# Citrate test



## Rick (Jul 26, 2015)

Applying lemon juice as a source of citric and malic acid

Photo on top is supardii seedlings on July 4






Photo on bottom is today. Tried to get shot in same position, same time of day/light.
Probably just my imagination, but the bigger ones look greener.

The premiss is also very old school

https://books.google.com/books?id=H...citrate and nitrate balance in plants&f=false


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## polyantha (Jul 26, 2015)

Interesting test. I can already tell what ppl will discuss here soon. Hint: green leaves :evil:


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## SlipperFan (Jul 26, 2015)

How much lemon juice? How often?


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## gonewild (Jul 26, 2015)

Why are the plants yellow to begin with? oke:


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## Ozpaph (Jul 26, 2015)

nice roots coming out of the baskets.


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## Brabantia (Jul 27, 2015)

gonewild said:


> Why are the plants yellow to begin with? oke:


I suppose you want to say: why your leaves are turning yellow?
read :Here specialy the before last cause.
It may be also in relationship with the all nitrate fertilyser. A pinch of ammonium is not nocive. I am now using a fertiliser having 1/6 of its nitrogen in ammonium form because we have observed the same leaves yellowing with our Belgian MSU version.


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## gonewild (Jul 27, 2015)

Brabantia said:


> I suppose you want to say: why your leaves are turning yellow?
> read :Here specialy the before last cause.
> It may be also in relationship with the all nitrate fertilyser. A pinch of ammonium is not nocive. I am now using a fertiliser having 1/6 of its nitrogen in ammonium form because we have observed the same leaves yellowing with our Belgian MSU version.



Not exactly.... I was not asking why the leaves are "turning" yellow.
For the most part Ricks plants are not yellow so my question was directed at why these particular ones are yellow. I'm interested to know what is different with these, without assuming his fertilizer formula is not correct.


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## eggshells (Jul 27, 2015)

Probably the acid reduced the pH.


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## Rick (Jul 27, 2015)

SlipperFan said:


> How much lemon juice? How often?



I used a tablespoon per gallon of fert/irrigation water.

The crazy part is that the first application was only 24 hours prior to taking picture #2.

They are even greener today!


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## Rick (Jul 27, 2015)

eggshells said:


> Probably the acid reduced the pH.



Check out that link at the bottom of the page.

Providing an H+ sink for nitrate uptake is probably part of it. But citrate and malate have special contributions to plant metabolism


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## Rick (Jul 27, 2015)

gonewild said:


> For the most part Ricks plants are not yellow so my question was directed at why these particular ones are yellow. I'm interested to know what is different with these, without assuming his fertilizer formula is not correct.



Yes my question to figure out why particular plants and not universal.

My first whack is that nitrate uptake causes an alkalinity buildup in the roots.

So you need an acid sink to void the OH or you will reduce the uptake of nitrate. Also several metal become non available if root environment pH goes up (especially iron). 

Now if you water a lot with low alkalinity you can counter OH buildup. Add more moss, use ammonia instead of nitrate (see Brabantia's comment).... lots of ways to skin the "cat".

But since plants make and store lots of citrate and malic acids to specifically counter the above alkalinity dilemma, I thought I'd give this route a shot.



But


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## gonewild (Jul 27, 2015)

Rick said:


> Yes my question to figure out why particular plants and not universal.
> 
> My first whack is that nitrate uptake causes an alkalinity buildup in the roots.
> 
> ...



You said you "think" you say greening of the leaves the next day. That is something have have seen recently also. I've been testing a seaweed extract product being made by a Peruvian company. Used as a foliar spray I noticed leaves were darker green the next day. Can't explain the rapid reaction.
I started combining Humic/Fulvic acid with the seaweed spray and the result is darker green leaves in a rapid response.

I'm applying the mix only to the foliage and aerial roots on Phals and not watering the media. Are you using the citric acid in the irrigation water along with fertilizer or as a foliar spray?


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## Rick (Jul 27, 2015)

gonewild said:


> I'm applying the mix only to the foliage and aerial roots on Phals and not watering the media. Are you using the citric acid in the irrigation water along with fertilizer or as a foliar spray?



