The Nitrogen response

[Stephen Eugene Robinson]

One of the troubles I have had with my aquaponics tank has been nitrogen buildup in the form of nitrates.   Plants need different nutrients to grow.  Limit one nutrient, and that limits the absorption of all of the others.  I guessed that the limiting nutrient might be either potassium, iron, or magnesium, not sure which would make the difference.  I am still not completely sure, but when I dosed with the 3, the plants went into a growth spurt.  It was like putting a green light on nitrogen use, and the nitrogen in the water dropped.  I saw this this morning, and I was very pleased. I think I will try to find a potassium test kit.  My new Nitrate level is 100ppm and has been cut in half, and I am feeding the fish what they will eat.

 

Another thing I found was a hydroponic model for tomato growth from University of Ohio.  I found a couple things I might be doing that is counterproductive.  For one, in the fruiting stage, soil temperature (read that tank temperature) should be around 72, not 78 like I had it, and pH should be around 6 and not 7.

 

Now these are real numbers with real reasons behind them.  So, last night with great sadness, I lowered the temp on my heating elements.  Even more sadly, my power use will go down.  The pain.  I can also relax and let nature take its course with pH.  My buffer costs will go down.

 

Will all this make a difference?  University of Ohio thinks so.  These guys probably have done scientific tests to back up their claims.

 

I am a retired engineer.  I like claims that have substance behind them, but I will also jump into something like Aquaponics knowing nothing about it - Frantic learning ensues.  Angst at not knowing rules my life, blood pumps, web searches happen, and finally - almost as an afterthought, the nitrogen level normalizes.

 

Sigh

 

Now what?

[Vlad Jovanovic]

Hi Eric. It would be silly to suggest that hydroponic experiments 'don't count' in AP, just that the O.U studies have nothing to say about crashing you bio-filter, mainly because they don't have a bio-filter to contend with :)  And that trying to run a newly cycled AP system under optimal hydroponic pH and/or nutrient levels might not be advisable or even necessary (or even possible for that matter). Most of what we know on the plant side of things comes from the hydro world and are a great source of reading material/info.

Eric Warwick said:

Ok, so hydroponic experiments do "count" in aquaponics because, THAT'S HOW PLANTS GROW. However, if you run your pH too low then a bacteria crash could happen. There are a plethora of reasons why plants don't work sub-optimally. The main reason being nutrient deficiencies. K, Fe, and Mg deficiencies  are actually common so, providing these in a foliar spray you would help the plant grow--take in more nitrates. As for your pH, it's good.

[Nate Storey]

Terri,

You're right the nitrification processes taking place in low pH systems is an interesting phenomena- one that flies in the face of many wastewater studies as well AP teachings.  I believe that we see a combination of sub-optimal nitrification by dominant nitrifyers along with nitrification by other oxidizing bacteria.  Essentially, we're not dealing entirely with the bacterial genera relied upon in waste treatment, but with many other varieties that perform nitrification in more acidic environments (i.e. acidic soils).  There may be more ammonium uptake, but I think that is less likely than nitrification by acid loving nitrifyers.  There needs to be research on this.

Terri Mikkola said:

A few thoughts on Nitrification

TAN is the measurement of both ammonia (NH3) and ammonium (NH4). Which form is present depends on the pH. High pH = NH3 / Low pH = NH4

Nitrification requires NH3 to be present as a food source for Ammonia Oxidizing Bacteria [AOB] (common genera - nitrobactor & nitropira) At a pH of <= 6.5 AOB begin to starve and conversion to nitrite begins to cease.

Both AOB and Nitrite Oxidizing Bacteria [NOB] (common genera - nitrobactor & nitrospira) require a chemical form of carbon (not organic). CO2 (carbon dioxide) and CaCO3 (calcium carbonate a.ka. alkalinity) are common sources of carbon. Low CO2 and/or alkalinity = low carbon availability = death. In addition, the nitrification process itself is acidic and will consume alkalinity.

Note, there is a complex relationship between CO2, carbonic acid, and alkalinity in water, which I won't go into with this post.

Nitrification is an aerobic process (requires dissolved oxygen). For every lb of NH3-N converted to NO3 it takes 4.3 lbs of oxygen.

These principles are standard for wastewater treatment and aquaculture and are the product of hundreds of studies. So why do we see some AP systems with low pH and alkalinity levels produce adequate levels of nitrogen for the plants?

I have a few ideas - not based on research

The majority of nitrifcation studies were performed with waste streams that had higher ammonia concentrations than what would typically be found in low density aquaponic systems. It could be that Nitrospira or another type is more prevalent than Nitrosomonas in LD AP systems because it can thrive with low levels of NH3 and NO2 as would be seen in an acidic environment. Secondly it could be that the NH4/ NO3 ratio is high due to the acidic environment and the plants are uptaking more ammonium than nitrate.

[Vlad Jovanovic]

Hi Nate, 

I think I may have found why the Cu and Zn is a bit as you say "excessive"? This is from a book I've started to re-read since this last discussion...(the italics and bold emphasis are mine)...

Hydroponic Cropping 215

 

…EDTA form of Fe is not recommended since EDTA is toxic to the plant (Rengel,

2002). The chelate diethylenetriaminepentaacetic acid (DTPA) form of Fe is

the accepted chelated form since DTPA toxicity is thought not to exist. Rengel

(2002) observed that the inclusion of Fe-EDTA in a nutrient solution resulted

in reduced uptake and translocation of the micronutrients Cu and Zn within

the plant. It is not known if the DTPA form of chelated Fe will have the same

effect on these two micronutrients. Other chelated forms of Fe, HEEDTA, NTA,

and EDDHA, have been used, but to a lesser degree than either EDTA or

DTPA. Several inorganic forms of Fe have been found suitable as Fe sources

in nutrient solution formulations, such as iron ferrous sulfate, FeSO4•7H2O;

iron ferric sulfate, Fe2(SO4)3; ferric chloride, FeCl3•6H2O; and iron ammonium

sulfate, FeSO4(NH4)2SO4•6H2O.

The author has frequently observed low Cu and Zn contents in tomato

leaf samples submitted for analysis and interpretation. The questions that need

to be answered are, “do these low levels reflect an inadequate amount of Cu

and Zn in the nutrient solution,” or “is it a factor related to cultivar adsorption

capacity, or is it the influence of the Fe chelate in the nutrient solution on

Cu and Zn adsorption?” My best guess would be the influence of the presence

of the chelate in the nutrient solution. In earlier experiments, I have found

that if the Fe source was an inorganic one (see pages 57 and 398), low Cu

and Zn leaf contents were not frequently observed.

Nate Storey said:

Hi Vlad, you have the right idea.  foliar sprays are really good ways to get around pH limitation by carbonates.  The ideal scenario is RO removal of carbonates- but that isn't always realistic.  Different plants have different nutrient requirements in regards to micro, secondary and primary plant nutrients, so you won't always see a lag in nitrate uptake with some crops while others are experiencing the bottleneck, so it's good to keep track and always be watching for the slightest signs of deficiency.  The whole high pH issue can complicate things because relatively small swings can limit certain nutrients that may already be scarce in solution.  It can be a bit complicated so the trick is to control for as many variables as possible and then treat each deficiency in turn.  Using a foliar spray typically gets around this but locks you into a long-term treatment regime as you aren't really treating the problems in-solution.  

Scenarios where this becomes really pronounced are when there's an increase in algal production, when there is a seasonal temperature drop or increase and when pH runs out of the typical system range.  Basically, when system chemistry is off (not outside of "safe" bounds but outside of "normal" bounds)- nutrient issues can become exaggerated.

