you were saying was adding N to the sub vs
the water column slows plant growth down. I think you can slow down growth
many ways to provide a more stable long term plant tank. Light is one of
the best, non CO2 is also, even low amounts of PO4(limited or slightly
limited) has a less deterious affect on plant health and growth than N. The
other issue is plants without roots or that are typicallly attached or
floating.

Slowing N uptake down (thus providing more stable supply of N) can be done
a a variety of ways, P limitation , Non CO2, less light, adding more fish
load, or my personal favorite, grow crypts and slower growing plants and
have only a few fast growers etc, adding wood and attached plants etc etc. 
A slight PO4 limtation is what the orginal PMDD algae control article
suggested and is well founded, as long as there's some PO4 even some slight
limitation, Paul and Kevin 's PMDD approach did take care of the plant's
needs. 

I added jobes and other concotions to the substrate in a number of tanks
over the years. Unless I limited something in the water column, I did not
find that rich substrates helped plant growth. If you have a rich water
column, then the plants wikll take it from there and not the substrate. Try
it and see. I could not show any growth increases or better health from
this when I made certain the water column was well supplied and non
limiting.   

I don't see a gain except within a certain confined routine that some might
wish to use. And it's hard to undo once in place, but possible(the voice of
experience here). Water column is easy to change, do a water change. I do
not think there is any significant gain from a small amount of NH4 either.
NO3-NH4 is not really an issue when all the organic material is defining
the redox potential in the substrate you suggest, not the balance between
NO3/NH4. In reducing substrates all your NO3 is going to be lost to N2 gas
rather quickly anyway. It's take some serious reduction to go back to
NO3=>NH4 and that's not a large pathway in terms of energy or amount. I
dount that occurs in most substrates we keep in any significant manner. The
flux required would add too much oxidization from above to make it a
significant pathway.  

Everyone thought adding all this stuff in the substrate back about 10-20
years ago was the cat's meow. Some still do. But the reason was that kept
the algae away, we know that not to be true with exception to NH4. So why
not max everything except the light? Then you get the most out of the
light, slower or faster growth based on lighting seems like the best bet
for the newbie and the advanced person. Lower light tanks with all the
CO2/water column/or substrate methods will allow a better stable growth
than solely adding everything to the substrate. Light is the energy source.
That is what will slow algae growth down significantly because you cannot
slow algae growth down with CO2 or most nutrients with exception to NH4.    

Less lighting provides:
Less nutrient demand(no matter where source the nutrients are coming from,
sediment or water column) with less light, less demand on CO2 systems, less
demand on your initial set up cost, heat, electrical cost etc. Slower
growth while still maintaining health and rich foliage can be done this way
very effectively.  
Rich substrates are a good idea for a back up plan or for convienace or for
those who don't care for a rich water column substrate. But I have not
found them to grow plants better or help against algae in and of
themselves. That was the assumption from days past.

Still, I'd like to find a way to provide long term fairly constunt flux of
NPK from some material to the substrate for the just in case situation or
where I leave for a couple of weeks and need to supply the plants.

Generally, if you have a dosing pump, there would be no need for
this/these. But I can soak the jobes for a a few weeeks to remove the
NH4/urea and then dry them out and add those when I leave for a few weeks.
Cheap, easy etc.

Regards, 
Tom Barr  



 


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