[APD] RE: N in the gravel/substrate

["Thomas Barr" <tcbiii at earthlink_net>]

"It is my understanding from postings several years ago that
denitrification,
the conversion of nitrogen compounds to N2 as gas, by bacteria requires that
other nutrients, notably carbohydrates, be accessible locally to the
denitrifying bacteria. See
<http://www.ozestuaries.org/indicators/Def_denitrification.html> which gives
a macro-chemical reaction for denitrification and
<http://webserver.cr.usgs.gov/nawqa/splt/journals/PFENNING1.html> a study
which examines the effects of temperature & organic carbon upon
denitrification."

Well for NO3 to occur, you'll need a source of electron acceptors such as
carbon.
The more carbon(richer OM) the lower the Redox values.
There's a range of Eh's for Denitrification.
Also plant roots and plant health plays a large role(Adds O2 to the
substrate and raises Eh's would reduce Denitrification).
This is a BIG problem for farming since much of the N fertilizer applied to
soil is released as N2 gas(around 1/2 of the fertilizer applied).

Us? Naw. 
How to test?
Try the tank w/o plants(remove the plants) and with, measure the amount of
NO3 removal. This is not a critical method but would give you a rough idea
certainly if the difference was significant. There are a couple of other
ways also but are more involved.
  
"If we put pellets of a commercial fertilizer inside clay balls and put
these
balls into the substrate, I think that N diffusion through the clay will be
so slow as to be negligible."

Yep.

 "Likewise carbohydrates & other carbon sources
will not diffuse into the clay either. The clay must be of sufficient fine
texture & uniform consistency as is the case with pottery clay."

Yep.

"We could design an experiment to measure N loss from a clay ball. Is there
a
reasonable experiment to measure the N content within a clay ball after it
has been submerged for 3 to 6 months?"

Depends on OM loading and the Eh's.
OM loading might be averaged I'd suppose for a plant tank per unit time.
The loss itself should not be too bad from the clay.

" I'm thinking that we could just take
the clay ball and put it into a blender with a litre or so of distilled
water and then titrate the N in solution. I'm guessing that running the
blender for 10 minutes or so would be enough time to extract the N from the
clay into solution. As a control, we could perform a similar extraction upon
an identical clay fertilizer ball which has not been submerged."

Well one would be aerobic vs anaerobic(submerged). Not sure if that's a
control.

"Goes without
saying that we weigh the samples at the start to control the amount of N
going into the clay ball. By knowing the starting N value & extracted value
in the control, we have a measure of the effectiveness of the extraction
process."

Hummh, I suppose. I have other notions about how to go about it.

"** Question: I don't know how to go about precisely measuring the N content
of a water sample; can someone suggest a practical at-home method? I suppose
I could get some very rough approximations by using nitrate & ammonia test
kits."

At home, Lamott test kit would be about the closest thing.
Rough estimate but...........good enough to measure significant losses,
gains for the plants.

But would you really want something that held 100ppm of NO3?
I mean if it only held 10ppm of NO3, how long would this last as a good N
source for plants?
Awhile, but not that long long.

Other issues would be how much is getting bound from the water column
diffusion above from fish waste etc in a fish tank, you can remove the
fish/critters in a test, but realistically most folks would have a source
and a continous source of OM.

"I've seen aquatic plants benefit from Osmocote (R) Controlled Release
Fertilizer 14-14-14 inside clay balls. The MATERIAL SAFETY DATA SHEET from
CAROLINA BIOLOGICAL suggests that it is comprised of ammonium nitrate,
calcium phosphate, potassium sulfate, ammonium phosphate, & calcium fluoride
and that it is coated with a resin made from vegetable oil reacted with a
cyclic diene."

Yea, and I've heard enough about issues with Osmocoat. This is fine for
soil/emergent growth, but just like JOBES sticks, I'd not do it.