As for chelated micro nutrients- they work great but are usually unnecessary.  The biggies in AP (because of low conc.s in feed) are Fe, Mg, Zn, and Ca/K (depending on supp.s).  Most systems have some exposed galvanized steel and Zn is really soluble so Zn is usually not a problem (actually, looking at this product, the amount of Zn might actually be a problem for your fish over time- the plants won't take up that much Zn and it's really really toxic to fish), Mg deficiencies will often show up but don't impact production as much as aesthetic most of the time because they're low level deficiencies, so the Ca/K and Fe deficiencies are the real worries.  Chel. Fe is a required addition to almost all AP systems, Chel. Cu- I'm not so sure.  I've never seen an actual Cu deficiency in an AP system or encountered one that I though was a Cu deficiency- It's actually something that you don't really want making it's way into your fish either.  Mn can be deficient, but I think it's rare, and Mo is almost never deficient in AP systems- there's more than enough in fish feed. . .  I think that staying away from copper is a good idea.  I would stick with the Chel. Fe and treat in very low quantities with that particular product very rarely if ever- perhaps save it in case a weird deficiency shows up.   To be fair, I tend to stay away from most micronutrient supp.s because they're expensive and not (in my experience) necessary.  Most commercial fish feeds have more than enough of these micronutrients to suffice and plants require them in extremely low quantities (i.e. there's enough Mo in a healthy seed for many crops that it can often germinate and go though a substantial part of it's life in a Mo absent environment without exhibiting deficiency- just living off of the Mo in the seed from it's mother plant.)   That's not to say this stuff would hurt your system (except Cu buildup-and it would over time- that amount of Cu is a bit excessive if you ask me. . . and probable the Zn too), that's just to say it's unnecessary.

Sorry about the novel.

Nate

Vlad Jovanovic said:

That's really good to know Nate. I had no idea that such a deficiency could cause such a dramatic difference in nitrate uptake. Is this true with non-fruiting/short term plants like lettuce as well? Are there any set of conditions where this phenomenon becomes more pronounced than others? I have relatively hard water and I'll have 18,000 liters of it, so I probably wont be buffering my system with KHCO3 soon after cycling. I had hoped to use home-brewed worm tea as a foliar spray and thought that that if I use KHCO3 in that way (foliar spary early on) as well, it could be detrimental to the "living web" of beneficial organism that worm tea seems to produce on leaves. Do you feel that this is a safe assumption?

 

My other question if i may is, what are your thoughts on adding chelated (EDTA) micro nutrients (fish safeness)? The product I have access to is:

 Fe 0.76%

Mn 3.48%

Mo 0.485%

Zn 1.02%

Cu 0.76% (this is the one that worries me most, is this a valid concern at this concentration)

I have a separate EDDHA Fe 6% for iron that I was hoping to alternate between with the above product, unless the above product is a no go... 

I would really appreciate your thoughts on all these things.

Nate Storey said:

Vlad, Stephen is right- nitrates can become limited, not in solution but in plant uptake and metabolism if there is another major limiting plant nutrient (K is most common when hydrated lime is being used to raise pH).  You can impact uptake rates by supplementing scarce or absent nutrients- so what Stephen saw in his nitrate drop was probably a real result of nutrient supplementation of an absent or scarce nutrient.  Now the trick Stephen, is to figure out what nutrient your system needs.  What do you raise pH with?  If it's hydrated lime then I guarantee it's most likely a solution K deficiency.  If you switch to KOH for pH moderation, you'll see a bump in nitrate consumption.  Ca and K compete, in solution so most likely your K is precipitating out.  Have you noticed any plant nutrient deficiency symptoms?  Another one might be Mg.  I would encourage the occasional supp. of epsom salts-magnesium sulfate as well.  

I run two 2000 gallon systems consistently between the high fives and about 6.4.  Why? Because I have massive enough BSA that my nitrification rates are still acceptable.  My systems run consistently between 0.5 and 1.0 ppm ammonia as a result, but that's not enough to impact fish health, and definitely maximizes my plant nutrient uptake.  It lets me push my plants on pretty rigorous schedules and turn out top-quality stuff.  Lower pHs will always perform a little better from a plant production perspective, and if your fish are adjusted it usually isn't a problem!

[Nate Storey]

Nice find Vlad!  I've wondered about this- I'm not sure if it's interference with active uptake (passively or actively) or whether it's a nutrient addition/dosage issue. . . It seems to me that it might be both- I think that many managers are wary of micronutrients that lead to toxicities so they err on the side of less rather than more in regards to Cu and Zn.  With Zn, too, I think that people forget that increased levels of P and Fe in solution reduce the availability of Zn- so when Zn deficiencies become apparent it's more likely tied to higher P conc.s.  But I also think there's a physiological reason for reduced uptake- one of my theories is that active uptake of these elements by plant produced chelation means that the plant will actively bind and move whatever chelated ion is most prevalent in solution- so, you end up with high concentrations of chelated iron in solution that outcompetes the chelated Zn, Cu for absorption.  I really don't know- just a guess at one or two of the dozens of interesting interactions that are likely happening. . . I think the author is definitely onto something when he talks about chelated Fe liminting Zn and Cu though- probably a competition thing.  Hmm.  I'll have to hunt down that book and read up!  Thanks for the insight!

Vlad Jovanovic said:

Hi Nate, 

I think I may have found why the Cu and Zn is a bit as you say "excessive"? This is from a book I've started to re-read since this last discussion...(the italics and bold emphasis are mine)...

Hydroponic Cropping 215

 

…EDTA form of Fe is not recommended since EDTA is toxic to the plant (Rengel,

2002). The chelate diethylenetriaminepentaacetic acid (DTPA) form of Fe is

the accepted chelated form since DTPA toxicity is thought not to exist. Rengel

(2002) observed that the inclusion of Fe-EDTA in a nutrient solution resulted

in reduced uptake and translocation of the micronutrients Cu and Zn within

the plant. It is not known if the DTPA form of chelated Fe will have the same

effect on these two micronutrients. Other chelated forms of Fe, HEEDTA, NTA,

and EDDHA, have been used, but to a lesser degree than either EDTA or

DTPA. Several inorganic forms of Fe have been found suitable as Fe sources

in nutrient solution formulations, such as iron ferrous sulfate, FeSO4•7H2O;

iron ferric sulfate, Fe2(SO4)3; ferric chloride, FeCl3•6H2O; and iron ammonium

sulfate, FeSO4(NH4)2SO4•6H2O.

The author has frequently observed low Cu and Zn contents in tomato

leaf samples submitted for analysis and interpretation. The questions that need

to be answered are, “do these low levels reflect an inadequate amount of Cu

and Zn in the nutrient solution,” or “is it a factor related to cultivar adsorption

capacity, or is it the influence of the Fe chelate in the nutrient solution on

Cu and Zn adsorption?” My best guess would be the influence of the presence

of the chelate in the nutrient solution. In earlier experiments, I have found

that if the Fe source was an inorganic one (see pages 57 and 398), low Cu

and Zn leaf contents were not frequently observed.

Nate Storey said:

Hi Vlad, you have the right idea.  foliar sprays are really good ways to get around pH limitation by carbonates.  The ideal scenario is RO removal of carbonates- but that isn't always realistic.  Different plants have different nutrient requirements in regards to micro, secondary and primary plant nutrients, so you won't always see a lag in nitrate uptake with some crops while others are experiencing the bottleneck, so it's good to keep track and always be watching for the slightest signs of deficiency.  The whole high pH issue can complicate things because relatively small swings can limit certain nutrients that may already be scarce in solution.  It can be a bit complicated so the trick is to control for as many variables as possible and then treat each deficiency in turn.  Using a foliar spray typically gets around this but locks you into a long-term treatment regime as you aren't really treating the problems in-solution.  

