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Allelopathy interactions and some substrate gripes
- To: <Aquatic-Plants at actwin_com>
- Subject: Allelopathy interactions and some substrate gripes
- From: Thomas Barr <tcbiii at earthlink_net>
- Date: Wed, 02 Oct 2002 22:34:08 -0400
- In-reply-to: <200210020748.g927m7o26489 at acme_actwin.com>
- User-agent: Microsoft-Outlook-Express-Macintosh-Edition/5.02.2022
Fertilzation the substrate or the water column:
A number of methods have been proposed with folks going for a lean water
column with some traces dosed and some traces added to the substrate.
This is a popular method for getting one up on algae.
Hopefully by adding enough fish there will be enough NO3 and a little PO4.
K+ is often added but too little in my opinion and others in the trace
I've thought a bit about substrates lately and read a few articles on them
as they function in natural systems vs water nutrients in natural systems.
Being where I am, I have had a chance to go to these places and see first
hand a number of observations.
I don't add much to the substrate except the basic flourite/onyx sand and
some mulm and ground peat. Some add jobes but I've not found them to be that
effective as keeping up with the water column. They also have NH4, and it's
not the P or the K or the NO3 that's causing the problem with them. I've
tried that already by adding them separately and figuring out it's not the
NO3 or PO4, it's the NH4 that's the evil doer.
Those NO3/PO4 and K are better absorbed IMO through the leaves. I've added
sources of N under roots but the amount of N coming out or up when you prune
remove or thin plants is too variable for me. If you plan on leaving the
plant there for a long time etc, then it's fine I guess but there is no
control so to speak when dosing the substrate. How do you regulate the
amount delivered to the roots?
If you add too much then the root has to use energy keeping excess
out(gatekeeping), too little and it's trying to go after it and then it has
to transport it up to the growing apical meristem.
Using the water column makes sense since you can add the just right amount
and test to see how fast it's removed.
That water is going by the nutrients(in a jobe stick) at a relatively slow
rate and hopefully being absorbed in the water quickly by the plants and not
But that method has no control. If you pull one up , then you have a high
level of nutrients in the tank. That's fine IF it's a NO3 based fertilizer,
but if it's got NH4.........you are going to have algae.
So for a general easy to use consistent method, dosing the water column seem
far more appropriate to me. At least I can test, get the correct ranges I
want, adding more nutrients easier, change the frequency of dosing, not
effected by thermal currents due to changes in the room temps and over all a
more testable and consistent nutrient supply to the plants.
I must stress that N limitation in plants causes serious break down of
nutrient uptake and metabolic plant functions.
And while a number of folks say it stays down in the substrate, flow out and
in the substrate does occur. You can try to deny it, but even plain old sand
etc will have anywhere from 0.25liters to 1 liter per day/per meter ^2 flow
in/out of the sand layer at the 2-3mm range. That's not a lot but that water
is taking those nutrients right up into the water column.
The NH4 is being consumed if the flow is slow, sticks are old, the NH4
levels being add are slow and steady. But it's not the most controlled way
to deal with it. It is easy though.
As far as plant health, it does seem a bit of hit and miss with a number of
folks. Myself and a few others that I've talked with that used these in the
past, have not had guaranteed great plant response and in many cases adding
more did nothing at all.
I tried the reverse with using water column dosing minus the NH4 and got a
far better responses on every plant I've tried.
I've heard this statement that plants prefer substrate fertilization and NH4
over NO3 but I tell you, I cannot see it in my tanks. I see a much more
dramatic plant response and a much faster response.
If these statements that get repeated allover the web many times are true
what am I doing wrong?
The CO2 is the same, the lighting, the plants, there's no algae either way.
I will say that substrate iron is a good thing even with the _best_ water
column dosing and careful control over all the other water column
parameters. That I can see and attest to.
But not the macro's.
Sure plants will use some nutrient from the roots IF there's not much in the
water column. But if supplied, then they will take it from the water column.
I am unaware of any hobby grade test kits to measure substrate nutrient
levels. So how much is enough down there? Should it be added?
I suppose so if you plan on not dosing much to the water column or
infrequently, or have a lower light tank where one can rely primarily on the
substrate transport for nutrients. But you gain nothing from trying this
except less plant growth based on what I've seen when I took such low light
tanks and raised up the water column nutrients.
Then I got better growth, less algae on the glass etc.
These observations prove to me (although not formal test per se, they have
been consistent and done over time and have been repeated) that the water
column nutrient limitation idea is not correct. Both at high and low light,
the algae have the same access to the nutrients as the plants do.
Someone always comes along and says: "What about allelopathic chemicals?"
I've spent some time discussing this one with a few researchers specifically
in aquatic plants that have reviewed and had graduate students working on
these types of things as they themselves have also, and they say the
chemical allelopathic interaction is slight to negligible at _Best_.
I agree as those large frequent water changes attest to. Plants would have
to spill out a lot of chemicals or very powerful one very fast all the time.
Ground up plant pulp is also not the same as plant allelopathic chemicals.
These chemicals have half lifes also in many cases and rapidly degrade and
new production would be needed.
But the real kicker that punches a hole in this argument is this:
a comparative study of each of the some 250-400 plant species that are kept
in the aquarium today.
Now some may have allelopathic chemicals and these are slight from what I've
read and talked about, but many plants simply do not make _any_ Allelopathic
chemicals at all. Many plants have never been test at all. But the bulk of
the interactions in what has been observed is slight interactions but
certainly true for land based plants.
But that involves the roots........where that low flow occurs so it's
possible plant plant allelopathic interactions are much more possible and
more likely present in anaerobic substrates vs an aerobic one like a
flourite substrate with those large grains but that nice micro habitat in
the internal spaces of each grain that is always protected.
I and many other folks have had only a few species in their tanks yet also
had no algae. In each tank I've ever kept, I've found the same pattern of a
lack of algae if the plant are healthy, never mattered if if was particular
species or not.
If allelopathy was a cause for this effect of no algae, why do we see it in
so many plant species?
I just don't buy all 250-400 species of plants has strong allelopathic
Even the ones that do have them are weak at best. In a very stable non CO2
tank where the chemicals have plenty of time to build up I can say this
occurs and may have a larger interaction, but not in a tank where the water
changes are frequent.
Same thing for the root-root interactions. Terrestrials are different,
seldom disturbed anaerobic substrates are also different like that in a non
CO2 soil based tank, but even there, I've replaced the soil with the
flourite and it's done the same performance and better in the long term IMO.
Okay, I'll get off da stump for today:-)