[APD] Re: N in the the soil

["Jim Seidman" <james at mail1_seidman.net>]

Tom, I wanted to clarify a few things I said.

The Jobes Spikes for Ferns and Palms, as far as I can tell, *only* add N, P,
and K. The ingredient list doesn't list anything that should affect GH, KH,
micronutrients, etc. When I referred to "Jobes Spikes" I meant the Ferns and
Palms variety, not the more common houseplant ones.

This is what led to my conclusion that one of the macronutrients was causing
the problem. Just adding macronutrients to the substrate made the problem go
away.

As to the soil becoming "depleted," I of course won't pretend that this was
a controlled experiment. However, a number of hobbyists using soil have
found that they needed some sort of N supplementation after a year or two.
It certainly seems plausible that breakdown of organic products in the soil
could free up N for a while, and then run out.

As to why Echinodorus would want to take up NO3 through the roots, perhaps
that's where the nitrate reductase is. For example, in Lemna minor most
nitrate reductase is in the roots. Therefore most NO3 taken in through the
fronds must be transported to the roots for reduction. Many other aquatic
plants also show higher levels of nitrate reductase activity in the roots
than the shoots. Maybe Echinodorus similarly performs its reduction in the
roots, and in my low-light environment just cannibalizes old leaves instead.
I am of course just guessing.

Others have seen similar symptoms in their Echinodorus and used clay balls
with KNO3 to fix the problem. So I'm skeptical that my rapid improvement was
somehow due to the spike mysteriously affecting CO2 or Fe or anything like
that.

It sounds like the proper controlled experiment here is not a RFUG
environment, but a split-chamber where the roots are in a completely
separate solution. It would then be possible to see where the uptake was
really occurring. And it would be important to remember that the results
could well vary with lighting as well.

- Jim



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