Scenarios where this becomes really pronounced are when there's an increase in algal production, when there is a seasonal temperature drop or increase and when pH runs out of the typical system range.  Basically, when system chemistry is off (not outside of "safe" bounds but outside of "normal" bounds)- nutrient issues can become exaggerated.

As for chelated micro nutrients- they work great but are usually unnecessary.  The biggies in AP (because of low conc.s in feed) are Fe, Mg, Zn, and Ca/K (depending on supp.s).  Most systems have some exposed galvanized steel and Zn is really soluble so Zn is usually not a problem (actually, looking at this product, the amount of Zn might actually be a problem for your fish over time- the plants won't take up that much Zn and it's really really toxic to fish), Mg deficiencies will often show up but don't impact production as much as aesthetic most of the time because they're low level deficiencies, so the Ca/K and Fe deficiencies are the real worries.  Chel. Fe is a required addition to almost all AP systems, Chel. Cu- I'm not so sure.  I've never seen an actual Cu deficiency in an AP system or encountered one that I though was a Cu deficiency- It's actually something that you don't really want making it's way into your fish either.  Mn can be deficient, but I think it's rare, and Mo is almost never deficient in AP systems- there's more than enough in fish feed. . .  I think that staying away from copper is a good idea.  I would stick with the Chel. Fe and treat in very low quantities with that particular product very rarely if ever- perhaps save it in case a weird deficiency shows up.   To be fair, I tend to stay away from most micronutrient supp.s because they're expensive and not (in my experience) necessary.  Most commercial fish feeds have more than enough of these micronutrients to suffice and plants require them in extremely low quantities (i.e. there's enough Mo in a healthy seed for many crops that it can often germinate and go though a substantial part of it's life in a Mo absent environment without exhibiting deficiency- just living off of the Mo in the seed from it's mother plant.)   That's not to say this stuff would hurt your system (except Cu buildup-and it would over time- that amount of Cu is a bit excessive if you ask me. . . and probable the Zn too), that's just to say it's unnecessary.

Sorry about the novel.

Nate

Vlad Jovanovic said:

That's really good to know Nate. I had no idea that such a deficiency could cause such a dramatic difference in nitrate uptake. Is this true with non-fruiting/short term plants like lettuce as well? Are there any set of conditions where this phenomenon becomes more pronounced than others? I have relatively hard water and I'll have 18,000 liters of it, so I probably wont be buffering my system with KHCO3 soon after cycling. I had hoped to use home-brewed worm tea as a foliar spray and thought that that if I use KHCO3 in that way (foliar spary early on) as well, it could be detrimental to the "living web" of beneficial organism that worm tea seems to produce on leaves. Do you feel that this is a safe assumption?

 

My other question if i may is, what are your thoughts on adding chelated (EDTA) micro nutrients (fish safeness)? The product I have access to is:

 Fe 0.76%

Mn 3.48%

Mo 0.485%

Zn 1.02%

Cu 0.76% (this is the one that worries me most, is this a valid concern at this concentration)

I have a separate EDDHA Fe 6% for iron that I was hoping to alternate between with the above product, unless the above product is a no go... 

I would really appreciate your thoughts on all these things.

Nate Storey said:

Vlad, Stephen is right- nitrates can become limited, not in solution but in plant uptake and metabolism if there is another major limiting plant nutrient (K is most common when hydrated lime is being used to raise pH).  You can impact uptake rates by supplementing scarce or absent nutrients- so what Stephen saw in his nitrate drop was probably a real result of nutrient supplementation of an absent or scarce nutrient.  Now the trick Stephen, is to figure out what nutrient your system needs.  What do you raise pH with?  If it's hydrated lime then I guarantee it's most likely a solution K deficiency.  If you switch to KOH for pH moderation, you'll see a bump in nitrate consumption.  Ca and K compete, in solution so most likely your K is precipitating out.  Have you noticed any plant nutrient deficiency symptoms?  Another one might be Mg.  I would encourage the occasional supp. of epsom salts-magnesium sulfate as well.  

I run two 2000 gallon systems consistently between the high fives and about 6.4.  Why? Because I have massive enough BSA that my nitrification rates are still acceptable.  My systems run consistently between 0.5 and 1.0 ppm ammonia as a result, but that's not enough to impact fish health, and definitely maximizes my plant nutrient uptake.  It lets me push my plants on pretty rigorous schedules and turn out top-quality stuff.  Lower pHs will always perform a little better from a plant production perspective, and if your fish are adjusted it usually isn't a problem!

[Vlad Jovanovic]

In the previous paragraphs the author spoke of just what you had said about (excessive) P and its relation to Zn uptake...

"...excessive P (greater than 1.00% of the dry weight) in recently mature leaves can result in
Zn deficiency (Jones, 1998a)...

So I'm thinking maybe the manufacturers of this type of product try to compensate (for possible situations like your theory) by bumping up the Cu and Zn, thereby increasing (or what would 'normally be' "overdoing it") their concentrations and thereby (hoping to achieve) an increase in uptake..? (that last one is just my theory, so it very well may not be so... :)

Nate Storey said:

Nice find Vlad!  I've wondered about this- I'm not sure if it's interference with active uptake (passively or actively) or whether it's a nutrient addition/dosage issue. . . It seems to me that it might be both- I think that many managers are wary of micronutrients that lead to toxicities so they err on the side of less rather than more in regards to Cu and Zn.  With Zn, too, I think that people forget that increased levels of P and Fe in solution reduce the availability of Zn- so when Zn deficiencies become apparent it's more likely tied to higher P conc.s.  But I also think there's a physiological reason for reduced uptake- one of my theories is that active uptake of these elements by plant produced chelation means that the plant will actively bind and move whatever chelated ion is most prevalent in solution- so, you end up with high concentrations of chelated iron in solution that outcompetes the chelated Zn, Cu for absorption.  I really don't know- just a guess at one or two of the dozens of interesting interactions that are likely happening. . . I think the author is definitely onto something when he talks about chelated Fe liminting Zn and Cu though- probably a competition thing.  Hmm.  I'll have to hunt down that book and read up!  Thanks for the insight!

Vlad Jovanovic said:

Hi Nate, 

I think I may have found why the Cu and Zn is a bit as you say "excessive"? This is from a book I've started to re-read since this last discussion...(the italics and bold emphasis are mine)...

Hydroponic Cropping 215

 

…EDTA form of Fe is not recommended since EDTA is toxic to the plant (Rengel,

2002). The chelate diethylenetriaminepentaacetic acid (DTPA) form of Fe is

the accepted chelated form since DTPA toxicity is thought not to exist. Rengel

(2002) observed that the inclusion of Fe-EDTA in a nutrient solution resulted

in reduced uptake and translocation of the micronutrients Cu and Zn within

the plant. It is not known if the DTPA form of chelated Fe will have the same

effect on these two micronutrients. Other chelated forms of Fe, HEEDTA, NTA,

and EDDHA, have been used, but to a lesser degree than either EDTA or

DTPA. Several inorganic forms of Fe have been found suitable as Fe sources

in nutrient solution formulations, such as iron ferrous sulfate, FeSO4•7H2O;

iron ferric sulfate, Fe2(SO4)3; ferric chloride, FeCl3•6H2O; and iron ammonium

sulfate, FeSO4(NH4)2SO4•6H2O.

The author has frequently observed low Cu and Zn contents in tomato

leaf samples submitted for analysis and interpretation. The questions that need

to be answered are, “do these low levels reflect an inadequate amount of Cu

and Zn in the nutrient solution,” or “is it a factor related to cultivar adsorption

capacity, or is it the influence of the Fe chelate in the nutrient solution on

Cu and Zn adsorption?” My best guess would be the influence of the presence

of the chelate in the nutrient solution. In earlier experiments, I have found

that if the Fe source was an inorganic one (see pages 57 and 398), low Cu

and Zn leaf contents were not frequently observed.

