Good bookmark worthy link on plant nuttrients/ratios

Tom Barr

Staff member
Jan 23, 2005
The Relative Nutrient Requirements of Plants

Figure 1 gives an explanation why a limiting nutrients can still produce growth, however, generally at a reduced slower rate. If you limit a nutrient too strongly, then you pass a threshold and stunt or harm the plant so much that it's hard for it to recover.

You'll also note that "maximum yield" in the second part's Law of diminishing soil yield = to maximum sustained growth rates essentially. Your total yield will decline if you limit a nutrients/CO2 or light.

Now look at Baule's General Effect Law.
Note that effect was the same even though the dose was changed for each test plot.

Now to an aquarists, how might that appear say if you did a lean vs a rich dosing routine?

Pretty much the same.
However, the total growth would be more in the richer routine.

This too had issues with "h".

See Figures 2-3.
Liebscher's Law of the Optimum.

Efficacy, we can modify things easily in our tanks to target this range.
If kept stable over several week's time, the plants will really go to town and grow like mad.

Now look at figure 4.
If we always maintain luxury consumption(the right hand side of that graph). then grow rate is not affected.

If you go down to the min, we still have growth, less etc, but no death/real issues, but if you go below that for any one nutrient, then you have a very bad situation.

At issues is why go that low or allow this?
In agriculture production, fertilizers cost $$, so they try and maximize the use.
Not really an issue in our tanks, cost of ferts relative to tank size is minimal.

Some enjoy false claims as to algae at higher levels, but these are resoundly and easily falsified as reasons, poor methodologies are root cause for failure rather than the method or high nutrients.

If you maintain nutrients above that critical level, you will have rapid healthy growth.

Note, these studies where done under non CO2 limiting conditions, adding that very critical part to such studies with aquatic submersed vegetation is very important to consider.

Now look at figs 7-8.

This is how one nutrients can affect the other.
This is very common and why correlation is not causation for nutrients.

If you limit say CO2, how would that affect NO3 uptake?
Would it slow it down?
Yes, it would.

This increase in NO3 ppms or less uptake might be construed as excess NO3 = algae. Note, that few give hard data for how much excess is, they know that it increases and the reports for how much ppm are all over the place.

Likewise, an increase in PO4 led many to conclude PO4 excess = algae as well.

Today we know neither is the true, I was able to isolate and prove that these where the limiting nutrients controlling algae in our tanks.

There are still folks that want to claim otherwise.

However, they are easily falsified, yet enjoy spreading the myth. such myths do little for the hobby.

Also, you'll note that this simple concpet and information about the correlative effect on other nutrients and limitation have been around for many many years now. This is nothing new.

I am not "smart" etc, I just am skeptical. Then I go about setting things up to see.

I am still mythed given the available information out there, that many folks in the hobby as well as companies still maintain that excess NO3/PO4 cause algae in planted tanks.

When I nail them on it, they then switch over to fish health, that too is something they have never bothered to test to see if their hypothesis is correct either. :rolleyes: :rolleyes:
Is there no end to the mockery of logic?

The information is available, they just have not bothered to look it up or correct themselves. Either they do not care any longer, know they are wrong but keep looking anyways ( fooled into believing correlation = causation, keep looking pal!), perhaps it's just pride alone, I cannot say.

Still, it worries me that such folks give advice in this hobby that, researchers, farmers and horticulturist know not to be true and have tested.

More in the next post.

Tom Barr

Tom Barr

Staff member
Jan 23, 2005
Take a look at Figure 9.
Assume that the nutrient B is Nitrogen, say NO3.
And that nutrient A is CO2 or carbon.

See how a 5ppm NO3 affects the uptake of CO2?
Do you think the demand for CO2 is more critical in that case or at 40ppm?

How about timing of dosing?
Would you have more wiggle room if you dosed say 5x a week at 5ppm or 1x a week?

How about at 40ppm?
1x a week or 5x a week?

You might have excess, but the rate will be more stable for uptake of both A and B.

We do a water change to prevent he build up using EI and virtually every method has some export or has a lower rate of growth(less light/CO2 limitation etc) to manage NO3.

Look at figure 10 and how it affects the other nutrient again.

Look at Figure 11 now.
This one is interesting as the responses to different nutrients, NH4 and K+, produce quite different shaped curves.

How might adding NH4 vs K+ influence plants in our system?
How might excess K+ cause some to believe that their stunted tips are K+ blocking Ca++ when others cannot reproduce the affect when done on purpose in a reference tank?

NH4 is pretty steady going up, K flattens pretty quick.

Finally the last section/figures involves growth trajectories.
These are more real world models.

Through time growth will slow down in many species, but most of the aquatic plants if pruned and kept somewhat constant will keep the high growth rate up.

If you reduce light, obviously the growth rate will slow and the nutrient uptake will slow as well, CO2 demand etc.

Give this a good read.
Then you can go beat up on Amano's claims about algae, or Dupla or whom ever or other folks that make correlation their causation.

Learn and isolate things, test them to see if they are true, do not assume things that often appear to conflict with the observations.

Tom Barr