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[APD] Re: N #5

>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

That does not imply anything though.

I can say "Adding a lotto ticket to my tank on a full moon cause algae to go away.
My algae went away when I did it."

It does not mean much. Just a pattern you saw what? Once? There are several things that could be, not just N. 
It's not the most obvious thing but many folks want to assume that.

If we assume this line of thinking to be true, we'd still assume that excess PO4 caused algae.
It's just something that backed up when plant growth was poor or the plants were limited by something else.
Not PO4 cuases algae like everyone had said for years/decades, centuries, eons......

>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.

Yep, I agree with that. 
But it depends on the method of dosing.
You can reply on the substrate more, but can you measure the N in the substrate? Yes, but it's tough for a hobbyist.
I have far more control over the water column.

That's why I start there.
Then building on that knowledge I moved back into adding macro's into the macro poor substrates to see if this helps when the water column is rich in macros.

I never found any differences in plant growth and certainly never with any of these 3 mentioned sword plants, all of which grow faster than I ever cared for when I dosed just the water column.

This was controlled since I had good levels of nutrients in the water column and knew the substrate had nothing added as far as macro's(less than yours or equal when your was low at best).
So I know what the macro's will do if they are added and the differences you should see with substrate vs water column dosing. I already addressed the flow issues in the substrate. 

Even if you like substrate dosing, that's great, but improving the water column dosing routine will __only help__ this method as well, never hurt it. I've provided a simple easy to do method for maintaining the water column dosing already.

>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.

But it's a floating plant. Most of the plant with leaves is out of the water.
But perhaps Swords, especially emersed grown, will have much more NR in their roots, but the plants can change these locations. All that NR will use up O2 also.

 Therefore most NO3 taken in through the
>fronds must be transported to the roots for reduction. 

Then translocated up to the leaves?
You have assume some energy and transport cost with that. Why not use what's already there(why transport if they don't have to)?

>Many other aquatic
>plants also show higher levels of nitrate reductase activity in the roots
>than the shoots. 

Nah nah, just a minute there. Plants that have been grown in lab conditions with good levels of NO3 in the water column?

Or plants in nature where the levels of NO3 are very low and the substrate is rich?
This makes a __huge__ difference.

While wetland plants do have NO3 in the substrate, generally there's also a lot of NH4. 

>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.

Could be, sounds like it to me. Leaves are **storage organs**. Plants decide if the leaf is worth keeping or not.
In bad conditions, the plant will drop it or suck out all the goodies.
Aquatic plants are highly prone and adapted to this. Keeps the new growth always algae free. 

>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

Me too. CO2 perhaps, but you'd see other things occuring if that was whacked.
But as far as your NO3 in the water column, did you also add K+(for that 50ppm of NO3, did you use KNO3?)
Also what type of test kit did you use for NO3 measurements.
It seems nit picky but it can cause issues and lead to wrong conclusions.
Try adding K2SO4 next time and monitor the NO3 as well.

>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. 

Not really, although this would work to some degree.
Plants leech things out into the water column also, so it will not stay down there in the substrate. Plants can and do reabsorb. Diffusion out of the substrate also plays a role.

>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

They did a root vs water column experiment in Demark with several common aquatic plants.
Not with Swords though(FW Biology Feb 2002).
In non limiting water columns, the plants did not grow any better/worse.
They even cut the roots off to see.
Even with roots removed, the plants grew at the same rate.
That pretty much removes any root NO3 sources don't you think?

But it was not done with the 3 listed plants you mentioned.
That is a key point.

But I've NEVER had any of the issues or problems you are having or the several other folks and I do not use macros in the substrate, I do for experimental reasons but I've never found any need to mess with them based on the research available, my own practical experiments/experience and many years of growing swords. They were my favorite plants before I really got into CO2 tanks about 12 years ago. 

I must have done hundreds of plants w/o substrate ferts over a long time peroids. Never had an issue with good water column dosing.

Will adding substrate ferts they hurt? No, will they help directly? No, unless you limit the water column. 
At least they don't cost as much as cables:-)

Tom Barr


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