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Re: Urea as fertilizer

> Date: Fri, 24 Oct 1997 23:39:24 +0530 (IST)
> From: Anupam Basu <anupam at comports_com>
> Subject: Urea as fertilizer?
> Hello,
> 	I am an absolute beginner with plants and would like help in
> clearing a doubt. A friend of mine told me that he has been using urea
> crystals as fertilizer with great results in his tank for some time now.
> Has anyone tried this? Is it safe and if it is, what's the recommended
> dosage? Any idea on how it might affect the water chemistry and the fish?
> 	Thanks for any information.
> Anupam.

I haven't tried it myself, but here's some info on potential effects.

Urea breaks down in water to produce ammonia and carbon dioxide.  The
fertilizer value would be mostly from the ammonia, which is an excellent
source of nitrogen for plants.  Pure urea would have no other value - it
would not provide iron or trace elements, for instance.

Ammonia (NH3) can also occur as ammonium ion (NH4+), and when the pH is
not high (say below about 7.5), virtually all of the ammonia will be
present as ammonium ion.  This is important, because the NH3 form is toxic
to aquatic animals, while ammonium ion is not.  You can avoid immediate
problems with ammonia toxicity by always keeping your pH nuetral or
acidic.  Even then there may be problems from short-term increases in pH
leading to toxic conditions, so be careful.

If you use a nitrifying filter, then a part (possibly a large part) of the
ammonia will be converted to nitrate by bacterial nitrification.  Some
will be lost through that route even without a filter.  Nitrate is not as
good a nitrogen source as ammonia and at sufficiently high concentrations
nitrate may be damaging.  Also, the bacterial action will tend to acidify
your tank.  You may have to be very careful about maintaining a regular
schedule of water changes to avoid the potential tank crash.

All in all, it seems like it would work but its risky.  Fish and other
aquatic animals in a tank provide a steady supply of ammonia in their
waste, so if your aquarium contains animals, then you will already have an
ammonia source.  You have to determine for yourself whether the additional
fertilizer is worth the risk to your animals.  Your friend's experience
should help you decide.

Roger Miller