Nate Storey said:

Hi Vlad, you have the right idea.  foliar sprays are really good ways to get around pH limitation by carbonates.  The ideal scenario is RO removal of carbonates- but that isn't always realistic.  Different plants have different nutrient requirements in regards to micro, secondary and primary plant nutrients, so you won't always see a lag in nitrate uptake with some crops while others are experiencing the bottleneck, so it's good to keep track and always be watching for the slightest signs of deficiency.  The whole high pH issue can complicate things because relatively small swings can limit certain nutrients that may already be scarce in solution.  It can be a bit complicated so the trick is to control for as many variables as possible and then treat each deficiency in turn.  Using a foliar spray typically gets around this but locks you into a long-term treatment regime as you aren't really treating the problems in-solution.  

Scenarios where this becomes really pronounced are when there's an increase in algal production, when there is a seasonal temperature drop or increase and when pH runs out of the typical system range.  Basically, when system chemistry is off (not outside of "safe" bounds but outside of "normal" bounds)- nutrient issues can become exaggerated.

As for chelated micro nutrients- they work great but are usually unnecessary.  The biggies in AP (because of low conc.s in feed) are Fe, Mg, Zn, and Ca/K (depending on supp.s).  Most systems have some exposed galvanized steel and Zn is really soluble so Zn is usually not a problem (actually, looking at this product, the amount of Zn might actually be a problem for your fish over time- the plants won't take up that much Zn and it's really really toxic to fish), Mg deficiencies will often show up but don't impact production as much as aesthetic most of the time because they're low level deficiencies, so the Ca/K and Fe deficiencies are the real worries.  Chel. Fe is a required addition to almost all AP systems, Chel. Cu- I'm not so sure.  I've never seen an actual Cu deficiency in an AP system or encountered one that I though was a Cu deficiency- It's actually something that you don't really want making it's way into your fish either.  Mn can be deficient, but I think it's rare, and Mo is almost never deficient in AP systems- there's more than enough in fish feed. . .  I think that staying away from copper is a good idea.  I would stick with the Chel. Fe and treat in very low quantities with that particular product very rarely if ever- perhaps save it in case a weird deficiency shows up.   To be fair, I tend to stay away from most micronutrient supp.s because they're expensive and not (in my experience) necessary.  Most commercial fish feeds have more than enough of these micronutrients to suffice and plants require them in extremely low quantities (i.e. there's enough Mo in a healthy seed for many crops that it can often germinate and go though a substantial part of it's life in a Mo absent environment without exhibiting deficiency- just living off of the Mo in the seed from it's mother plant.)   That's not to say this stuff would hurt your system (except Cu buildup-and it would over time- that amount of Cu is a bit excessive if you ask me. . . and probable the Zn too), that's just to say it's unnecessary.

Sorry about the novel.

Nate

Vlad Jovanovic said:

That's really good to know Nate. I had no idea that such a deficiency could cause such a dramatic difference in nitrate uptake. Is this true with non-fruiting/short term plants like lettuce as well? Are there any set of conditions where this phenomenon becomes more pronounced than others? I have relatively hard water and I'll have 18,000 liters of it, so I probably wont be buffering my system with KHCO3 soon after cycling. I had hoped to use home-brewed worm tea as a foliar spray and thought that that if I use KHCO3 in that way (foliar spary early on) as well, it could be detrimental to the "living web" of beneficial organism that worm tea seems to produce on leaves. Do you feel that this is a safe assumption?

 

My other question if i may is, what are your thoughts on adding chelated (EDTA) micro nutrients (fish safeness)? The product I have access to is:

 Fe 0.76%

Mn 3.48%

Mo 0.485%

Zn 1.02%

Cu 0.76% (this is the one that worries me most, is this a valid concern at this concentration)

I have a separate EDDHA Fe 6% for iron that I was hoping to alternate between with the above product, unless the above product is a no go... 

I would really appreciate your thoughts on all these things.

Nate Storey said:

Vlad, Stephen is right- nitrates can become limited, not in solution but in plant uptake and metabolism if there is another major limiting plant nutrient (K is most common when hydrated lime is being used to raise pH).  You can impact uptake rates by supplementing scarce or absent nutrients- so what Stephen saw in his nitrate drop was probably a real result of nutrient supplementation of an absent or scarce nutrient.  Now the trick Stephen, is to figure out what nutrient your system needs.  What do you raise pH with?  If it's hydrated lime then I guarantee it's most likely a solution K deficiency.  If you switch to KOH for pH moderation, you'll see a bump in nitrate consumption.  Ca and K compete, in solution so most likely your K is precipitating out.  Have you noticed any plant nutrient deficiency symptoms?  Another one might be Mg.  I would encourage the occasional supp. of epsom salts-magnesium sulfate as well.  

I run two 2000 gallon systems consistently between the high fives and about 6.4.  Why? Because I have massive enough BSA that my nitrification rates are still acceptable.  My systems run consistently between 0.5 and 1.0 ppm ammonia as a result, but that's not enough to impact fish health, and definitely maximizes my plant nutrient uptake.  It lets me push my plants on pretty rigorous schedules and turn out top-quality stuff.  Lower pHs will always perform a little better from a plant production perspective, and if your fish are adjusted it usually isn't a problem!

[Vlad Jovanovic]

Jones, J. Benton, 1930–
Hydroponics : a practical guide for the soilless grower / J. Benton Jones, Jr. — 2nd ed.
p. cm.
Includes bibliographical references and index.
ISBN 0-8493-3167-6 (alk. paper)
1. Hydroponics. I. Title.
SB126 .5 .J65 2005

here is the info on the book. Second edition from 2005 if your interested. 

Vlad Jovanovic said:

In the previous paragraphs the author spoke of just what you had said about (excessive) P and its relation to Zn uptake...

"...excessive P (greater than 1.00% of the dry weight) in recently mature leaves can result in
Zn deficiency (Jones, 1998a)...

So I'm thinking maybe the manufacturers of this type of product try to compensate (for possible situations like your theory) by bumping up the Cu and Zn, thereby increasing (or what would 'normally be' "overdoing it") their concentrations and thereby (hoping to achieve) an increase in uptake..? (that last one is just my theory, so it very well may not be so... :)

Nate Storey said:

Nice find Vlad!  I've wondered about this- I'm not sure if it's interference with active uptake (passively or actively) or whether it's a nutrient addition/dosage issue. . . It seems to me that it might be both- I think that many managers are wary of micronutrients that lead to toxicities so they err on the side of less rather than more in regards to Cu and Zn.  With Zn, too, I think that people forget that increased levels of P and Fe in solution reduce the availability of Zn- so when Zn deficiencies become apparent it's more likely tied to higher P conc.s.  But I also think there's a physiological reason for reduced uptake- one of my theories is that active uptake of these elements by plant produced chelation means that the plant will actively bind and move whatever chelated ion is most prevalent in solution- so, you end up with high concentrations of chelated iron in solution that outcompetes the chelated Zn, Cu for absorption.  I really don't know- just a guess at one or two of the dozens of interesting interactions that are likely happening. . . I think the author is definitely onto something when he talks about chelated Fe liminting Zn and Cu though- probably a competition thing.  Hmm.  I'll have to hunt down that book and read up!  Thanks for the insight!

Vlad Jovanovic said:

Hi Nate, 

I think I may have found why the Cu and Zn is a bit as you say "excessive"? This is from a book I've started to re-read since this last discussion...(the italics and bold emphasis are mine)...

