# Nutrient question - concentration



## sWozzAres (30 Jul 2010)

I am reading the EI article on this site.



> We can see therefore that if a 20 Gallon tank is lit by 20 watts of light the uptake is slow, letâ€™s say 1 ppm per day as an example. All I need to do is to ensure that the tank always has at least 1 ppm to supply the needs of the plants in the tank. If I added a second 20 watt bulb the uptake demand would increase to perhaps 2 ppm per day. If I continued to only supply 1 ppm per day the assembly line would soon grind to a halt. I need to supply at least 2 ppm per day.



This essentially says that if a plant requires 1ppm per day, then all that is required is that you have at least 1ppm in your tank and the plant won't have any problems. So how does concentration fit into this?

Let's say you have 2 identical tanks, except the concentration of say Nitrate is 2ppm in one tank and 20ppm in the other. Any plant will have 10x less chance of coming across a Nitrate molecule in the 2ppm tank, than it will in the 20ppm tank, simply by virtue of the fact that it has to wait for molecules to drift past. 

So surely, having 2ppm Nitrate in a tank with a plant that requires 1ppm will mean it grows slower than if it were in a tank with 20ppm. Taking the example in the quote above, a 1ppm plant in a 1ppm tank will not remove 1ppm from the tank because as the concentration drops off to zero, the plant has to wait increasingly longer for a molecule to arrive.


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## ceg4048 (30 Jul 2010)

Hi,
    Yes, I agree with this. Higher nutrient concentrations produce higher growth rates, all other things being equal. At some point the concentration level becomes so high that a further increase in concentration does not produce faster growth rates because nutrient availability will be higher than the ability of the plant to process the nutrients.

I say "all other things being equal", but of course all other things are practically never equal. If flow is anaemic for example then it effectively lowers the odds of the ion finding it's way into the plant. Raising the concentration level above the theoretical upper limits will result in improved performance.

The uptakes and uptake requirements are driven by light. If the concentration levels are below the minimum requirement for the lighting level the result is malnutrition. If the concentration levels are higher than the minimum requirement then the growth rates increase.

Cheers,


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## dw1305 (30 Jul 2010)

Hi all,
I think your right in principle. Here is a quote from Leggett, J. & Frere M. (1971) "Growth and Nutrient Uptake by Soybean Plants in Nutrient Solutions of Graded Concentrations" _Plant Physiology _*48*:457-460. 


> Soybean plants (_Glycine max_ "Hawkeye", grown in nutrient solutions maintained at graded concentrations showed a large response in both shoot dry weight and total ion uptake. Growth rate was dependent upon nutrient concentration, even when quantity of nutrient was not limiting.


 and this one suggests that if plants have been deprived of a nutrient they absorb it preferentially when they are exposed to it.  LEE, R. (1982) "Selectivity and Kinetics of Ion Uptake by Barley Plants Following Nutrient Deficiency" _Annals of Botany_ *50* pp 429-449


> Barley plants grown without an external supply of phosphorus, sulphur, chlorine or nitrogen subsequently absorbed these nutrients, as phosphate, sulphate, chloride and nitrate, more rapidly than did nutrient, sufficient control plants under similar conditions. .....


However, plants are very efficient at obtaining the ions they require from solution, so I don't think that finding the "1 molecule in a million" will be too much of a problem, particularly for plants from naturally nutrient poor habitats. I think that if you want to achieve the maximal growth rate for your plants that nutrients should always be in excess.

Personally I'm more interested in the other end of the spectrum, the slowest growth rate you can have whilst the plant remains healthy. This is going to vary from plant to plant, _Microsorum pteropus_ or a moss might be able to remain healthy where levels of macro-nutrients are only measurable in ppb, whilst a more nutrient demanding plant may decline and be unable to grow at nutrient levels 1 or 2 orders of magnitude greater.

To use an analogy from terrestrial plants, a 100 year old _Cryptomeria japonica_ Bonsai, a Bristlecone Pine (_Pinus aristata_) or a Birch ( _Betula_ spp.) tree from the tundra tree line may be healthy, but only a few cm's high. They haven't achieved anything like their maximum growth rate, but they have managed to survive. 

Similarly a lot of tropical trees (and Ash _Fraxinus excelsior_) show an adaptation called "inanition", where the seedlings can survive many years with little apparent growth when net light levels are just above compensation point, but should a gap occur, say because a "forest giant" tree has fallen, allowing the light in the plants can switch to maximum growth mode, competing to get up into the light before the canopy closes over again. Once this process is switched on they can't revert, it is a "_race for the sun_" and the losers will perish. Most plants don't have this, if light (or any other nutrient) levels are below the threshold needed for normal growth they will die, what differs is the threshold level. As a general rule it is "_live fast and die young_", and all the really old organisms are ones which grow slowly in nutrient depleted conditions (Tortoises, Bristlecone pines, Tuatara, Albatrosses etc. )

cheers Darrel


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## sWozzAres (30 Jul 2010)

So where does EI sit with this, since maximal uptake rate is fundamental to the development of the theory, and uptake rate might depend to some extent on concentration, do we know the concentration levels that were used to get these uptake figures?

