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R: Solid fertilizer and 100 mg/l of NO3

> Da: Stephen Pushak <teban at powersonic_bc.ca>
> A: aquatic plants digest <Aquatic-Plants at actwin_com>; psvicini at mdnet_it
> Oggetto: re: Solid fertilizer and 100 mg/l of NO3
> Data: marted́ 13 gennaio 1998 11.02
> Ordinary fertilizers are quite soluble. Gravel, sand and other
> relatively coarse materials have little ability to prevent nitrate and
> other nutrients from diffusing out of the substrate.
> I think you are right to use a much smaller amount of fertilizer. You
> might try just a few pellets mixed into clay balls and allowed to dry.
> The clay forms a very dense and impermeable matrix as it dries. When you
> put one of these dried balls into the substrate, it takes quite a long
> time for the water to penetrate and the nutrient diffusion is very,
> very, very much slower in the tiny spaces between the microscopic clay
> particles (compared to gravel) which are fractions of microns in size.
> The extremely fine pottery clays may be superior to the clay sand
> mixtures you might find outside. The other benefit of using a clay ball
> is that the clay itself is able to adsorb nutrient ions onto it's
> extremely large surface area. We may also over estimate the ability of a
> particular material to adsorb a relatively large amount of ions. 
> Can anyone tell us how many milligrams of NH4+ one kilogram of clay with
> a CEC of 100 centimoles of exchangeable charge positions per kilogram
> could adsorb if it were somehow able to completely occupy all of it's
> CEC capacity with the ammonium?
> Note: I think that the majority of cation exchange sites get occupied by
> calcium ions! reason: 1) we need fairly high Ca concentrations (perhaps
> to compensate for this) 2) the Ca ion binds more readily to CE sites.
> Is anyone interested in repeating the phosphate diffusion experiment
> done recently with a Jobe's stick but this time using a clay ball? I'd
> be very interested to see if the experimental result matches the theory!
> Steve Pushak
> Aquatic Gardeners Association member

The experiment you are describing is a good one, but there will be a lot of
different situations in wich the fertilizer inside will dissolve faster,
slower, better, worse. For example think about a clay ball of 2 cm of
diameter with one gram of fertilizer in the middle and think about a 1 cm
ball with 5 g in the middle. Then this experiment should be done under some
kind of condition. We should use no fertilizer with P, RO water, keep a
nutrient balanced system, keep the temperature stable, keep the light
stable and be able to see if the fertilizer dissolves completely and how
long it lasts. Also fish can be a problem they will be able to give
nutrients and leaves decaying?

Well there are a lot of situations to keep in mind maybe another system
it's easier or
we need to start and report results of this experiment from now.

Anyway next time I will add less fertilizer in something like a clay ball
or tablets or anything wich can help preventing too fast dissolving.

Simone Vicini (psvicini at mdnet_it)