Aquarium Plant Fertilizers - Sources of Nitrogen

[jaypeecee]

Hi Everyone,

Ever since reading Diana Walstad's Ecology of the Planted Aquarium book on the topic of most plants preferring ammonium over nitrate, I have been digging deeper into this. And, I have found some interesting stuff that I'd like to share. In particular, I have been drawn to the use of Urea. My understanding is that aquarium plants absorb Urea and break it down into ammonium and carbon dioxide. I believe plants use an enzyme called urease to do this. So, presumably this ammonium (inside the plant structure) doesn't pose a risk to tank livestock such as fish?

I discovered a fertilizer known as Eudrakon N as follows:

Eudrakon N Nitrogen Fertilizer Solution

However, the blurb for this product does state that "Urea...can be directly absorbed by plants on the one hand or also hydrolyzed by the bacteria in the tank into ammonium and CO₂". This being the case, choosing the optimum dose of Eudrakon N would be important to maintain ammonium at a safe level for fish and inverts. And this would apply to other urea-containing fertilizers.

In a sense, this thread is an extension of the following thread that I unintentionally hijacked:

Olympus is Calling.

Thanks again to @Zeus.

I have more to add but that should hopefully get the ball rolling!

JPC

 

[jaypeecee]

My understanding is that aquarium plants absorb Urea* and break it down into ammonium and carbon dioxide. I believe plants use an enzyme called urease to do this. So, presumably this ammonium (inside the plant structure) doesn't pose a risk to tank livestock such as fish?

Hi @dw1305 & Everyone,

Have I got my facts right here? Any feedback would be appreciated.

* from the water column

JPC

 

[dw1305]

Hi all,

Have I got my facts right here?

Yes, I think so. The chemical reaction, which urease catalyses, is:

CO(NH2)2 + H2O → CO2 + 2NH3

So, presumably this ammonium (inside the plant structure) doesn't pose a risk to tank livestock such as fish?

Yes again, I must admit I've looked on ammonia and urea as having much the same risk involved, which I should have known isn't really right (<"from your link">).

I thought that the liquid fertiliser manufacturers were using urea (CO(NH2)2) as a nitrogen source because it is a lot cheaper to buy than ammonium nitrate (NH4NO3), and <"their mixes are so weak"> that you would literally have to pour the whole bottle in to kill your livestock, but I think I did them a disservice, and actually adding urea is a lot safer than adding an ammonia containing salt.

cheers Darrel

 

[jaypeecee]

Hi Darrel,

Well, well! I re-read the following thread late last night and picked out something that Clive said (post #31):

Dosing with Ammonia and Urea

This just about says it all:

"Previous studies have found that urease enzymes can be intracellular, cell surface bound, or extracellular..." which sounds to me like the transformation can occur above, below or within the plant's tissue structure".

JPC

 

[dw1305]

Hi all,

sounds to me like the transformation can occur above, below or within the plant's tissue structure".

Plants are a bit different to animals, they are much leakier structures, so there is less of a clear differentiation between "inside" and "outside". They need to be full of spaces, so that gases can diffuse in and out, and a lot of the internal space is filled up with lacunae "holes" (aerenchyma etc).

My guess is that even "extracellular" just means that the enzymes are located somewhere within the lacunae of the mesophyll layer, but not bound to cell surface

This is a cross-section through <"the floating leaf of a Potamogeton sp"> (it is floating because you can see that there are stomata only in the upper (adaxial) leaf surface).



cheers Darrel

 

[jaypeecee]

adding urea is a lot safer than adding an ammonia containing salt.

Hi @dw1305

Hold that thought (i.e. what you stated immediately above)! In the present context of what we are discussing, you may be correct. But, one thing I've discovered about Urea is that it sometimes can contain a high level of heavy metals. Sufficient dilution may take care of this. We probably need to re-visit this.

JPC

 

[jaypeecee]

Hi @dw1305

Wow, Darrel. I'm learning so much right now. What a great picture in your last post. Now I see why you often refer to plants as 'leaky structures'.

JPC

 

[dw1305]

Hi all,

But, one thing I've discovered about Urea is that it sometimes can contain a high level of heavy metals.

There is some discussion of impurities in urea in the <"biuret posts">. If the urea is fertiliser grade it should be fine, but I'd steer well clear of any sold as a de-icer.

Now I see why you often refer to plants as 'leaky structures'.

They are pretty leaky all over, the roots don't have have as many obvious "holes" but they are continually sloughing off cells from the root tip and leaking from root hairs. There is more discussion of this on the <"Radial Oxygen Loss"> (ROL) posts.

You can also see why plants might use less oxygen at night than you might imagine, and it is back to the same spaces. When a plant is "pearling" it means that all of those internal spaces are saturated with oxygen and it is outgassed as oxygen gas into water, (which is also 100% oxygen saturated) and the "pearl" rises to the surface as a bubble. When light levels fall back <"below LCP">, and the plant becomes a net oxygen user a lot of the oxygen it uses comes from those internal spaces, where now CO2 levels rise.