Hydroponic Cropping 215

 

…EDTA form of Fe is not recommended since EDTA is toxic to the plant (Rengel,

2002). The chelate diethylenetriaminepentaacetic acid (DTPA) form of Fe is

the accepted chelated form since DTPA toxicity is thought not to exist. Rengel

(2002) observed that the inclusion of Fe-EDTA in a nutrient solution resulted

in reduced uptake and translocation of the micronutrients Cu and Zn within

the plant. It is not known if the DTPA form of chelated Fe will have the same

effect on these two micronutrients. Other chelated forms of Fe, HEEDTA, NTA,

and EDDHA, have been used, but to a lesser degree than either EDTA or

DTPA. Several inorganic forms of Fe have been found suitable as Fe sources

in nutrient solution formulations, such as iron ferrous sulfate, FeSO4•7H2O;

iron ferric sulfate, Fe2(SO4)3; ferric chloride, FeCl3•6H2O; and iron ammonium

sulfate, FeSO4(NH4)2SO4•6H2O.

The author has frequently observed low Cu and Zn contents in tomato

leaf samples submitted for analysis and interpretation. The questions that need

to be answered are, “do these low levels reflect an inadequate amount of Cu

and Zn in the nutrient solution,” or “is it a factor related to cultivar adsorption

capacity, or is it the influence of the Fe chelate in the nutrient solution on

Cu and Zn adsorption?” My best guess would be the influence of the presence

of the chelate in the nutrient solution. In earlier experiments, I have found

that if the Fe source was an inorganic one (see pages 57 and 398), low Cu

and Zn leaf contents were not frequently observed.

Nate Storey said:

Hi Vlad, you have the right idea.  foliar sprays are really good ways to get around pH limitation by carbonates.  The ideal scenario is RO removal of carbonates- but that isn't always realistic.  Different plants have different nutrient requirements in regards to micro, secondary and primary plant nutrients, so you won't always see a lag in nitrate uptake with some crops while others are experiencing the bottleneck, so it's good to keep track and always be watching for the slightest signs of deficiency.  The whole high pH issue can complicate things because relatively small swings can limit certain nutrients that may already be scarce in solution.  It can be a bit complicated so the trick is to control for as many variables as possible and then treat each deficiency in turn.  Using a foliar spray typically gets around this but locks you into a long-term treatment regime as you aren't really treating the problems in-solution.  

Scenarios where this becomes really pronounced are when there's an increase in algal production, when there is a seasonal temperature drop or increase and when pH runs out of the typical system range.  Basically, when system chemistry is off (not outside of "safe" bounds but outside of "normal" bounds)- nutrient issues can become exaggerated.

As for chelated micro nutrients- they work great but are usually unnecessary.  The biggies in AP (because of low conc.s in feed) are Fe, Mg, Zn, and Ca/K (depending on supp.s).  Most systems have some exposed galvanized steel and Zn is really soluble so Zn is usually not a problem (actually, looking at this product, the amount of Zn might actually be a problem for your fish over time- the plants won't take up that much Zn and it's really really toxic to fish), Mg deficiencies will often show up but don't impact production as much as aesthetic most of the time because they're low level deficiencies, so the Ca/K and Fe deficiencies are the real worries.  Chel. Fe is a required addition to almost all AP systems, Chel. Cu- I'm not so sure.  I've never seen an actual Cu deficiency in an AP system or encountered one that I though was a Cu deficiency- It's actually something that you don't really want making it's way into your fish either.  Mn can be deficient, but I think it's rare, and Mo is almost never deficient in AP systems- there's more than enough in fish feed. . .  I think that staying away from copper is a good idea.  I would stick with the Chel. Fe and treat in very low quantities with that particular product very rarely if ever- perhaps save it in case a weird deficiency shows up.   To be fair, I tend to stay away from most micronutrient supp.s because they're expensive and not (in my experience) necessary.  Most commercial fish feeds have more than enough of these micronutrients to suffice and plants require them in extremely low quantities (i.e. there's enough Mo in a healthy seed for many crops that it can often germinate and go though a substantial part of it's life in a Mo absent environment without exhibiting deficiency- just living off of the Mo in the seed from it's mother plant.)   That's not to say this stuff would hurt your system (except Cu buildup-and it would over time- that amount of Cu is a bit excessive if you ask me. . . and probable the Zn too), that's just to say it's unnecessary.

Sorry about the novel.

Nate

Vlad Jovanovic said:

That's really good to know Nate. I had no idea that such a deficiency could cause such a dramatic difference in nitrate uptake. Is this true with non-fruiting/short term plants like lettuce as well? Are there any set of conditions where this phenomenon becomes more pronounced than others? I have relatively hard water and I'll have 18,000 liters of it, so I probably wont be buffering my system with KHCO3 soon after cycling. I had hoped to use home-brewed worm tea as a foliar spray and thought that that if I use KHCO3 in that way (foliar spary early on) as well, it could be detrimental to the "living web" of beneficial organism that worm tea seems to produce on leaves. Do you feel that this is a safe assumption?

 

My other question if i may is, what are your thoughts on adding chelated (EDTA) micro nutrients (fish safeness)? The product I have access to is:

 Fe 0.76%

Mn 3.48%

Mo 0.485%

Zn 1.02%

Cu 0.76% (this is the one that worries me most, is this a valid concern at this concentration)

I have a separate EDDHA Fe 6% for iron that I was hoping to alternate between with the above product, unless the above product is a no go... 

I would really appreciate your thoughts on all these things.

Nate Storey said:

Vlad, Stephen is right- nitrates can become limited, not in solution but in plant uptake and metabolism if there is another major limiting plant nutrient (K is most common when hydrated lime is being used to raise pH).  You can impact uptake rates by supplementing scarce or absent nutrients- so what Stephen saw in his nitrate drop was probably a real result of nutrient supplementation of an absent or scarce nutrient.  Now the trick Stephen, is to figure out what nutrient your system needs.  What do you raise pH with?  If it's hydrated lime then I guarantee it's most likely a solution K deficiency.  If you switch to KOH for pH moderation, you'll see a bump in nitrate consumption.  Ca and K compete, in solution so most likely your K is precipitating out.  Have you noticed any plant nutrient deficiency symptoms?  Another one might be Mg.  I would encourage the occasional supp. of epsom salts-magnesium sulfate as well.  

I run two 2000 gallon systems consistently between the high fives and about 6.4.  Why? Because I have massive enough BSA that my nitrification rates are still acceptable.  My systems run consistently between 0.5 and 1.0 ppm ammonia as a result, but that's not enough to impact fish health, and definitely maximizes my plant nutrient uptake.  It lets me push my plants on pretty rigorous schedules and turn out top-quality stuff.  Lower pHs will always perform a little better from a plant production perspective, and if your fish are adjusted it usually isn't a problem!

[Nate Storey]

I bet you're right Vlad- the issues with P compet. with Zn is a concentration issue more than anything else.  Without reducing P (which might not be possible for some hydro. producers) you can only increase Zn to alleviate the effects of in-solution competition and selective uptake.  I bet they formulate "early" formulas for really balanced systems and more heavy-handed "heavy" formulas with higher micronutrient conc.s for when solutions start to swerve into higher concentrations of one element or another. . . which raises some interesting questions for AP practitioners- for us P removal can only happen as discharge or as biomass. . . so perhaps larger producers need to consider a nutrient moderation bed where P removal or biological manipuation of certain elements can take place.  I've considered this for chelation (using barley beds to produce chelatins for my system), but I'm starting to believe that these types of remediation beds have a place in systems for a number of reasons- especially nutrient moderation.

Vlad Jovanovic said:

In the previous paragraphs the author spoke of just what you had said about (excessive) P and its relation to Zn uptake...

"...excessive P (greater than 1.00% of the dry weight) in recently mature leaves can result in
Zn deficiency (Jones, 1998a)...

