# Organic vs inorganic PO4, NO3?



## Laith (Sep 4, 2004)

Maybe somebody can clarify something for me. I keep reading about the differences between organic and inorganic PO4 and NO3.

I'm still trying to get my head around what exactly the difference is. I mean as far as I remember from chemistry, PO4 is PO4 is PO4 is PO4... and the same for NO3.

Is the PO4 bonded to different elements when its called organic versus inorganic? Perhaps the organic has a Carbon atom attached or something while the inorganic does not? I mean there must be a difference in the chemical composition to justify the different impacts on plants/fish that are talked about...


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## Mnemia (Nov 23, 2004)

I believe you are correct.

Check this out: http://en.wikipedia.org/wiki/Phosphate

That says that "inorganic phosphate" refers to what we normally think of and dose, which is phosphate in the ionic form. It says that "organic phosphate" simply refers to phosphate stored in a biological molecule, such as ATP (major energy carrier in biological systems).


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## Laith (Sep 4, 2004)

Excellent! many thanks! 

So basically this means that in the water column we will have free phosphate ions (inorganic phosphate) as well as organic phosphate in the form of phosphate bound in DNA and what are basically proteins?

So the plants can only/more easily use the inorganic phosphate?

Are we talking a similar story with the organic and inorganic NO3?


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## imatrout (May 12, 2005)

I have also seen threads stating that common hobby test kits only measure organic (un-usable by plants) PO4. Does anybody have information that confims this or suggests otherwise?


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## Milan (Jul 6, 2005)

imatrout said:


> I have also seen threads stating that common hobby test kits only measure organic (un-usable by plants) PO4. Does anybody have information that confims this or suggests otherwise?


In my mind, this is completely incorrect. Firstly, PPS calibrates tests against KNO3 and PO4, so THEY DO MEASURE inorganic form. Secondly, in the past most of the tanks completely relied on organic source of PO4 and NO3, so IT IS USABLE by plants.


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## defdac (May 10, 2004)

> Secondly, in the past most of the tanks completely relied on organic source of PO4 and NO3, so IT IS USABLE by plants.


Only if the substrate contains mineralization-bacteria that converts the organic PO4/NO3 (DOP/DON) to inorganic PO4/NO3 (DIP/DIN).

So fish poo DOP/DON will essentially only contribute to plants via microbial activity, which may or may not be present.

That's why big wc:s that removes DOP/DON with new high inorganic DIP/DIN-levels often is a more sure way of good growth than relying on bacteria that may or may not be present for the most part in the substrate.


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## Milan (Jul 6, 2005)

Well, ... what I was referring to is the source of NO3/PO4. So, KNO3 being inorganic, and fish poo (whatever it is) being organic. Of course you need bacteria to process fish poo into NO3, but IMO the end product is NO3 regardless of where it came from. In other words there is no diferrence in between NO3 that came from fish poo, from the one from KNO3. Correct me if I'm wrong ...


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## defdac (May 10, 2004)

Milan said:


> Of course you need bacteria to process fish poo into NO3,


This takes time and requires the right kind of bacteria to be present and the right type of redox and all of a sudden you need to be concerned how to grow bacteria instead of plants.



> but IMO the end product is NO3 regardless of where it came from. In other words there is no diferrence in between NO3 that came from fish poo, from the one from KNO3. Correct me if I'm wrong ...


Yes NO3 is NO3.

But organic NO3 is not inorganic NO3 and you grow plants with inorganic NO3 and bacteria with organic NO3.


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## Milan (Jul 6, 2005)

Now, you completely confused me ...

What's wrong with having bacteria to produce NO3? Isn't that the (beneficial) fact of nature? I don't think it would hurt plants, unless I'm missing something. And finally, my comment was about registering such NO3 (as a bacterial product) on common NO3 tests. I'm damn sure it would show up.


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## Mnemia (Nov 23, 2004)

Milan said:


> Now, you completely confused me ...
> 
> What's wrong with having bacteria to produce NO3? Isn't that the (beneficial) fact of nature? I don't think it would hurt plants, unless I'm missing something. And finally, my comment was about registering such NO3 (as a bacterial product) on common NO3 tests. I'm damn sure it would show up.