Total irrigation drench, but spraying the leaves too. Came across a paper on effects to sweet basil, and it needs to go through the roots for max effect (comparison of foliar trial to hydroponic trial).

And to be specific, I'm using lemon juice which has about 1g/oz of citric acid and about 1/20th malic acid + and whatever unknowns.

Since just about every plant makes citric and malic acid, it should be in kelp products too. But since I stopped using kelp a long time ago its not part of this trial.


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## gonewild (Jul 27, 2015)

Rick said:


> Total irrigation drench, but spraying the leaves too. Came across a paper on effects to sweet basil, and it needs to go through the roots for max effect (comparison of foliar trial to hydroponic trial).
> 
> And to be specific, I'm using lemon juice which has about 1g/oz of citric acid and about 1/20th malic acid + and whatever unknowns.
> 
> Since just about every plant makes citric and malic acid, it should be in kelp products too. But since I stopped using kelp a long time ago its not part of this trial.



Since I see a similar rapid green effect without the soil drench maybe your results are not do to altering the root zone as much as altering the leaf.
I don't remember if the seaweed extract I'm testing has citric acid but it is very different from the typical kelp, I think I sent you a copy of the analysis some time back. I'll try to find out if it does have citric acid.
Have you tried using humic/fulvic acid instead of the citric?


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## Rick (Jul 27, 2015)

gonewild said:


> Have you tried using humic/fulvic acid instead of the citric?



Nope, but lots of precedent for citric acid already.

1)Frequently used as a metals chelator in fertilizers now
2)Frequently used as a pH regulator for commercial greenhouse irrigation water.
3) Plants naturally contain citrate and malic acid in them to use for things like Nitrate transport.
4) Citrate is a common ingredient in orchid flasking media

5) I used lemon juice a lot lately for removing hard water deposits from plant leaves (Stone hates that white @%[email protected]$ on my plants), and I noticed a bump in "greenness" a day or so after cleaning off the leaves. Lemon juice contains about 1 gram/oz of citric acid and about 0.05g/oz of malic acid.

Although this would suggest a foliar input, that 1977 link I attached (under the pics) would suggest this is primarily a root zone function. But this is really hard to separate in practical application. For instance after wiping off the leaves I would hose down the plant so whatever was on the leaves would drip down to the roots.

Might also look to see expected citrate exudates from mosses and lichens.
But there is also a lot of pH regulation that goes on in the rhyzosphere that goes on between the plant, bacteria, fungi, and bryophytes.


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## Rick (Aug 2, 2015)

eggshells said:


> Probably the acid reduced the pH.



Well I checked pH for a 1/tblspn per gal addition and the pH is low (~4.0)

But I'm also starting out with very low alkalinity in the irrigation water, so easy to push pH down. I'm going to check different dilutions of lemon juice for pH and alkalinity.


Also noting that lemon juice has quite a bit of calcium, magnesium, and potassium (!!!)

So certainly not a very controled way of testing citrate only.:wink:

Although it seems to be producing all around positive results.


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## gonewild (Aug 2, 2015)

The Ag supply stores here have 50kg sacks of Citric acid. I have no idea what they use it for. I'll have to ask. It cant be to lower pH because low acidity here is a major problem.


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## Rick (Aug 2, 2015)

gonewild said:


> The Ag supply stores here have 50kg sacks of Citric acid. I have no idea what they use it for. I'll have to ask. It cant be to lower pH because low acidity here is a major problem.



http://www.ces.ncsu.edu/depts/hort/floriculture/plugs/alkalinity.pdf

Here's a pretty good article on the use of various acids (including citric) for adjusting irrigation water pH / alkalinity. It also has a pretty good treatise on the difference between pH and alkalinity, with the correct application of acids based on alkalinity control rather than pH.

I believe there's a lot more to the story of citrate and malate than just pH.


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## Rick (Aug 2, 2015)

Ok

After taking a series of dilutions to the lab, my starting pH of my fert/irrigation water is 6.8su with alkalinity of only 20. It only took 1/8 - 1/4 tsp/gal of lemon juice to drop the pH to around 5.0 - 5.5. 

