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Re: urea and some questions about NPK ratios

Paul Krombholz wrote:

>.... but the 45 ppm of urea killed all my Daphnia, and brought on a
green water takeover.  The conclusion is that you can safely load up the
>water column with a lot more nitrate nitrogen than urea nitrogen, and that
you should regard both urea and ammonia as potentially damaging.  ....
>The all-purpose Miracle-Gro has all its nitrogen as either urea or
ammonium, and so it should be added in small amounts.  On the other hand,
>if you are dosing with KNO3, you can add larger, less frequent doses.

Just to be clear, my reason for the Miracle-Gro is a source of Phosphorus.
I was not adding it for Nitrogen. Its ratio of N:P is around 1:1. I do not
believe this is enough for aquatic plants, expecially at the small amount
of the provided P. However the small, non damaging amounts of NH4 or urea
at this dosage may be one of MG's other miracles. Regardless, another
SUPPLEMENTAL source of N would be needed (same for the K, and the other
nutrients). This is where the KNO3 and trace element supplements come in. 

Paul, you mentioned Hoagland's solution. Can you review for us its ratios
of N:P:K  and if it is used by researchers to just grow algae or also for
aquatic plants. I see that there are lots of other solutions out there, but
dont know what their various purposes are. It would be interesting to see
how their ratios relate to Gerloff's critical concentration ratios for
Elodea I wrote about last week (11-2-8). These and similar non-uniform
ratios helped me come to the conclusion that our NPK fertilization should
not be 1:1:1.

I would also like to hear your opinion (and from others) of the need for
different relative amounts of N, P and K  vs. sufficient MINIMUM amounts of
each (in both cases, the max concentrations must not be so high that they
are harmful). Yes, the plant will store excess N-P-K, and I doubt that the
plant cares if their NPK is 11-2-8 or 15-1-7, BUT it might care if it were
10-10-10. So, do we need to be careful about providing relatively TOO MUCH
of one ingredient (like P) or relatively too little (like N)?  .... In that
regard, is KNO3 a good source of N and K, because it provides N and K in
the ratio 14:39 (~1:3). I dont like to overdose K in soft water.

Also, do we want to provide the certain ratios to get the best plant
growth, to produce a certain morphology (color, size, shape), to get the
plant to flower/reproduce..... OR.... to avoid plant growth problems
because of the relative or absolute amounts of stored nutrients (luxury
consumption).... ie what can be the effect of too much?  The outdoor
gardeners can jump in here to describe the role of fertilizers in
horticulture. On the other hand, does it have nothing to do with effects on
the aquatic plant, but instead, is it to AVOID algae growth, perhaps
because the plant CANNOT soak up and store more than a certain amount of a
certain nutrient (say P)....or because it will be more inclined to leak
some nutrients out at high storage levels.... and this leaves excess food
which may contribute to more algae. This is not a concern for outdoor use.
There, economics may be a bigger factor.  

Speculation on these topics is certainly allowed.

Neil Frank / Aquarian Subjects
Interesting old books and magazines (but most plant books are already gone)