Re: Aquatic Plants Digest V2 #536

>From: Miles Morrissey <mmorriss at sophia_smith.edu>
>Subject: Substrate vs water column

>                I have recently set up a 20 G long with a vermiculite/soil/
>worm castings substrate covered with a couple of inches of gravel.  I do
>20-30 % water changes every other week with ph 7.5 water and have a DIY
>CO2 infusion setup that keeps the water ph below 7.0.  My question:  Is
>the substrate enough fertilizer for the plants or do I also need to
>supplement with fertilizer in the water column?  I have heard that a
>fertile substrate can provide all needed nutrients to the plants through
>thier roots.  I am not talking about hard to grow plants here.  Vals. two
>E. species swords, bacopa, cabomba sp?  h. polysperma, ludwigia,
>sagittaria and anubias nana.  What do people think?

The substrate can supply everything, except possibly calcium, for the short
run (several months), but with continued growth it is going to run out of
various nutrients that can easily be supplied via the water.  Probably the
first to run out will be potassium and nitrogen.  Later on, magnesium,
phosphorus, and sulfur.  Much later (6 months to 1 year), if the soil
becomes packed with roots so that it is thoroughly oxygenated (roots have
air channels), the supply of reduced, soluble iron in the soil can become
oxidized and unavailable and  fertilization via the water with chelated
iron may cause a noticable increase in growth.  Having peat or other
slow-decaying organic matter mixed in with the soil can keep iron
solubilized and available for roots a lot longer.

Paul Krombholz                  Tougaloo College, Tougaloo, MS  39174
Goofing off instead of working in pleasant, although cooler, Jackson,