So 1tblspoon per gal is major overkill if you're not battling a bunch of stored alkalinity.

I need to run a couple pour through's.:wink:


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## Secundino (Aug 3, 2015)

Isn't citric acid - lemon juice - very unstable? The buffer system of a given amount of water usually is tending to return to the first values, more so if in contact with any kind of substrate. Ask someone with fish tanks!
Years ago I tried to reduce the pH of my aquaria with lemon juice (and with wine-vinegar without sulfites) and the resulting mess (yes I did know before, but somehow didn't want to believe it) was terrible. Lemon juice was directly - two hours!! - transformed by bacteria into white clouds (=more bacteria!) which consumed the oxygen of the well aired tank; I had to evacuate all fish and shrimps - they survived all - and after changing the complete water body three times, the aquarium was stable again, with the same pH it had before the catastrophe. 
Quint essence: organic acids are readily consumed by soil bacteria (essentially the same in water bodies) wich feed the plants. 
If you want to reduce the pH consistently, you'd have to use a strong acid (HCl); it works and favours ... algae!
But of course, for plants the use of citric acid with this side effect would be desirable.


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## Ray (Aug 3, 2015)

Aquatic systems and soils are entirely different environments from most orchid media. I fail to see how there would be a problem with the use of citric acid. Let's not forget that both MSU formulas and K-Lite contain it to increase solubility.

I also don't see how the use of a strong acid favors algae.


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## Secundino (Aug 3, 2015)

Of course the environment is different. I was not speaking about environments. I was speaking about water, precisely water bodies. If you water an orchid - in whatever a soil, soil-substrate, hidroponic methods - there is a water body in touch with that substrate and the roots. This water body may be continuous or intermittent (to our eyes), but it is there and the physics and chemical process' are essentially the same. The way an acid changes the pH is identical, and the way substrate maintains the buffer system of the water is identical. I did not say that the buffer system is the same for each and every body of water, I do say that the buffering system works accordingly. 

In one of the spanish orchid forums there are momentaneously praising the benefits of watering with sugar water. Well, the effect is just the same: the glucose boosts the microbial community in the substrate which in turn results in more metabolites available for the plant roots.
evil: Waiting for the complaints about ants and pathological fungi which benefit equally!)

I strongly feel I shouldn't have compared to my aquaria (orthodox orchidist are very huffy with this things), I just wanted to try to explain this observation Rick had made: The crazy part is that the first application was only 24 hours prior to taking picture #2. And (you are free to believe it) lemon juice is very quickly metabolised.

And I don't know HOW mineral acids favour algae growth; though I've an idea; I just can tell that this are my observations.


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## naoki (Aug 3, 2015)

Lime/Ca induced Fe deficiency?

It seems a bit far-fetched that the color changes in 24 hours, but if you look at the p.9 of the following, there are some experiments of acid foliar application to re-green Fe deficient leaves.

https://www.researchgate.net/profil..._L.)_trees/links/0fcfd50b77f3de7c31000000.pdf

One hypothesis is that physiologically inactive Fe pools in the leaf apoplast (outside of the cells in the cell walls) get remobilized by the lower pH of apoplast (from the intro of the paper).


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## Stone (Aug 3, 2015)

I used citric acid for years to bring water pH down from 10 to 6.
Works fine.


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## gonewild (Aug 3, 2015)

The greening effect is probably not related to pH but rather to some form of chelation. Since lemon juice contains both citric and salicylic acids this study may explain the foliar application result.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4215826/

It's possible that the acid combination chelated iron within the leaf and the iron allowed for more chlorophyll production in a fast 24 hour period.... maybe.

I don't think that a pH change would cause the leaves to get greener in 24 hours.


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## myxodex (Aug 6, 2015)

Interesting result and discussion. I second Rick's comment that these TCA cycle have special roles in metabolism. Both plants and fungi excrete organic acids into their substrates. Malic, citric, succinic and fumaric acids have been detected in forest leaf litter in some studies. 

