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[APD] feeding N at roots

Amit Brucker asked:
> Can you elaborate a bit on this:
> "....Feeding N at the roots can reduce the
> amount of extra trimming you have to do on stem plants, which can grow
> like weeds if you are feeding N in the water heavily. What I
> mean is you
> can slack off the hydroponic N dosing and still keep that favourite
> centre-piece plant flourishing."

Amit, what was your specific curiosity? I can tell you a little bit
about making & using clay balls if that helps. I'll also delve into the
technical aspects of nutrient uptake particularly by roots. I've tried
to keep it as accurate as possible however, please do correct any
incorrect or misleading statements particularly about nutrient uptake.

You have to obtain some clay that is about the consistency of
plasticine. Pottery clay is available from pottery supply outlets for
about $20 for 20 Kg. You could also use powdered clay & mix it with
water or get clay from a ditch or cut bank. You need some fertilizer; I
like to use slow release coated Osmocote (tm) which contains ammonium
nitrate. Many kinds of fertilizers have been used; there's no rule which
says you can't use a different kind of fertilizer. I can't really tell
you what is the best to use; I don't think it makes a big difference but
I would recommend staying with ammonium nitrate or perhaps another
nitrate fertilizer. I know people who use chelated trace nutrients &
other fertilizers of all kinds. I've even put F-T-E, Fritted Trace
Elements, into clay balls. I couldn't observe any improvement beyond the
use of basic nitrogen fertilizers but I can say that there weren't any
overt undesirable side-effects. I couldn't tell you if my plants were
grateful or not, for the most part, they seemed to feign indifference to
these minor improvements.

You take a glob of clay & flatten it out. Press about 10-15 granules of
fertilizer into the clay ball & form it around the fertilizer to enclose
it completely. Roll it between the palms until its the shape of a
marble. There's no rule about how many granules you have to use; I just
flatten my clay glob out & glom it onto a small cluster of fertilizer
that I spread on the work surface. If any bits of fertilizer are
exposed, you can cover them with another little blob of clay. Repeat
this operation a dozen or a hundred times until you have enough clay
balls to satisfy your needs or exhaust your dedication to the task. Let
them dry hard. Drying can be speeded up by placing the damp clay balls
onto newspaper, improving air circulation, heat or by other tricks which
you can dream up. Or you can just ignore them for a few days as I do.
When the balls are dry, they are ready to use. They are probably ok to
use even when not dry; as I say, there are no rules. Remember that they
get water logged a few hours after they are submerged. Perhaps they are
easier to poke in when they are hard and you don't have to worry about
squashing them open as might happen when soft. I prefer to think that
the drying process helps to chemically bind nutrients to the crystalline
edges & corners of the clay micro-particles and that these weak bonds
help to occlude the nutrients later when they are submerged. I wear
rubber gloves when I'm working with clay since it rapidly draws the oils
from your skin & can cause skin problems. Powdered clay contains
silicates so you should take care not to inhale clay dust; its not good
for your lungs a-tall.

I put my balls into plastic snack bags, ten to a bag. You could go 12 to
a bag to make an even dozen or 4, 8, 7 or 13 for any numerological or
superstitious reasons of your own. I use ten because its the number of
my fingers. I deny any metaphysical motivations for my choice, however
the reader is free to draw his own conclusions. I package them only for
convenience of storage, handling & sales; an alternative is to place
them in decorative bowls conveniently strewn about your recreation room.
Be sure your guests don't mistake them for chocolates, unless of course
your guests are of the undesirable sort.

Application in existing aquariums:
Poke several dried balls down into the substrate about an inch from the
main stem of the plant all around it. I push them down to a depth about
to my second knuckle. The more I install, the deeper I install them. You
want the balls to be quite close to the roots for reasons that will be
explained below. I only use the balls on Crypts, Sword plants and
Aponogetons. There's no rule that prevents you from fertilizing stem
plants however I find that most stem plants grow too rapidly in my tanks
for my preferences and require very little encouragement.

