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RE: Balancing Act
Susan Romano recently wrote:
>Great website recommendations on plant nutrients, James! Just what I was
>looking for to brew up some trace elements. I used to use Flourish, not
>Kent, although I haven't ruled that out yet if I could determine all of its
>ingredients. Upon viewing these websites I was interested to see that iron
>is required slightly less than chlorine. Perhaps aquatic plants have
>different requirements to terrestrial plants as I've not noticed that
>mentioned before in fertilizer recipes. Sulphur is sixth on the list.
>Tropica's Master Grow has plenty and yet Flourish has none. Kent is
>anybody's guess. Has Dupla ever published all of it's ingredients? Are all
>of the elements listed on the Essential Plant Nutrients chart required to
>eliminate the Law of the Minimum. If so, no one complete fertilizer has
them
>all as far as I am aware of. The Beneficial Plant Nutrients were listed as
>sodium, silica, cobalt and selenium. Would any or all of these be benefial
>to our purpose?
Thank Steve Pushak for the web site links, that's where I got them. Steve
has done a tremendous job of researching a lot of different sites which
pertain to plant nutrition.
As to the actual ratios of elements shown on those sites, and what I quoted
to you in my last APD post, one thing has to be kept in mind. Those were the
ratios found in dry plant material. All plants have the ability to store
nutrients - the amount, or the ratio, present in dried plant tissue is not
necessarily the same as what is required for growth and reproduction during
life. Also, plant roots are in some ways like people - they don't just
absorb the elements which they need, they take in anything which is
available. Practically every element known to occur in Nature can be found
in plant tissue in _some_ amount, not just those which are essential.
Sulfur deficiency symptoms generally affect new leaves and are similar in
appearance to Nitrogen deficiency symptoms (this is from Jeff Dietsch
http://www.voicenet.com/~dietsch/defici~1.html). But Sulphur is generally
present in tap water and is also added with fish food, so don't assume that
the problem is Sulfur deficiency unless you are using R/O water or have no
fish in the tank. As a Sulpher source, you could try several of the PMDD
components (Epsom Salts does contain sulphur). Most good aquarium
fertilizers should have sufficient Sulphur in them, Tropica Master Grow
contains it, as does Flourish (guaranteed analysis 0.23% by weight, from
their web site). Flourish Tabs, also made by Seachem, is primarily Calcium
(20.0%) and Sulphur (35.0%). They also provide a whole host of
micronutrients to the root zone of the plants.
Remember that when you are considering a commercial product that it might be
part of a "product family", with several components designed to work
together in a complimnetary fashion and meant to be used together. This is
certainly true with the Dupla range, the ADA products and those from
Seachem. Seachem, to their immense credit, are not afraid to post the
guaranteed analysis of their products and Tropica is of the same mind -
Master Grow lists it's ingeredients as well. But if you use one of these
products on its own, without using the complimentary products, you are
risking nutrient deficiencies unless you are either really lucky or
extremely knowledgeable about the conditions in your tank. It's like trying
to live on a diet of Twinkies and Coke - tastes good in the short term but
not necessarily good for you in the long run.
As far as "eliminating" the Liebig Law, I don't think that you are trying to
do that - you can't change the laws of Nature, you accomodate them. All
plants need a certain range of a number of elements present in order to
thrive. Too much or too little of one or more can cause problems - the trick
is to provide ALL of them, in sufficient quantities while avoiding excesses
(this is one problem frequently noted with soil substrates - sometimes you
see toxicity problems due to too much of a "good thing").
If you follow the links from Steve's web site and do all the reading, you
will see how difficult it is to actually determine if in fact certain
nutrients are actually essential or not and if a real "deficiency" situation
exists. The best we can hope to do, as aquarists, is rely on annecdotal
evidence and try different things, one at a time, in an attempt to correct
the "problem". A number of elements are listed as "beneficial" rather than
"essential" merely due to the fact that at present science has been able to
demonstrate that _for certain plants_ the absence of the element can cause
problems, but this has not been proven to hold true for _all_ plants. An
example would be Silica. This element is used by diatoms as a structural
component of their tissues. It is also encorporated in the stems of Corn
plants and certain grasses. But we don't grow Corn in our aquariums, and we
generally try to inhibit the growth of diatoms, so we don't go out of our
way to add Silica to our tanks. Indeed, Kent Marine is now making a special
R/O membrane designed to remove Silica from a water supply. It is, I
believe, more of a problem in marine tanks than in our freshwater ones.
I don't think as a matter of actual practice that our task as aquatic
gardeners is as difficult or as precarious as all of the preceeding would
have a casual reader believe. An aquarium is in some respects like an
engine. We add light and nutrients as the fuel - the more we add, the faster
the engine runs. When I was a teenager I grew great plants (Crypts, mainly)
under only 120 W of incandescent light in an unfertilized substrate (if you
forget the fact that is was full of mulm). The plants grew well enough, I
had to thin them out every couple of months, so I was happy, as were they.
But the types of tanks we are discussing here, where metal halide lighting,
CO2 injection, supplemental macro and micro nutrient fertilization is
provided is like comparing a Ferrari with a Model T Ford. Both will get you
from A to B, but one will do so a lot faster. We are still not seeing
"optimal" plant growth but we are approaching it. And any system, when run
to extremes, has a tendancy to become unstable and require ever more
tinkering and intervention to keep it running smoothly. For most of us, and
for most of our tanks, proper regular maintenance which includes copious
water changes and the regular addition of balanced nutirent fertilizers will
eliminate most problems.
James Purchase
Toronto