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-Ding- ! Tuesday night mud rasslin' agin Ma!
> sp>The plain fact is you're not going to get very many
> sp>nutrients from [laterite]. You will be relying upon supplying all the nutrients
> sp>in solution, in the water. And there is nothing wrong with that.
> This fact is not that plain. In fact, once the Duplarit has been in the
> tank for
> awhile AND the nutrients in solution have been carried down into the
> by substrate heating cables where they bound by negative binding sites in the
> laterite, THEN, if fact, the laterite IS providing nutrients AND in a
> manner at that.
BZZZT!! Warning, Warning! Will Robinson! Silly statement alert again!
Nutrients get carried down into the substrate by the substrate heating
cables? This is pure speculation, isn't it!? You KNOW that there have
been no scientific studies which substantiate this hypothesis. It's far
more likely that the plants themselves are going to be creating a flow
stream into the substrate. There actually is evidence to support this
theory: the aquatic plant transpiration stream. Check out the TAG
article on guttation in Salvinia and radioactive tracers in rooted
plants. (if my memory is correct)
What is the CEC of laterite again? How many grams of it do you have? How
many milli-moles of cations is this super charged laterite supposed to
capture again? And exactly which ion species is the laterite going to
have the highest affinity for?
Now how does this work? Is it magnetism? How fast are the plants drawing
nutrients out of the laterite-gravel substrate? How fast is it being
sucked in? Is the concentration of nutrients in the overlying water
higher or lower in nutrients than the concentration of nutrients in the
interstitial water? Is the availability of the nutrients in solution
higher or lower than that of nutrient ions attracted to cation exchange
sites or to positively charged sites?
Now let's send a hypothetical sample of laterite for nutrient analysis
and a hypothetical sample of soil for analysis. Question: which one has
more micro nutrients? which one has more macro nutrients?
Isn't this plain? Seems plain enough to me. Oh, well if you really want
to see the real numbers, Shaji Bhaskar and Neil Frank did just this and
submitted samples of laterite and other soils for analysis. The results
were... well.. predictable. Dirt wins over laterite. You're might
challenge that the soil samples do not contain samples of all soils. I
assert that the analysis of garden soil is typical and representative.
We don't even have to go as far as analyzing hundreds of samples.
Lateritic soil is -by definition- a geologically aged mineral soil high
in iron oxides and hydroxides which has been leached almost entirely of
George requested a definition of "growing better". Well this is a tough
one but let's apply some brain power to this teaser. Growing better must
be when the plants have better growth! Well, actually we can quantify
this a little more. Let's say that better growth is growth which is
faster. and better. healthier. colourful. vibrant. huge. big. flowering.
Sure, if you're growing Hygrophila polysperma, there doesn't seem to be
much point in stimulating growth rates. If you are growing
Cryptocorynes, improving the growth conditions is everything.
Now just to show that I'm not just making this stuff up as George is
implying, here is a direct quote from Dr Dave Huebert, a noted botanist,
and sometimes contributor to the APD discussion.
"Preference for root uptake of P and N:
"In a landmark paper published in Science 207: 987 to 989 (1980) two
Canadians by the name of Carrignan and Kalff clearly demonstrated that
rooted aquatic plants will absorb the majority of P from the sediment
EVEN UNDER HYPEREUTROPHIC CONDITIONS! This was the first paper which
unambiguously showed the preference of aquatic plants for sedimentary P.
Nitrogen studies are somewhat less clear, mainly because N is so
difficult to work with. Nichols and Keeney, Fresh.Biol.6:145 to 154 were
perhaps the first to indicate that rooted aquatic plants acquire the
majority of N from the sediment. After that was an excellent study by
Barko and Smart. They turned the question around somewhat and asked
"which nutrients can be left out of the water". Their results clearly
showed that N was not needed in the water column for optimal growth. I
asked the same type of question in a paper published in 1982 and came up
with the same result (Huebert and Gorham (Aquatic Bot. 16: 269 to 283).
These experiments, and several others, indicated that with a fertile
substrate the only nutrients required in the water column are Ca, Mg, K
and of course CO2 (I must admit, though, that the evidence for
micronutrients is scant and it is in fact likely that water column
additions of micronutrients is a good strategy ... though my swords and
Sagittaria are completely indifferent to whether or not I add
micronutrients) Little work has been done since the mid eighties since
the dozen or so published studies were fairly clear in their results and
there is not much money for this type of research (its also difficult
and time consuming).
"On the other side of the coin, there have been a plethora of studies
which indicate clearly that rooted aquatic plants will not grow
optimally on a sand or other infertile substrate no matter how richly
you fertilize the water column (perhaps the earliest is by Pond, 1905)"