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Re: Substrate longevity

Karen mentioned having very old tanks that became rootbound to the point
that they were difficult to manage.

I believe that I read somewhere, possibly when communicating with Dave
H, that the root to shoot ratio in plants is often determined by the
availability of nutrients. A plant which is low in nutrients will divert
more of its available energy into growing roots whereas a plant with
sufficient nutrients will grow large leaves and stems. This makes sense
because there's no gain in growing more photosynthesis surface if the
plant can't access sufficient nutrients.

This suggests that a root bound tank might be one which has been low on
nutrients for a long time. If left on its own for long enough, a planted
aquarium will eventually fill up with plants and as the substrate
fertility is reduced, more root growth will be stimulated. I think the
best strategy would be to periodically uproot several of the plants and
sell them off. You certainly need to do this with several varieties of
Crypts or they'll take over.

Another point brought up by Bob Dixon about substrate longevity was
about the need to add substrate fertilizer to replenish nutrients which
are eventually used up. This is a good point but I think by substrate
longevity, we really mean the useful life of the substrate. In this case
we are perhaps extending the useful life of the substrate. 

Consider an analogy of houseplants which become rootbound. They do need
to be repotted periodically. I think its often suggested that the roots
themselves should be trimmed when repotting, "to encourage new root
growth". I don't know if there is validity to that but the idea of
pruning roots in the aquarium has been mentioned once or twice and
perhaps we could discuss that idea?

Steve Pushak                              Vancouver, BC, CANADA 

Visit "Steve's Aquatic Page"      http://home.infinet.net/teban/
 for LOTS of pics, tips and links for aquatic gardening!!!