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[APD] Re: N in the the soil

>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.)

Generally, all substrates are fairly porous as far flux in/out. Unless you use soil etc, which you do.  
Rather than the porosity, the organic matter you have in your tank plays a much large role. 
Your tank also need more O2 and there is an associated cost with root transported O2 vs obtaining it from the water column above, diffusion in/out is a two way street.
If the plant is going to transport the NO3 to the leaves anyway, why take it into the roots?
The volume of O2 is larger, Ech and Crypts roots are well developed for this purpose and for another even more basic reason: they are amphibious plants that live along the backs of streams and flower emergent.

They need huge roots to hang on when the water current is high.  
Also, the soil provides the bacteria with a carbon source, once that carbon source is consumed etc, then the bacteria stop cycling the substrate but hopefully by then there is enough mulm building up.

Let us take a step back here to your orginal tank issue:

>>I was having trouble a couple of months ago with my E. bleheri, E. tenellus,
>>and E. parviflorus. These were in soil-substrate tanks, and I believe the
>>soil substrate had been providing N to the roots for some time, and finally
>>ran out. The leaves were suffering chlorosis and the older leaves were

Mummm..**soil** substrate that's been depleted?
This was a controlled test that you want to debate? 

>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.

I think a deficency is in there somewhere.
Maybe soil inhibits your growth after awhile, after it's depleted and it starts to break down further?
You could argue that also I suppose.
A soil substrate that goes sour.

>>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?

We both used Jobes. You saw green, I saw red.
I got no response when the water column was rich. I reported this years ago here on the APD.
You already had macros in the form of soil in this tank, I added macros to a tank without any then noted any changes with a good water column routine.
>>[Echinodorus and Crypts] do amazingly well with water column dosing only. 
>>I know this very well as I've had both 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.

There is nothing significant in the substrate as far NO3. Here's why:

You say the water flow around the roots provides all the NO3 they need.
I say the flux alone is enough without the current of the RFUG.
Plants will also leak out nutrients from their leave into the water column. 

Fast forward to a non flowing substrate, flourite with no NO3 added. Same results.

So I have provided two differing flow rates through a substrate with the same results without any N added or macros. The no flow flourite seems to do even better IME. But I cannot say it was due to N, in the floiurite tank there was no N added. Later, I tried adding them to flourite, I never got any response unless I did not dose the water column. 

So that seems to put a stop to the notion the RFUG's provide a significant amount of NO3 to the roots because that is certainly not occuring in 4-6 inches of flourite wityh mulm accreartion blocking flows.

Thing is, that you cannot really get away with a 100% substrate only experiment nearly as well as a pure water column nutrient dosing(RFUG). This allows a backdoor way to test for nutrients in the substrate.

Neither method is perfect, but if it's a significant role player, I should see a little something, to date I never have, but I do keep entertaining the idea:)
I wanna see the difference actually, but it's just not there. 

>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.

I'll reject the allelopathic reasoning for previous argued points and to keep this on a more relevant issue, growth rates.

The growth rate of swords vs Crypts, which grows faster generally?
Both can get weedy, but swords do tend to be nutrient bullies/hogs.

So while Crypts are fine at low nutrient levels, less light, the swords are faster growing plants generally and enjoy more light. I'd say Crypts are more tolerant of low nutrients, N in particular but this is species dependent within Cryptocoryne also. 

>>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.

That's the point.(homogenous environment)
Then you use a non flow routine without any Macros added(Heterogenous) but still dosed to the water column.
Then you go back and try adding macros to both set ups and note any differences. 
This explores all the possible combinations.
You can add heating cables in there if you wish as well.
Then you understand the different methods well and know what each result produces.

Why would the RFUG do poorer or similar if it had NO3 being supplied to the roots and the non flow did not?

This proves the point.
Adding nutrients to the substrate for the roots should work best with a RFUG since it also will supply the macro's dowen there, but I found that did not produce the best growth/health.

No flow did without the macro's down there. 

> 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.

So you did add jobes spikes?
That's what I used in my experiments with instead of macro only. 
I never found any differences in growth. 

>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.

I doubt it though.
Try adding the PO4/K/NO3 etc seprately to the water column and then to the substrate.
Which produces pearling faster?

Nutrient status of the plant also plays a large role.

> 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

I never have in keeping aquatics plants to date, not even a hint of a problem with any Sword plant. 
Everytime it's been CO2/ water column related.
Fe is the only nutrient I can say without a doubt that needs to be in the substrate as well as possibly the water column for a CO2 enriched tank. And that is only plant specific, swords did not fall into that group.

You can try it yourself if you can maintain the plant's nutrients and the CO2 etc at a stable level in the water column. I did this several times with a number of plants. 
Never found any differences unless I did not add something to the water column.

Unless you are careful about the water column and dosing there, you will see a difference, plants will take nutrients from the substrate if it runs out in the water column.

Jobes adds more than macros? That I'm not sure of, the MG stick do, I'd assume these do as well but they do not report it, but they also do not deny it either.

Try starting with a no N/P/K substrate and get the plants growing well without substrate ferts FIRST for awhile(3 weeks or so), then try to add it and see if it helps or not.

Thanks for the comments BTW.

Tom Barr


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