For me the most curious effect of these acids is that discovered in the 1970's in the plant tissue culture setting. Oddly, NH4 is used rather poorly as a sole N source for plant cells in tissue culture. This can be boosted by adding one of the TCA organic acids to the medium; succinic and alpha-ketoglutaric are the most effective, but both citric and malic acids have an effect. Sorry I didn't copy the link to this but the reference is below. 
Behrend,J. and Mateles, R.I. (1976) Plant Physiol 58: 510 - 512

Another intriguing study by the same group indicates that the use of nitrate as the sole N source can be inhibited by adding single amino acids to the medium, all that is except arginine (and possibly alanine) which also can counter the inhibitory effect of the others when added together.
Behrend,J. and Mateles, R.I. (1975) Plant Physiol 56: 584 - 589


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## Rick (Aug 11, 2015)

I was out of town all last week and my wife didn't give any lemon juice the entire time. But progress in general continues. I've restarted the lemon juice at ~1/8 tsp per gallon of fertigation water.


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## Rick (Aug 11, 2015)

gonewild said:


> The greening effect is probably not related to pH but rather to some form of chelation. Since lemon juice contains both citric and salicylic acids this study may explain the foliar application result.
> http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4215826/
> 
> It's possible that the acid combination chelated iron within the leaf and the iron allowed for more chlorophyll production in a fast 24 hour period.... maybe.
> ...



There's also some evidence that plants can use organic acids as a source of carbon for respiration (which ultimately is the whole point of photosynthesizing in the first place).


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## gonewild (Aug 11, 2015)

Rick said:


> There's also some evidence that plants can use organic acids as a source of carbon for respiration (which ultimately is the whole point of photosynthesizing in the first place).



If lemon juice is providing needed carbon, wouldn't this indicate a shortage of carbon in the atmosphere?


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## Secundino (Aug 11, 2015)

Yes, definitely. We'are out of CO2.


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## Rick (Aug 11, 2015)

gonewild said:


> If lemon juice is providing needed carbon, wouldn't this indicate a shortage of carbon in the atmosphere?



No, but organisms are conservative. Why waste energy fixing carbon from CO2 if you can get prefixed food from other sources in the environment?


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## cnycharles (Aug 15, 2015)

Could be other limiting factor restricting the normal carbon uptake, or the organic acids greening things up is like us eating white bread or soda and getting a boost


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## Rick (Oct 4, 2015)

*Found a new cool paper*

http://www.hindawi.com/journals/aag/2014/147278/

Gives doses too.

Note indications for use of both malic and citric acids which both found in lemon juice.


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## Rick (Oct 18, 2015)

cnycharles said:


> Could be other limiting factor restricting the normal carbon uptake, or the organic acids greening things up is like us eating white bread or soda and getting a boost
> 
> 
> Sent from my iPhone using Tapatalk



http://www.docsdrive.com/pdfs/ansinet/pjbs/2004/187-196.pdf

Going full circle on the eco-relevance of organic acids to orchids. Mycorrhrizal fungi seem to be a pretty awesome source of citric and malic acid.

So maybe orchids never truly give up there dependence on mooching off the fungus after developing their own photosynthetic capacity.


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## Rick (Oct 18, 2015)

http://link.springer.com/article/10.1007/s11676-012-0284-y

Crazy Aspergillus flavus and other citric acid producing fungus were common endophytes in a vanda a bulbo species.

I also found an article on the full scale production of citric acid (which uses A. flavus).


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## terryros (Oct 18, 2015)

Rick - I have been wondering if you have found any evidence for an adverse effect from excess lemon juice, assuming that the pH in the root zone is not dropped too low? I really want to use the lemon juice to acidify my fertigation solution enough to overcome a pretty alkaline growing media. You have come down on the amount that you use in your environment, but I am wondering about adverse effects of using more than 5 mL (1 teaspoon) per gallon?


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## Rick (Oct 18, 2015)

terryros said:


> Rick - I have been wondering if you have found any evidence for an adverse effect from excess lemon juice, assuming that the pH in the root zone is not dropped too low? I really want to use the lemon juice to acidify my fertigation solution enough to overcome a pretty alkaline growing media. You have come down on the amount that you use in your environment, but I am wondering about adverse effects of using more than 5 mL (1 teaspoon) per gallon?
> 
> 
> Sent from my iPad using Tapatalk HD



I found a paper that indicated root damage would occur (very quickly) at low pH, but the detrimental pH level was based on the calcium concentration (i.e. more calcium = more safety at a given pH).

