Thanks for the pdf,
In that paper, they study non adapted plants, they just add it and then measure over 48 hours of exposure.
In aquariums, most plants are well adapted to the conditions.
There is a lag time for NO3 but once it starts, does adding NH4Cl stop it once again and inhibits it?
Also, you can see much different uptake rates for various plant species.
You also are left with the linear model for NH4 uptake or a MM model. In both cases, you have to add a fair amount of NH4 to do this. You can add a lot of NO3 on the otherhand (several day's worth/supply).
You can and may use NH4 at high levels using flushing methods and daily large water changes with no ill effects.
Say about 0.8ppm per day.
I think after some time, you can modify this and reduce the NH4CL dosing some to suit the demands, while the NH4 uptake appeared linear, for how long does that occur?
Clearly once the plant has adapted and has all the non limiting N, this has to slow down otherwise the plant will die from NH4 poisoning, they use NH4 to kill plants BTW as a herbicide for this very reason.
So clearly, there are limits here.
This study, nor others address these types of questions.
So it really remains unknown, the evidence is not conclusive.
I'd say there's some evidence on both sides.
But the real question that is important: does NH4 as a source in practical terms, increase plant growth significantly?
How is this N uptake rate influenced when CO2 ppm' are changed/limiting/excess or if they are stable over time?
That's an interesting question. ... and one that seems to be most relevant.
The CO2 carbon supply raises it's ugly little head. Emergent plants do not have this issue, so often they are better suited to answer such questions.
Light is in ft candles, this can be modified however.
the author points out that this might be important in low nutrient systems(NO3 vs NH4), but as aquarist/hortuculturist, we do not have that problem or issue, we can have any range of NO3 or NH4 or both. So the relative importance of this only becomes crucial when you run things really lean. In non CO2 dosed tanks where the main N input is fish waste/food, reduced and bound N, moistly as NH4, as NO3 is very mobile in water.........this seems like the main player.
At high CO2, the residual ppm's of NO3 can be saturating, say at 20-30ppm. At that concetration or higher, the uptake is independent of concentration. An eqauilivlent ppm of NH4 will be about 3.5x less.
So 4-5 ppm of NH4. The curve of the NO3 is fairly linear once it gets going to about 18-20ppm.
NH4 is linear mostly.
So 4-5ppm is fairly good for a similar amount.
A daily rate of uptake, assumig n that all NO3 and all NH4 dosed gets to the plants:
1-6 ppm of NO3, with 3-4ppm being a typical max.
0.3ppm to 1.8 per day, with a typical range of 0.8ppm-1.2ppm
You can see that if the NH4 builds up and the bacteria does not respond, you are in trouble using NH4 vs NO3.
Eg if the CO2 goes sour etc.
And you keep adding the NH4.
This is my concern.
Newbies doing it and everyone also bugs me, I know someone will kill their fish doing this, when the gain is still pretty questionable.
I've had better gains by focusing more on reducing Nh4 and dealing with CO2 really well.
You get maybe say 30% more growth with NH4 vs NO3 under some conditions.
But............you get 1000-2000% or more, with good CO2, or say just 300% better with say 15ppm vs 35ppm of CO2.
The greatest N demand is for carbon fixation in the enzyme Rubsico.
So plenty of CO2= less N demand and plenty of ATP's and NADPH's for "work" instead of going after CO2.
You can add it and try it, just be careful in what you conclude. If you run higher lights and are not that good with CO2, this might not be the wisest thing to do.
The above is a good estimative index of NH4, I'd suggest using a daily, even 2x a day dosing, like if you feed the fish 2x daily, you can squirt a bit in(I'd also go liquid like traces to dose more precise amounts).
I might be wrong about algae and NH4 signaling, it might be some dependence on CO2 as well.
The two together seem to wreck havoc, CO2 alone can also. Adaptive issues, species differences and time might also lead us to some wrong conclusions about preference.
It's not an easy thing to get at.
A good study would use N15 and follow who got what as far as a NH4-15 and NO3-15 labeled sources and see if the induced algae spores took the labeled NH4-15.
energetically, there's no argument that NH4 is easier, what the issue is, under our situation and what is best for the method/us/the fish/plants really that much more significant to warrant using and managing something much more volatile??
That is the meat of the issue, the trade off, is it worth it?
Do I want more plant growth? More effective N use?
Maybe not, maybe I have lower light to reduce the issues and work, growth.
Adding more might not be my goal.
As long as the plant has N from some source.
These issues have not been consider thoroughly IMO.
Regards,
Tom Barr