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Re: Aquatic Plants Digest V6 #269

> From: "Jim Seidman" <js4 at seidman_net>
> Subject: Re: NO3 vs NH4
> Tom Barr wrote, in part:
> >Folks parrot "a plant perfers NH4+ over NO3-" but as far as
> >growth is concerned, a balanced ratio grows plants the best(A
> >anion/cation balance provides the best uptake/growth), so say
> >for corn, it's about 1:4.
> Tom, do you think there's any difference between NH3 and NH4+?

Plants generally have access to NH4, not NH3 except in very very
small amounts.
> My
> understanding is that ammonia, unlike ammonium, doesn't go
> through ion
> uptake channels. Rather, its symmetric structure and neutral
> charge allow it
> to permeate the plant directly, such that the plant doesn't
> have to expend
> any energy on uptake.

But the plant also has no control of what comes in.....this can
kill plant cell/tissues/organs if there is too much of this
ion(this is not your/our case here).

Due to the pH in our tank waters, this ion is generally in the
form of NH4(a large %), a few serpintine soils with high pH's
may have this issue. Plant roots zones generally have active H+
pumps in the regions around the roots, NH3 => NH4+. 

The other main point is that there's not much NH4 around as it
is. Your test kits did not find any(no surprise there) and there
will 17 times less of the NH3. So now we are talking about very
very small amounts of something.   
> I'm curious whether your experiments dosing with NH4+ salts
> were in tanks
> with a pH high enough to convert a significant amount of NH4+
> to NH3. I
> would think this would make a difference.

Why would I have such a high pH?
Even with rock hard KH etc, the pH required is still pretty high
to have this be significant. I don't think it'd help either way
in growing plants and might harm the plants since many of the
nutrients such as trace metals are much easier to assimilate at
lower pH's. This is one reason why serpintine soils are lousy
and only a few specialized plants can grow there. Soil pH's are
7-8 but pore water pH's are close to 11.

Teasing apart the high pH required/introduced + dealing with
this high pH effects on other parts of water chemistry is going
to be tough. It'd be tough to say if it was due to the NH3 alone
or not.   
> My tank has a pH of about 8.0, so I'd expect roughly a 17:1
> ratio of NH4+ to
> NH3, meaning 5.5% would be NH3. This may not sound like much,
> but if it gets
> consumed quickly then more NH4+ would turn into NH3 to
> maintain the
> equilibrium.

I think if you have actively growing plants you have nothing to
worry about here(NH3). There are few places in the world where
this might be an issue. More of an issue for
fish/critters/biogeo cycling etc. Mono lake(pH10.1), rift soda
lakes(~pH12) in Africa etc.
> I hope this proves to be true. My ammonia, nitrite, and
> nitrates are all
> stubbornly stuck at undetectable levels, despite the moderate
> lighting (120W
> on 125 gallons) and lack of CO2. I'm somewhat nervous that
> this is going to
> lead to problems down the road.

Don't be.
Toss some floating water sprite etc in the tank and that will
slop up the nutrients and have enough CO2/light.

Check out the %% ratio for NH3:NH4 at pH's less than 7.2-7.4.
It's not much. My pH's generally are less than this, 6.2-6.8
range for most of the taps. Even at your pH, it's not going to
be an issue for plants, you cannot even detect any NH4+ which is
17x more prevelant.

In non CO2/carbon enriched tanks, the NH3:NH4 is removed pretty
fast and there's little to be had. Either the plants or the
bacteria get it, or if bacteria convert it to NO3, then the
plants will likely get it(some anaerobic bacteria can also:
NO3=>N2). Unless your NO3 is building up high, there's little
need for concern. 

We might want to express the NH4 with the NH3(say NH4+/NH3), but
it's generally just dealt with as NH4 for biological purposes.

The short of it, don't worry about it unless you plan on dosing
it etc which is a bad idea anyway for planted tanks generally. 

Tom Barr  

> - - Jim

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