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Re: [APD] Re: N in the the soil

I wonder if another variable here may be how the plant was grown. Would the
plant develop differently if it is grown with a significant substrate N
source(and potentially deficient water column N) than with an essentially N
free substrate or a substrate with N concentrations similar to the water column.

just a thought.

-Matt Andrews

Jim Seidman wrote:
> 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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