So after a couple of shots at a tablespoon per gallon I got scared and went to 6-8 drops per gallon (watering every day). pH is around 5.5 to 5.9 Root growth is still great after 2+ months.


Coming up with a way to dose optimally is not going to be easy.

I hope you poked through some of those papers I linked.

The upshot is that orchids contain endphytic fungi species that supply organic acids like citrate and malate. One species of orchid endophyte Aspergillis niger is what is commercially used to make citric acid for soft drinks like Coca Cola!


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## abax (Oct 18, 2015)

Any differences in lime juice as opposed to lemon juice?


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## Rick (Oct 18, 2015)

abax said:


> Any differences in lime juice as opposed to lemon juice?



Don't know with regards to orchid culture. I found a paper on the citrate content of various citrus juices and concentrates, and there are subtle differences between lemon vs lime.

But don't know if it will make any difference to orchids.


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## consettbay2003 (Oct 19, 2015)

Would bottled lemon juice be acceptable or do you recommend freshly squeezed?


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## Ray (Oct 19, 2015)

Rick,

I got a small citric acid sample from a vendor. If I wanted to try a test and modify the K-lite I'm using, about how much would you suggest I add?

I had thought, based upon some of your comments, that about the same as the citric acid it already contains might be OK.


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## naoki (Oct 19, 2015)

Ray said:


> Rick,
> 
> I got a small citric acid sample from a vendor. If I wanted to try a test and modify the K-lite I'm using, about how much would you suggest I add?
> 
> I had thought, based upon some of your comments, that about the same as the citric acid it already contains might be OK.



Gazania rigens study (Rick's message #33) used 100 and 300 mg/l (ppm) for foliar spray. Malate or citrate at 300ppm was the best most of the time (increase in the root dry mass and root/shoot ratio). Maybe a good starting point? Interestingly G. riggers is a C4 plant. Malate is a transport acid of carbon in C4 pathway. So it would be relevant in CAM plants (they use C4 pathway), too. Maybe early morning foliar spray of malate to CAM might be effective (Paphs are C3, though).

citrate and malate are easily available and cheap.

This one uses malate and citrate foliar spray on lily (closer to orchids than Gazania). They use 750 and 1500ppm + a couple drops of tween-20 (soap) per 500ml + 0.1% glycerin.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3355684/
An interesting part is that Malate did increase the chlorophyll contents slightly (statistically significant, but not dramatic effect), consistent with Rick's original observation. I couldn't get the exact time frame of acid application and chlorophyll measurement, but I'm guessing that the response was relatively quick in the lily. Another interesting part is that citrate reduced the weight of bulbil (asexual reproductive structure at the base of leaves). So it is influencing the resource allocation pattern.


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## terryros (Oct 19, 2015)

1. I saw an article that showed a toxic effect to leaves of some types of plants with citrate at a high concentration. What I can't do is get from say 300 mg/mL of citrate or malate to an amount of lemon juice to add because I can't find a clear reference giving even a range of either citrate or malate concentrations in lemon juice.

2. An interesting other issue is that I saw that lemon juice is a "good" source of potassium, but I don't know whether that is meaningful with the mounts of lemon juice we are talking about. It may make K-Lite a good partner because we start from a lower base. IF the only beneficial substances in lemon juice are the citrate and malate and these are cheap and easy to deal with as an additive AND come as non-potassium salts, I can see wanting to get the pure substances to add rather than lemon juice. But, maybe like kelp extracts, there are various magical substances in lemon juice.


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## naoki (Oct 19, 2015)

How about this?
http://online.liebertpub.com/doi/abs/10.1089/end.2007.0304
Lemon juice: 48.7g/l of citrate
Lime juice: 46.7g/l

So 1 tsp/gallon gives 63.4ppm and 60.8ppm.