""From what I can gather from the web, ammonia is not transported within the
vascular system of the plant but is converted to amides or ureides and then
reconverted to ammonia in the shoots & subsequently to amino acids. Nitrates
& nitrites can be transported from the roots to shoots where it is reduced
to ammonia via nitrogen reductase & nitrite reductase enzymes. See
<http://www.nrsl.umd.edu/courses/nrsc401/mineralassimilation.doc>""

This is a transportation issue, not metabolism/uptake.
NO3 can be assimilated through the leaves(Why transport it there when it's
already present there?)

"Ammonia as the sole N source causes acidification of the rhizosphere
therefore a mixture of ammonia & nitrate yields better results. See
<http://www.hort.purdue.edu/newcrop/ncnu02/v5-453.html>"

Very good, this is something I told folks a long time ago.
But the best method I've seen for aquarist is supplying the NH4 (and a
little NO3)from fish waste, the rest via KNO3 etc.
Perhaps Greg can figure out a way to bind NH4 to something in the
substrate/tabs etc without it causing issues. 

"It has been said that aquatic plants absorb N as ammonia in the substrate;
perhaps this is because ammonia predominates there, not because of a
biological imperative."

Generally both are true.

>>From my experiences, it takes a while (weeks?) before plant roots can grow
root hairs into the clay ball to begin absorbing N from it even if the clay
ball is situated in contact with the primary root stem."

Yes, depends on the plant in question, Crypts/Anubias etc, certainly.

" Chemotrophism is the
property of plant roots which causes them to grow in the direction of
nutrients. If you uproot a plant grown upon a clay fertilizer ball for
several months, you will find a mass of roots around & penetrating the clay
ball. Therefore it would be wise to provide N hydroponically at the least
until the roots have penetrated."

You can see this with Flourite grains all the time.

"If we assume that the majority of N from a clay ball is removed via the
vascular transpiration stream, will the plant utilize all of this N or will
some of it leak to the surroundings? Presumably there is leakage due to
normal tissue senescence. Presumably not all N is relocatable (mobile)
within the plant."

Leakage will occur, depends on the growth rates, the plant and a host of
other issues.
And "Mobility" is relative.

"I doubt that even after several months, that the plant roots can entirely
drain a clay ball of N; other factors would limit growth & uptake; the plant
can only use so much N. Another experimental study could measure the amount
of N remaining in a clay ball after 3, 6 and 12 months."

Yes, something could be done but it would take a fair amount of work to
yield anything but a rough idea. 

"All this work can be done without resorting to tissue analysis but I think
tissue analysis would be the best way to evaluate the effectiveness of such
a substrate N strategy. Certainly we can observe growth rates, leaf color &
size as well as the response of filamentous algae to a lowered N
concentration in solution."

Yes, I think a rough idea would perhaps help, but if it's say a 20%
difference(large in terms of a growth difference) you might not see it.

A simple method form NH4 vs none/NO3:

Add fish/critters, or don't.
The fish added tank will have better plant health and color, less algae
etc. There are other things added besides NH4, but this is likely the
largest contribution to the plant.Also this gets back to the idea of less
dosing/more balancing the plant/fish population which is often a goal of
many folks.

I've dosed NH4 directly into non fish tanks to see. It's not a cation you
want to fiddle with unless you enjoy green water and Staghorn algae etc and
don't mind dealing with algae removal.

The host of issues with Jobes can be very telling on the APD and other
list/forums as far as the improvements and experiences to draw upon.

I think Greg Morin has a good idea with bound NH4 as a plant source and
without adding too much and have other bacterial processes act upon its
complexed nature, is perhaps the better method by dosing this to the water
column little by little.

There is certainly less variabilty in the water column abnd  much easier
place to dose little by little vs the substrate unless you would be
interested in dosing the substrate every 2-4 weeks etc. Not sure that would
help.
Agar would work pretty of something like or bound NH4 etc in some form or
another but it should not be too rich in NH4.
NO3 would be good but it can only hold so much N in either form before it
runs out etc.

But some folks might like this.
I have not found it too useful.

Just add your peat/mulm to the substrate(whatever it might be), have plenty
of fish, algae eaters, dose the KNO3/SeaChem nitrogen.

Regards, 
Tom Barr
 
>Steve P



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