So I'm thinking maybe the manufacturers of this type of product try to compensate (for possible situations like your theory) by bumping up the Cu and Zn, thereby increasing (or what would 'normally be' "overdoing it") their concentrations and thereby (hoping to achieve) an increase in uptake..? (that last one is just my theory, so it very well may not be so...

Nate Storey said:

Nice find Vlad!  I've wondered about this- I'm not sure if it's interference with active uptake (passively or actively) or whether it's a nutrient addition/dosage issue. . . It seems to me that it might be both- I think that many managers are wary of micronutrients that lead to toxicities so they err on the side of less rather than more in regards to Cu and Zn.  With Zn, too, I think that people forget that increased levels of P and Fe in solution reduce the availability of Zn- so when Zn deficiencies become apparent it's more likely tied to higher P conc.s.  But I also think there's a physiological reason for reduced uptake- one of my theories is that active uptake of these elements by plant produced chelation means that the plant will actively bind and move whatever chelated ion is most prevalent in solution- so, you end up with high concentrations of chelated iron in solution that outcompetes the chelated Zn, Cu for absorption.  I really don't know- just a guess at one or two of the dozens of interesting interactions that are likely happening. . . I think the author is definitely onto something when he talks about chelated Fe liminting Zn and Cu though- probably a competition thing.  Hmm.  I'll have to hunt down that book and read up!  Thanks for the insight!

Vlad Jovanovic said:

Hi Nate, 

I think I may have found why the Cu and Zn is a bit as you say "excessive"? This is from a book I've started to re-read since this last discussion...(the italics and bold emphasis are mine)...

Hydroponic Cropping 215

 

…EDTA form of Fe is not recommended since EDTA is toxic to the plant (Rengel,

2002). The chelate diethylenetriaminepentaacetic acid (DTPA) form of Fe is

the accepted chelated form since DTPA toxicity is thought not to exist. Rengel

(2002) observed that the inclusion of Fe-EDTA in a nutrient solution resulted

in reduced uptake and translocation of the micronutrients Cu and Zn within

the plant. It is not known if the DTPA form of chelated Fe will have the same

effect on these two micronutrients. Other chelated forms of Fe, HEEDTA, NTA,

and EDDHA, have been used, but to a lesser degree than either EDTA or

DTPA. Several inorganic forms of Fe have been found suitable as Fe sources

in nutrient solution formulations, such as iron ferrous sulfate, FeSO4•7H2O;

iron ferric sulfate, Fe2(SO4)3; ferric chloride, FeCl3•6H2O; and iron ammonium

sulfate, FeSO4(NH4)2SO4•6H2O.

The author has frequently observed low Cu and Zn contents in tomato

leaf samples submitted for analysis and interpretation. The questions that need

to be answered are, “do these low levels reflect an inadequate amount of Cu

and Zn in the nutrient solution,” or “is it a factor related to cultivar adsorption

capacity, or is it the influence of the Fe chelate in the nutrient solution on

Cu and Zn adsorption?” My best guess would be the influence of the presence

of the chelate in the nutrient solution. In earlier experiments, I have found

that if the Fe source was an inorganic one (see pages 57 and 398), low Cu

and Zn leaf contents were not frequently observed.

Nate Storey said:

Hi Vlad, you have the right idea.  foliar sprays are really good ways to get around pH limitation by carbonates.  The ideal scenario is RO removal of carbonates- but that isn't always realistic.  Different plants have different nutrient requirements in regards to micro, secondary and primary plant nutrients, so you won't always see a lag in nitrate uptake with some crops while others are experiencing the bottleneck, so it's good to keep track and always be watching for the slightest signs of deficiency.  The whole high pH issue can complicate things because relatively small swings can limit certain nutrients that may already be scarce in solution.  It can be a bit complicated so the trick is to control for as many variables as possible and then treat each deficiency in turn.  Using a foliar spray typically gets around this but locks you into a long-term treatment regime as you aren't really treating the problems in-solution.  

Scenarios where this becomes really pronounced are when there's an increase in algal production, when there is a seasonal temperature drop or increase and when pH runs out of the typical system range.  Basically, when system chemistry is off (not outside of "safe" bounds but outside of "normal" bounds)- nutrient issues can become exaggerated.

As for chelated micro nutrients- they work great but are usually unnecessary.  The biggies in AP (because of low conc.s in feed) are Fe, Mg, Zn, and Ca/K (depending on supp.s).  Most systems have some exposed galvanized steel and Zn is really soluble so Zn is usually not a problem (actually, looking at this product, the amount of Zn might actually be a problem for your fish over time- the plants won't take up that much Zn and it's really really toxic to fish), Mg deficiencies will often show up but don't impact production as much as aesthetic most of the time because they're low level deficiencies, so the Ca/K and Fe deficiencies are the real worries.  Chel. Fe is a required addition to almost all AP systems, Chel. Cu- I'm not so sure.  I've never seen an actual Cu deficiency in an AP system or encountered one that I though was a Cu deficiency- It's actually something that you don't really want making it's way into your fish either.  Mn can be deficient, but I think it's rare, and Mo is almost never deficient in AP systems- there's more than enough in fish feed. . .  I think that staying away from copper is a good idea.  I would stick with the Chel. Fe and treat in very low quantities with that particular product very rarely if ever- perhaps save it in case a weird deficiency shows up.   To be fair, I tend to stay away from most micronutrient supp.s because they're expensive and not (in my experience) necessary.  Most commercial fish feeds have more than enough of these micronutrients to suffice and plants require them in extremely low quantities (i.e. there's enough Mo in a healthy seed for many crops that it can often germinate and go though a substantial part of it's life in a Mo absent environment without exhibiting deficiency- just living off of the Mo in the seed from it's mother plant.)   That's not to say this stuff would hurt your system (except Cu buildup-and it would over time- that amount of Cu is a bit excessive if you ask me. . . and probable the Zn too), that's just to say it's unnecessary.

Sorry about the novel.

Nate

Vlad Jovanovic said:

That's really good to know Nate. I had no idea that such a deficiency could cause such a dramatic difference in nitrate uptake. Is this true with non-fruiting/short term plants like lettuce as well? Are there any set of conditions where this phenomenon becomes more pronounced than others? I have relatively hard water and I'll have 18,000 liters of it, so I probably wont be buffering my system with KHCO3 soon after cycling. I had hoped to use home-brewed worm tea as a foliar spray and thought that that if I use KHCO3 in that way (foliar spary early on) as well, it could be detrimental to the "living web" of beneficial organism that worm tea seems to produce on leaves. Do you feel that this is a safe assumption?

 

My other question if i may is, what are your thoughts on adding chelated (EDTA) micro nutrients (fish safeness)? The product I have access to is:

 Fe 0.76%

Mn 3.48%

Mo 0.485%

Zn 1.02%

Cu 0.76% (this is the one that worries me most, is this a valid concern at this concentration)

I have a separate EDDHA Fe 6% for iron that I was hoping to alternate between with the above product, unless the above product is a no go... 

I would really appreciate your thoughts on all these things.

Nate Storey said:

Vlad, Stephen is right- nitrates can become limited, not in solution but in plant uptake and metabolism if there is another major limiting plant nutrient (K is most common when hydrated lime is being used to raise pH).  You can impact uptake rates by supplementing scarce or absent nutrients- so what Stephen saw in his nitrate drop was probably a real result of nutrient supplementation of an absent or scarce nutrient.  Now the trick Stephen, is to figure out what nutrient your system needs.  What do you raise pH with?  If it's hydrated lime then I guarantee it's most likely a solution K deficiency.  If you switch to KOH for pH moderation, you'll see a bump in nitrate consumption.  Ca and K compete, in solution so most likely your K is precipitating out.  Have you noticed any plant nutrient deficiency symptoms?  Another one might be Mg.  I would encourage the occasional supp. of epsom salts-magnesium sulfate as well.  

