Re: substrate heating

>From: eis at alto1_altonet.com (Paul Nicholson)
>Date: Fri, 8 Mar 1996 12:46:02 -0800
>Subject: substrate heating
>In a lot of the recent discussion about substrate heating, everyboody seems
>to agree that there is an an advantage to keeping plant roots warm. The
>other attributed benefit is the increased circulation in the substrate
>which is necessary to get nutrients to the roots.

I am glad that the conversation about heating is starting to make sense. 
I am also inclined to favor the comments of John Davis
<JDAVIS at bio_tamu.edu>, who said

  "I think the answer to the question is probably going to be 'E',  all of the 
above.  I think that the main reason that substrate heating does any good at 
all is that it stimulates bacterial growth in the substrate."

For this reason and for potential circulation, substrate heating may be MOST
IMPORTANT when a tank is first set up. From that point on, the root systems
from healthy plants can take over. If the roots are disturbed thru heavy
gravel washing, transplanting/replanting, etc, then the heating or
artificial circulation could again be beneficial.

Keep in mind what John also said " But if you heat, and then the 
heating goes out, then you may experience a population crash or at least a 
change in the eclogy of the substrate."
I am glad that the conversation on substrate heating has returned to the
question of the differential benefits of coils vs. heating pads, etc. For
years, I have heated the substrate from below the tank because of the
enclosed multilevel tank stands I use. The upper tanks get heated from the
lighting system of the lower tanks. While this may not necessarily cause
circulation (I will let the physicists argue this one out), it should
increase microbial activity, and keep the root temps from being too low. I
also insulate the bottom of some tanks which also keeps substrate
temperature more similar to water column. 

 I am also intrigued by the importance of a  granular substrate. As Paul
says, "a compact substrate containing soil, fine sand, clay or silt this
amount of pressure differential will be insufficient to produce flow
rates of around 1cm/day which would be about what we wanted" Doesn't Optimum
Aquarium and other advocates of heating coils suggest a certain size gravel

Compaction has been one of my concerns and is THE reason I have experimented
with vermiculite. I have also seen some plants grow better in coarser
substrates (e.g. gravel without soil vs. sand with other ammendments) which
may have something to do with the amount of O2 that will be present, as well
as the ability for 'natural' circulation of water (from diffusion,
transpiration, etc). For the latter, the tanks do not have heating coils,
but could have artificial circulation from other sources of heat <VBG>.

The idea of 'natural' circulation is consistent with Paul's conjecture #2 that 
" in a granular substrate, heating coils might help circulation but
the plants are probably doing most of the work on their own."

Neil Frank                 Aquatic Gardeners Association,  Raleigh NC