Yes, I think it's definitely true that such nitrate shows up on test kits. Otherwise, why would measurable nitrate levels rise in an aquarium by biological action? And it's definitely true that the "inorganic" nitrate (ie, KNO3) shows up as well, since I've tested KNO3 in RO water and seen this. So I think it's definitely wrong to suggest that our test kits can't pick up either "organic" or "inorganic" nitrate.

I also think it's probably incorrect to say that plants can't use one form or the other. There may be differences in the amount of energy needed to extract the nitrogen, and that could cause plants to "prefer" one complexed form over another...but I think they will use any form of nitrate if it is all that is available. In fact they will use ammonia, nitrite, or nitrate. Plants aren't all that picky.


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## defdac (May 10, 2004)

I'm talking about fast leaf uptake. There you have to have inorganic NO3 from for example KNO3 and not fish poo that has to be cycled through the bacteria in the substrate.

That's why you can register high NO3/PO4-levels with crappy growth-rates and low pearling, and when you dose inorganic NO3/PO4 from KNO3/KH2PO4 the pearling starts immediately.

With highlight-tanks it sure is important to be able to guarantee all inorganic macronutrients are in place.

with lowlight-tanks with a peat/soil-substrate there is no need to worry. Just feed the fish. The organic NO3/PO4 will be converted fast enough for the slow growth rates under the low light.


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## defdac (May 10, 2004)

Mnemia said:


> I also think it's probably incorrect to say that plants can't use one form or the other.


From http://fins.actwin.com/aquatic-plants/month.200404/msg00426.html

_Periphyton has the ability to remove very very low amounts of PO4 and
organic DOP. Plants do not use this fraction. That we do know._


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## RTR (Oct 28, 2005)

Isn't it most likely to be that most DON is inaccessible to plants? Is the bacterial digestion not a necessity before the inorganic NO3 is available? The fact that the bacterial digestion is on-going in the subtrate and filters and maybe even in the water column is secondary. Just how complex a raw material can/will the plants take in for practical use as simple building blocks?


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## plantbrain (Jan 23, 2004)

Let me add something that will bug you even more:
There are different types of DON/DOP and some are more labile than others depending on it's source, temp, redox conditions, plant health etc.

But doing a large water change and then adding inorganic fractions back again is a fairly straight forward thing that removes many unknowns and grows plants well. 

But......you need to be sure the CO2 is good, the water change can add a fair amount of CO2 and make you think the effect is nutrients rather than CO2.

After 2-4 days, the growth is still going good, then it's not the CO2.

Regards, 
Tom Barr


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## Mnemia (Nov 23, 2004)

Tom, maybe you can settle this in my mind.

I've been searching around through scientific literature on Google Scholar, etc (no idea how good they are for plant biology since it's not my field). I've seen several things on there suggesting that plants can in fact take up some forms of DOP/DON, although most papers also say that it's easier for them to take up the inorganic ions. DOP/DON seem like very broad terms to me, so I would imagine there might be some variation and that it might not be possible to make a categorical statement. What is the correct explanation? I don't have the knowledge to judge that kind of scientific literature in isolation. Can plants take up nitrogen or phosphorus that are bound to biological molecules like amino acids, or proteins, or not? 

I understand that doing large waterchanges to reduce the dissolved organic nutrients and then replacing them with inorganic nutrients makes things more stable and favors the plants over algae or bacteria. Is this because the plants preferentially take up the inorganic forms, or because the microorganisms cannot take them up as readily? Or do the plants lack the enzymes, etc to break down the biological molecules?


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## plantbrain (Jan 23, 2004)

Plants can and do take up other forms of N and P, Liebig believed that not to be the case.

But which will do better? the inorganic form is the most easily assimilated, many species of algae need only a small amount and they live in a place where getting it ASAP is more critical than the plants with their reserves, roots etc.

So the generalizatuion is correct, but there are always exceptions.
Excel vs CO2 type of thing.


Regards, 
Tom Barr


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