Also, is it possible that there is a concentration level above which plant growth is inhibited? 

Darrel - interesting as usual


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## dw1305 (30 Jul 2010)

Hi all,


> Also, is it possible that there is a concentration level above which plant growth is inhibited


 Yes there is, again it will depend on the plant. For all the essential nutrients (both macro & micro elements) as concentration goes up from a minimum the plant growth curve will be sigmoidal, with a linear lower phase (more nutrient, more growth) until it flattens (more nutrient, no more growth) and then eventually growth will decline (more element inhibited growth and eventually death) as the levels of the element either become toxic (at only a few ppm for something like zinc (Zn)) or interfere with the uptake of other essential elements (for example high soil calcium (Ca) levels  interfere with magnesium Mg uptake in Citrus etc.).

It is usually drawn as a parabola, but for an element like N it would be a flat topped parabola, where luxury absorption occurs (the plants takes up the element but growth is not enhanced).






from http://www.netdor.com/ernestm/AGRON2.HTM.

The actual values for the curves depend on nutrient and plant, an example would be the toxicity of "normal" levels of soil P for many S. African and  Australian _Protea & Banksia_ spp. this is because they have evolved to grow in very phosphorus poor conditions, and are extremely efficient at scavenging any available phosphorus, fine when it is, and always will be, in short supply, not so good where it is freely available as they can't stop getting _"too much of a good thing"_, and poison themselves. 



> South African Proteaceae are adapted to the low soil phosphorus (P) concentrations of the Cape Floristic Region. The efficient P uptake by Proteaceae means that these plants experience phosphorus  (P) toxicity at lower rhizosphere [P] levels than crop plants. This is only problematic when cultivating Proteaceae (and many plants from this region) on previously agricultural land with high residual soil [P].



from Hawkins, H-J. _et al_. (2008) "Phosphorus toxicity in the Proteaceae: A problem in post-agricultural lands"
_Scientia Horticulturae_ 117:4, pp 357-365.

cheers Darrel


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## ceg4048 (31 Jul 2010)

sWozzAres said:
			
		

> So where does EI sit with this, since maximal uptake rate is fundamental to the development of the theory...


This is not correct. Maximum uptake rates are not a prerequisite of this methodology. Maximum uptake rates only occur under maximum lighting and unlimited CO2. These are the endpoints of the uptake envelop. EI does not "require" maximum uptake. I think you might have confused this issue. EI does not enforce conditions of maximum uptake. What it can do is to ensure that maximum nutrient uptake will be satisfied if the environmental conditions call for maximum uptake. This is a huge difference. EI ensures that whatever uptake is necessary is satisfied. If your lighting is limited, or if your CO2 is limited then these become the limiting growth factors, not the nutrient loading.



			
				sWozzAres said:
			
		

> ...uptake rate might depend to some extent on concentration, do we know the concentration levels that were used to get these uptake figures?


Under unlimited lighting and unlimited CO2 the unlimited concentration values are clearly listed at the top of the article. This is how the suggested concentration levels were derived and thus, this is how the dosing scheme was developed. EI is a methodology wherein an attempt is made to avoid starvation. No attempt is made to enforce maximum growth rates. 

People seem to get wrapped around the axle on this and yet the concept is so simple. Let's say that in order for the human body to avoid starvation under any set of conditions (running, cold weather, lifting weights) one needs to eat no fewer than 1500 calories per day. I could easily set my eating habits to 1501 calories per day. That would give me a margin of 1 calorie per day under to most stressful conditions. If I were not being stressed, 1500 calories would be more than enough, and my margin of survival would be higher. If it turns out that my regimen was not stressful then it might be that I would burn only 1000 calories per day. Under these conditions I would have a 501 calorie margin for starvation. I would gain weight more quickly compared to the person under duress burning 1500 calories per day. For the 1000 calorie per day person EI allows the daily calorie uptake to be dropped to 1001 calories per day due to the lack of stress, but there is no penalty for keeping the daily uptake to 1501.



			
				sWozzAres said:
			
		

> Also, is it possible that there is a concentration level above which plant growth is inhibited?


For the vast majority of aquatic plants, if there are toxic or inhibitive levels, no one has yet experienced them. I have never seen or heard of a submersed aquatic macrophyte suffering PO4 toxicity, and I have driven the values far beyond what any sane individual would attempt. The more NO3/PO4 I added the more amazing the plant became. The bottom line is that you'll never reach whatever theoretical toxicity limits there are if you follow or even grossly exceed the EI dosing level guidelines. What you will experience if you fall below the dosing requirements for those lighting and CO2 conditions though is failing health, in the same way as if the fellow under duress drops his nutrient intake to below 1500 calories per day.