I run two 2000 gallon systems consistently between the high fives and about 6.4.  Why? Because I have massive enough BSA that my nitrification rates are still acceptable.  My systems run consistently between 0.5 and 1.0 ppm ammonia as a result, but that's not enough to impact fish health, and definitely maximizes my plant nutrient uptake.  It lets me push my plants on pretty rigorous schedules and turn out top-quality stuff.  Lower pHs will always perform a little better from a plant production perspective, and if your fish are adjusted it usually isn't a problem!

[Vlad Jovanovic]

Interesting...I can see where such a bed my come in handy as excessive P almost always seems to be more of a problem than it's deficiency.

 The 'heavy handed' formula was all that I could find here, so mixing up my own nutrient formulas is looking more and more appealing (and possibly necessary:)... I have like 5 or 6 different experiments going on from organic hydro, peeponics, a couple of different temp related ones etc.. I pulled the plug on a couple of greenhouse temp related ones today and will try to write up the details in a couple of updates and/or new blogs (nothing terribly exiting, just some things that happen to be of interest to me that I would like to do and see for myself... Here is a picture I took earlier today of what I believe is actually temperature related P deficiency. This pepper plant was fed a P rich nutrient solution every 3 days (Secondary and TE's included) primary nutes 13-40-30 alternating with 20-5-10 at EC1.8micro seimens each for the 4 weeks that it spent in isolation (it was 4 1/2 weeks old and growing normally prior to that). 'Ample' lighting was used, but I kept it at temps well below optimum (12-17 Celsius). Which I believe interfered with P uptake. That much I'm certain of, but

what I don't know though is weather P, like FE is mobile in plants. I have begun 'flushing' and will tone down the nutes just a bit and see what happens now that is is in a much more temperature friendly environment. (25 to 32 degrees Celsius). What I am certain of is that the plant will make a complete recovery as far as new growth is concerned. What I don't know is whether the already affected leaves will revert to a normal state. I'm sure that I could just Google it (or even ask you :) but where the fun be in that? 

Nate Storey said:

I bet you're right Vlad- the issues with P compet. with Zn is a concentration issue more than anything else.  Without reducing P (which might not be possible for some hydro. producers) you can only increase Zn to alleviate the effects of in-solution competition and selective uptake.  I bet they formulate "early" formulas for really balanced systems and more heavy-handed "heavy" formulas with higher micronutrient conc.s for when solutions start to swerve into higher concentrations of one element or another. . . which raises some interesting questions for AP practitioners- for us P removal can only happen as discharge or as biomass. . . so perhaps larger producers need to consider a nutrient moderation bed where P removal or biological manipuation of certain elements can take place.  I've considered this for chelation (using barley beds to produce chelatins for my system), but I'm starting to believe that these types of remediation beds have a place in systems for a number of reasons- especially nutrient moderation.

Vlad Jovanovic said:

In the previous paragraphs the author spoke of just what you had said about (excessive) P and its relation to Zn uptake...

"...excessive P (greater than 1.00% of the dry weight) in recently mature leaves can result in
Zn deficiency (Jones, 1998a)...

So I'm thinking maybe the manufacturers of this type of product try to compensate (for possible situations like your theory) by bumping up the Cu and Zn, thereby increasing (or what would 'normally be' "overdoing it") their concentrations and thereby (hoping to achieve) an increase in uptake..? (that last one is just my theory, so it very well may not be so...

Nate Storey said:

Nice find Vlad!  I've wondered about this- I'm not sure if it's interference with active uptake (passively or actively) or whether it's a nutrient addition/dosage issue. . . It seems to me that it might be both- I think that many managers are wary of micronutrients that lead to toxicities so they err on the side of less rather than more in regards to Cu and Zn.  With Zn, too, I think that people forget that increased levels of P and Fe in solution reduce the availability of Zn- so when Zn deficiencies become apparent it's more likely tied to higher P conc.s.  But I also think there's a physiological reason for reduced uptake- one of my theories is that active uptake of these elements by plant produced chelation means that the plant will actively bind and move whatever chelated ion is most prevalent in solution- so, you end up with high concentrations of chelated iron in solution that outcompetes the chelated Zn, Cu for absorption.  I really don't know- just a guess at one or two of the dozens of interesting interactions that are likely happening. . . I think the author is definitely onto something when he talks about chelated Fe liminting Zn and Cu though- probably a competition thing.  Hmm.  I'll have to hunt down that book and read up!  Thanks for the insight!

Vlad Jovanovic said:

Hi Nate, 

I think I may have found why the Cu and Zn is a bit as you say "excessive"? This is from a book I've started to re-read since this last discussion...(the italics and bold emphasis are mine)...

Hydroponic Cropping 215

 

…EDTA form of Fe is not recommended since EDTA is toxic to the plant (Rengel,

2002). The chelate diethylenetriaminepentaacetic acid (DTPA) form of Fe is

the accepted chelated form since DTPA toxicity is thought not to exist. Rengel

(2002) observed that the inclusion of Fe-EDTA in a nutrient solution resulted

in reduced uptake and translocation of the micronutrients Cu and Zn within

the plant. It is not known if the DTPA form of chelated Fe will have the same

effect on these two micronutrients. Other chelated forms of Fe, HEEDTA, NTA,

and EDDHA, have been used, but to a lesser degree than either EDTA or

DTPA. Several inorganic forms of Fe have been found suitable as Fe sources

in nutrient solution formulations, such as iron ferrous sulfate, FeSO4•7H2O;

iron ferric sulfate, Fe2(SO4)3; ferric chloride, FeCl3•6H2O; and iron ammonium

sulfate, FeSO4(NH4)2SO4•6H2O.

The author has frequently observed low Cu and Zn contents in tomato

leaf samples submitted for analysis and interpretation. The questions that need

to be answered are, “do these low levels reflect an inadequate amount of Cu

and Zn in the nutrient solution,” or “is it a factor related to cultivar adsorption

capacity, or is it the influence of the Fe chelate in the nutrient solution on

Cu and Zn adsorption?” My best guess would be the influence of the presence

of the chelate in the nutrient solution. In earlier experiments, I have found

that if the Fe source was an inorganic one (see pages 57 and 398), low Cu

and Zn leaf contents were not frequently observed.

Nate Storey said:

Hi Vlad, you have the right idea.  foliar sprays are really good ways to get around pH limitation by carbonates.  The ideal scenario is RO removal of carbonates- but that isn't always realistic.  Different plants have different nutrient requirements in regards to micro, secondary and primary plant nutrients, so you won't always see a lag in nitrate uptake with some crops while others are experiencing the bottleneck, so it's good to keep track and always be watching for the slightest signs of deficiency.  The whole high pH issue can complicate things because relatively small swings can limit certain nutrients that may already be scarce in solution.  It can be a bit complicated so the trick is to control for as many variables as possible and then treat each deficiency in turn.  Using a foliar spray typically gets around this but locks you into a long-term treatment regime as you aren't really treating the problems in-solution.  

Scenarios where this becomes really pronounced are when there's an increase in algal production, when there is a seasonal temperature drop or increase and when pH runs out of the typical system range.  Basically, when system chemistry is off (not outside of "safe" bounds but outside of "normal" bounds)- nutrient issues can become exaggerated.

