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Slow turnover of water in substrate

Hi Roger,

Looks like you are the right person for some explanation.
I have posted this awhile back but did not get any reply.
Would appreciate your input.

Casey Huang

yhplsing at singnet_com.sg  

Hi All,

Could someone please offer an explanation concerning
oxygen requirements for plants root.

According to TOA there should be slow / small movement
of water in the substrate through substrate heating so
as not to have too much oxygen in the substrate inorder
to get reduction type of processes for the nutrients in
substrate so that the nutrients can be easily absorbed
by the plants. 

According to books about Hydroponics the nutrients are
mixed by aeration with the air hose in the culture trough
to have more oxygen in the nutrients to support the
metabolic processes associated with root formation and
subsequent growth.

The same for Aeroponics which is self explanatory from
Aero in the word Aeroponics.



yhplsing at singnet_com.sg

>> Subject: Heating cables
>> I'm confused about this whole heating cable thing.  Perhaps this is partly
>> just a conflict of approaches between differing schools of thought.
>There's a large matter of degree here.  I once measured the discharge
>through each lift tubes of a UGF at 160 gallons/hour - so a total of 320
>gallons/hour circulated through the substrate.  The substrate contained
>less than 2 gallons of water (3 square feet of substrate, 3 inches thick
>with 35% porosity), so it took only about 23 seconds for the ugf to turn
>over all the water in the substrate.  You might say the the average
>"residence time" for water in the substrate was 23 seconds. In fact some
>parts of the substrate would probably get little or no flow while other
>parts would turn over much faster than that.
>This very rapid turnover doesn't allow very many reactions between the
>water and the substrate and means that the chemical and biological
>environment in the substrate is pretty much the same as it is in the
>rest of the tank - your plants (almost) might as well be floating.
>Slow turnover allows interaction between the water and the substrate; e.g.
>it allows oxygen in the water to be depleted by bacterial activity and
>allows nutrients in the water to bind to exchange sites in the substrate.
>It also allows time for nutrients that are released within the substrate -
>ammonium from burrowing snails, for instance - to be used before it
>circulates back into the open water in the tank.

>Roger Miller