Extrapolating data obtained from terrestrial plants to aquatics does not always work, so one has to be careful. There are many nutrient toxicity issues in terrestrial plants which are completely irrelevant when applied to S.A.Ms.

Cheers,


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## dw1305 (2 Aug 2010)

Hi all,
We did have a thread on this a while ago. It is here <http://www.ukaps.org/forum/viewtopic.php?f=19&t=8592>. 
I haven't got any experience of growing aquatic plants in very high nutrient situations, although I have worked with both terrestrial plants grown hydroponically, and aquatic macrophytes grown in landfill leachate, in both these cases the levels of salts in the growing medium would be very high, with conductivities of above 3000 micro S (3 milli siemens). 

cheers Darrel


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## sWozzAres (5 Feb 2012)

ceg4048 said:
			
		

> ...The more NO3/PO4 I added the more amazing the plant became. ...



So if your tank is consuming 15ppm NO3 per week, and you are putting 15ppm NO3 into your tank each week, then the plants will do better if you already have say 20ppm in the tank, rather than 5ppm?


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## ceg4048 (5 Feb 2012)

Holy Cow, this thread is from 2 years ago. I can see that I'll need to go get a Master's Degree in advanced "necromongering"...  

Anyway, to try an pick up the pieces of my life (if I can remember what this was all about) what a tank consumes is based not only on demand, but also on what is available. So up to a point, the more you feed the more the plants will uptake. Barr refers to this as "luxury uptake", and it's kind of like putting away pennies in the piggy bank for a rainy day. In any case, yes, satisfying or exceeding the demand is always better than falling below the demand. This is a fundamental pillar of the EI methodology.

Cheers,


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## Morgan Freeman (5 Feb 2012)

Interesting thread, even if I felt I understood E.I before it's always good to refresh.


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## sWozzAres (10 Feb 2012)

so assuming non limiting conditions, there is a "minimum concentration recommendation in order to for a plant to grow consistently throughout the lighting period"

a plant consuming 5ppm a day, in a tank with only 5ppm will slow down in it's growth during the day as it becomes increasingly harder to find the nutrient. put it in water that already has 20ppm and it will grow consistently - nutrient availability is the same, or at least saturates the plants requirement throughout the lighting period

in principal and generally speaking of course

The reason I am interested in this is because I have a new tank and I am dosing daily. During the startup period, I am  doing 95% water changes which effectively resets nutrients. Putting in a daily dose of nutrients after resetting the tank will leave concentration very low so I am wondering if it's better to dose the tank back up to respectable concentration level before resuming daily dosing.


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## ceg4048 (10 Feb 2012)

I reckon you might be over-thinking the whole issue. Unlimited means unlimited, not minimum concentration recommended. When you use a eutrophic dosing scheme like EI you are generally speaking about nutrient concentration levels far above minima. 

Also we're not really concerned about consistency of growth throughout the lighting period. This is not something that we can concern ourselves with because the plant determines when growth occurs. A plant may grow at night, when there is no light. Photosynthesis is all about food production. In between the period of food production and growth lots of other things occur, such as protein production, food storage and translocation - as well as food consumption.

What we're trying to do is to keep the breadbasket full so that when the plant needs a nutrient it's available and can pull it from the location where the nutrient is stored. Have you ever seen  movies or pictures of the front car of a steam locomotive (where is Dolly Sprint 16V when you need him)? There is a pile of coal on the floor to feed the fire. There is a maximum temperature that the fire can reach to make steam and to propel the train. As long as there is sufficient coal and a guy to shovel it into the fire then the locomotive can maintain it's speed. If the guy doing the shoveling runs low on coal or if there is a shortage of water then everything slows down. Eutrophic dosing means that we keep a big enough pile of coal on the floor in front of the guy to shovel into the fire and so he never runs low or has to start thinking about conserving what's left of the fuel on the floor.

So it's not our intent to micromanage growth. A 5ppm per day uptake rate would be far beyond what most tanks can accomplish. After you do a water change then dose your daily amount because it's unlikely that you are anywhere near the maximum uptake concentration levels - unless you are using insane levels of lighting and CO2 and/or if your flow is very weak.

The thing about eutrophic dosing is that you can easily do what you propose; dose double or treble on the water change day and you may see a difference, or you may not. I do not know for sure because I do not know the uptake rates or the dosing rates being used in that particular tank. Or you could just not worry about it and carry on.

If there are no signs of deficiency or no signs of "deficiency related" algae then there really is nothing to worry about. You could also generally dose double every day if you feel that there is a risk of a nutrient shortfall. It's really up to you  to decide how much resulting maintenance, trimming and so forth you want to do. The barometer we use for nutrient dosing as it relates to "minima" is simply the appearance (or lack thereof) of deficiency syndromes and deficiency related algae. If the aquarium is healthy and if there are no deficiency related algae then this is considered a successful strategy. Any concentration level above these values is strictly gravy.

Hope this clarifies.

Cheers,


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## sWozzAres (10 Feb 2012)

ceg, thanks I appreciate your input


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