Application in new aquariums:
I usually install a layer of soil-mud mixed with a little peat &
micronized iron into my empty sterilized tank. If I know the placement
of my key feature plants such as a centre piece Sword then I will put
the clay balls directly into the mud while its still plastic. I let the
mud dry until its quite hard. If I'm in a rush, I will put several
layers of newspaper onto the mud to absorb moisture. I remove the
newspapers the next day & hopefully there is no surface moisture
visible. If there is, the aquarium can be cloudy later when it is
filled. Once the mud is dry, I can situate my plants according to the
planting scheme, starting from one end & working to toward the opposite
end. Planting is always much easier when there is no water in the
aquarium for at least three reasons: a) you can see what you are doing
b) plants don't get disturbed & float to the surface c) my armpits &
sleeves stay dry. I add a small pile of gravel into the corner to a
depth of about 1", lay the plant specimen with its leaves lying across
the gravel surface & the roots nicely spread out onto the mud layer. At
this time, clay balls can be placed between the roots, near to the plant
stem. Another scoop of gravel is placed onto the roots & I gently
position the plant stem the way I want it. It doesn't have to be
perfectly vertical since the plant may not be rigid enough & I don't
want to cover the leaves with gravel as I work across the tank. Once all
the roots are covered with a nice layer of gravel, I can fuss with the
plants a little bit, add some water & fuss a bit more. I find that I
disturb the gravel the least if I place an empty tin can sideways onto
the substrate & position the fill tube of the Python inside the can so
that it is also lying lengthwise on the tank bottom. The tin can
prevents the water current from disturbing the plants before they have
anchored themselves & prevents digging channels into the gravel or
creating a mud cloud.

Application in pots:
When I first install a plant into a soil pot, I fill the pot with a
mixture of mud, peat & micronized iron and anything else that strikes my
fancy. I've been known to put a 1/4 teaspoon of bone meal and/or a 1/4
teaspoon of hydrated lime mixed into soil however that is a digression.
This is a good time to install 3 or 4 clay fertilizer balls intertwined
with the roots of the potted subject. Then I cover the roots & clay
balls with aquarium gravel, position the subject upright and plunk the
whole caboodle into the tank. I often dry the soil mud in my pots weeks
or months in advance. Its easy to prepare a half dozen pots in this way,
than to try to make one in a hurry the day after I've acquired a
fantastic new specimen that simply must be planted immediately. I take
comfort that the drying process prevents any stray puffs of muddy water
form occurring upon submergence and helps to chemically bond ions into
the crystal structures of the soil particles. The clay ball needs to be
placed right next to the roots so that the root hairs can grow into the
ball for sustenance. This is critical for success.

How it works:
Clay is, by definition, comprised of extremely fine particles less than
0.002mm in diameter typically an amorphous mixture of alumina-silicates.
The purpose is to form a dense barrier to slow down the diffusion of
nutrient ions into the aquarium water. Clay is the least permeable
natural material available aside from solid igneous rock. I will defer
to Roger Miller on the subject of rocks or clay since this is just one
of his domains of expertise. The diffusion of nutrients through clay is
very slow, much slower than it would be through agar for example. The
more you want to reduce the rate of diffusion, the larger the layer of
clay surrounding the nutrients in the core should be. Be aware that if
your clay balls are soft when installed its easy to damage them if you
use the finger push method. If they have flaws or cracks, these will
permit water to circulate directly to the fertilizer prills resulting in
a higher rate of diffusion into the aquarium water. Generally you want
the plant to extract the nutrients by its roots, not by diffusion or
leakage into the aquarium water.