Table 2 of 
http://www.sciencedirect.com/science/article/pii/S1466856405001086
contains other acid. Malic acid is about 5% (in weight) of citrtrate, so it is a minor component in lemon juice.


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## terryros (Oct 19, 2015)

I confirm your math! It would take about 5 teaspoons (1.67 tablespoons) per gallon to get to the 300 ppm (or mg)/L you mentioned. I won't do the metric conversions, but it doesn't make Rick's initial 1 tablespoon per gallon look at all excessive.

For me, the pH lowering effect of the lemon juice is essential because I have a potting mix that is on the alkaline side to begin with. A more acid fertigation solution might help with nutrient availability for a few things at least. I think that I now know the safe range of lemon juice to play with and can now focus on the pour-through pH result after fertilizing with different strengths as my target. Makes more sense to me than phosphoric acid.


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## Stone (Oct 19, 2015)

terryros said:


> > I confirm your math! It would take about 5 teaspoons (1.67 tablespoons) per gallon to get to the 300 ppm (or mg)/L you mentioned. I won't do the metric conversions, but it doesn't make Rick's initial 1 tablespoon per gallon look at all excessive.
> 
> 
> 
> It's good when others work out things like quantities!


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## terryros (Oct 20, 2015)

Naoki - can you be as good a detective for the potassium concentration in lemon juice??


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## naoki (Oct 20, 2015)

I think Table 2 of http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1704416/pdf/canmedaj01453-0070.pdf
has the info about K and Na in Lemon juice (RealLemon and Sunkist):
K: 27-29 mmol/l = 1053-1131 mg/l (ppm)
Na: 9-10 mmol/l = 207-230 mg/l


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## terryros (Oct 21, 2015)

My quick math says we don't need to worry about a few teaspoons of lemon juice into a gallon of solution doing much with potassium!


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## myxodex (Oct 21, 2015)

naoki said:


> Gazania rigens study (Rick's message #33) used 100 and 300 mg/l (ppm) for foliar spray. Malate or citrate at 300ppm was the best most of the time (increase in the root dry mass and root/shoot ratio). Maybe a good starting point? Interestingly G. riggers is a C4 plant. Malate is a transport acid of carbon in C4 pathway. So it would be relevant in CAM plants (they use C4 pathway), too. Maybe early morning foliar spray of malate to CAM might be effective (Paphs are C3, though).
> 
> citrate and malate are easily available and cheap.
> 
> ...



Thanks for the link Naoki. 
I found some other papers that indicate that malic acid can increase and/or preserve the chlorophyll content of cut flowers post harvest (i.e. not preharvest treatment). Succinic acid can have the same effect for some plants.

http://scialert.net/fulltext/?doi=ajpp.2011.167.175&org=10
http://www.idosi.org/wasj/wasj12(9)/37b.pdf


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## myxodex (Oct 21, 2015)

terryros said:


> 1. I saw an article that showed a toxic effect to leaves of some types of plants with citrate at a high concentration. What I can't do is get from say 300 mg/mL of citrate or malate to an amount of lemon juice to add because I can't find a clear reference giving even a range of either citrate or malate concentrations in lemon juice.
> 
> 2. An interesting other issue is that I saw that lemon juice is a "good" source of potassium, but I don't know whether that is meaningful with the mounts of lemon juice we are talking about. It may make K-Lite a good partner because we start from a lower base. IF the only beneficial substances in lemon juice are the citrate and malate and these are cheap and easy to deal with as an additive AND come as non-potassium salts, I can see wanting to get the pure substances to add rather than lemon juice. But, maybe like kelp extracts, there are various magical substances in lemon juice.



For those thinking of experimenting with malic acid, please be aware that it is chiral (unlike citric acid), and is most commonly available as the DL racemic mix, meaning that 50% is the unnatural D form. This commercial DL malic acid mixture is used as an acidulent / taste modifier in commercially produced beverages and acidic desserts and is considered to be food safe, although it's use is not permitted for organic product certification in the USA. Pure L-malic acid (as found in fruits) is more expensive to manufacture, but it is this natural L-malic acid that will have been used in most published experiments. If it's inexpensive and doesn't specify that it's L-malic acid then it will almost certainly be the DL mixture. 