You can an example of this when @Geoffrey Rea <"wrote">

............Have actually found a caveat to this @alto

Borrowed a dissolved o2 meter from a friend at uni and found that on a mature high tech setup I was running, the air stones running at night were bringing night time o2 levels below what was available if solely relying on what was produced through photosynthesis alone during the photoperiod.........

cheers Darrel

 

[jaypeecee]

Hi @dw1305

With reference to heavy metals in urea...

If the urea is fertiliser grade it should be fine...

Please take a look at the attached draft standard, paragraph 4.3.

JPC

 

[dw1305]

Hi all,

Please take a look at the attached draft standard

That one is from Uganda, but I don't know how it would relate to the EU standard.

cheers Darrel

 

[jaypeecee]

That one is from Uganda, but I don't know how it would relate to the EU standard.

Hi @dw1305

In my field of work, many of the EU Standards were ISO Standards. So, we have things like ISO9001 relating to Quality Management, for example. And this Uganda standard cites ISO 17318 in Paragraph 4.3, Table 2. Also, take a look at:

ISO 17318:2015

Fertilizers and soil conditioners — Determination of arsenic, cadmium, chromium, lead and mercury contents

www.iso.org

JPC

 

[jaypeecee]

Hi Folks,

I recently mentioned this elsewhere on UKAPS but I should be getting a small quantity of high purity urea fairly soon. Looking forward to doing some experiments with this both as a source of nitrogen and carbon dioxide. I will update this thread in due course.

JPC

 

[jaypeecee]

Hi Everyone,

Just to let anyone interested know that I started using urea on 30 January (2021). This is in a plant-only tank. The plants are Java Fern, Congo Fern and Frogbit. I am using pharmaceutical grade urea as agricultural urea appears to contain a lot of impurities including biuret, formaldehyde and heavy metals. Urea is the only source of nitrogen in the tank. Phosphorus, potassium, iron and trace elements are provided by the Flourish range of Seachem products. Calcium and magnesium are obtained from Tropic Marin Re-Mineral Tropic. Carbon for the plants is provided by atmospheric CO2 (for the Frogbit) and urea (for the Ferns). I am using rainwater. Water temperature is 26/27C. Water pH is from 6.8 to 7.9 (measured using an ETI8000 pH meter). I am having difficulty stabilizing pH but hope to try boric acid. I want to avoid using organic acids such as acetic or citric in order to ensure that the only source of carbon is as stated previously. That's why I have just chosen boric acid, which I hope to obtain soon. Lighting is provided by a cheap-and-cheerful AquaOne 30 nano cube light.

I'll add a photo of the setup - possibly a bit later this evening.

Any, and all, comments welcome.

JPC

 

[jaypeecee]

Hi Everyone,

Here's the tank...

JPC

 

[sparkyweasel]

Very interesting.
If I may, I would suggest adding a submerged plant that is not a fern, just in case they react differently.
Looking forward to seeing how it goes.

 

[jaypeecee]

If I may, I would suggest adding a submerged plant that is not a fern, just in case they react differently.

Hi @sparkyweasel

Thanks for the feedback. My problem at the moment would be finding a suitable plant as the tank is a mere 12 litres. And, I'd need to get it online as I'm at home 24/7. What would you suggest? I now have Amazon Frogbit on the surface but that's another story.

BTW, it's good to be in touch with you.

JPC

 

[sparkyweasel]

Perhaps one of the smaller Cryptocorynes then, Dwarf Hairgrass or Pygmy Chain Swords? The last might be best as they spread faster so you might be more easily able to judge how well they grow.

Thanks, and you. 🙂
I haven't been very active on here recently, but I'm keeping an eye on the more interesting threads. 🙂

 

[sparkyweasel]

I've just checked where it was I got some from recently.
Tennellum
They were nice and healthy, and cheap. 🙂

 

[Oldguy]

Please take a look at the attached draft standard, paragraph 4.3.

Why in the above draft standard is urea called calcium ammonium nitrate?

 

[jolt100]

Why in the above draft standard is urea called calcium ammonium nitrate?

CAN is not the same as Urea, perhaps it's a mistake in the draft? But it could be they call all nitrogen fertilisers "urea"? The CAS numbers of the two products are completely different but the Ugandan draft doesn't quote anything.
The Iso standard quoted is only a method of test not a product standard. Much better to look at commercial specifications available in Europe: eg from Source Chemicals....
Molecular Weight: 60.06 g/mol
Melting Point: 132.7 °C
Solubility in water (% weight): 480 g/l at 20 C - completely soluble
Total Nitrogen (%m/m): <46%
Biuret (%m/m): <1%
Moisture (%m/m): <0.3%
Formaldehyde (mg/Kg): <10
Ammonia: <100mg/Kg
pH (10% Solution): <10

If you Google urea there's plenty of sources with specs.

Cheers
John