As for chelated micro nutrients- they work great but are usually unnecessary.  The biggies in AP (because of low conc.s in feed) are Fe, Mg, Zn, and Ca/K (depending on supp.s).  Most systems have some exposed galvanized steel and Zn is really soluble so Zn is usually not a problem (actually, looking at this product, the amount of Zn might actually be a problem for your fish over time- the plants won't take up that much Zn and it's really really toxic to fish), Mg deficiencies will often show up but don't impact production as much as aesthetic most of the time because they're low level deficiencies, so the Ca/K and Fe deficiencies are the real worries.  Chel. Fe is a required addition to almost all AP systems, Chel. Cu- I'm not so sure.  I've never seen an actual Cu deficiency in an AP system or encountered one that I though was a Cu deficiency- It's actually something that you don't really want making it's way into your fish either.  Mn can be deficient, but I think it's rare, and Mo is almost never deficient in AP systems- there's more than enough in fish feed. . .  I think that staying away from copper is a good idea.  I would stick with the Chel. Fe and treat in very low quantities with that particular product very rarely if ever- perhaps save it in case a weird deficiency shows up.   To be fair, I tend to stay away from most micronutrient supp.s because they're expensive and not (in my experience) necessary.  Most commercial fish feeds have more than enough of these micronutrients to suffice and plants require them in extremely low quantities (i.e. there's enough Mo in a healthy seed for many crops that it can often germinate and go though a substantial part of it's life in a Mo absent environment without exhibiting deficiency- just living off of the Mo in the seed from it's mother plant.)   That's not to say this stuff would hurt your system (except Cu buildup-and it would over time- that amount of Cu is a bit excessive if you ask me. . . and probable the Zn too), that's just to say it's unnecessary.

Sorry about the novel.

Nate

Vlad Jovanovic said:

That's really good to know Nate. I had no idea that such a deficiency could cause such a dramatic difference in nitrate uptake. Is this true with non-fruiting/short term plants like lettuce as well? Are there any set of conditions where this phenomenon becomes more pronounced than others? I have relatively hard water and I'll have 18,000 liters of it, so I probably wont be buffering my system with KHCO3 soon after cycling. I had hoped to use home-brewed worm tea as a foliar spray and thought that that if I use KHCO3 in that way (foliar spary early on) as well, it could be detrimental to the "living web" of beneficial organism that worm tea seems to produce on leaves. Do you feel that this is a safe assumption?

 

My other question if i may is, what are your thoughts on adding chelated (EDTA) micro nutrients (fish safeness)? The product I have access to is:

 Fe 0.76%

Mn 3.48%

Mo 0.485%

Zn 1.02%

Cu 0.76% (this is the one that worries me most, is this a valid concern at this concentration)

I have a separate EDDHA Fe 6% for iron that I was hoping to alternate between with the above product, unless the above product is a no go... 

I would really appreciate your thoughts on all these things.

Nate Storey said:

Vlad, Stephen is right- nitrates can become limited, not in solution but in plant uptake and metabolism if there is another major limiting plant nutrient (K is most common when hydrated lime is being used to raise pH).  You can impact uptake rates by supplementing scarce or absent nutrients- so what Stephen saw in his nitrate drop was probably a real result of nutrient supplementation of an absent or scarce nutrient.  Now the trick Stephen, is to figure out what nutrient your system needs.  What do you raise pH with?  If it's hydrated lime then I guarantee it's most likely a solution K deficiency.  If you switch to KOH for pH moderation, you'll see a bump in nitrate consumption.  Ca and K compete, in solution so most likely your K is precipitating out.  Have you noticed any plant nutrient deficiency symptoms?  Another one might be Mg.  I would encourage the occasional supp. of epsom salts-magnesium sulfate as well.  

I run two 2000 gallon systems consistently between the high fives and about 6.4.  Why? Because I have massive enough BSA that my nitrification rates are still acceptable.  My systems run consistently between 0.5 and 1.0 ppm ammonia as a result, but that's not enough to impact fish health, and definitely maximizes my plant nutrient uptake.  It lets me push my plants on pretty rigorous schedules and turn out top-quality stuff.  Lower pHs will always perform a little better from a plant production perspective, and if your fish are adjusted it usually isn't a problem!

[Nate Storey]

Interesting Vlad- I'll be excited to hear what you find out.  In regards to P mobility in the plant- I won't ruin it for you.  :)  You can usually figure out whether a nutrient is mobile or not by figuring out what it is used for. . . and then figuring out if this is something that can be dissasembled and moved somewhere else, or is just discarded with the primary cell structure when that particular tissue dies. . . this has been a very fun conversation by the way.  Plant nutrients are so much fun.

[Vlad Jovanovic]

Thanks Nate, its always a pleasure (as well as a huge learning experience) conversing with you...

Shucks, when you put it that way (about mobility and what the element is used for) I think I have a pretty good idea now of what will happen and whether P is mobile or not...

Since I do remember that P is an important component of DNA as well as RNA and that both are linked together by P bonds...P certainly should be vital in building proteins and probably other important compounds. Very basic important to energy type compounds like ATP (in which P also plays a vital role) which a plant produces through photosynthesis (which I'm guessing is why plants deficient in P are always so stunted and stay small)...I'm also sure that the purple discoloration is caused by the build up of sugars (also energy related), though excactly how and why the purple and not say, orange I have no idea . My guess based on the info you gave me to work with, is that P is probably SUPER DUPER mobile in plants..?

[Marc]

Hydro vs Aqua

VERY DIFFERENT... In a hydro system YOU provide ALL the food, the plants will need specific pH ranges (plant dependant, know you plants requirements). Lower pH in water vs soil (usually between 5.8 - 6.2) for most plants, fyi. Different nutes for different plants... Nitrate vs Ammonia

Aquaponics and higher pH. (here is your tip of the week) One reason you see your pH maintaining at around 7-8 is due to the bacteria itself (bacteria tend to be high pH whereas fungi will lower in pH). They, the bacteria, WILL raise the pH naturally. The whole reason the plants in the aquaponic system are able to "pull" nutrients outside an "optimal pH" isn't so much the resting pH, it's the living microbes within the system breaking things down and making them plant available regardless of pH. Bacteria, fungi, nematodes (good ones), zoa's etc are what feed a plant living in the soil or an organic based water system, they create the perfect environment around the rhizosphere and 'carry' the food to the roots. People don't realize that a plant will release an exudate (carbon/carbo) via the root system to attract the other microbes... In essense the plants tell the soil, or in this case, the water they are hungry.

The way plants feed in a water based system depends on the inputs. IF you use a chemical/synth fertilizer, they will be immediately available to the plant as soon as they hit the roots they wash over and the pH is acceptable, whereas in your aquaponic system the microbes are what make the nutrient bio-available via their life processes. In a chemical based system pH maintainence is critical because outside of the correct parameters that nutrient will NOT be available or worse precipitate out (as so stated below due to bicarbonates, you can use an RO filter to remove the bicarbonates, fyi). This is not the case with aquaponics, due to the living ecosystem constantly battling in the tank and the beds.

We add worms to the substrate why? to break down food? somewhat, more so to add MORE microbes to the "stew" Microbes that will balance the formula for reasons scientist world wide still have yet to understand fully...

As for aqua deficiency's usually - K, Ca, Fe as stated below knowing which is the culprit can be tricky! K - leaf margins brown out and die, Ca - spotting of the leaf usually near its tip, Fe - detected easily due to new growth being white-ish.

Media issue stated below, LECA - lightwieght expanded clay aggrogate/Hydroton/Co-co puffs, is high in pH, 7.5 roughly, it WILL effect the pH of the solution. I use expanded shale which has a pH around 7.1 but as an added bonus sports high amounts of silicate (K)... Just something I've learned via trial and error (as is most of what I know).

Hope this helped a little,
M

[Vlad Jovanovic]

Agreed. Although I believe you meant to say that nitrifying bacteria will lower your system pH over time, and not raise it...

Though I have to disagree that maintaining a certain pH range is not critical in AP. You will crash your bio-filter if you let your pH (which again, due to the nitrification process constantly lowering pH over time) fall to low and do not intervene to buffer it back up. A system crash to me would be a critical event