Whether the D-form would have any toxic effect on plants I don't know and I have been unable to find an answer to this question. I did find out that D-malic acid is metabolised by the E.coli in our gut to pyruvic acid, but I could not find any references about D-malic acid and plant metabolism. The D isomers of some amino acids are toxic to plants and so I've decided to err on the side of caution and avoid using the DL mix on plants. 

I bought some malic acid from an online (local) supplier that claimed it was " the pure natural L-form " (in bold print no less), but it was not labelled as such on the container I recieved. When I tracked down the original manufacturer's specification it turned out to be the DL mixture after all. If you really want to be sure about malic acid, use natural fruit juice or be prepared to spend a lot more by buying it from a scientific supply company. There is a US supplier that apparently does sell genuine L-malic acid (food supplement/detox market) at a reasonable price but I didn't get around to inquiring whether they ship to the UK.

As for fruits, apples have high malic acid content. A popular English cooking apple, the Bramley, has between 0.8 and 1.2 % malic acid (w/v of juice) and other tart cooking apples will also also have high concentrations. Sweet raw-eating apples come in around 0.4% and the more tart ones like Granny Smith's about 0.6-0.7%.


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## naoki (Oct 21, 2015)

Interesting point, myxodex. According to this:
http://www.plantphysiol.org/content/69/2/456.short
The uptake rate of L-malate by vacuoles gets drastically reduced with the excess of D-malate in CAM plants. CAM plants open stomata at night and stores CO2 in the form of malate, which moves into the vacuoles. Then the CO2 get released from malate during the day time, so that photosynthesis can work without opening the stomata. The paper didn't give the details or interpretation of the results, but it seems that D- form could interfere with this process. So it is probably better to stick with L- form.


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## Brabantia (Oct 22, 2015)

terryros said:


> I confirm your math! It would take about 5 teaspoons (1.67 tablespoons) per gallon to get to the 300 ppm (or mg)/L you mentioned. I won't do the metric conversions, but it doesn't make Rick's initial 1 tablespoon per gallon look at all excessive.


I am curious to know the Ph of a solution 20 ppm N from KLite at which 100 ppm of citric acid has been added. Using RO or rain water of course. Don't forget also that the degradation of citric acid will also decrease the Ph of the substrate.


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## SlipperKing (Oct 22, 2015)

terryros said:


> 1. I saw an article that showed a toxic effect to leaves of some types of plants with citrate at a high concentration. What I can't do is get from say 300 mg/mL of citrate or malate to an amount of lemon juice to add because I can't find a clear reference giving even a range of either citrate or malate concentrations in lemon juice.
> 
> 2. An interesting other issue is that I saw that lemon juice is a "good" source of potassium, but I don't know whether that is meaningful with the mounts of lemon juice we are talking about. It may make K-Lite a good partner because we start from a lower base. IF the only beneficial substances in lemon juice are the citrate and malate and these are cheap and easy to deal with as an additive AND come as non-potassium salts, I can see wanting to get the pure substances to add rather than lemon juice. But, maybe like kelp extracts, there are various magical substances in lemon juice.





Brabantia said:


> I am curious to know the Ph of a solution 20 ppm N from KLite at which 100 ppm of citric acid has been added. Using RO or rain water of course. Don't forget also that the degradation of citric acid will also decrease the Ph of the substrate.



I personally would use caustion watering my Paphs/Phrags at 300mg. I'm currently using N at 10 ppm with the addition of citric acid to adjust the feed rain water to pH 5.6. It takes approx. 1.5 tbp in 55 gals of rain water to reach pH 5.6. I think serious root damage at the min if 1.5 tbp per gal was used.


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## terryros (Oct 22, 2015)

I have found that 10 mL/gallon of lemon juice (which is under 100 ppm citrate) reduces my fertilization solution pH such that the pour-through pH after feeding is about 6.6, right where I would like it. I don't need it any lower. However, the fertilization solution with this amount of lemon juice is about 4.3 for me, with a TDS of about 250 (EC 0.5). I think this is about where I would like things to be. I wouldn't push the citrate beyond this.


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