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[APD] RRe: N and Echinordorus in the roots

Tom Barr writes:
>So if N is requitred for good growth and your test at 50ppm NO3 showed
>issues, why do my plants do so well, err too well, when the NO3 is less
>much less than 50ppm? 

I really don't know the answer. I already gave my best two guesses in my
earlier message, but I'll repeat them.

Guess #1) Your substrate is more porous, and therefore some of the NO3 from
the water column winds up around the roots. (Since I have fine play sand
over soil, I'd say my substrate porosity is quite low.)

Guess #2) There is something else going on in my tank, such as an excess of
a chemical that interferes with leaf uptake of NO3, that makes my
Echinodorus behave differently from yours.

>Something else was causing the problem.... not N or a macro substrate

If that's the case, why did adding a substrate fertilizer that contains only
macronutrients solve the problem?

>[Echinodorus and Crypts] do amazingly well with water column dosing only. 
>I know this very well as I've had boith genera for a very long time using
>RFUG's with plain old dirty sand.

Going back to my first guess above, an RFUG will force NO3-containing water
through the substrate and near the roots. In other words, using a RFUG means
that whatever you put in your water winds up in your substrate as well. I
don't see how this proves that the Echinodorus are taking up the NO3 through
their leaves.

And going back to my second guess, my Crypts never displayed symptoms of N
deficiency even when I was keeping NO3 at 5ppm. So if it's a chemical issue
in my tank, such as an excess of another nutrient or an allelopathic
interaction, it's one that affect Echinodorus but not Crypts.

>You need some control(the RFUG are very good for this) and to account for
>the other parameters(CO2/Fe, PO4, K GH etc) before you can make this

Again, you'll have to explain to me how a RFUG is good for a leaf vs. root
uptake experiment, since it mixes what's in the two environments. As to
accounting for the other parameters, are you suggesting that adding the
Jobes spikes changed CO2, Fe, or GH? Certainly it would provide some
substrate PO4 and K, but as I said those were already in high supply in my
water column.

I suppose there could be an alternate explanation that Echinodorus doesn't
prefer root uptake of NO3, but does prefer root uptake of PO4 and/or K, and
the spike provided those. But that's not anything that I've heard of anyone
else reporting, while a number of hobbyists have needed to use substrate
supplementation of N.

- Jim

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