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re: Use of nitrate

>From: krombhol at freud_inst.com (Paul Krombholz)
>Date: Sat, 1 Jul 1995 17:20:12 +0600
>Subject: Re:Use of nitrate
>
>Hi Joanne.  Aquatic plants do very well on nitrates.  I once grew 8 genera,
>including Vallisneria, Elodea, Ceratophyllum, and even Aponogeton
>madagascareinsis, in sterile culture,(well, almost sterile, at least
>algae-free), in flasks with nitrate as their only source of nitrogen.  They
>all grew very rapidly and used up all the nitrate supplied.  This is not to
>say that they can't also use ammonia.  I believe that if you have
>measurable nitrate, even as low as 1PPM, that should be plenty for your
>plants.

I think I can add some information on the ammonium vs. nitrate debate.

About a year ago there was an article by Diana Walstad that said something
to the effect that aquatic plants preferred ammonium over nitrate.

She based her article on a peer-reviewed publication that cited
results from a study done with Spirodela (a kind of large duckweed).
This floating plant was grown in a mix of equal concentrations of
ammonium, nitrite and nitrate.  Tests showed that the ammonium was
absorbed first, and nitrate last.  Nitrate *was* used up, but only
after practically all the ammonium ions were gone.

I'll agree with Paul that as long as some nitrates are present, the
plants are probably not lacking in N.  As he implies, it is possible
to take the "lower is better" dogma too far.  If nitrates read zero,
you probably should be adding some nitrogen.

-Shaji
-------------------------------------------------------------------------
Shaji Bhaskar                                              bhaskar at bnr_ca
BNR, 35 Davis Dr., RTP, NC 27709, USA                      (919) 991 7125