BryceM

Yes, polarity of the ions is one of the important factors, but the biochemical pathways are far more complex than this simple explanation. Cell membrane physiology as it relates to nutrient uptake is quite interesting. This process is highly regulated by the needs of the cell and different species utilize different strategies for assimilating nitrogen.

The enzyme mediated biochemical reactions that take place inside the cell allow most plants more than one option to assimilate nitrogen from the environment. Depending on the species, NH4+ is more easily assimilated (requiring less energy expenditure) than nitrate, nitrite, urea, or atmospheric N2.

The whole process is quite interesting and worthy of a far deeper discussion than usually takes place on a hobbyist level. If I get a minute, I'll dig into my old texts to see if I can find something that will shed some light on the subject.

For starters, this goes over just a few of the most basic aspects of nitrogen fixation from the form of N2 to NH4. This doesn't really answer the question of the the preferential source of nitrogen for aquatic plants, but it does shed a bit of light on the complexity of the invovled biochemistry.

The subsequent chapters address some of the nitrate/ammonium pathways.

Coralite

Hey Bryce,
Thanks for the elaboration. I know I was oversimplifying and I would love to hear an abridged overview of how different ions travel from the water through biochemical pathways to where they are used by plant physiology.

JamesC

Before dosing urea



After dosing urea




James

kekon

I also used urea. Moreover, i dosed 3 forms at the same time (NO3, CO(NH2)2 and NH4). I also noticed bigger leaves grow on some plants. The point is (but i'm not 100% sure yet) that by dosing urea and NH4 one can keep lower NO3 levels but maintaining the same growth which is achieved by dosing only NO3 but in higher levels. I didn't notice issues with any type of algae. I was encouraged by "Drak" firm which produces N fertilizer for planted tank which includes 3 forms of nitrogen. The daily dose is 1 ppm NO3, 0.1 ppm NH4 and 0.33 ppm urea.

Amoeba1

Hi James, what are your observations after dosing urea together with NO3?

Zapins

Hmm... any updates on using ammonia or urea in lieu of NO3?

JamesC

Funny you should mention it as I've just stopped dosing the urea about 3 weeks ago and gone back to straight potassium nitrate. So far to be honest I haven't noticed any real change so am now coming round to the idea that perhaps it wasn't the dosing of urea that had the effect as during the dosing of the urea I also suffered stunting at times.

I still have the Ludwigia Glandulosa which sometimes grows fine and other times doesn't. I'm still at a loss as why it happens. And before others jump in and say CO2 I'm going to say that I've had CO2 and flow levels really high and have also given the Ludwigia Glandulosa it's own personal supply of CO2 mist. I'm now strating to believe that it is to do with growth rates and that trying to make it grow too fast causes the deformations. I've dropped the T5's in favour of the old T8's and will note to see if this makes any difference.

One thing I have noticed is that the blyxa japonica does a lot better with higher nitrate levels.

James

Mr_docfish

One thing I have noticed (it was obvious after I finally thought of it) is I have been using ammonium nitrate NH4NO3, and testing weekly for nitrate only.... I have been keeping the NO3 at 15-20ppm, and now I keep it at 10ppm.... with much better results now.... I was over dosing the total N by not considering the NH4.....
I feel silly having said this, I should have noticed a long time ago.

kekon

I saw similar effects and it seems better growth occurs when NO3 is lower.
Blyxa Japonica is a plantwhich really appreciates high NO3 levels; i've never had any issues with this plant. I grows like a weed at NO3 10 ppm or more but some plants are severely stunted.
I'm still waiting for my ordered circulation pump but i think it will not help much.
I noticed that NH4 and urea work better in very soft water. In harder water NO3 is better. Generally speaking it seems that the harder the water the more NO3 can be dosed without harming the plants.

nfrank

i have been re-doing my dry fert regime... both in composition and amounts..... and have been thinking about adding additional N (without adding more K) to supplement what i provide thru weekly water changes. In the past i have used NaNO3 to supplement KH2PO4 and KNO3. This is not ideal since sodium nitrate adds unnecessary Na+, I am now considering urea and figured i would join this discussion.

Conceptually, urea is more appealing to me than NH4NO3 (as used by some products, like Amano's)... and maybe safer if overused, since it takes a few days for residual material to convert to NH4. Because i have choromines (NH2Cl) in my tap water, i am already providing some type of NH4 salt in potentially large amounts after a water change. The average chloramine concentration of Raleigh tap water is 3.5 mg/L!! I now live near the water treatment plant, so i expect my level to be on the high side. Adding prime breaks the NH4 chlorine bond and yields some type of ("detoxified")ammonium salt. So, a 50% water change can be provding a large amount of this stuff. No wonder the plants pearl like crazy (OK, some of that is due to dissolved gases )

I came across this article which talks about fate of urea in the aquatic environment. http://www.cryotech.com/products/pdf/ureafate.pdf It says that "urea completely degrades within 4 - 6 at 20degC" (into CO2 and ammonium). Based on the 40ppm "allowable" levels for salminid species, there is a reason to be somewhat comfortable with dosing of 0.5mg/L as used by the previous posters to this thred. I previously recommended short term concentrations of NH4 not to exceed 0.1mg/L.
http://www.thekrib.com/Chemistry/ammonia-toxicity.html

Seems like urea (in dry form) can be used at higher levels than NH4. It also provides a little bit of CO2