The roots of aquatic plants will grow toward a nutrient source by a
process termed chemotropism. See
ml> Some nutrients passively diffuse toward the roots or into the water.
Nutrient uptake is accelerated when the root hairs come into very close
proximity of nutrients. Root cells do this by pumping hydrogen ions
(protons) into the rhizosphere, "the soil zone immediately surrounding
plant roots, which is modified by the increased number of micro
organisms (e.g. Rhizobia) that live there, in association with plant
roots". See <www.jic.bbsrc.ac.uk/exhibitions/bio-future/glossary.htm>.
This causes a negative charge on the root membranes and positive ions,
cations, are electrically drawn into the root hairs. The rhizosphere is
a zone of higher oxygen content which helps to protect the aquatic plant
roots from damage by corrosive chemicals such as ammonia which naturally
occur from decomposition in the absence of oxygen. A short distance away
from a root fibre, there will be a low oxygen zone where anaerobic
bacteria are using nitrates and sulphates as electron donors to fuel
biochemical activities. These reducing zones are where iron & phosphates
become reduced and soluble. Microscopic root hairs grow out from the
root fibres and extend right into the reduced zones in order to access
iron & other nutrients. These root hairs can absorb ammonia, nitrites &
nitrates. Within the roots, toxic ammonia is converted to amides or
ureides prior to entering the vascular system of the plant where it is
moved up into the shoots where it is again converted to amino acids or
to ammonia to build simple sugars, complex proteins or finally into
cellulose & lignin, the structural building material of plants. Nitrates
& nitrites can be circulated directly within the vascular system however
they must be reduced back to ammonia via nitrogen reductase & nitrite
reductase enzymes before they can be metabolized. According to my
references (albeit relating to terrestrial growth), its best to maintain
a balance of nitrates and ammonia. Too much ammonia results in
acidification of the rhizosphere. This is why I recommend ammonium
nitrate based fertilizer. See

I recently conducted a trial using clay balls with urea as the
fertilizer. Urea readily breaks down to form ammonia; both are quite
corrosive so take care in handling. I wanted to see if ammonia leached
into the aquarium and if the roots of the subject plants were damaged in
any way by these small, localized pockets of ammonia/urea. Since I used
quite a lot of urea, I did end up with measurable ammonia in the water,
enough to create a minor problem with green water but not enough to
bother the fish. The plants have been growing quite well, especially the
primary subject, a small ruffled sword, which has become quite robust
now. It had been languishing previously. No damage to the roots is
evident at this time; at least none this is discernable from external
observation of the robust growth of the subject.

It has been pointed out that aquatic plants can easily satisfy their
nitrogen requirements entirely from the water. This is quite correct.
The strategy with clay fertilizer balls is to provide a more continuous
supply of nitrogen and to target specific plants. I suspect that you
could also provide nitrogen almost entirely from the clay balls. General
growth in the aquarium will not be as lush as with regular hydroponic
additions of nitrate but lush growth has its draw-backs too. I would
hesitate to rely solely upon geoponic nitrogen for Lace plants; to
ensure vigorous growth & the long term viability of the rhizome, one
should still add hydroponic nitrogen.

I've estimated that clay balls continue to provide nutrients for 6
months or more however I have no concrete evidence to support this aside
from subjective observations of my own & others. Of course it depends
upon how big the clay balls are, how much nutrients are placed within
them & serendipity according to how well the plant roots get into the
supply. You may only need a single application to grow a large vigorous
sword plant, a couple feet in diameter. Plants such as Swords or Lace
plants can grow very vigorously and large. A lace plant can throw off
new leaves every few days; the growth rate is simply prodigious! I
suspect that you would not overfeed these plants by adding more clay
balls in six months or so. I have had my best results with augmenting
potassium nitrate to the aquarium water regularly; sufficient nitrogen
is a key factor to success with the Lace plant. It is my opinion that
many so-called dormant lace plants were simply the result of
insufficient nutrients, especially nitrogen, when the stored reserves in
the rhizome are exhausted.

Paul Krombholz has observed that Lace plants do not seem to do as well
in strong reducing substrates while others have had tremendous success
growing them even in composted manure substrates. Its important to
realize that manure would provide an abundant supply of nitrogen for
several months. Lately we have been getting Lace plant specimens that
grow extremely well in aquariums. Is this simply because we understand &
provide the nutrients required for this plant or do we have a mutated
specimen? Perhaps both. Rapid growth mutations occur commonly in the
artificial environment of the aquarium but which might not be
competitive in a natural environment.


I will sell ready made mail order clay balls in any amount. In large
amounts they wholesale for $0.25 each and sell retail in stores at $5
for a bag of 10. At club auctions, they have sold for $20-25 for a bag
of a hundred. Clubs are welcome to place a bulk order; I can supply
retailers or distributors if anyone business minded is interested.

You can contact me by email at teban at powersonic_bc.ca, by phone at
604-591-5512 or by post:

Steve Pushak
11451-80A Ave
Delta, BC
V4C 1Y8

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